The main parts of the 10kV switchgear include: vacuum circuit breakers , current transformers, on-site installation of microcomputer protection devices, operating circuit accessories (handles, indicator lights, pressure plates, etc.), various position auxiliary switches . Among them, the circuit breaker and the current transformer are installed inside the switch cabinet, and the microcomputer protection, accessories, and watt-hour meter are installed in the relay room (using the previous name, in fact, there is no relay), the terminal block and various power supply air The switch is installed inside the relay chamber, and the terminal block is connected to the circuit breaker mechanism through a control cable or a dedicated socket.
To understand the secondary wiring of the switchgear, we need to find two drawings: the protection schematic diagram and wiring diagram provided by the manufacturer; the secondary schematic diagram, wiring diagram, terminal diagram, and circuit breaker mechanism schematic provided by the switchgear manufacturer .
The drawings from the factory are the original basis for the design of the switchgear manufacturers, and also the basis for us to review the drawings of the switchgear manufacturers. The schematic diagram of the switch factory is generally modified according to the schematic diagram of the comprehensive factory, and then the input of current, voltage and signal quantity and the output of the control quantity are schematically shown.
Secondary wiring of the cabinet in the 10kV cable outlet
The KYN28A (GZS1) mid-mounted cabinet is the most used 10kV switchgear type in urban substations . From the front, it is clearly divided into three parts. The top is the relay room, the middle is the circuit breaker room, and the bottom is the empty room (nothing). High-voltage equipment such as busbars are installed in the cabinet on the back. As shown in Figure 8-1-1.
Figure 8-1-1
1, relay room
The panel of the relay room is equipped with a microcomputer protection device, an operating handle, a protection outlet pressure plate, an indicator light (a red light in place, a green light in a position, and a yellow light in the energy storage); and a terminal block and a microcomputer protection control circuit are installed in the relay room. DC power switch, microcomputer protection working DC power supply, energy storage motor working power switch (DC or AC). Figure 8-1-1 is a picture of the early switchgear, where the relay compartment is the location where the ammeter and indicator light are mounted.
2, circuit breaker room
The most commonly used circuit breaker for 10kV mid-mounted cabinets is the VS1 vacuum circuit breaker. The wiring in the circuit breaker mechanism is connected to the terminal block of the relay room through a dedicated socket. One section of the plug is fixedly connected to the circuit breaker mechanism, and the other section is a special plug. The matching socket is installed at the upper right of the circuit breaker chamber, and the outlet wire of the socket is connected to the terminal block of the relay room. In order to understand the secondary circuit, we need to have a certain understanding of the operation process.
The center-mounted cabinet circuit breaker has three positions: disconnection, test, and operation (it is worth noting that the circuit breaker handcart and the circuit breaker are two concepts, and the circuit breaker handcar is actually the circuit breaker and its seat). In normal operation, the circuit breaker handcart is in the running position, the circuit breaker is in the closing position, the secondary line plug is connected with the socket; after the manual trip, the circuit breaker is in the open state, the handcart is in the running position; the special rocker will be used to open the circuit. The handcart is shaken out to the test position, and the secondary plug can be unplugged (the handcart cannot be pulled out when it is in the running position); continue to shake, the handcart exits the circuit breaker room and is in the disconnected position.
Disconnected position: The circuit breaker is not connected to the primary equipment (busbar), the operating power is lost (the secondary plug has been unplugged), and the circuit breaker is in the open position;
Test position: The secondary plug can be plugged into the socket to obtain power. The circuit breaker can be closed and opened, and the corresponding indicator light is on; the circuit breaker is not connected to the primary equipment, and various operations can be performed, but it does not have any influence on the load side, so it is called the test position.
Operating position: The circuit breaker is connected to the primary equipment. After closing, the power is transmitted from the busbar to the transmission line via the circuit breaker.
The center cabinet does not have the concept of a disconnector in the traditional sense. When the handcart is in the test position, it is equivalent to the traditional disconnector disconnection, that is, the circuit breaker has a significant disconnection point from the main circuit (primary bus). Figure 8-1-2, 8-1-3 shows the internal section of the VS1 vacuum circuit breaker and GZS switchgear.
Figure 8-1-2
Figure 8-1-3
Figure 8-1-2 shows the VS1 circuit breaker handcart, which is placed in the switchgear like a drawer. The purple frame is the pulley on the track, and the red frame is the secondary wiring plug (in the unplugged state). Inside the green box is the moving contact of the circuit breaker. The equipment in the frame in Figure 8-1-3 is the same as 8-1-2, and the secondary wiring plug is in the plugged position.
The model we selected is: NSR RCS-9611A for microcomputer protection and KZN1 switch cabinet for Changshu switch factory. (The middle cabinets of different manufacturers have a variety of strange models)
3, RCS-9611A
RCS-9611A is a microcomputer protection device used by NARI for small current grounding system lines. It is equipped with three-stage overcurrent, three-stage zero-sequence overcurrent/small current grounding line selection and reclosing. The current voltage circuit is shown in Figure 8-2-1, the operation circuit is shown in Figure 8-2-2, and the input voltage circuit is shown in Figure 8-2-3.
As can be seen in Figure 8-2-1, the analog quantities that need to be connected are: bus voltage, line voltage (almost no 10kV line will install line PT), protection current (three-phase, 10kV line in actual engineering is generally only configured Two-phase CT), measuring current (two-phase), zero-sequence current.
As can be seen in Figure 8-2-2, this operating loop is much simpler than the operating loop of the RCS-941. The equipment in the red frame (handle, pressure plate) is not part of the RCS-9611, they are supplied by the switchgear cabinet manufacturer and are mounted on the relay room panel.
Figure 8-2-3 shows the remote signal loop of the device. Unlike the protection device of the 110kV voltage class device, the protection, measurement and control of the 35/10kV device is an integrated design, that is, integrated in one device. In contrast, in the RCS-941A, you certainly can't find a measurement current, a digital input loop. It requires a CSI-200E or other control device or a conventional control panel to work with it to provide these functions.
4, KZN1-12-04 switchgear
The main wiring of the primary equipment of 10kV line is shown in Figure 8-3-1. Compared with the overhead line, there are fewer isolation switches, B-phase current transformers, and more zero-sequence current transformers TA.
The role of the B-phase current transformer: It is mentioned in the general book that only A and C phase current transformers are installed. Why do you install B-phase CT now? This is mainly due to the small current grounding line selection function. The 10kV overhead line is allowed to continue to run for a period of time during single-phase grounding, but it is necessary to determine which line is grounded so that the line can be checked and repaired as soon as possible, that is, "choose line". The line selection is based on whether the zero sequence current of the line is zero. The zero-sequence current is the vector sum of the three-phase current. The theoretical value is zero when normal. When the single-phase is grounded, the measured zero-sequence current is not zero, and the line fault can be judged. Therefore, three-phase CT is required to calculate the zero-sequence current. . For the cable outlet, a dedicated zero-sequence current transformer is arranged on the high-voltage (10kV) cable, and the sum of the three-phase CT is not needed to calculate, so the A and C two-phase CT can be configured to realize the protection function. This is not in contradiction with the statement in the book.
The secondary schematic diagram of the 10kV switchgear is drawn according to the schematic diagram of RCS-9611A, which is mainly divided into current and voltage loop, operation loop and switch input loop. As shown in Figure 8-3-2, 8-3-3, 8-3-4, 8-3-5, respectively.
Figure 8-3-2 is the current loop, including: protection, measurement, metering, small current grounding line selection, protection device and meter are installed on the switchgear, all wiring is connected by the switch factory. The small current grounding line selection device is installed in the main control room, and the zero sequence currents L401 and N400 need to be connected to the device by the control cable.
Figure 8-3-3 shows the voltage loop, including: protection voltage (and measurement voltage) and metering voltage, all drawn from the small busbar at the top of the cabinet. The protection voltage must pass through an air switch before entering the protection device, as shown in Figure 4QF. The metering voltage is not used.
Figure 8-3-4 shows the operation loop, which mainly includes the control handle, the cooperation between the microcomputer operation circuit and the circuit breaker mechanism. The picture is a bit small, please (click to enlarge). In many simplified drawing methods, the closing circuit of the circuit breaker mechanism is often drawn as shown in Figure 8-3-5: "Spring has stored energy S1 normally open" "Circuit breaker opening DL normally closed" "Closed The coil HQ" is composed in series, or "test position SW, running position YW normally open and parallel" is added to indicate that "the circuit breaker handcart can only be closed when it is in the test position and the running position". In fact, the VS1 circuit breaker is often equipped with a closing lock electromagnet, which has a hand brake travel switch (similar to a relay) control. When the handcart is in the test position and the position outside the operating position, the electromagnet loses power. The auxiliary contact breaks the closing circuit, which belongs to the electrical locking of the central cabinet (there is still a lot of electrical locking of the central cabinet, such as the electric door can not open the back door of the switch cabinet, etc.).
The 10kV center cabinet has perfect electrical lockout and mechanical lockout function. When the handcart is in the non-test/operating position, the mechanical lockout function will automatically complete the lockout of the closing operation, so it is no longer necessary to use SW in the closing circuit. YW is blocked. (Test position S8, running position S9 is often marked as SW, YW for understanding)
Figure 8-3-6 is the switch input circuit. For the center cabinet, the most important signals include: test position (S8 normally open), running position (S9 normally open), ground knife joint (QE normally open) The spring does not store energy (S1 normally closed). The position of the circuit breaker can be omitted, because the microcomputer protection can be judged according to the HWJ and TWJ of its own operation circuit.
In summary, for the secondary design, the 10kV switchgear is the most trouble-free, only need to lead the zero-sequence current to the small-current grounding line selection device, and the rest of the secondary wiring is completed by the manufacturer.
The view of the wiring diagram is not repeated here. The key point is to refer to the schematic diagram and then compare the numbers of the two installation units.
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