Center-mounted cabinets are called metal-armored removable center-mounted closed switchgear. It belongs to a high-voltage power distribution device with a maximum working voltage of 3.6 / 7.2 / 12kV. It is an indoor complete power distribution device of a three-phase AC 50Hz single-bus section system or a double-bus section system. It is used to receive and distribute 3.6-12kV network power, and implement control protection, monitoring and measurement of power circuits. The center-mounted switchgear is mainly used for power plants, small and medium-sized generators, power system secondary power substations, power transmission, industrial and mining enterprises and institutions, and large-scale high-voltage motors.
Ground switch rear and center
There are two installation methods for the grounding switch of the center cabinet: rear and center. When the grounding switch is placed behind, you must enter from the lower cabinet door on the front side of the center cabinet when performing cable construction or maintenance, which is not convenient for construction. The front and rear doors of the center cabinet must be "five-proof" interlocked with the grounding switch. When the grounding switch is centered, cable construction or maintenance enters through the lower cabinet door on the rear side. Usually, the lower and front sides of the lower part of the cabinet are separated by iron plates, and there is no live conductor on the front side.
High-low structure and contour structure
The standard center-mounted cabinet has a high-low structure, with a front side height of 2300mm and a rear side height of 2000mm; while the constant-height structure has the same height before and after.
The bus bars of the high and low cabinets are arranged in a zigzag pattern, the instrument room is an independent structure and can be disassembled; the bus bars of the high cabinets are arranged in a vertical zigzag shape, and the meter room and the cabinet are an integrated structure. The contour structure has more installation space than the high and low structure, which is also convenient for production and operation and maintenance.
Improve the "five defenses" function
The center cabinet is matched with the chassis of the circuit breaker hand truck through the transmission mechanism of the cabinet to realize the "five defenses" function of electrical operation. Under some new electrical conditions and operating modes, some of the "five defense" functions of the mid-mounted cabinet can no longer meet the requirements, and the "five defense" function must be improved.
Ground on / off lock
The power supply line of the center-mounted cabinet adopts the "hand in hand" power supply method, and when the circuit breaker in the center-mounted cabinet is located at the test position, the outlet side may still supply power from other substations. Before closing the grounding switch, you must ensure that there is no power at the outlet side. Currently, there are three main locking operation methods.
First, rely on the line side to show the function of the blocking device. As long as the line-side live display lockout device indicates no power and the lockout is turned on, the operation of the grounding switch can be performed.
Second, open the door and check the electricity. When the circuit breaker is in the test position and the live display device detects no voltage on the line, open the cabinet door to verify that there is no voltage, and then close the grounding switch.
Third, use electric handcart. Before closing the grounding switch, pull the circuit breaker handcart out of the cabinet, then push it into the electric handcart, and close the line grounding switch after confirming that there is no voltage.
Method 1 has a large amount of operation, which is equivalent to twice the power failure operation of the electric check trolley. At present, there is only bus power check and grounding operation. The second method is adopted by some power departments, and the operation procedure is more complicated.
The second method is to adopt a more current method for the middle cabinet. When the circuit breaker is in the test position, the grounding switch can be closed only when there is no power on the line side, and the live display device is powered and normal, and the blocking solenoid is powered and normal. If any of the live display device or the blocking solenoid fails or loses power, the closing operation cannot be performed. At present, there has been no live-on and grounding switch accident due to the blocking failure of the live display device. When the live display sensor is faulty or disconnected, it will be reflected by the indicator on the live display.
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