Schemes for connecting substations to the network. Electrical diagrams of power plants and substations Scheme 4 3 switches for connection

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 a substation is the diagram of the LV network for which the substation in question is intended to supply power. The optimal power and range of a substation are determined by the load density in the area where it is located and the design of the LV network.

Substation electrical connection diagrams are selected depending on their purpose. According to the method of connection to power lines, they distinguish dead-end(Fig. 2.9, a, d), branch(Fig. 2.9, b, d, g, i), checkpoints(Fig. 2.9, c, f, h, k) and nodal(Fig. 2.9, j) substations.

Rice. 2.9. Main types of connection of substations to the network:

a, b, c – radial with one overhead line; d, e, f – double radial; g, h, i – with two nutrition centers; k, l – with three or more power centers (CP)

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 node substations increases with increasing network voltage, while the share of dead-end and branch substations decreases. The most common type of 110...330 kV substation is walk-through.

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

It is advisable to use through-and-node connection diagrams for newly constructed substations (see Fig. 2.9). These schemes have higher reliability of power supply to consumers.

The selection of switchgear circuits (SG) for substations is made from among the standard ones (Fig. 2.10, Table 2.3) taking into account their scope. On the HV and MV side of substations these are, as a rule, open switchgear switchgears (ORU).

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

One and a half scheme

6 or more

Fig.2.10. Typical schemes of RU 35…750 kV. Numbers – numbers of standard schemes

10(6) kV switchgear diagrams are shown in Fig. 2.11. A circuit with one sectioned bus system (Fig. 2.11 b, c) is used with two transformers with unsplit 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 circuits: a – with one non-sectional bus system; b, c – with one sectioned bus system; d – with two partitioned bus systems The number of outgoing lines on the MV and LV sides is determined by their

throughput

and installed power of transformers (Table 2.4).

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

Scheme with two switches per connection

Scheme with two working and bypass busbar systems The diagram shown in Figure 10.3 makes it possible to carry out revisions of any bus system and any switch without interrupting the operation of connections, and also allows you to group these connections in any way. As a rule, both bus 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, As a rule, both bus systems are in operation with a corresponding fixed distribution of all connections: lines lines W2, W4, W6 T2 connected to a second bus system A2, bus coupling switch A2, and only half of the accessions. The considered scheme is recommended for 110-220 kV switchgear on the HV and MV side of substations with a number of connections of 7-15, as well as at power plants - with a number of connections of up to 12.

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

Figure 10.3 - Schemes with two working and bypass bus systems

The circuit with two switches per circuit is a variation of the circuit with two bus systems and is shown in Figure 10.4. Increased reliability and maintainability is achieved by installing switches in series with each disconnector.

The advantages of such a scheme are the ease of repairs of any bus system and the possibility of removing switches for repairs without operating live disconnectors. Damage to the tires does not lead to connection failure here.

Figure 10.4 - Circuit with two switches per circuit

The main disadvantage of the scheme is its high cost.

One-and-a-half diagram shown in Figure 10.5 A, ensures inspection of any switch or bus system without disrupting the operation of connections and with a minimum number of operations when removing these elements for repair. In this case, the disconnectors only provide a visible break. The one and a half circuit combines the reliability of a circuit with busbars and the maneuverability of a polygon circuit. The disadvantages of the one-and-a-half scheme include the complexity of relay protection of connections and the need to select switches and all other equipment for double rated currents.

4/3 scheme 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 a circuit with a double bus system, but only 1/3.

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

Description of the main circuit

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

The main circuits of substations are subject to the same basic requirements for reliability, maintenance safety, durability, maintainability, efficiency and maneuverability as the main circuits of power stations.

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

The number of transformers in the substation has a certain significance for the choice of circuit. According to current practice, no more than two transformers are usually installed at 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 a substation is permitted in cases where consumers in the area belong to categories 2 and 3, which allow short-term interruptions in power supply necessary to switch on backup power from the network.

At the substation 500 kV. a one-and-a-half circuit was used (3 switches and 2 connections). The connections are not fixed at any one SB, but are included in the gap between the circuit breakers. 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 switch or bus system is carried out without disrupting the operation of connections and with a minimum number of operations when removing these elements for repair; disconnectors are used only during repairs (providing a visible break to the switchgear elements under voltage); Both bus systems can be switched off simultaneously without disrupting the operation of the connections. 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 rated currents.

The increased number of switches in a one-and-a-half circuit is partially compensated by the absence of inter-bus switches.

Description of the main equipment of the 500 kV substation

At the 500 kV substation there are two incoming and two outgoing 500 kV lines, as well as two autotransformers that convert the voltage of 500 kV to 330 kV. The main equipment of the substation includes: autotransformers, high-voltage circuit breakers and disconnectors used for switching operations and disconnecting abnormal operating modes . Current and voltage measuring transformers. Numerous connecting buses and busbars for connecting equipment to each other. The substation also has a technical building, where there are constantly personnel on duty monitoring the substation’s performance, and all the relay protection and automation panels are located.

LECTURE NOTES ON THE DISCIPLINE

“ELECTRICAL PART OF STATIONS AND SUBSTATIONS” part 2

For bachelors in the direction _"Energy and electrical engineering"_140400

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

Art. teacher Galkin A.I.

Novocherkassk 2014

Switchgear diagrams

Earlier, in part 1, the formulation was given switchgear(RU) as an element block diagram power facility (station or substation).

RU is an installation designed for receiving and distributing electricity at one voltage and containing switching devices (switches and disconnectors, and at substations there may be separators and short circuiters), 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 are connected to the switchgear accession. To the main accessions may include: power lines ( W), power transformers ( T) and generators ( G) (if this is a generator voltage switchgear at a thermal power plant).

The entire variety of switchgear can be divided into circuits RU with busbars and diagrams RU without busbars . The latter, in turn, can be divided into RU according to simplified schemes and on RU based on ring circuits .(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 ( T.A.) and another disconnector ( QS2).

Let's look at some of the most common switchgear schemes in each of these groups.

RU according to simplified schemes. RU according to simplified diagrams are various versions of line-transformer blocks 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 as arrows and the power transformers are shown as crossed out (voltage adjustment under load). Lines and power transformers are not elements of the switchgear, but are connections to the switchgear. The switchgear diagram shows switches, disconnectors, current transformers and voltage transformers.

RU according to the block line - transformer circuit (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 blocks line - transformer with switches and a non-automatic jumper on the side of the lines (Fig. 8.1, V).

Switchgear according to the bridge diagram (Fig. 8.1, G And d) are used on the high side of transit substations, which are included in the cutting 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). During the repair of the elements of the automatic jumper, in order not to interrupt the transit of power, a non-automatic jumper (without a switch) is provided, which is called a repair one.

Rice. 8.1. RU according to simplified schemes:

A- block with disconnector; b- the same, but with a switch; V- two blocks with switches and a non-automatic jumper on the line side; G- a bridge with switches in the transformer circuits and a repair jumper on the transformer side;

Continuation of Fig. 8.1:

d- a bridge with switches in the line circuits and a repair jumper on the line side; 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

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

Busbars are 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. On the side of the busbar, a disconnector is installed, which is called busbar, then a switch is installed, after the switch - a current transformer, and behind it, on 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 circuits with one working bus system (usually partitioned);

· switchgear circuits with one working and bypass bus systems;

· switchgear circuits with two working and bypass bus systems;

· circuits with two working bus systems and three switches for two connections.

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

Rice. 8.2 Switchgear circuit with one working bus system: a – non-sectional with a switch; b – sectionalized by a switch.

At power plants, such a circuit in a sectionalized version can be used in 6 kV auxiliary power switchgear circuits or in a 6-10 kV generator switchgear at a thermal power plant.

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

Switchgear circuit with one working and bypass bus system used at stations and substations at voltages 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) of the switch in the connection circuit during its repair or inspection using a bypass switch ( QB1 in Fig.8.3) without interrupting the connection power supply. The current path bypassing the circuit breaker being repaired is created using a bypass switch and a bypass bus system. Often the working bus system in this scheme is sectioned, as shown in the figure. During 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.

We will consider the basic operations of replacing a switch in a connection circuit with a bypass one, taking into account the switching rules, using the example of a switch Q1 in the line circuit W1:

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

After that turn on QB1 and this supplies voltage to the bypass bus. This is done to check the bypass bus insulation.

The next step is to disable QB1.

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

Turn on again QB1.

Now we have two paths for current 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 bus disconnector QSB1.

However, this scheme retains the disadvantage that when repairing a busbar section, the connection between the connections of this section is lost. A circuit with two working bus systems does not have this drawback; it often also has a bypass bus.

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

Switchgear circuit with two working and bypass bus systems used for switchgear voltages of 110, 220 kV, if the number of connections is at least seven. In this scheme, part of the connections is connected to one working bus (K1), and part - to another (K2). But any connection can be transferred from one busbar system to another using a QK bus coupling switch and busbar connection disconnectors. (In this operation, the bus coupling switch QK and the disconnectors in its circuit must be in the on state.) This is used when repairing any working bus. The presence of a bypass switch and a bypass bus provides the same advantages as in the previous circuit.

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

The disadvantage of this scheme, like the previous ones, remains that in the event of an emergency shutdown of one of the operating buses (for example, as a result of a short circuit on the bus), it will be disconnected and the connection between the connections that are connected to this bus will be lost.

Scheme with two working bus systems and three switches for two connections recommended for use in switchgear with voltages of 330 – 750 kV and with a number of connections of six or more. In this scheme, due to additional expense switches (conventionally 1.5 switches per connection, hence the second name of the “one and a half” circuit), high operational flexibility and reliable communication between connections are 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 switch, all connections remain in operation, and in the event of an emergency shutdown of one of the operating buses, the connection between connections is not lost, since it is carried out through the bus remaining in operation

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 the current transformers become more complicated, because Current transformers here are installed in the circuit of switches and in order to obtain the connection current it is necessary to sum (according to Kirchhoff’s first law) the currents of the secondary windings of two transformers.

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

Switchgear circuits based on ring circuits (polygons). Used in switchgear 110-220 kV and more. In ring circuits (polygon circuits), switches are connected to each other to form a ring. Each element - line, 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 connections of an element into a general circuit increase flexibility and reliability of operation, while the number of switches in the circuit under consideration does not exceed the number of connections. In a triangle circuit, there are three switches for three connections, so the circuit is economical.

In ring circuits, revision of any switch is carried out without interrupting the operation of any element. So, when inspecting switch Q1, it and the disconnectors installed on both sides of the switch are turned off. In this case, both lines and the transformer remain in operation, but the circuit becomes less reliable due to a broken ring. If in this mode a short circuit occurs on line W2, then switches Q2 and Q3 are turned off, as a result of which both lines and the transformer will remain without voltage. 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 line W1 and failure of switch Q1, switches Q2 and Q3 are switched off. Probability of coincidence

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

damage on the line with a revision of the switch, as mentioned above, depends on the duration of the repair of the switch. Increasing the overhaul period and operating reliability of switches, as well as reducing repair duration, significantly increases the reliability of circuits.

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

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

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

The disadvantages include more Difficult choice current transformers, switches and disconnectors. Current transformers are installed here, as in the one-and-a-half circuit, 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 when designing the electrical part of a power plant (substation), since it determines the complete composition of elements and connections between them. The selected main diagram is the initial one when drawing up circuit diagrams electrical connections, auxiliary circuit diagrams, secondary connection diagrams, wiring diagrams, etc.

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

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