Schemes for connecting substations to the network. Schemes of electric power plants and substations One and a half scheme

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 side high voltage 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 are called sections of tires of a rigid or flexible design with a small electrical resistance designed to connect 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 power switchgear circuits own needs 6 kV or in a generator switchgear 6 - 10 kV 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 (one in this moment) 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 case of 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 that are connected to 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 scheme, due to additional expense switches (conditionally 1.5 switches per connection, hence the second name of the “one and a half” circuit) achieves high operational flexibility and reliable connection between connections 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 secondary windings 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 attachment of an element in general scheme 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. Complete shutdown 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, 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 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. 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 line W1 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 plants 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 scheme is the initial one when compiling circuit diagrams 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 circuit and the connections between them are depicted in accordance with the standards unified system design documentation (ESKD).

Page 17 of 111

The simplest type of main circuit, which appeared earlier than others, is a circuit with one non-partitioned bus system (Fig. 2-1, a); The advantages of the scheme lie in its extreme simplicity, visibility in kind, and minimal costs for the construction of the switchgear. However, this scheme does not provide sufficient reliability of power supply. Damage to busbars, busbar disconnectors or any switch causes the complete extinction of all connections. Tire repair requires a power outage to all consumers. The revision of any circuit breaker is also associated with the repayment of its connection for the entire time of work.
It is possible to reduce the amount of repayments with one bus system by sectioning it (Fig. 2-1, b). However, a significant reduction in the volume of repayments in such a scheme during accidents can be achieved only with its deep sectioning, when the number of sections is equal to the number of connections.

Rice. 2-1. Single bus system: a - non-sectional; b - sectioned; in - ring; g - with a bypass disconnector


Rice. 2-2. Bridge schemes; a- simple; b-with two disconnectors in the jumper; c - with three switches; Mr. double
This makes the scheme uneconomical, and the need to pay off connections during the repair of their switches remains.
Replacing some of the switches with sectional disconnectors to reduce the cost of a sectioned circuit significantly reduces its reliability and can only be allowed on small low-responsibility installations in cases where repair conditions are decisive.
An increase in the reliability of a circuit with one busbar system can be achieved by turning it into a ring system by connecting the busbar ends to each other (Fig. 2-1, c). However, the advantages of the ring circuit, which consist in the two-way supply of connections, are realized only with its deep sectioning. The revision of the connection switch here also leads to the repayment of this connection for the duration of the repair.
The addition of a bypass disconnector /, which allows revisions of the connection switch without interrupting the power supply to consumers, increases the maintainability of the ring circuit (Fig. 2-1, d).
The bypass disconnector can be installed on the jumper between adjacent lines (Fig. 2-2, a), The resulting bridge circuit has noticeably greater flexibility and maintainability, since it is possible to revise any linear switch without extinguishing the connection, so that the revision of the jumper disconnector is not required the disconnection of both lines, it is enough to install a second bypass disconnector in series with it (Fig. 2-2, b). However, the best results are obtained by combining the bridge scheme with the sectioning of the busbars between the feeders. The resulting bridge circuit with three switches (Fig. 2-2, c) is very convenient for feeding a two-transformer substation with a transit line, as well as for injecting power into a small two-unit power plant with a block diagram.


Fig, 2-3. Polygon schemes: a - simple; b - connected; in - with a diagonal connection; g - with twin connections
The double bridge circuit (Fig. 2-2, d) allows you to have an extra connection at increased voltage. Schemes fig. 2-2, c and d are used in the first phase of the construction of a power plant or with a small number of connections. These circuits are quite economical, since the number of switches in them is one less than the number of connections.
The desire to increase the efficiency of ring circuits while maintaining their technical advantages has led to the creation of polygon-type circuits. As can be seen from fig. 2-3, a, the polygon scheme differs from the annular one by the absence of connection switches. In this scheme, the switches are installed in the cut of the tires closed in a ring. The connections are connected to the busbars between the circuit breakers via disconnectors. Thus, each connection is connected to the circuit immediately through two switches, which, when switching the connection, must both turn on or off. After disconnecting the connection, the ring - will be open, and it can be closed again only after disconnecting the connection disconnector. The number of switches in the polygon is equal to the number of connections, i.e. the same as in the non-partitioned ring, however, due to the placement of the switches in the corners of the polygon, the circuit has all the advantages of a deeply partitioned circuit. Another advantage of the polygon scheme is the small amount of redemption even with the most severe damage to one of the switches (no more than two connections are lost). The revision of any circuit breaker requires a minimum of operations and can be carried out without disturbing the operation of the connection.
The disadvantages of the polygon scheme include the complexity of the relay protection of connections and the choice of current transformers, in which it should be possible to repair any of the three switches in the common circuit.
Another disadvantage of the circuit is the need for a more frequent revision of the switches, since any short circuit disconnection is carried out in it by two switches at once.
Finally, a short circuit during the revision period of one of the switches can lead to serious difficulties, when the breakdown of the circuit into unrelated parts is likely to cause a power imbalance (in a part of the circuit there will be a lack or even complete absence of power supplies, while at the same time in another parts power cannot be used).
To mitigate these shortcomings, limit the number of attachments, and hence the number of sides of the polygon, to six; with a larger number of connections, they are divided between two or even three interconnected polygons (Fig. 2-3, b). In some cases, the number of sides of the polygon is allowed to be more than six, but diagonal connections are made at the same time (Fig. 2-3, c).
If it is possible to provide a redundant supply of the connections via the network, the polygon scheme can be made even more economical by pairing the connections (Fig. 2-3, d). In this case, the number of switches is halved, for example, in a square circuit, eight connections can be connected. In the event of a short circuit on one of the connections, both are temporarily disconnected, but the power of the undamaged one can be quickly restored. In the event of a short circuit in the bus section, the line connections must receive backup power from the mains. Of course, in this case, the generator connection will be disconnected for the duration of the restoration of damaged busbars, which will also take place in schemes with unpaired connections.
The paired circuit can be greatly improved by adding a disconnector (1 in Fig. 2-3, d) between the paired connections. In this case, either of the two bays can be disconnected and connected without temporarily disconnecting the other bay. It is sufficient to turn off disconnector 1 first in case of disconnection of the connection, and turn on this disconnector last when connecting.


Rice. 2-4. Schemes of a triangle (a) and a square (b)
Examples of the simplest polygon schemes are triangle schemes (Fig. 2-4, a) and square (Fig. 2-4, b), which can be successfully used with a small number of connections.
An improvement to the single busbar design is the addition of a special bypass busbar to the working system (Figure 2-5). In this case, each connection can be connected to the bypass bus system through its own bypass disconnector, and the bypass system itself is connected to the working system using a bypass switch. The withdrawal of the connection switch for repair is simple and is carried out as follows: 1) the bypass switch is turned on; 2) the connection bypass disconnector is switched on, the switch of which must be inspected; 3) the connection switch is turned off, and its circuit is disassembled. After grounding is applied, the circuit breaker is ready for repair.

Rice. 2-6. Dual bus system
The scheme with one working and one bypass busbar system has the following advantages: revision of any circuit breaker can be performed without interrupting the operation of the connection; there are no bus junction disconnectors (personal errors are excluded).


Rice. 2-5. Single busbar system with bypass bus

Rice. 2-7. Scheme with two main and one bypass bus systems


Rice. 2-8. Circuit with two switches per circuit
The scheme has the following disadvantages: it is necessary to install bypass and sectional switches; revision of the main working busbar system is impossible without repayment of connections; a short circuit on the working busbar system leads to the extinguishing of all connections of one section; damage to the section switch leads to the extinguishing of all connections of both sections.
A natural development of the circuit with one bus system is the circuit with two working bus systems (Fig. 2-6). The busbar switch allows for arbitrary separation of connections between busbar systems, thus creating various options for operating network diagrams depending on the requirements of the system and the operating conditions of the power plant. Sectional switches reduce the amount of redemption in case of short circuits on the busbars.
The advantages of the scheme with two working bus systems are, firstly, in fast recovery supply of connections in the event of a short circuit in one of the sections by switching them to an undamaged busbar system and, secondly, by facilitating the repair of busbars and busbar disconnectors.
Repair of the connection switch is possible here only when installing removable bypass jumpers and transferring the action of the relay protection of the connection to the busbar switch, which in this circuit replaces the switch being reviewed. Since the installation of jumpers instead of the switch is carried out with the voltage removed from the connection, the preparation of the switch for repair inevitably causes a break in the operation of this connection.
This shortcoming can be eliminated by adding bypass buses to the two working systems (Fig. 2-7). The resulting scheme with two main and one bypass bus systems with one switch per circuit, having all the advantages of a simple scheme with two systems, has a higher maintainability.


Rice. 2-9. Scheme with fixed connections: transformer - tires (a); line - tires (b)
Over the past 20 years, it has become widespread in our country at powerful block stations due to the fact that it makes it possible to revise any bus system and any switch without interrupting the operation of the connections, and also allows you to group these connections in an arbitrary way.
However, in modern conditions, with an increase in voltage up to 750-1150 kV and an increase in unit capacities of units up to 1.2 GW, and individual stations up to 4-6 GW, this system becomes insufficiently reliable and economical. A large power loss (2-3 GW) in case of failure of any 750 kV auxiliary switch and the significant cost of installing these switches (6-8 million rubles) limit the scope of circuits with bypass buses with voltages of 110-220 kV.
The two circuit breaker per circuit (double circuit) circuit is a variation of the dual busbar circuit (Figure 2-8). An increase in reliability and maintainability in it is achieved by installing in series with each disconnector a fork of switches.
The advantages of such a scheme are the ease of repair of any busbar system and the possibility of bringing the circuit breakers into repair without operations by disconnectors under current. Busbar damage does not lead to termination of the connections here.
However, if a short circuit on the busbars occurs during the revision of one of the busbar systems, it will be accompanied by the complete repayment of all connections.
To disadvantages double circuit we must also include the need for more frequent revisions of the circuit breakers, since faults on the lines are switched off by two circuit breakers at once. But the main disadvantage of the circuit is its excessive cost due to the large number of switches and current transformers. Therefore, its use is not currently recommended.
A variant of the double circuit is a circuit with fixed connections of a transformer-bus (Fig. 2-9, a) or a line-tire (Fig. 2-9, b). Conclusion to the revision of any switch is possible here without disrupting the operation of the connections with a minimum of switching in the circuit. However, the scheme also has major drawbacks: damage to the tires means the loss of a block or line; line fault is switched off by all circuit breakers


Rice. 2-10, One and a half pattern (a) and 4/3 pattern (b)
(more often revisions of switches); with the number of connections greater than five, the circuit requires the installation of a large number of switches; tire revision requires block redemption or line shutdown; damage to the busbar system during the revision of another system leads to the complete repayment of the entire installation.
Taking into account all these shortcomings, the use of schemes with fixed connections is allowed only with a small number of connections in some rare cases.
For powerful block power plants, one-and-a-half schemes and 4/3 schemes, as well as schemes of “pure” generator-transformer-line (G-T-L) blocks, are becoming more and more widely used.
The one-and-a-half scheme (Fig. 2-10, a) has the following advantages: any circuit breaker or busbar system is inspected without disturbing 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. As can be seen, the one and a half circuit combines the reliability of a busbar circuit with the maneuverability of a polygon circuit.
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.
The 4/3 circuit (Fig. 2-10, b) is similar to the one and a half, but more economical, since it does not have 1/2 more switches per circuit than in the double busbar circuit, but only 1/3 .
Schemes of a "clean" G-T-L block are used only at voltages of 110-220 kV and a relatively short length of block lines, since these circuits poorly use the capabilities of block lines: their throughput at voltages of 330-750 kV significantly exceeds the power of block generators , and when the generator is stopped for repairs, the line of the unit cannot be used to reduce losses in the network (Fig. 2-11).


Rice. 2-11. "Clean" blocks G-T-L
Much better than the one proposed by L. I. Dvoskin scheme G-T-L with an equalizing polygon and a bypass bus system, in which the number of switches is only one more than the number of connections, and bypass buses and an equalizing polygon allow you to maneuver the lines in normal mode, in case of accidents and repairs, preventing power imbalances and interruptions in the operation of connections. It should only be noted the complication of the relay protection of a block transformer connected to the circuit by three switches,

Scheme with two switches per connection

Scheme with two working and bypass busbar systems

The scheme shown in Figure 10.3 makes it possible to carry out revisions of any busbar system and any circuit breaker without interrupting the operation of the connections, and also allows you to group these connections in an arbitrary way.

As a rule, both busbar systems are in operation with a corresponding fixed distribution of all connections: lines W1, W3, W5 and transformer T1 connected to the first bus system A1, lines W2, W4, W6 and transformer T2 connected to a second bus system A2, bus connection switch QA included. 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 is turned off QA and only half of the attachments. 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 for power plants - with the number of connections up to 12.

a) the main scheme; b), c) scheme options.

Figure 10.3 - Schemes with two working and bypass bus systems

The two-breaker per circuit circuit is a variation of the two-busbar circuit and is shown in Figure 10.4. An increase in reliability and maintainability in it is achieved by installing in series with each disconnector a fork of switches.

The advantages of such a scheme are the ease of carrying out repairs of any busbar system and the possibility of bringing the circuit breakers into repair without operations by disconnectors under current. Busbar damage does not lead to termination of the connections here.

Figure 10.4 - Diagram with two switches per circuit

The main disadvantage of the scheme is its high cost.

One and a half scheme shown in Figure 10.5 a, provides an audit of any circuit breaker or busbar system without disturbing the operation of the connections and with a minimum number of operations when these elements are taken out for repair. In this case, the disconnectors perform only the provision of a visible break. The one and a half circuit combines the reliability of a busbar circuit with the maneuverability of a polygon circuit. The disadvantages of the one-and-a-half scheme include the complication of relay protection of connections and the need to select switches and all other equipment for double the rated currents.

Diagram 4/3 shown in Figure 10.5 b similar to one and a half, but more economical, since it does not have 1/2 more switches per circuit than in the double busbar scheme, but only 1/3.

Figure 10.5 - Schemes: a- one and a half; b- 4/3

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 network diagram for which it is intended to power. The optimal power and range of the PS are determined by the density of loads in the area of ​​​​its location and the scheme of the LV network. With a high density of loads, a complex and branched LV network, the expediency of substation HV substations should be considered to increase the reliability of power supply and reduce the cost of building a LV network. Normative documents have not established the classification of substations according to their place and method of connecting to the network. Based on the types of network configuration used (see clause 4.2) and possible schemes for connecting the substation, they can be divided into the following (7): dead-end - powered by one (clause 4.7, a) or two radial lines; scheme 4.7, a is considered as the first stage of network development with subsequent transformation into scheme 4.7, b or 4.7, e; branch lines - attached to one (7, c) or two (7, d) passing overhead lines on branches; scheme 4.7, c is the first stage of development with subsequent transformation into scheme 4.7, d or e; walk-through - connected to the network by entering one line with two-way power supply (7, d); nodal - connected to the network by at least three supply lines (7, f, g). Branching and passing PSs are combined by the term intermediate, which determines the placement of the PS between two network CPUs (or nodal PSs).
Passage or nodal substations, through the buses of which flows between individual points of the network are carried out, are called transit. In the technical literature and some regulatory documents, the term reference substation is sometimes used, which, as a rule, means a substation of a higher voltage level (for example, a 220/110 kV substation when considering a 110 kV network). However, the same term is used to define the operational role of the MS. Therefore, for substations that feed the network of the voltage under consideration, it is advisable to use the term power center (CPU). In table. 4.3 shows the data of a statistical analysis of the frequency of application of the above schemes for connecting substations in networks of 110–330 kV. From the above data, it can be seen that the majority of substations join the network via two lines. There is a trend towards an increase in the share of such schemes due to a decrease in the share of substations connected at the first stage along one line. The share of nodal substations increases with increasing network voltage, while the proportion of dead-end and branch substations decreases. The most common type of 110–330 kV substation is a walk-through substation. Table 4.3


An analysis of the schemes for constructing electrical networks of 110–330 kV shows that it is advisable to connect up to four overhead lines 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 HV CP network. Schemes for connecting the substation to the network, allowable amount intermediate substations between two CPUs are selected depending on the load and responsibility of substation consumers, the length of the considered network section, the feasibility of its sectioning and the need to maintain power transit. For some consumer groups (railway traction substations, pumping and compressor stations of main pipelines, oilfield facilities in Western Siberia, the largest cities), these issues are regulated by departmental and normative documents. Recommendations on substation connection schemes for typical consumer groups are given below (see clauses 4.5–4.9). For the implementation of step-down substation projects in the schemes for the development of power systems and electric networks, the following must be preliminarily determined: the substation location area, electrical loads for the billing periods, switchgear voltages, the number and power of transformers, the number, direction and load of lines by voltage, type and power of the KU, calculated values ​​of short-circuit currents, recommendations on the main wiring diagram. Basic requirements for the main circuits of electrical connections: the circuit must provide reliable power supply to connected consumers in normal, repair and post-emergency modes in accordance with the load categories for the reliability of power supply, taking into account the presence or absence of independent backup power sources; the scheme should ensure the reliability of power transit through the substation in normal, repair and post-accident modes in accordance with its value for the considered section of the network; the scheme should be as simple as possible, visual, economical and provide the possibility of restoring power to consumers in a post-accident situation by means of automation without personnel intervention; the scheme should allow the stage-by-stage development of the reactor facility with the transition from one stage to another without significant reconstruction work and interruptions in the supply of consumers; the number of simultaneously operating circuit breakers within one switchgear should be no more than two in case of line damage and no more than four in case of transformer damage. One of the most important principles for building a network that ensures the requirements of reliability and minimum reduced costs is the unification of design solutions for substations. The greatest effect can be achieved with the unification of mass-use substations, which are elements of the distribution network of power systems. A prerequisite for this is the typification of the main circuits of electrical connections that determine technical solutions in the design and construction of substations. Standard schemes were approved by JSC FGC UES on December 20, 2007 (STO 5694700729.240.30.010-2008). The main electrical connection diagram of the substation is selected using typical diagrams of 35-750 kV switchgear, which are widely used in the design. Deviations from standard schemes are allowed subject to feasibility studies and agreement with the approving authorities. In the latest edition, the number of typical schemes has been significantly increased (from 14 to 20); at the same time, 11 schemes recommended in the first place were selected from this number. However, it should be noted that the introduction of a number of new schemes seems to be insufficiently motivated, since it does not take into account the principles of network construction. 8 shows typical diagrams of RU 35-750 kV, and in table. 4.4 - list of schemes and their scope. Typical switchgear circuits are indicated by two numbers indicating the mains voltage and circuit number (for example, 110-5N, 330-7, etc.). The scheme numbers have not changed since the first edition of the standard schemes; in the future, some schemes were excluded from the number of typical ones.


During the period of construction of electrical networks at a high pace, at the stage of "electrification in breadth" (1960–1985), at 110 kV substations (partially - 35 and 220 kV) with simplified circuits for high voltage separators and short circuiters became widely used as switching devices. The simplicity of design and their relative cheapness in comparison with circuit breakers made it possible to ensure the mass construction of substations in a short time. At the same time, these devices have certain design defects and operational shortcomings. The fundamental disadvantage of circuits with separators and short circuits is that an artificially created short circuit to disconnect the damaged section of the network during a dead pause with the help of a separator sharply increases the total duration of the most difficult operating conditions for switches at adjacent substations. Therefore, at present, the use of separators and short circuits at newly constructed substations has been discontinued, and during the reconstruction of existing substations, they must be replaced by circuit breakers. The index "H" (3H, 4H, 5H, 5AN) has been added to the numbers of typical circuits in which separators and short circuits are replaced by switches. For VN switchgear, characterized by a smaller number of connections, as a rule, more simple circuits: without switches or with one or less switches per connection. For SN switchgear, schemes with bus systems and with more than one circuit breaker (up to 1.5) per connection are used. Table 4.4

Continuation of the table. 4.4
Continuation of the table. 4.4
The end of the table. 4.4


Block circuits 1, 3H are, as a rule, the first stage of a two-transformer PS with the final circuit "dual block without a jumper". Scheme 1 is used in a polluted atmosphere, where it is advisable to install a minimum of switching equipment, or for 330 kV substations fed by two short overhead lines. The dual 3H circuit is used instead of the 4H circuit in a cramped area. Bridge circuits 5, 5H and 5AH are widely used in 110–220 kV networks. At the first stage, depending on the network layout, a scheme of an enlarged unit (two transformers and one overhead line) or installation of one transformer is possible; in the latter case, the number of switches is determined by necessity. Scheme 6, newly introduced in the new edition of standard schemes, is, in essence, one of the options for the first stage. Polygon schemes. Scheme 7 is used at a voltage of 220 kV when it is impossible to use the 5N or 5AN schemes, and at a voltage of 330–750 kV - for all substations connected to the network via two overhead lines. At a voltage of 110 kV, it is practically not used. At the first stage, with one AT, three switches are installed. Pattern 8 (hexagon) is included in the latest revision to replace the extended quad pattern. Due to the inherent disadvantages of the 8 scheme (a network break when the repair of any switch coincides with automatic shutdown one of the connections) has no practical application. For 110–220 kV nodal substations, preference is given to schemes with one busbar system, and for 330 kV substations - “transformer-bus” or one and a half schemes. Schemes with one and two bus systems are used for HV switchgears of 35-220 kV nodal substations and SN (LV) switchgears of 330-750 kV substations. Scheme 9 is used, as a rule, on the MV and LV side of the 110–330 kV substation. Scheme 110-12 is used on the HV side of nodal substations in a 110 kV network (usually 4 overhead lines), schemes 110-12 and 220 * 12 - on the side of the mains substation 220 (330) / 110 / LV kV and 500/110 / LV kV. A limitation for the use of scheme 12 and its replacement with scheme 13 is the connection to each section of the busbars of the substation more than one radial overhead line. However, as follows from Section 4.2, the preservation of radial overhead lines for a long time is unlikely. When considering the scope of schemes 12-14, one should be guided by the "General technical requirements for substations of 330-750 kV of a new generation" (JSC FGC UES, 2004), according to which single sectioned busbar systems are usually used for 220 kV switchgears , double and bypass bus systems are used only with special justification, in particular in insufficiently reliable and non-redundant electrical networks. Since the basis for the rational construction of a 110–220 kV distribution network is the use of closed or double radial configurations (see clause 4.2), the main recommended scheme for a 110–220 kV switchgear is a single sectioned busbar system (diagram 9). Under these conditions, inclusion in the number of recommended new circuits with one bus system - with the connection of transformers through a fork of two switches or "responsible" overhead lines through a one-and-a-half chain (schemes 9N, 9AN and 12N) - seems unmotivated, and the conditions for their use are uncertain: considering the requirements for selecting the power of transformers with the provision of full load power when they are turned off (see clause 5.3.12), it is impossible to identify “increased requirements” under which it is advisable to duplicate MV circuit breakers in the transformer circuit; in a closed distribution network with time-varying regimes and the role of individual sections, it is not possible to single out more or less responsible lines. Schemes transformers - tires and with one and a half switches for connection 15–17 are used for HV switchgear of substations 330–750 kV and switchgear SN SS 750/330, 500/220 and 1150/500 kV. Schemes 16–17 for voltages of 220–500 kV are usually used on the MV side. With four AT (schemes 15, 16) or the number of lines is more than six (schemes 16, 17), as well as the system stability conditions, the need for bus sectioning is checked. Switchgear schemes 10 (6) kV are given in 9. The circuit with one busbar system partitioned by the circuit breaker (9, 1) is used with two transformers with non-split LV windings, the circuit with two busbar partitioned systems (9, 2 ) - with two transformers with a split LV winding or twin reactors, a circuit with three or four single sectioned busbar systems (9, 3 ) - with two transformers with a split LV winding and twin reactors. With appropriate justification, it is allowed to install a second sectional switch. The synchronous compensator is connected directly to the LV AT winding according to the block diagram (9, 4) with the start through the reactor.

Batteries of static capacitors, when connected to LV, are usually connected to LV switchgear sections. For a 20 kV switchgear - a voltage that has received limited distribution (see clause 4.1) - it is mainly recommended to have a circuit with one sectioned busbar system (circuit 9), for separate connections with dead-end single-transformer substations - a block circuit (3N). For substations with HV 35-220 kV, factory production of block complete transformer substations (KTP) - KTPB has been mastered (see clause 5.8). 10 shows diagrams of 110 kV KTPB produced by the plant, made according to simplified diagrams with switches on the HV.

220 kV KTPB diagrams with simplified diagrams on the HV side are shown at 11. The expedient number of 110 kV overhead lines extending from substations with 220 kV HV is given below: