Medium Voltage Grounding Switch Introduction-2

Role of the power system grounding switch

- To cause artificial grounding and meet protection requirements. Ensure that there is an obvious mechanical grounding point in the circuit, determine that there is no residual voltage in the line, and ensure the safety of maintenance and line shutdown;.

- Replacing the carrying ground wire, grounding the equipment during maintenance of high-voltage equipment and lines to protect safety.

- The location of the grounding switch configuration in general will be on both sides of the circuit breaker next to the isolation switch, which plays a role when the circuit breaker maintenance on both sides can be effectively grounded to ensure personal safety. Does not require a closing function, can only withstand short-circuit current, that is, dynamic thermal stabilization.

- The line side of the grounding, mainly with the closing short-circuit current and opening and closing induction current, to protect the lower level equipment from damage;

When the circuit breaker equipment is pointed at the test position, the grounding switch can be closed only when the line side indicates no power, and the charged display device indicates power and normal operation, and the blocking solenoid indicates power and normal operation. Failure or de-energization of either the energized display device or the blocking solenoid will prevent the closing operation. Failure or disconnection of the energized display sensor will be reflected by an indicator light on the energized display.

Regarding the closing of the earthing switch, many customers require 5 closures of class E2. The closing test is carried out at rated voltage and the closing short-circuit currents are 63/80/100/130 kA. Factors affecting the closing capacity are mainly.

Closing speed

Closing speed is fast enough to reduce the pre-breakdown contact erosion, short arc burning time. The closing speed of 12/24kV earthing switch in air is 4-5m/s, and only 2-3m/s in SF6, while the environmental protection gas is close to the insulation strength of air, so the closing speed of SF6 earthing switch cannot pass the closing test.

The closing speed of 40.5kV earthing switch in air has to be increased to 6-7m/s.

Contact shape

The use of round, rod-shaped static contacts uniform electric field, the same dynamic contacts should also be a good shape, the electric field is evenly distributed to reduce the electrical breakdown distance.

Contact material

The same strong abrasion-resistant contacts can also reduce abrasion, especially for high voltage switches such as 40.5kV and above, the use of copper tungsten arc-inducing contacts, or copper tungsten alloy as the head of the contacts can also reduce abrasion.

Contact pressure

Contact pressure is the key index to judge the ability of the earthing switch to withstand thermal stability. The contact resistance is calculated according to the contact pressure to calculate the voltage drop at the contact connection, and the voltage drop is used to judge whether the contacts will be welded under thermal stability. And the influence of contact pressure on closing is reflected in the ability of the contact to stop quickly after closing without bouncing back and causing ablation.

Neutralization

Closing has high requirements on the neutralization of the contacts. Skewing and poor neutralization will cause the contacts to be skewed and burned, and one side of the contacts will be seriously eroded, which will affect the next few closing.

Connection arrangement

Connection arrangement involves the direction of electric power when closing, the direction of electric power is favorable to the closing, it will speed up the closing speed, reduce the ablation, and vice versa, it will reduce the closing speed and increase the contact ablation time.

Insulation medium

Insulating medium directly affects the pre-breakdown distance, thus affecting the degree of ablation, SF6 gas insulation strength, only 1/3 of the air, so the same closing speed contact ablation contact is obviously small. And because the gas gap in SF6 is small, the length of the movable knife is short, so the closing line speed of SF6 grounding switch is generally smaller than that of air, and it is necessary to increase the angular speed to improve the line speed.

Conclusion

Closing speed, connection arrangement and contact pressure are the main factors affecting the closing capability, and the contact material of the high voltage earthing switch is also a key factor. Various factors need to complement each other, blindly increase the closing speed need to increase the spring energy, accidentally increasing the operating force, the life of the switch is affected by the high cost; and through reasonable design, such as the connection arrangement, the electric power to help close, can play twice the result with half the effort.

Tests on grounding switches

In the switchgear internal insulation test, it often appears that the grounding switch alone can pass the withstand voltage, put inside the switchgear cabinet can not pass the withstand voltage, especially between the air breaks, the electric field situation has changed, the local field strength enhancement, resulting in the inability to pass the general alone to play the 110kV impact can pass the cabinet 95kV;

Dynamic thermal stability test, grounding switch 4s, grounding circuit 2s, grounding switch three-phase dynamic thermal stability test, you need to be able to quickly open immediately after the grounding circuit single-phase dynamic thermal stability, for the soft connection cross-sectional area is a test.

Short-circuit closing test E1 level 2 times, E2 level 5 times, closing speed, contact material, etc. to determine the closing ability;

-Mechanical life test 3000 times;

-Mechanical interlocking test.