What Is a Scissor-Switch?

Scissor-type isolating switch is a kind of isolating switch similar to scissors. Scissor type disconnector is flexible and convenient to operate. It is widely used in 220kV substations. The size optimization of the scissors type conductive arm makes the operation reliable and stable. Its biggest advantage is that it does not need to stop the bus when repairing the disconnector, which is beneficial to the safe and reliable operation of the power grid.

Flexible operation of scissor disconnectors

1. Hidden safety hazards of soft bare copper wire performance

The conductive part of the 220kV electric scissors-type isolating switch has three movable parts, two of which are connected by multiple soft and bare copper wires. Most of the current passes through the soft and bare copper wires. The wires are all in the active state. In this case, the moving part may sometimes have poor contact. The flexible wires may appear broken strands, exploded strands, oxidation and other phenomena, which will reduce the performance of the soft bare copper wires and cause the reliability of the operation of the scissors type disconnector reduce.

2. Hidden safety risks of loose pins

The conductive parts of the 220kV electric scissors-type isolating switch, including the moving contacts, are connected to each other through pins. If the pins become loose and fall off, it will not only affect the conductive performance, but also affect the normal closing and closing. In particular, after the movable contact pin is loosened, the spring cantilever is displaced to reduce the contact pressure, increase the contact resistance, cause the contact part to overheat, and cause an arc discharge short circuit accident.

3. Hidden dangers of blocking performance

After the disconnector is closed, if the forearm shaft does not pass the dead point, the mechanism cannot be locked, and an accident may occur that the disconnector is automatically disconnected with a load.

4. Hidden dangers of motor failure

In operation, if there is a short-circuit fault in the control circuit of the disconnector, if the motor power is not disconnected, it may cause the disconnector to close or disconnect automatically, resulting in serious consequences.

5. Hidden dangers of discharge phenomenon

After the disconnector is closed, if the contact pressure is not enough (less than 300N), the disconnector will overheat and cause discharge.

(1) Observed with a telescope during the operation of the GW6-220GDW electric scissors-type isolating switch, no abnormal phenomenon was seen in the contact of the dynamic and static contacts, mainly because the movable contact is longer, although it appears to be in contact, the actual pressing force not enough.

(2) During the acceptance inspection of the transmission isolating switch, it was found that the transmission part was tightened. When closing, the transmission main shaft connected to the operating mechanism box was severely distorted (the main shaft is a 4-point steel pipe). In addition, the small crank shaft fan plate Because the transmission part is stuck and deformed seriously, although the board is only 15cm, its small deformation will cause the disconnecting switch's moving contacts to be closed. Although there is only a small deviation, it is likely to cause a large accident.

(3) Through on-site observation and analysis, there is a hidden danger of discharge during operation of the 220kV electric scissors-type isolating switch. The reason is that there are factors in terms of manufacturing quality accuracy, and it is not actually in place when operating the isolating switch, causing the moving contacts to Caused by insufficient pressure on the static contact ^[1]

(1) Improve the equipment maintenance process and quality to ensure that the rotating part is free from jamming and out-of-stock; after the maintenance, the shaft pins of each rotating bearing should be coated with lubricating oil. When the operating personnel accepts the isolating switch, they must check it carefully We must pass the acceptance check.

(2) Add points and closing indication marks on the equipment, and there are static reference objects under or on the cross rod. GW6-220GDW isolating switch, underneath the cross-rod is a stationary unloaded channel steel. When the disconnector is adjusted or checked to ensure that it is in the correct position, an indicator head is fixed on the crossbar and moves synchronously with the crossbar. After commissioning or maintenance on the stationary channel steel, it is pulled several times. to make sure.

(3) GW33-252DW isolation switch, because there is no tie rod, so the "open" and "close" instructions are set between the drive spindle and the bracket tube (also known as the clamp assembly). The driving spindle is controlled by a motor, which drives the crossbar to move. The bracket tube supports the spindle tube and is stationary. The "point" and "close" instructions set above can more clearly judge whether the disconnector is indeed closed or opened. When the indication is not in the marked position, it means that the isolating switch is not opened or closed. It should be opened or closed again until the operation is completed.

(4) When performing the reverse operation, comprehensively determine the closing and opening positions of the disconnector: After closing, carefully check the contact of the dynamic and static contacts should be good, the mechanical instructions should be at the closing position, and the disconnector with a tie rod, Attention should also be paid to observe that the forearm shaft is stuck to the dead point, check that the pins of each part have not fallen off, and that the inspection mechanism has no deformation. After opening, check that the mechanical instructions are in the opening position, and that the overall moving contact bracket descends correctly in place. When opening and closing operations, you must observe carefully. The transmission part must move at a uniform speed. If a stuck phenomenon is found, you must report to the station manager and handle it in time. Be sure to check the operation quality.

(5) Since it is necessary to comprehensively observe the opening and closing positions of the electric scissors-type isolating switch, the items for checking the position of the isolating switch should be filled in the operation ticket in order to remind the operator to carefully check the operation quality.

(6) When inspecting the scissors-type isolating switch during inspection, carefully observe whether the shaft pin of the isolating switch has come off, and whether there are burns on the static and dynamic contacts. Carefully check whether the copper wire of the soft connection part of the disconnector is intact, whether there are broken strands or exploded strands; the infrared switch should be used to measure the contact part of the disconnector, the shaft pin and the soft bare copper wire periodically or at peak load. Temperature to determine whether there is overheating, such as overheating should be reported in time.

(7) The motor operation control power supply of each electric scissors-type isolating switch must be in the disconnected position when normal. Close it before operating the isolating switch, and disconnect it immediately after operation. The door of the power box of the electric scissors-type isolator switch motor should be closed tightly to prevent the accident of automatic disconnection or closing of the isolator switch under load.

In order to ensure the safe and reliable operation of the 220KV electric scissors-type isolating switch in operation, it is necessary to strengthen the training work, requiring each operator to be aware of the problems existing in the operation of this kind of isolating switch. Check to prevent accidents during operation ^[2] .