LECTURE SUMMARY ON THE DISCIPLINE

"ELECTRIC PART OF STATIONS AND SUBSTATIONS" Part 2

For bachelors in the direction _” Energy and Electrical Engineering”_140400

for profiles: “ Electric power systems and networks”, “Power plants”, “Relay protection and automation of electric power systems”, “Power supply”

Art. teacher Galkin A.I.

Novocherkassk 2014

Switchgear diagrams

Earlier, in the 1st part, the switchgear (RU) was formulated as an element of the block diagram of a power facility (station or substation).

A switchgear is an installation designed to receive and distribute electricity at one voltage and contains switching devices (switches and disconnectors, and substations may have separators and short circuits), measuring devices (current and voltage transformers) and conductors providing communication between devices.

There is a wide variety of switchgear schemes that differ in reliability, operational flexibility and, accordingly, cost. There is a dependence: the higher the reliability and operational flexibility of the reactor plant, the higher its cost. Various accession. To the main accessions include: power lines ( W), power transformers ( T) and generators ( G) (if it is a generator voltage switchgear at a CHPP).

The whole variety of RP can be divided into schemes Switchgear with busbars and schemes Switchgear without busbars . The latter, in turn, can be divided into Switchgear according to simplified schemes and on Switchgear based on ring schemes .(polygons) In many switchgear circuits, you can find parts of the circuit that contain three elements connected in series: a disconnector ( QS1), switch ( Q), current transformer ( TA) and another disconnector ( QS2).

Consider some of the most common switchgear schemes in each of these groups.

RU according to simplified schemes. Switchgear according to simplified schemes are various options for line blocks - a transformer or bridges, are not typical for power plants and are usually used on the high voltage side of substations with a small number of connections. This also includes the entry-exit scheme.

Variants of these schemes are shown in Fig. 8.1. Here the lines are shown with arrows and the power transformers are shown with crosses (voltage regulation under load). Lines and power transformers are not elements of the switchgear, but are connections to the switchgear. The switchgear diagram shows circuit breakers, disconnectors, current transformers and voltage transformers.

RU according to the block line - transformer scheme (Fig. 8.1, b) is used at dead-end single-transformer substations as a HV switchgear with one supply line. At two-transformer dead-end substations with two supply lines, a switchgear is used according to the scheme of two block lines - a transformer with switches and a non-automatic jumper on the side of the lines (Fig. 8.1, in).

RU according to the bridge scheme (Fig. 8.1, G and d) are used on the high side of transit substations, which are included in the cut of the transit line. Within the substation, power transit occurs through an automatic jumper circuit containing a switch. In addition to this switch, there are two more switches in the bridge circuit. They can be installed either on the side of power transformers (Fig. 8.1, G) or from the side of the lines (Fig. 8.1, d). At the time of repair of the elements of the automatic jumper, in order not to stop the transit of power, a non-automatic jumper (without a switch), which is called a repair one, is provided.

Rice. 8.1. RU according to simplified schemes:

a- block with disconnector; b- the same, but with a switch; in- two blocks with switches and a non-automatic jumper from the side of the lines; G- a bridge with switches in the transformer circuits and a repair jumper on the side of the transformers;

Continuation of fig. 8.1:

d- a bridge with switches in the circuits of lines and a repair jumper from the side of the lines; e- entry-exit

At transit single-transformer substations, switchgear is used according to the entry-exit scheme (Fig. 8.1, e). There is also a repair jumper without a switch here

Switchgear diagrams with busbars. Switchgear with busbars consists of busbars to which various accession. To the main accessions include: power lines, power transformers and generators (if it is a generator voltage switchgear).

busbars called sections of tires of a rigid or flexible design, with low electrical resistance, intended for connecting connections.

In circuits with busbars, the following devices are installed in the main connection circuit. From the side of the busbar, a disconnector is installed, which is called a busbar, then a switch is installed, after the switch - a current transformer, and behind it, from the connection side, another disconnector, which is called linear or transformer (depending on the connection).

Among the many switchgear with busbars, the following can be distinguished:

· switchgear diagrams with one working bus system (usually partitioned);

· switchgear diagrams with one working and bypass bus systems;

· switchgear diagrams with two working and bypass bus systems;

· schemes with two busbar systems and three circuit breakers for two connections.

Switchgear diagram with one working busbar system is simple, visual, economical, but does not have sufficient operational flexibility. When repairing a switch or other device in the connection circuit, it loses power, and when a bus or bus section is repaired, all connections associated with this bus (section) lose their connection.

Rice. 8.2 Scheme of the switchgear with one working busbar system: a - non-sectional circuit breaker; b - sectioned by a switch.

At power plants, such a circuit in a sectioned version can be used in circuits of a 6 kV auxiliary supply switchgear or in a 6-10 kV generator switchgear at a CHPP.

At substations, such a circuit in a sectioned version can be used in switchgear circuits on the low voltage side of 6 - 10 kV (sometimes 35 kV) (LV switchgear).

Switchgear diagram with one working and bypass bus system used at stations and substations at a voltage of 110, 220 kV, if the number of connections is less than seven. An important advantage of this scheme is the ability to replace any (at the moment one) switch in the connection circuit during its repair or revision with a bypass switch ( QB1 in Fig. 8.3) without interrupting the power supply of the connection. The current path around the breaker being repaired is created with the help of a bypass breaker and a bypass busbar system. Often the working bus system in this scheme is sectioned, as shown in the figure. In normal operation, the bypass busbar system is not energized and its busbar disconnectors ( QSB) are disabled. Both the bypass switch and the disconnectors in its circuit are in the off position.

The main operations for replacing a circuit breaker in the connection circuit with a bypass one, taking into account the switching rules, we will consider using the example of a circuit breaker Q1 in the circuit line W1:

First, turn on the disconnectors in the bypass circuit QB1, moreover, in the plug of the disconnectors, they include the one that is connected to the same section as W1.

After that include QB1 and this applies voltage to the bypass bus. This is done to test the isolation of the bypass bus.

The next step is to disable QB1.

Now that the insulation level has been verified, turn on the busbar disconnector QSB1 in chain W1.

Re-include QB1.

Now we have two paths for the current to flow in the circuit. W1: one through Q1 and the other through QB1.

Now you can disable Q1 and disconnectors in its circuit, with the exception of the busbar disconnector QSB1.

However, this scheme retains the disadvantage that when repairing a section of working tires, the connection between the connections of this section is lost. The scheme with two working bus systems is deprived of this drawback, it often also has a bypass bus.

Rice. 8.3 Scheme with one working sectioned and bypass busbar system (current and voltage transformers are not shown): QSB1, QSB2, QSB3 - busbar disconnectors of the bypass busbar system in connection circuits; Q1 - switch in the connection circuit; QS1 and QS2 - bus and line disconnectors in the connection circuit; QB1 - bypass switch; QK1 (QK2) - section switch.

Switchgear diagram with two working and bypass bus systems it is used at a voltage of switchgear 110, 220 kV, if the number of connections is not less than seven. In this scheme, part of the connections is connected to one working bus (K1), and part to the other (K2). However, any feeder can be transferred from one busbar system to another using the QK busbar coupler and feeder busbar disconnectors. (In this operation, the bus coupler switch QK and the disconnectors in its circuit must be in the on state.) This is used when repairing any working tire. Having a bypass switch and a bypass bus provides the same benefits as the previous circuit.

Rice. 8.4 Scheme with two working and bypass bus systems (current and voltage transformers are not shown): QK - bus connection switch; QB - bypass switch; K1 - the first working bus system; K2 - the second working bus system; KV - bypass bus system.

The disadvantage of this scheme, as well as the previous ones, is that in the event of an emergency shutdown of one of the working buses (for example, due to a short circuit on the bus), it will be turned off and the connection between the connections associated with this bus will be lost.

Scheme with two operating busbar systems and three switches for two connections recommended for use in a switchgear with a voltage of 330 - 750 kV and with six or more connections. In this circuit, due to the additional consumption of circuit breakers (conditionally 1.5 circuit breakers per connection, hence the second name of the “one-and-a-half” circuit), high operational flexibility and reliable communication between connections is achieved in many emergency and operational situations.

Among the advantages of the scheme, it can be noted that during the repair or revision of any circuit breaker, all connections remain in operation, and in the event of an emergency shutdown of one of the working buses, the connection between the connections is not lost, since it is carried out through the remaining bus

Among the disadvantages, one can point out the need to switch connections with two switches and the increased cost. In addition, in this circuit, the secondary circuits of current transformers become more complicated, because. current transformers are installed in the circuit of switches and in order to obtain the connection current, it is necessary to sum (according to the first Kirchhoff law) the currents of the secondary windings of the two transformers.

Rice. 8.5 One-and-a-half scheme of the switchgear (current and voltage transformers are not shown): K1 and K2 - working bus systems.

Switchgear schemes based on ring schemes (polygons). Are applied in RU 110-220 kV and more. In ring circuits (polygon circuits), switches are interconnected to form a ring. Each element - a line, a transformer - is connected between two adjacent switches. The simplest ring diagram is the triangle diagram (Fig. 8.6 a). Line W1 is connected to the circuit by switches Q1, Q2, line W2 - by switches Q2, Q3, transformer - by switches Q1, Q3. Multiple connection of an element to the general circuit increases the flexibility and reliability of operation, while the number of switches in the circuit under consideration does not exceed the number of connections. In the triangle circuit for three connections, there are three switches, so the circuit is economical.

In ring circuits, the revision of any switch is carried out without interrupting the operation of any element. So, during the revision of the switch Q1, it is also disconnected by the disconnectors installed on both sides of the switch. In this case, both lines and the transformer remain in operation, however, the circuit becomes less reliable due to a broken ring. If in this mode a short circuit occurs on line W2, then the switches Q2 and Q3 are turned off, as a result of which both lines and the transformer will remain without voltage. A complete shutdown of all elements of the substation will also occur in the event of a short circuit on the line and failure of one switch: for example, in the event of a short circuit on the W1 line and failure of the switch Q1, switches Q2 and Q3 are switched off. Match Probability

Rice. 8.6 Ring circuits (polygons) (current and voltage transformers not shown).

damage on the line with the revision of the circuit breaker, as mentioned above, depends on the duration of the repair of the circuit breaker. The increase in the overhaul period and the reliability of the circuit breakers, as well as the reduction in the duration of the repair, significantly increase the reliability of the circuits.

In ring circuits, the reliability of the circuit breakers is higher than in other circuits, since it is possible to test any circuit breaker during the normal operation of the circuit. Testing the switch by turning it off does not disturb the operation of the connected elements and does not require any switching in the circuit.

On fig. 8.6, b a diagram of a quadrilateral (square) is presented. This circuit is economical (four switches for four connections), allows testing and revision of any switch without disturbing the operation of its elements. The circuit is highly reliable. Disconnection of all connections is unlikely, it can occur if the revision of one of the switches, for example Q1, is identical, the W2 line is damaged and the switch of the second circuit Q4 fails. When repairing the W2 line, the switches Q3, Q4 and disconnectors installed in the direction of the lines are turned off. Connection of connections W1, T1 and T2 remaining in operation is carried out through switches Ql, Q2. If T1 is damaged during this period, then the switch Q2 will turn off, the second transformer and the W1 line will remain in operation, but the power transit will be disrupted. Installing line disconnectors QS1 and QS2 eliminates this disadvantage.

The advantage of all ring circuits is the use of disconnectors only for repair work. The number of disconnector operations in such circuits is small.

The disadvantages include a more complex selection of current transformers, switches and disconnectors. Current transformers are installed here, as well as in the one and a half scheme, in the circuit of switches

Main Wiring Diagrampower stations or substations are a set of main electrical equipment (generators, transformers, lines), busbars, switching and other primary equipment with all connections made between them in kind.

The choice of the main circuit is decisive in the design of the electrical part of the power plant (substation), since it determines the complete composition of the elements and the connections between them. The selected main circuit is the initial one when drawing up circuit diagrams of electrical connections, auxiliary circuits, secondary connection diagrams, wiring diagrams, etc.

In the drawing, the main circuits are shown in a single-line version with all elements of the installation in the off position. In some cases, it is allowed to depict individual elements of the circuit in the working position.

All elements of the scheme and the connections between them are depicted in accordance with the standards of the unified system for design documentation (ESKD).

a) Types of schemes and their purpose

The main electrical connection diagram of a power plant (substation) is a set of main electrical equipment (generators, transformers, lines), busbars, switching and other primary equipment with all connections made between them in kind.

The choice of the main circuit is decisive in the design of the electrical part of the power plant (substation), since it determines the complete composition of the elements and the connections between them. The selected main circuit is the starting point when drawing up circuit diagrams of electrical connections, auxiliary circuits, secondary connection diagrams, wiring diagrams, etc.

In the drawing, the main circuits are shown in a single-line version with all elements of the installation in the off position. In some cases, it is allowed to depict individual elements of the circuit in the working position.

All elements of the scheme and the connections between them are depicted in accordance with the standards of the unified system for design documentation (ESKD).

Under operating conditions, along with the principal, main diagram, simplified operational diagrams are used, in which only the main equipment is indicated. The duty personnel of each shift fills out the operational diagram and makes the necessary changes to it in terms of the position of switches and disconnectors that occur during duty.

When designing an electrical installation, before developing the main circuit, a block diagram of the generation of electricity (power) is drawn up, which shows the main functional parts of the electrical installation (switchgears, transformers, generators) and the connections between them. Structural diagrams serve to further develop more detailed and complete circuit diagrams, as well as for general familiarization with the operation of an electrical installation.

b) Basic requirements for the main circuits of electrical installations

When choosing electrical installation diagrams, the following factors should be taken into account:

the importance and role of the power plant or substation for the power system. Power plants operating in parallel in the power system differ significantly in their purpose. Some of them, the base ones, carry the main load, others, the peak ones, work part-time during maximum loads, and others carry the electrical load determined by their heat consumers (CHP). The different purpose of power plants determines the feasibility of using different electrical connection schemes, even if the number of connections is the same.

Substations can be designed to supply individual consumers or a large area, to connect parts of the power system or different power systems. The role of substations determines its scheme;

position of the power plant or substation in the power system, circuits and voltages of adjacent networks. High voltage busbars of power plants and substations can be the key points of the power system, combining several power plants for parallel operation. In this case, through the tires there is a power flow from one part of the power system to another - power transit. When choosing schemes for such electrical installations, the need to maintain power transit is taken into account first of all.

Substations can be dead-end, walk-through, tap-off; the circuits of such substations will be different even with the same number of transformers of the same power.

6-10 kV switchgear schemes depend on consumer power supply schemes: power supply via single or parallel lines, availability of backup inputs for consumers, etc.;

All consumers in terms of reliability of power supply are divided into three categories.

Category I power receivers - power receivers, the interruption of power supply of which can lead to a danger to people's lives, significant damage to the national economy, damage to expensive basic equipment, mass defective products, disruption of a complex technological process, disruption of the functioning of especially important elements of public utilities.

From the category I electrical receivers, a special group of electrical receivers stands out, the uninterrupted operation of which is necessary for an accident-free shutdown of production in order to prevent a threat to human life, explosions, fires and damage to expensive equipment.

For the power supply of a special group of power receivers of category I, additional power is provided from a third independent power source. Independent power sources can be local power plants, power grid power plants, special uninterruptible power units, batteries, etc.

Category II electrical receivers are electrical receivers whose power supply interruption leads to massive undersupply of products, massive downtime of workers, mechanisms and industrial transport, disruption of the normal activities of a significant number of urban and rural residents. These power receivers are recommended to be supplied with power from two independent sources that mutually reserve each other; breaks are allowed for them for the time necessary to turn on the backup power by the actions of the on-duty personnel or the mobile operational team.

It is allowed to supply electrical receivers of category II through one overhead line, if it is possible to carry out emergency repairs of this line for a period of not more than 1 day. Power supply is allowed via one cable line, consisting of at least two cables connected to one common device. If there is a centralized reserve of transformers and it is possible to replace a damaged transformer within a period of not more than 1 day, power from one transformer is allowed.

Category III power receivers - all other power receivers that do not fit the definitions of categories I and II.

For these power receivers, power supply can be carried out from one power source, provided that power supply interruptions necessary for repair and replacement of a damaged element of the power supply system do not exceed 1 day.

The prospect of expansion and intermediate stages of development of the power plant, substation and adjacent section of the network. The scheme and layout of the switchgear should be selected taking into account the possible increase in the number of connections with the development of the power system. Since the construction of large power plants is carried out in stages, when choosing an electrical installation scheme, the number of units and lines introduced in the first, second, third stages and during its final development is taken into account.

To select a substation scheme, it is important to take into account the number of high and medium voltage lines, the degree of their responsibility, and therefore, at various stages of the development of the power system, the Substation scheme may be different.

The phased development of the switchgear scheme of a power plant or substation should not be accompanied by radical alterations. This is possible only when the prospects for its development are taken into account when choosing a scheme.

When choosing diagrams of electrical installations, the permissible level of short-circuit currents is taken into account. If necessary, the issues of sectioning networks, dividing the electrical installation into independently operating parts, installing special current-limiting devices are solved.

From a complex set of conditions that affect the choice of the main circuit of an electrical installation, the main requirements for circuits can be distinguished:

reliability of power supply to consumers; suitability for repair work; operational flexibility of the electrical circuit; economic expediency.

Reliability is a property of an electrical installation, a section of an electrical network or a power system as a whole to ensure uninterrupted power supply to consumers with electricity of standardized quality. Damage to equipment in any part of the circuit, if possible, should not disrupt the power supply, the supply of electricity to the power system, the transit of power through the busbars. The reliability of the circuit must correspond to the nature (category) of consumers receiving power from this electrical installation.

Reliability can be assessed by the frequency and duration of interruptions in the power supply to consumers and the relative emergency reserve, which is necessary to ensure a given level of trouble-free operation of the power system and its individual nodes.

The suitability of an electrical installation for repairs is determined by the possibility of repairs without disrupting or limiting the power supply to consumers. There are schemes in which, in order to repair the circuit breaker, it is necessary to turn off this connection for the entire time of repair, in other schemes, only temporary disconnection of individual connections is required to create a special repair scheme; in the third, the repair of the switch is carried out without disrupting the power supply, even for a short time. Thus, the suitability for carrying out repairs of the circuit under consideration can be quantified by the frequency and average duration of outages of consumers and power sources for equipment repairs.

The operational flexibility of the electrical circuit is determined by its suitability for creating the necessary operating modes and carrying out operational switching.

The greatest operational flexibility of the circuit is provided if operational switching in it is carried out by switches or other switching devices with a remote drive. If all operations are carried out remotely, and even better by means of automation, then the elimination of an emergency condition is significantly accelerated.

Operational flexibility is measured by the number, complexity and duration of operational switches.

The economic feasibility of the scheme is estimated by the reduced costs, which include the costs of the construction of the installation - capital investments, its operation and possible damage from a power outage.

c) Structural diagrams of power plants and substations

The structural electrical circuit depends on the composition of the equipment (the number of generators, transformers), the distribution of generators and the load between switchgear (RU) of different voltages and the connection between these RU.

On fig. 1 shows block diagrams of CHP. If the CHPP is built near electricity consumers U = 6 ÷ 10 kV, then it is necessary to have a generator voltage switchgear (GRU). The number of generators connected to the GRU depends on the load of 6-10 kV. On fig. 1, and two generators are connected to the GRU, and one, as a rule, more powerful, to the high voltage switchgear (RU VN). The 110 - 220 kV lines connected to this switchgear communicate with the power system.

If the construction of energy-intensive industries is envisaged near the CHPP, then they can be powered by 35 - 110 kV overhead lines. In this case, a medium voltage switchgear (RU SN) is provided at the CHPP (Fig. 1, b). Communication between switchgears of different voltages is carried out using three-winding transformers or autotransformers.

With a slight load (6-10 kV), it is advisable to block the connection of generators with step-up transformers without cross-coupling at the generator voltage, which reduces short-circuit currents and allows using a complete switchgear to connect 6-10 kV consumers instead of an expensive GRU (Fig. 1, c). Powerful power units 100 - 250 MW are connected to the VN switchgear without a tap to supply consumers. Modern powerful CHP plants usually have a block diagram.

Picture 1. Structural diagrams of CHP

Figure 2. Structural diagrams of IES, HPP, NPP

Figure 3. Structural diagrams of substations

On fig. 2 shows block diagrams of power plants with predominant distribution of electricity at increased voltage (CPP, HPP, NPP). The absence of consumers near such power plants makes it possible to abandon the GRU. All generators are connected in blocks with step-up transformers. Parallel operation of the blocks is carried out at high voltage, where a switchgear is provided (Fig. 2, a).

If electricity is supplied at the highest and medium voltage, then the connection between the switchgear is carried out by a communication autotransformer (Fig. 2, b) or an autotransformer installed in the unit with a generator (Fig. 2, c).

On fig. 3 shows block diagrams of substations. At a substation with two-winding transformers (Fig. 3, a), electricity from the power system enters the HV switchgear, then it is transformed and distributed among consumers in the LV switchgear. At the nodal substations, the connection between the individual parts of the power system and the power supply to consumers is carried out (Fig. 3, b). It is possible to construct substations with two medium voltage switchgear, HV switchgear and LV switchgear. At such substations, two autotransformers and two transformers are installed (Fig. 3, c).

The choice of one or another structural scheme of a power plant or substation is made on the basis of a technical and economic comparison of two or three options.

WIRING DIAGRAM ON THE 6-10 kV SIDE

a) Scheme with one busbar system

The simplest scheme of electrical installations on the 6-10 kV side is a scheme with one non-sectioned busbar system (Fig. 4, a).

The scheme is simple and clear. Power sources and 6-10 kV lines are connected to the busbars using switches and disconnectors. One switch is required for each circuit, which serves to turn off and turn on this circuit in normal and emergency modes; If it is necessary to disconnect the line W1, it is enough to open the switch Q1. If the switch Q1 is taken out for repair, then after it is turned off, the disconnectors are turned off: first the linear QS1, and then the bus QS 2.

Thus, operations with disconnectors are necessary only when the connection is withdrawn in order to ensure safe work. Due to the uniformity and simplicity of operations with disconnectors, the accident rate due to incorrect actions of the on-duty personnel with them is small, which is one of the advantages of the considered scheme.

Figure 4. Schemes with one busbar system, unsectioned (a) and sectioned by switches (b)

The scheme with one busbar system allows the use of complete switchgears (KRU), which reduces the cost of installation, allows the widespread use of mechanization and reduces the construction time of the electrical installation.

Along with the advantages, the scheme with one non-partitioned bus system has a number of disadvantages. To repair busbars and busbar disconnectors of any connection, it is necessary to completely remove the voltage from the busbars, that is, turn off the power sources. This leads to a break in the power supply to all consumers for the duration of the repair.

In the event of a short circuit on the line, for example, at point K1 (Fig. 4, a), the corresponding switch (Q4) should turn off, and all other connections should remain in operation; however, if this switch fails, the power supply switches Q5, Q6 will open, leaving the busbars de-energized. A short circuit on the busbars (point K2) also causes the power supply to be turned off, i.e., the power supply to consumers is interrupted. These shortcomings are partially eliminated by dividing the busbars into sections, the number of which usually corresponds to the number of power sources.

On fig. 4b shows a diagram with one busbar system. separated by a switch. The circuit retains all the advantages of circuits with a single busbar; in addition, an accident on the busbars leads to the disconnection of only one source and half of the consumers; the second section and all connections to it remain in operation.

The advantages of the scheme are simplicity, clarity, economy, sufficiently high reliability, which can be confirmed by the example of connecting the main step-down substation (MSS) to the busbars of the electrical installation with two lines W3, W4 (Fig. 4, b). In case of damage to one line (short circuit at point K2), switches Q2, Q3 are turned off and QB2 is automatically turned on, restoring power to the first section of the GPP via line W4.

In the event of a short circuit on the tires at point K1, the switches QB1, Q6, Q3 are turned off and QB2 is automatically turned on. When one source is switched off, the remaining power source takes over the load.

Thus, the power supply of the GPP in the considered emergency modes is not disturbed due to the presence of two supply lines connected to different sections of the station, each of which must be designed for full load (100% reserve on the network). With such a reserve on the network, a scheme with one partitioned bus system can be recommended for responsible consumers.

However, the scheme also has a number of disadvantages.

In case of damage and subsequent repair of one section, the responsible consumers, normally fed from both sections, remain without a reserve, and consumers that are not redundant via the network are disconnected for the entire time of repair. In the same mode, the power supply connected to the repaired section is turned off for the entire repair period.

The last drawback can be eliminated by connecting power sources to two sections simultaneously, but this complicates the design of the switchgear and increases the number of sections (two sections for each source).

In the considered circuit (Fig. 4, b), the sectional switch QB1 is switched on in normal mode. This mode is usually adopted in power plants to ensure parallel operation of generators. At substations, the sectional switch is disabled in normal mode in order to limit short-circuit currents.

The scheme with one busbar system is widely used for substations at a voltage of 6-10 kV and for supplying the own needs of stations, where its advantages can be fully used, especially due to the use of switchgear.

At the generator voltage of power plants that supply most of the electricity to nearby consumers, it is possible to use a circuit with one busbar system connected in a ring (Fig. 5). The busbars are divided into sections according to the number of generators. Sections are interconnected by means of sectional switches QB and sectional reactors LRB, which serve to limit the short-circuit current on the busbars. Lines 6-10 kV are connected to the busbars of the switchgear, fed through group twin reactors LR1, LR2, LR3 from the corresponding sections of the main switchgear. The number of group reactors depends on the number of lines and the total load of consumers 6-10 kV. Due to the low probability of accidents in the reactor itself and the busbar from the reactor to the main busbars and to the switchgear assemblies, the group reactor is connected without a circuit breaker, only a disconnector is provided for repair work in the reactor cell. For lines in these cases, switchgear cells are used.

Figure 5. Scheme with one busbar system connected in a ring

Each branch of the twin reactor can be designed for currents from 600 to 3000 A, i.e., it is possible to connect several 6 kV lines to each assembly. In the diagram (Fig. 5), eighteen lines are connected through three group reactors; thus, the number of connections to the main busbars is reduced compared to the scheme without group reactors by 15 cells, which significantly increases the reliability of the main busbars of the power plant, reduces the cost of building the switchgear by reducing the number of reactors and reduces the installation time due to the use of complete cells for connection lines 6-10 kV.

Responsible consumers are powered by at least two lines from different twin reactors, which ensures the reliability of power supply.

If the generator voltage buses are divided into three or four sections that are not connected in a ring, then it becomes necessary to equalize the voltage between the sections when one generator is turned off. So, when the generator G1 is turned off, the load of the first section is powered by the generators G2 and G3 remaining in operation, while the current from G2 passes through the LRB1 reactor, and the current from G3 passes through two reactors - LRB2 and LRB1. Due to the voltage loss in the reactors, the voltage level on the sections will not be the same: the highest on the VZ section and the lowest on the V1 section. To increase the voltage on section B1, it is necessary to shunt the LRB1 reactor, for which the circuit has a bypass disconnector QSB1. In the mode under consideration, the second shunt disconnector is not switched on, as this will lead to parallel operation of the generators G2 and G3 without a reactor between them, which is unacceptable under the conditions of short circuit disconnection.

The order of operation of the bypass disconnectors should be as follows: turn off the sectional switch QB, turn on the bypass disconnector QSB, turn on the sectional switch QB.

The more sections at the power plant, the more difficult it is to maintain the same voltage level, therefore, with three or more sections, busbars are connected into a ring. In the circuit in Fig. 5, the first section can be connected to the third sectional switch and the reactor, which creates a busbar ring. Normally all section switches are on and the generators are running in parallel. In the event of a short circuit on one section, the generator of this section and two section switches are turned off, however, the parallel operation of other generators is not disturbed.

When one generator is turned off, the consumers of this section receive power from both sides, which creates a smaller voltage difference across the sections and allows you to select sectional reactors for a lower current than in a circuit with an open busbar system.

In the circuit of the ring, the rated current of sectional reactors is taken approximately equal to 50 - 60% of the rated current of the generator, and their resistance is 8-10%.

b) Scheme with two busbar systems

Taking into account the characteristics of power receivers (categories I, II), their power supply scheme (lack of a reserve through the network), as well as a large number of connections to busbars for the main switchgear of a CHP plant, a circuit with two busbar systems can be provided during a feasibility study (Fig. 6), in which each element is connected through a fork of two busbar disconnectors, which makes it possible to work both on one and on the other busbar system.

Figure 6. Scheme with two busbar systems

On fig. 6, the circuit is shown in working condition: generators G1 and G2 are connected to the first busbar system A1, from which the group reactors and communication transformers T1 and T2 are powered. The working busbar system is partitioned by the QB circuit breaker and the LRB reactor, the purpose of which is the same as in the single busbar circuit. The second busbar system A2 is redundant, it is normally not energized. Both busbar systems can be interconnected by bus coupler switches QA1 and QA2, which are switched off in normal operation.

Another mode of operation of this circuit is also possible, when both busbar systems are energized and all connections are distributed evenly between them. This mode, called fixed circuit operation, is typically used on high voltage busbars.

The dual busbar arrangement allows one busbar system to be repaired while keeping all connections operational. So, when repairing one section of the working bus system A1, all connections are transferred to the backup bus system A2, for which the following operations are performed:

turn on the bus-connecting switch QA2 and remove the operating current from its drive;

check the included position QA2;

include disconnectors of all transferable connections on the A2 busbar system;

disconnect the disconnectors of all connections from the A1 busbar system, except for the disconnectors QA2 and the voltage transformer;

switch the power supply of the voltage circuits of the relay protection, automation and measuring instruments to the voltage transformer of the A2 busbar system;

check on the ammeter that there is no load on QA2;

the drive is supplied with operational current and switched off QA2;

make preparations for the repair of the tire section A1.

In the event of a short circuit on the first section of the working bus system A1, the generator G1, the sectional switch QB and the communication transformer T1 are turned off.

To restore the work of consumers in this case, it is necessary to perform switching:

turn off all switches that are not disabled by relay protection (dead-end line switches);

disconnect all disconnectors from the damaged section;

turn on the disconnectors of all connections of the first section to the redundant busbar system;

turn on the switch of the communication transformer T1, thereby applying voltage to the backup bus system to check its serviceability;

turn on the switches of the most responsible consumers;

deploy the G1 generator and, after synchronization, turn on its switch;

turn on the switches of all disconnected lines.

In this circuit, a bus coupler switch can be used to replace any bay switch.

The considered scheme is flexible and rather reliable. Its disadvantages include a large number of disconnectors, insulators, current-carrying materials and switches, a more complex design of the switchgear, which leads to an increase in capital costs for the construction of the GRU. A significant disadvantage is the use of disconnectors as operational devices. A large number of operations by disconnectors and complex interlocking between circuit breakers and disconnectors lead to the possibility of erroneous disconnection of the load current by disconnectors. The probability of accidents due to the incorrect action of the operating personnel in circuits with two busbar systems is greater than in circuits with one busbar system.

The dual busbar scheme can be applied to expandable CHP plants that have previously had such a scheme.

ELECTRICAL WIRING DIAGRAMS ON THE 35 kV SIDE AND ABOVE

a) Simplified switchgear diagrams

With a small number of connections on the side of 35 - 220 kV, simplified circuits are used, in which there are usually no busbars, the number of switches is reduced. In some circuits, high voltage switches are not provided at all. Simplified schemes make it possible to reduce the consumption of electrical equipment, building materials, reduce the cost of a switchgear, and speed up its installation. Such schemes are most widely used in substations.

One of the simplified schemes is the diagram of the block transformer - line (Fig. 7, a). In block diagrams, electrical installation elements are connected in series without cross connections with other blocks.

Figure 7. Simplified diagrams on the HV side:

a - block transformer - line with a VN switch; b - block transformer - line with a separator; c - two blocks with separators and a non-automatic jumper; g - bridge with switches

In the circuit under consideration, the transformer is connected to line W by switch Q2. In the event of an accident in the line, the Q1 switch is turned off at the beginning of the line (at the district substation) and Q2 from the side of the HV transformer; in the event of a short circuit in the transformer, Q2 and Q3 are turned off. In blocks generator - transformer - line switch Q2 is not installed, any damage in the block is switched off by generator switches Q3 and at the district substation Q1.

In the transformer-line blocks at substations (Fig. 7, b), QR separators and QN short circuits are installed on the high voltage side. To disconnect the transformer in normal mode, it is enough to disconnect the load with the Q2 switch on the 6-10 kV side, and then turn off the magnetizing current of the transformer with the QR separator. The admissibility of the last operation depends on the power of the transformer and its rated voltage.

In the event of a fault in the transformer, the protection relay trips circuit breaker Q2 and sends a pulse to open circuit breaker Q1 at the substation of the power system. The tripping impulse can be transmitted through a specially laid cable, through telephone lines or through a high-frequency channel of a high voltage line. After receiving a teleswitching impulse (TO), the switch Q1 is turned off, after which the separator QR is automatically turned off. The transit line, to which the transformer is connected, must remain energized, so after the QR trips, the switch Q1 is automatically closed. The pause in the automatic reclosing (AR) circuit must be coordinated with the opening time of the QR, otherwise the line will be closed for an uncorrected fault in the transformer.

Opening Q1 can be achieved without the transmission of a remote trip impulse. To do this, a short circuit QN is installed on the HV side. The transformer protection, when activated, gives a pulse to the QN drive, which, when activated, creates an artificial short circuit. The W1 line protection relay trips and trips Q1. The need to install a short circuiter arises from the fact that the relay protection of the W1 line in the substation of the power system may be insensitive to faults inside the transformer. However, the use of short-circuiting devices creates difficult conditions for the operation of the circuit breaker at the supply end of the line (Q1), since this circuit breaker has to disconnect non-remote short circuits.

The main advantage of the circuit (Fig. 7,b) is its cost-effectiveness, which has led to the widespread use of such circuits for single-transformer substations, which are connected by a blind tap to the transit line.

The reliability of the operation of the considered circuit depends on the accuracy and reliability of the separators and short-circuiters, therefore it is advisable to replace open-type short-circuiters with SF6 ones. For the same reasons, a QW load break switch can be installed instead of a separator.

At 35-220 kV two-transformer substations, a scheme of two transformer-line blocks is used, which, for greater flexibility, are connected by a non-automatic jumper of two disconnectors QS3, QS4 (Fig. 7, c). In normal mode, one of the jumper disconnects must be disabled. If this is not done, then in the event of a short circuit in any line (W1 or W2), both lines are disconnected by the relay protection, disrupting the power supply to all substations connected to these lines.

Transformer shutdowns (operational and emergency) occur in the same way as in the single block circuit (Fig. 7, b). A jumper of two disconnectors is used when disconnecting lines.

In case of a stable fault on line W1, Q1, Q3 are disconnected and the ATS action on the 6-10 kV side turns on the sectional switch QB, providing power to consumers from T2. If the line is taken out for repair, then the actions of the on-duty personnel of the substation or the operational mobile team turn off the line disconnector QS1, turn on the disconnector in the jumper and the transformer T1 is put under load by turning on the switch from the LV side (Q3) followed by disconnection of the sectional switch. This circuit can supply T1 from the W2 line when repairing the W1 line (or supplying T2 from the W1 line).

At 220 kV substations, disconnectors are installed in front of the QR1 and QR2 separators.

On the HV side of power plants, at the first stage of its development, it is possible to use a bridge circuit with switches (Fig. 7, d) with the possibility of subsequently switching to circuits with busbars.

In the circuit for four connections, three switches Q1, Q2, Q3 are installed (Fig. 7, d). Normally switch Q3 on the jumper between the two lines W1 and W2 (in the bridge) is on. In the event of a fault on line W1, switch Q1 is turned off, transformers T1 and T2 remain in operation, communication with the power system is carried out via line W2. In case of damage in the transformer T1 switch Q4 on the 6-10 kV side and switches Q1 and Q3 are switched off. In this case, the W1 line turned out to be disconnected, although there is no damage on it, which is a drawback of the bridge circuit. Considering that emergency shutdown of transformers is rare, then such a disadvantage of the circuit can be put up with, especially since after disconnecting Q1 and Q3 and, if necessary, taking the damaged transformer out for repair, disconnect the QS1 disconnector and turn on Q1, Q3, restoring the operation of the W1 line.

To keep both lines in operation during the revision of any switch (Q1, Q2, Q3), an additional jumper of two disconnectors QS3, QS4 is provided. Normally, one jumper isolator QS3 is open, all switches are on. For the revision of the switch Q1, first turn on QS3, then turn off Q1 and disconnectors on both sides of the switch. As a result, both transformers and both lines remained in operation. If in this mode a short circuit occurs on one line, then Q2 will turn off, i.e. both lines will remain without voltage.

For the revision of the Q3 switch, the jumper is also preliminarily turned on, and then Q3 is turned off. This mode has the same drawback: in the event of a short circuit on one line, both lines are turned off.

The probability of coincidence of an accident with the revision of one of the circuit breakers is the greater, the longer the repair time of the circuit breaker, therefore, this scheme is not used as the final version of the development at power plants.

On the side of 35 - 220 kV substations, it is allowed to use a bridge circuit with switches in the transformer circuit instead of separators and short circuits, if the installation of the latter is unacceptable due to climatic conditions.

b) Ring schemes

In ring circuits (polygon circuits), switches are interconnected to form a ring. Each element - a line, a transformer - is connected between two adjacent switches. The simplest ring scheme is the triangle scheme (Fig. 8, a). Line W1 is connected to the circuit by switches Q1, Q2, line W2 - by switches Q2, Q3, transformer - by switches Ql, Q3. Multiple connection of an element to the general circuit increases the flexibility and reliability of operation, while the number of switches in the circuit under consideration does not exceed the number of connections. In the triangle circuit for three connections, there are three switches, so the circuit is economical.

In ring circuits, the revision of any switch is carried out without interrupting the operation of any element. So, during the revision of the switch Q1, it is also disconnected by the disconnectors installed on both sides of the switch. In this case, both lines and the transformer remain in operation, however

Figure 8. Ring diagrams

the circuit becomes less reliable due to the breaking of the ring. If in this mode a short circuit occurs on line W2, then the switches Q2 and Q3 will open, as a result of which both lines and the transformer will remain without voltage. A complete shutdown of all elements of the substation will also occur in the event of a short circuit on the line and the failure of one switch: for example, in the event of a short circuit on the W1 line and failure of the switch Q1, the switches Q2 and Q3 will turn off. The probability of coincidence of damage on the line with the revision of the circuit breaker, as mentioned above, depends on the duration of the repair of the circuit breaker. The increase in the overhaul period and the reliability of the circuit breakers, as well as the reduction in the duration of the repair, significantly increase the reliability of the circuits.

In ring circuits, the reliability of the circuit breakers is higher than in other circuits, since it is possible to test any circuit breaker during the normal operation of the circuit. Testing the switch by turning it off does not disturb the operation of the connected elements and does not require any switching in the circuit.

On fig. 8b shows a diagram of a quadrilateral (square). This scheme is economical (four switches for four connections), allows testing and revision of any switch without disturbing the operation of its elements. The circuit is highly reliable. Disconnection of all connections is unlikely, it can occur if the revision of one of the switches, for example Q1, is identical, the W2 line is damaged and the switch of the second circuit Q4 fails. Disconnectors are not installed in the connection circuits of lines, which simplifies the design of the outdoor switchgear. When repairing the W2 line, the switches Q3, Q4 and disconnectors installed in the direction of the lines are turned off. Connection of connections W1, T1 and T2 remaining in operation is carried out via switches Q1, Q2. If T1 is damaged during this period, then the switch Q2 will turn off, the second transformer and line W1 will remain in operation, but the power transit will be disrupted.

The advantage of all ring circuits is the use of disconnectors only for repair work. The number of disconnector operations in such circuits is small.

The disadvantages of ring circuits include a more complex choice of current transformers, switches and disconnectors installed in the ring, since the current flowing through the devices changes depending on the operating mode of the circuit. For example, when Q1 is revised (Fig. 8, b), the current in the Q2 circuit doubles. Relay protection must also be selected taking into account all possible modes when bringing the ring switches into revision.

The quadrilateral scheme is used in switchgear of 330 kV and above at power plants as one of the stages in the development of the scheme, as well as at substations at a voltage of 220 kV and above.

The hexagon scheme (Fig. 8, c), which has all the features of the schemes discussed above, has received a fairly wide application. Switches Q2 and Q5 are the weakest elements of the circuit, since their failure leads to the disconnection of two lines W1 and W2 or W3 and W4. If power transit occurs along these lines, then it is necessary to check whether this will not violate the stability of the parallel operation of the power system.

In conclusion, it should be noted that the design of switchgears according to ring circuits makes it relatively easy to switch from a triangle circuit to a quadrilateral circuit, and then to a transformer-bus block circuit or to busbar circuits.

c) Schemes with one working and bypass bus system

One of the important requirements for circuits on the higher voltage side is the creation of conditions for revisions and testing of circuit breakers without interrupting operation. These requirements are met by a circuit with a bypass bus system (Fig. 9). In normal mode, the AO bypass busbar is de-energized and the QSO disconnectors connecting lines and transformers to the bypass busbar are off. The circuit provides for a bypass switch QO, which can be connected to any section using a fork of two disconnectors. Sections in this case are parallel to each other. The QO switch can replace any other switch, for which you need to perform the following operations: turn on the QO bypass switch to check the health of the bypass bus system, turn off QO, turn on QSO, turn on QO, turn off switch Q1, turn off disconnectors QS1 and QS2.

After these operations, the line receives power through the bypass bus system and switch Q0 from the first section (9, b). All these operations are carried out without interruption of the power supply along the line, although they are associated with a large number of switchings.

In order to save money, the functions of the bypass and section switches can be combined. On the diagram of Fig. 9, and in addition to the switch Q0 there is a jumper of two disconnectors QS3 and QS4. In normal mode this jumper is on, the bypass switch is connected to section B2 and is also on. Thus sections B1 and B2 are interconnected

Figure 9. Diagram with one working and bypass bus system:

a - a diagram with a combined bypass and sectional switch and separators in transformer circuits; b - mode of replacing the linear switch with a bypass one; c - circuit with bypass and sectional switches

through QO, QS3, QS4, and the bypass switch performs the functions of a sectional switch. When replacing any line switch with a bypass switch, disconnect the QO, disconnect the jumper isolator (QS3), and then use the QO for its intended purpose. For the entire time of repair of the linear switch, the parallel operation of the sections, and, consequently, the lines, is disrupted. Separators are installed in the transformer circuits in the circuit under consideration (QW load break switches can be installed). In case of damage in the transformer (for example, T1), the switches of the lines W1, W3 and the switch QO are switched off. After switching off the separator QR1, the switches turn on automatically, restoring the operation of the lines. Such a scheme requires precise work of automation.

The scheme according to fig. nine, a recommended for HV substations (110 kV) with the number of connections (lines and transformers) up to six inclusive, when the violation of the parallel operation of the lines is permissible and there is no prospect of further development. If the expansion of the switchgear is expected in the future, then switches are installed in the transformer circuits. Schemes with transformer switches can be used for voltages of 110 and 220 kV on the HV and MV side of substations.

In both schemes considered, the repair of a section is associated with the disconnection of all lines connected to this section and one transformer, therefore, such schemes can be used for paired lines or lines reserved from other substations, as well as radial ones, but not more than one per section.

At power plants, it is possible to use a scheme with one sectioned busbar system according to fig. 9, c, but with separate bypass switches for each section.

d) Scheme with two working and bypass bus systems

For switchgear 110 - 220 kV with a large number of connections, a scheme with two working and bypass busbar systems with one circuit breaker per circuit is used (Fig. 10, a). As a rule, both busbar systems are in operation with a corresponding fixed distribution of all connections: lines W1, W3, W5 and transformer T1 are connected to the first busbar system A1, lines W2, W4, W6 and transformer T1 connected to the second busbar system A2, the bus coupler switch QA is switched on. Such a distribution of connections increases the reliability of the circuit, since in the event of a short circuit on the buses, the bus connection switch QA and only half of the connections are disconnected. If the damage on the busbars is stable, then disconnected connections are transferred to a serviceable busbar system. The interruption in the power supply of half of the connections is determined by the duration of the switching. The considered scheme is recommended for 110 - 220 kV switchgear on the side of HV and MV substations with the number of connections 7-15, as well as at power plants with the number of connections up to 12.

Figure 10. Diagram with two working and bypass bus systems:

a - the main scheme; b, c - variants of schemes

For 110 kV switchgear and above, the disadvantages of this scheme become significant:

the failure of one circuit breaker during an accident leads to the disconnection of all power sources and lines connected to this busbar system, and if one busbar system is in operation, all connections are disconnected. The liquidation of the accident is delayed, since all operations for the transition from one bus system to another are carried out by disconnectors. If the power sources are powerful turbogenerator-transformer units, then starting them after a load shedding for more than 30 minutes may take several hours;

damage to the bus connection switch is equivalent to a short circuit on both bus systems, i.e. leads to the disconnection of all connected;

a large number of operations by disconnectors during the revision and repair of circuit breakers complicates the operation of the switchgear;

the need to install bus-coupling, bypass switches and a large number of disconnectors increases the cost of building the switchgear.

Some increase in circuit flexibility and reliability can be achieved by partitioning one or both bus systems.

At TPPs and NPPs, with the number of connections 12-16, one busbar system is sectioned, with a larger number of connections - both busbar systems.

At substations, one busbar system is sectioned at U = 220 kV with the number of connections 12-15 or when installing transformers with a capacity of more than 125 MBA; both busbar systems 110 - 220 kV are sectioned if the number of connections is more than 15.

If the busbars are sectioned, then in order to reduce capital costs, it is possible to use combined bus-coupling and QOA bypass switches (Fig. 10, b). In normal mode, the disconnectors QS1, QSO, QS2 are on and the bypass switch acts as a bus connector. If it is necessary to repair one circuit breaker, disconnect the QOA circuit breaker and the QS2 disconnector and use the bypass circuit breaker for its intended purpose. In circuits with a large number of lines, the number of such switchings per year is significant, which leads to complicated operation, so there is a tendency to refuse to combine the bus coupler and bypass switches.

In a circuit with sectioned buses, in case of damage on the tires or in case of a short circuit in the line and failure of the circuit breaker, only 25% of the connections are lost (for the duration of switching), however, in case of damage in the sectional circuit breaker, 50% of the connections are lost.

For power plants with powerful power units (300 MW or more), it is possible to increase the reliability of the circuit by connecting communication sources or autotransformers through a fork of two switches (Fig. 10, c). These switches in normal mode perform the functions of a bus connector. In the event of a failure on any busbar system, the autotransformer remains in operation, eliminating the possibility of losing both busbar systems.

e) Scheme with two busbar systems and three switches for two circuits

Switchgears 330 - 750 kV use a scheme with two busbar systems and three switches for two circuits. As can be seen from fig. 11, six connections require nine switches, i.e., for each connection of a “one and a half” switch (hence the second name of the circuit: “one and a half”, or “circuit with 3/2 switches per circuit”).

Figure 11. Scheme with 3/2 circuit breaker per connection

Each connection is switched on through two switches. To disconnect the line W1, it is necessary to open the switches Q1, Q2, to disconnect the transformer T1 - Q2, Q3.

In normal mode, all switches are on, both busbar systems are energized. For the revision of any switch, disconnect it and the disconnectors installed on both sides of the switch. The number of operations for bringing to revision is minimal, the disconnectors serve only to separate the circuit breaker during repair, they do not make any operational switching. The advantage of the circuit is that when any switch is revised, all connections remain in operation. Another advantage of the one-and-a-half scheme is its high reliability, since all circuits remain in operation even if the busbars are damaged. So, for example, during a short circuit on the first busbar system, the switches Q3, Q6, Q9 will turn off, the buses will remain without voltage, but all connections will remain in operation. With the same number of power supplies and lines, the operation of all circuits is maintained even when both busbar systems are turned off, and the parallel operation on the high voltage side can only be disturbed.

The scheme allows in the operating mode without operations by disconnectors to test the switches. Repair of tires, cleaning of insulators, revision of bus disconnectors are carried out without disrupting the operation of the circuits (the corresponding row of bus switches is turned off), all circuits continue to work in parallel through the busbar system that remains energized.

The number of necessary operations by disconnectors during the year to bring all switches, disconnectors and busbars into revision in turn is much less than in a circuit with two working and bypass busbar systems.

To increase the reliability of the circuit, elements of the same name are connected to different bus systems: transformers T1 , TK and line W2 - to the first bus system, lines W1, W3 - transformer T2 - to the second bus system. With this combination, in the event of damage to any element or busbars, with simultaneous failure of one switch and repair of the switch of another connection, no more than one line and one power source are disconnected.

So, for example, when repairing Q5, short circuit on line W1 and failure of switch Q1, switches Q2, Q4, Q7 are turned off, as a result of which, in addition to the damaged line W1, one more element, T2, will be disconnected. After opening these switches, line W1 can be disconnected by a line disconnector and transformer T2 is switched on by switch Q4. Simultaneous emergency shutdown of two lines or two transformers in the considered scheme is unlikely.

In the diagram in fig. 11 three chains are connected to the busbars. If there are more than five such chains, then it is recommended to section the tires with a switch.

The disadvantages of the considered scheme are:

disconnection of a short circuit on the line by two switches, which increases the total number of revisions of the switches;

increase in the cost of the switchgear design with an odd number of connections, since one circuit must be connected through two switches;

reducing the reliability of the circuit if the number of lines does not match the number of transformers. In this case, two elements of the same name are connected to one chain of three switches, so an emergency shutdown of two lines at the same time is possible;

complication of relay protection circuits;

increasing the number of switches in the circuit.

Due to its high reliability and flexibility, the circuit is widely used in 330 - 750 kV switchgear at powerful power plants.

At nodal substations, such a scheme is used with eight or more connections. With a smaller number of connections, the lines are included in a chain of three switches, as shown in fig. 11, and the transformers are connected directly to the busbars, without switches, forming a transformer-busbar unit.

CHP MAIN SCHEMES

a) Scheme CHP with generator voltage busbars

At CHPPs with 63 MW generators, electricity consumers located at a distance of 3-5 km can receive electricity at generator voltage. In this case, a 6-10 kV GRU is being built at the CHPP, as a rule, with one busbar system. The number and power of the generators connected to the GRU are determined on the basis of the consumer power supply project and must be such that when one generator is stopped, the remaining ones fully provide power to the consumers.

Communication with the power system and the issuance of excess power are carried out via 110 and 220 kV lines. If it is planned to connect a large number of 110, 220 kV lines, then a switchgear with two working and bypass busbar systems is being built at the CHPP.

With an increase in heat loads, turbine generators with a capacity of 120 MW or more can be installed at the CHPP. Such turbogenerators are not connected to the generator voltage busbars (6-10 kV), since, firstly, this will sharply increase the short-circuit currents, and secondly, the rated voltages of these generators are 15.75; 18 kV is different from distribution network voltage. Powerful generators are connected into blocks operating on 110 - 220 kV buses.

b) Block diagrams CHP

The growth in the unit capacity of turbogenerators used at CHPPs (120, 250 MW) has led to the widespread use of block diagrams. In the diagram shown in fig. 12, 6-10 kV consumers are powered by reacted taps from generators G1, G2; more distant consumers are fed through substations of deep input from 110 kV buses. Parallel operation of the generators is carried out at the highest voltage, which reduces the short-circuit current on the side of 6-10 kV. Like any block diagram, such a scheme saves equipment, and the absence of a bulky GRU allows you to speed up the installation of the electrical part. Consumer switchgear has two sections with ATS on the sectional switch. Switches Q1, Q2 are installed in generator circuits for greater reliability of power supply. Communication transformers T1, T2 must be designed to deliver all excess active and reactive power and must be equipped with an on-load tap-changer.

The transformers of blocks G3, G4 can also be provided with an on-load tap-changer, which allows to ensure the appropriate voltage level on the 110 kV buses when issuing reserve reactive power of the CHP operating according to the heat schedule. These transformers have an on-load tap-changer to reduce voltage fluctuations in MV installations.

With further expansion of the CHP, turbine generators G5, G6 are installed, connected in blocks. The 220 kV lines of these units are connected to a nearby district substation. There are no circuit breakers installed on the 220 kV side of the CHPP, the line is switched off by the circuit breaker of the district substation. In case of insufficient sensitivity of the relay protection of the substation to damage in the transformers T5, T6, the transmission of a teleswitching impulse (TO) is provided or short circuits and separators are installed. The generators are switched off by switches Q3, Q4.

Communication between the 110 and 220 kV switchgear is not provided, which greatly simplifies the layout of the 220 kV switchgear. As noted above, this is permissible if the connection of 110 and 220 kV networks is carried out at the nearest regional substation.

Modern powerful CHPPs (500-1000 MW) are built in block type. In the generator-transformer units, a generator switch is installed, which increases the reliability of the supply of SN and high-voltage switchgear, since this excludes numerous operations in the SN switchgear to transfer power from the working to the standby SN transformer. at each shutdown and start-up of the power unit and operations by high-voltage circuit breakers are excluded. It should not be forgotten that power units are switched off and on at CHPPs much more often than at CPPs or NPPs.

Figure 12. Scheme of a block CHP

MAIN SCHEMES OF IES

a) Requirements for schemes of powerful thermal power plants

The power of generators installed at thermal power plants is steadily increasing. Power units of 500 and 800 MW have been mastered in operation, units of 1200 MW are being mastered. The installed capacity of modern CPPs reaches several million kilowatts. On the buses of such power plants, communication is carried out between several power plants, power flows from one part of the power system to another. All this leads to the fact that large IESs play a very important role in the energy system. The following requirements are imposed on the electrical connection diagram of the IES:

1. The main circuit must be selected on the basis of an approved power system development project, i.e., the voltages at which electricity is produced, the load curves at these voltages, the network diagram and the number of outgoing lines, permissible short-circuit currents at elevated voltages, requirements for stability and sectioning of networks, the largest allowable loss of power in terms of reserve in the power system and the capacity of transmission lines.

2. At power plants with power units of 300 MW and more, damage or failure of any switch, except for bus-connecting and sectional ones, should not lead to the shutdown of more than one power unit and one or more lines, if the stability of the power system is maintained. In case of damage to the sectional or bus-coupling switch, the loss of two power units and lines is allowed, if the stability of the power system is maintained. If the damage or failure of one switch coincides with the repair of another, the loss of two power units is also allowed.

3. Damage or failure of any switch should not lead to disruption of transit through the busbars of the power plant, i.e. to the disconnection of more than one transit circuit if it consists of two parallel circuits.

4. Power units, as a rule, should be connected through separate transformers and switches on the high voltage side.

5. Shutdown of power transmission lines should be carried out by no more than two switches, and power units, auxiliary transformers - by no more than three switches of the switchgear of each voltage.

6. Repair of switches with a voltage of 110 kV and above should be possible without disconnecting the connection.

7. High-voltage switchgear circuits should provide for the possibility of network partitioning or dividing the power plant into independently operating parts in order to limit short-circuit currents.

8. When powered from this switchgear by two start-up auxiliary transformers, the possibility of losing both transformers in case of damage or failure of any switch should be excluded.

The final choice of the circuit depends on its reliability, which can be estimated by a mathematical method from the specific damage of the elements. The main circuit must meet the regime requirements of the power system, ensure minimal estimated costs.

b) Block diagrams generator - transformer and generator - transformer - line

In a block with a two-winding transformer, switches on the generator voltage, as a rule, are absent (Fig. 13, a). The power unit is switched on and off in normal and emergency modes by switch Q1 on the high voltage side. Such a power unit is called a monoblock. The connection of a generator with a block transformer and a tap to the MV transformer are carried out at modern power plants by closed complete current conductors with separated phases, which provide high reliability of operation, practically excluding phase-to-phase short circuits in these connections. In this case, no switching equipment between the generator and the step-up transformer, as well as on the branch to the transformer c. n. not provided. The absence of a circuit breaker on the branch to the MV leads to the need to turn off the entire power unit in case of damage in the MV transformer (Q1, switches on the 6 kV side of the MV transformer and the AGP generator are switched off).

Figure 13. Schemes of generator-transformer power units:

a, e - blocks with two-winding transformers; b - block with autotransformer; c - combined block; d- unit with generator 1200 MW

Given the high reliability of the transformers and the presence of the necessary power reserve in the power system, this scheme is accepted as a typical one for power units with a capacity of 160 MW or more.

On fig. 13b shows a diagram of a generator unit with an autotransformer. Such a scheme is used in the presence of two increased voltages at the IES. In the event of a fault in the generator, switch Q3 is switched off, the connection between the two overvoltage switchgears is maintained. In case of damage on buses with voltage of 110 - 220 kV or 500 - 750 kV, Q2 or Q1 will be disconnected, respectively, and the unit will continue to work on buses with voltage of 500-750 or 110 - 220 kV. Disconnectors between switches Q1, Q2, Q3 and the autotransformer are necessary to be able to bring the switches into repair while maintaining the unit or autotransformer in operation.

In some cases, in order to simplify and reduce the cost of the design of a switchgear with a voltage of 330 - 750 kV, a combination of two blocks with separate transformers for a common switch Q1 is used (Fig. 13, c). Switches Q2, Q3 are necessary to enable the generators for parallel operation and provide greater reliability, since in case of damage in one generator, the second generator remains in operation.

It should be noted that the presence of generator circuit breakers makes it possible to start the generator without using a start-up reserve transformer SN. In this case, when the generator switch is off, the power to the s.n. is fed through a block transformer and a working transformer s.n. After all start-up operations, the generator is synchronized and switched on by switch Q2 (Q3).

Instead of bulky and expensive air circuit breakers on generator voltage, load break switches can be installed. In this case, a fault in any power unit will trip the circuit breaker Q1. After separation of the damaged power unit, the serviceable unit is put into operation.

The use of integrated power units is permissible in powerful power systems with sufficient reserve and throughput capacity of interconnections, in case of layout difficulties (limited area for the construction of a switchgear with a voltage of 500 - 750 kV), as well as in order to save circuit breakers, air and cable connections between transformers and a switchgear of increased voltage.

1200 MW generators with two independent stator windings (six-phase system) are connected to a step-up transformer with two LV windings: one connected in a delta and the other in a star to compensate for a 30 ° shift between the voltage vectors of the stator windings (Fig. 13d).

In some cases, blocks with a generator switch are used (Fig. 13, e). Switching off and on of the generator is carried out by switch Q (or load switch QW), without affecting

Figure 14. Scheme of IES (8x300 + 1x1200) MW

Figure 15. Scheme of IES (6x800) MW

NPP MAIN SCHEMES

a) Special requirements for NPP schemes

Like the schemes of other power plants (CHP, CPP), NPP schemes must be carried out in accordance with the requirements set forth earlier in terms of reliability, flexibility, ease of operation, and economy.

Features of the technological process of nuclear power plants, the high power of reactor power units, reaching 1500 MW at modern power plants, the delivery of all power to the power system via 330 - 1150 kV lines impose a number of special requirements for nuclear power plants:

the main scheme of the NPP is selected on the basis of the scheme of networks of the power system and the section to which this power plant is connected;

the scheme for connecting the NPP to the power system should ensure, in normal initial modes at all stages of the construction of the NPP, the output of the full input power of the NPP and the preservation of the stability of its operation in the power system without the impact of emergency automatics when any outgoing line or communication transformer is disconnected;

in repair modes, as well as in case of failure of circuit breakers or relay protection devices, the stability of the NPP must be ensured by the action of emergency automatics for unloading the NPP. Considering these requirements, at NPPs, starting from the first commissioned power unit, communication with the power system is carried out by at least three lines.

When choosing the main scheme of a nuclear power plant, the following are taken into account: the unit capacity of the units and their number; voltages at which power is supplied to the power system; the value of flows between switchgear of different voltages; short circuit currents for each switchgear and the need to limit them; the value of the highest power that can be lost if any circuit breaker is damaged; the possibility of connecting one or more power units directly to the switchgear of the nearest regional substation; the use, as a rule, of no more than two high-voltage switchgears and the possibility of refusing the autotransformers of communication between them.

Switchgear 330-1150 kV NPP must be made extremely reliable:

damage or failure of any switch, except for a sectional or bus-connecting switch, should not, as a rule, lead to the shutdown of more than one reactor unit and such a number of lines that is permissible under the condition of the stability of the power system;

in case of damage or failure of a sectional or bus-coupling switch, as well as if damage or failure of one switch coincides with the repair of another, it is allowed to shut down two reactor units and such a number of lines as is permissible under the condition of stability of the power system;

disconnection of lines, as a rule, should be carried out by no more than two switches;

shutdown of step-up transformers, transformers with. n. and communications - no more than three switches.

Such requirements are met by circuits 4/3, 3/2 switches for connection, block circuits generator - transformer - line, circuits with one or two polygons.

Switchgear 110 - 220 kV NPP is made with one or two working and bypass busbar systems. The working busbar system is sectioned if the number of connections is more than 12.

b) Typical NPP schemes

Given the high requirements for NPP diagrams, design organizations develop the main electrical connection diagrams for each specific NPP. Let us consider the most characteristic NPP scheme with 1500 MW channel boiling reactors (RBMK-1500) and 800 MW turbine generators (Fig. 16). NPP power output is carried out at a voltage of 750 and 330 kV. 330 kV switchgear is constructed according to the scheme of 4/3 circuit breaker for connection. RU 750 kV is made according to the scheme of two connected quadrangles with switches in jumpers. Generators G3, G4 and G5, G6 form enlarged power units, which makes it possible to apply an economical quadrangle scheme after the commissioning of the third reactor power unit. The fourth reactor power unit with generators G7, G8 are connected to the second 750 kV quadrilateral. With further expansion of the nuclear power plant and the installation of the fifth reactor power unit, generators G7, G8 and newly installed G9, G10 will be combined into enlarged power units. The 750 kV lines have a carrying capacity of about 2000 MW, so three lines will fully ensure the output of the entire power of the connected power units, taking into account possible expansion.

Shunt reactors LR1 - LR3 are connected to the lines through separate circuit breakers. Communication between switchgear 330 and 750 kV is carried out by a group of three single-phase autotransformers (installation of a reserve phase is provided). Standby transformers p. n. connected RT1 - to the district substation 110 kV; RT2 - to switchgear 330 kV; RTZ - to the medium voltage of the communication autotransformer with the possibility of switching to a switchgear of 330 kV; PT4 - to the LV winding of the autotransformer.

Figure 16. Scheme of NPP with reactor power units 1500 MW

MAIN SUBSTATION DIAGRAM

General information

The main electrical connection scheme of the substation is selected taking into account the development scheme of the electrical networks of the power system or the power supply scheme of the area.

According to the method of connecting to the network, all substations can be divided into dead-end, branch, passing, nodal.

A dead-end substation is a substation that receives electricity from one electrical installation through one or more parallel lines.

The branch substation is connected by a deaf tap to one or two passing lines.

The walk-through substation is included in the cut of one or two lines with two-way or one-way power supply.

A nodal substation is a substation to which more than two supply lines are connected, coming from two or more electrical installations.

By purpose, consumer and system substations are distinguished.

The substation scheme is closely linked to the purpose and method of connecting the substation to the supply network and should:

ensure the reliability of power supply to consumers of the substation and power flows through intersystem or trunk communications in normal and post-emergency modes;

take into account the development perspective;

allow for the possibility of gradual expansion of switchgear of all voltages;

take into account the requirements of emergency automation;

provide the possibility of carrying out repair and maintenance work on individual elements of the circuit without disconnecting adjacent connections.

The number of simultaneously operating switches should be no more than:

two - in case of line damage;

four - in case of damage to transformers with voltage up to 500 kV, three - 750 kV.

In accordance with these requirements, typical switchgear diagrams of 6-750 kV substations have been developed, which should be used in the design of substations.

An atypical main circuit must be justified by a feasibility study.

Schemes of dead-end and branch substations

Dead-end single-transformer substations on the 35-330 kV side are made according to the transformer-line block scheme without switching equipment or with one disconnector (Fig. 17, a), if the line protection from the supply end has sufficient sensitivity to damage in the transformer. Such a scheme can also be used if the transmission of a remote tripping signal is provided for 330 kV substations with transformers of any capacity, and for 110-220 kV substations with transformers of more than 25 MB A. Disconnectors are not installed when cable entry into the transformer.

Fuses on the side of 35, 110 kV power transformers are not used. At dead-end and branch substations only for 110 kV, it is allowed to use circuits with separators (Fig. 17, b) with the exception of: substations located in cold climate zones, as well as in a particularly icy area; if the actions of separators and short circuiters lead to loss of synchronism of synchronous motors at the consumer; at substations of transport and oil and gas production; for connecting transformers with a capacity of more than 25 MBA; in the circuits of transformers connected to lines having an APV.

In the substation diagram according to Fig. 17, b on the 110 kV side there is a QS disconnector, a QR separator and in one phase - a QN short circuit, on the 6-10 kV side - a Q2 switch.

In cases where the circuits discussed above are not recommended, a typical circuit with a switch on the side of 35 - 500 kV is used (Fig. 17, c).

Figure 17. Block diagrams transformer - line:

a – without HV switch; b – with VN separator; c - with HV switch

Schemes of walk-through substations

If it is necessary to section off lines, transformer power up to 63 MB A inclusive and voltage 35 - 220 kV, bridge circuits are recommended (Fig. 18). The scheme shown in fig. 18, a, is used on the 110 kV side with transformer power up to 25 MB A inclusive. Repair jumper with disconnectors QS7, QS8 is normally disconnected by one disconnector (QS7).

Switch Q1 in the bridge is turned on if power transit occurs along lines W1, W2. If it is necessary to exclude the parallel operation of lines W1, W2 in terms of limiting short-circuit currents, switch Q1 is open. If the transformer (T1) is damaged, the switch on the side of 6 (10) kV Q4 is turned off, the short circuiter QN1 is turned on, the switch Q2 is turned off at the supply end of the line W1 and the separator QR1 is turned off, and then the disconnector QS1.

Figure 18. Bridge diagrams:

a - with a switch in the jumper and separators in the transformer circuits; b - with switches in the circuit of lines and a repair jumper from the side of the lines

If, according to the network operation mode, it is necessary to restore the W1 line, then the switch at the supply end of this line and the Q1 bridge switch are automatically turned on, thus, transit along the lines W1, W2 is restored. The repair jumper is used when revising the Q1 switch, for this QS7 is turned on, Q1 and QS3, QS4 are turned off. Transit on lines W1, W2 is carried out through a repair jumper, transformers T1, T2 in operation.

In networks of 220 kV and transformers up to 63 MB A inclusive, to increase the reliability of operation, the separators are replaced by switches Q1, Q2 (Fig. 18, b).

The repair jumper is open by the QS9 disconnector. Switch Q3 in the bridge is turned on, allowing power to pass through lines W1 and W2. In the event of an accident in the transformer T1 the circuit breaker on the 6 (10) kV side and circuit breakers Q1 and Q3 are switched off. After the disconnector QS3 is switched off, Q1 and Q3 are switched on and transit is restored. To repair Q1, turn on the repair jumper (disconnector QS9), turn off Q1 and disconnectors QS1 and QS2. If in this mode an accident occurs in T2, then Q2 and Q3 are turned off and both transformers remain without power. It is necessary to disable QS6 and enable Q3 and Q2, then T1 connected to both lines. This drawback can be eliminated if the bridge and the repair jumper are interchanged. In this case, in case of a fault in the transformer, one switch is turned off on the HV side of the transformer, the switch in the bridge remains on, which means that power transit through W1, W2 is preserved.

If the project of system automation in 220 kV lines provides for an AR, then instead of the considered scheme, a quadrangle scheme is recommended.

The quadrangle scheme is used with two lines and two transformers, if it is necessary to section off transit lines, with critical consumers and transformer power at a voltage of 220 kV 125 MB A or more, and any power at a voltage of 330 - 750 kV.

Schemes of powerful nodal substations

On the 330 - 750 kV busbars of the nodal substations, individual parts of the power system or the connection of two systems are connected, therefore, higher reliability requirements are imposed on the circuits on the HV side. As a rule, in this case, circuits with multiple connection of lines are used: ring circuits, circuits of 3/2 circuit breaker per circuit and transformer-bus circuits with connection of lines through two circuit breakers (with three and four lines) or with one and a half connection of lines (with five six lines).

On fig. 19 shows a diagram of a powerful nodal substation. On the 330 - 750 kV side, a bus circuit is used - an autotransformer. There are two switches in the circuit of each line, autotransformers are connected to the busbars without a switch (disconnectors with a remote drive are installed). When damaged T1 all switches connected to K1 are turned off, the operation of the 330-750 kV lines is not disturbed. After shutdown T1 disconnector QS1 is remotely disconnected from all sides and the circuit from the HV side is restored by closing all the switches connected to the first busbar system K1.

Depending on the number of 330-750 kV lines, it is possible to use ring circuits or a 3/2 circuit breaker circuit per circuit.

On the medium voltage side of 110-220 kV powerful substations, a circuit with one working and one bypass busbar systems or with two working and one bypass busbar systems is used.

When choosing a circuit on the LV side, the issue of limiting the short-circuit current is first of all solved. For this purpose, you can use transformers with an increased value of u to, transformers with a split LV winding, or install reactors in the transformer circuit. In the scheme shown in fig. 19, twin reactors are installed on the HH side. Synchronous compensators with starting reactors are connected directly to the outputs of LV autotransformers. Connecting powerful GCs to 6-10 kV buses would lead to an unacceptable increase in short-circuit currents.

Linear regulating transformers JIPT can be installed in autotransformer circuits on the LV side for independent voltage regulation.

Figure 19. Scheme of the nodal substation

Description of the main circuit

The main circuit of electrical substations is a combination of the main electrical equipment: transformers, lines, switches, busbars, disconnectors and other switching equipment with all electrical connections made between them.

The main substation circuits are subject to the same basic requirements for reliability, service safety, durability, maintainability, efficiency and maneuverability as for the main circuits of power plants.

Depending on the position of the substation in the system, these requirements, in particular the requirements of reliability and flexibility, may in some cases be less stringent.

The number of transformers in the substation is of particular importance for choosing a circuit. According to current practice, no more than two transformers are usually installed in substations.

According to the PUE, when developing the main circuit of electrical power circuits, it is necessary to take into account the categories of consumers to ensure the reliability of power supply. The installation of one transformer at the substation is allowed in cases where the consumers of the area belong to the 2nd and 3rd categories, allowing short-term interruptions in the power supply, necessary to turn on the backup power from the network.

At a 500 kV substation. a one and a half scheme was used (3 switches and 2 connections). Connections are not fixed on any one circuit, but are included in the gap between the circuit switches. The choice of this scheme is justified by its advantages over others and not so critical disadvantages.

The advantages of the one-and-a-half scheme include the following: revision of any circuit breaker or busbar system is carried out without disrupting the operation of the connections and with a minimum number of operations when these elements are taken out for repair; disconnectors are used only during repairs (providing a visible break to the energized switchgear elements); both busbar systems can be switched off at the same time without disturbing the operation of the feeders. The one-and-a-half scheme combines the robustness of a busbar arrangement with the maneuverability of a polygon arrangement.

The disadvantages of the one-and-a-half scheme include a large number of switches and current transformers, the complication of relay protection of connections and the choice of switches and all other equipment for double the rated currents.

The increased number of switches in the one-and-a-half circuit is partially offset by the absence of interbus switches.

Description of the main equipment of a 500 kV substation

The 500 kV substation has two incoming and two outgoing 500 kV lines, as well as two autotransformers that convert the voltage from 500 kV to 330 kV. . Measuring current and voltage transformers. Numerous connecting buses and busbars for connecting equipment to each other. There is also a technical building at the substation, where there is a constantly on-duty staff who monitors the performance of the substation, as well as all the relay protection and automation panels.

Step-down substations are designed to distribute energy over the LV network and create connection points for the HV network (switching points). The determining factor for choosing the location of the substation is the scheme of the low-voltage network, for the supply of which the substation in question is intended. The optimal power and range of the substation are determined by the density of loads in the area of ​​its location and the scheme of the low-voltage network.

Substation electrical connection diagrams are selected depending on their purpose. According to the method of connection to power lines, there are dead ends(Fig. 2.9, a, d), branch(Fig. 2.9, b, e, g, i), walk-through(Fig. 2.9, c, e, h, l) and nodal(Fig. 2.9, j) substations.

Rice. 2.9. The main types of connection of substations to the network:

a, b, c - radial with one overhead line; d, e, f - double radial; g, h, and - with two power centers; k, l - with three or more power centers (CPU)

Most substations are connected to the network via two lines, while the proportion of substations connected at the first stage via one line is decreasing. The share of nodal substations increases with the growth of the network voltage, while the share of dead-end and branch substations decreases. The most common type of substation 110 ... 330 kV is a checkpoint.

An analysis of the schemes for constructing an electrical network of 110 ... 330 kV shows that up to four overhead lines are connected to the nodal substations; a larger number of lines is, as a rule, a consequence of the uncontrolled development of the network, an unsuccessful choice of configuration or a delay in the construction at the considered point of the network of the high voltage CPU.

It is advisable to apply for newly constructed substations schemes of through and nodal connections (see Fig. 2.9). These schemes have higher indicators of reliability of power supply to consumers.

The choice of switchgear circuits (RU) of substations is carried out from among the typical ones (Fig. 2.10, Table 2.3), taking into account their scope. On the side of HV and MV substations, these are, as a rule, open switchgears (OSG).

Table 2.3. - Characteristics of some typical switchgear circuits 35 ... 750 kV

The number of the typical circuit in fig. 2.10	Scheme name	Application area	Additional terms
Voltage, kV	Substation side	Number of connected lines
5N	Bridge with switches in line circuits and a repair jumper on the line side	35…220	VN		Pass-through substations if it is necessary to keep transformers in operation in case of damage to overhead lines
	Quadrilateral	220…750	VN		1. An alternative to the "bridge" scheme for 110-220 kV substations. 2. For SS 330 - 750 kV as the initial stage of more complex schemes
	One sectioned bus system	35…220	HV, SN, LV	3 or more	The number of radial overhead lines is not more than one per section
9H	One sectioned busbar system with transformers connected via a junction of two circuit breakers	110…220	HV, CH	3 or more	1. The number of radial overhead lines is not more than one per section. 2. With increased requirements for maintaining transformers in operation
12N	One working sectionalized and bypass busbar system with transformers connected through a junction of two circuit breakers	110…220	HV, CH	3 or more	With increased requirements for maintaining the operation of transformers
	Bus transformers with one and a half line connection	220…750	HV, CH	5…6
	One and a half scheme	220…750	HV, CH	6 or more

Fig.2.10. Typical switchgear diagrams 35…750 kV. Numbers - numbers of typical schemes

10(6) kV switchgear diagrams are shown in fig. 2.11. A circuit with one partitioned busbar system (Fig. 2.11 b, c) is used with two transformers with non-split LV windings. A circuit with two sectioned buses (Fig. 2.11 d) is used with two transformers with split LV windings.

Fig.2.11. Low voltage switchgear diagrams:

a - with one non-sectioned bus system; b, c - with one sectioned bus system; d - with two sectioned bus systems

The number of outgoing lines on the MV and LV sides is determined by their capacity and the installed power of the transformers (Table 2.4).

The appropriate number of 110 kV overhead lines outgoing from substations with 220 ... 330 kV high voltage is given below.