There are 8 key parameters that you should notice during choosing

Medium voltage VCB(Vacuum circuit breaker) are crucial components in electrical power systems, used to interrupt fault currents and protect electrical circuits from damage. Here is an in-depth overview of the eight key parameters that define the performance and suitability of medium voltage VCBs:

Insulation distance:

Since the 10kV switchgear is used to distribute three-phase alternating current, a certain distance must be ensured between phases and between phase and ground. Otherwise, it will cause short circuits and discharges, posing a hazard to the entire power system.

When dry air is used as the insulation gas, the distance between phases and distance between phase and ground with dry air should not be less than 125mm. Ensuring sufficient insulation distance can effectively prevent discharge and short-circuit faults.

Creepage Distance:

According to standard requirements, the creepage distance should meet the corresponding specifications. This depends on the insulating materials and environmental conditions of the switchgear. Generally, for a 10kV switchgear, the creepage distance for pure porcelain insulation is 18mm/kV, and for organic insulation, it is 20mm/kV.

Five-prevention interlock of medium voltage VCB:

1. Prevent incorrect opening and closing of circuit breakers.
2. Prevent opening and closing of disconnectors under load.
3. Prevent live hanging (closing) of grounding wires (grounding switches).
4. Prevent closing circuit breakers (disconnectors) with grounding wires (grounding switches).
5. Prevent mistakenly entering live compartments.

Through mechanical interlock devices and electrical interlock logic, the safety of operators during the operation process is ensured.

IPX Waterproof Rating Guide:

Generally speaking, the protection level of 10kV high-voltage switch cabinets should not be lower than IP4X to prevent the invasion of external solid foreign matter and water. The main differences in dustproof and waterproof performance of high-voltage switch cabinet protection levels IP45, IP54, and IP67 are as follows:

IP45: All medium voltage VCB can be made

• In terms of dustproof, it can prevent the invasion of solid foreign objects with a diameter greater than 1-3mm.
• In terms of waterproof, it can prevent water splashing from all directions, but cannot prevent a large amount of water from invading.

IP54: There are environmental protection and gas-filled cabinets (the main body is waterproof, but the mechanism is not waterproof)

•  In terms of dustproof, it can completely prevent the invasion of foreign objects, but cannot completely prevent the entry of dust. However, the amount of dust entering will not affect the normal operation of the equipment.
• In terms of waterproof, it can prevent water splashing from all directions and also prevent water spray from entering.

IP67: There are gas-filled cabinets and solid cabinets

• In terms of dustproof, it completely prevents the invasion of foreign objects and dust.
• In terms of waterproof, it can be soaked underwater at a depth of 1 meter for 30 minutes without water ingress. After the product is taken out of the water, it can directly undergo a withstand voltage test immediately. Both the primary equipment and the secondary wiring part of the product can pass the withstand voltage test.

Overall, the larger the number after IP indicates a higher protection level and stronger protection ability.

Dynamic stability:

The switch cabinet should be able to withstand the electrical dynamic impact generated by short-circuit currents to ensure that the cabinet structure does not deform and the internal components are not damaged. This requires full consideration of the cabinet’s strength and support structure during the design.

In the power system, switch cabinets usually need to be able to withstand rated short-circuit breaking currents of 20kA, 25kA, 31.5kA, 40kA, or even 50kA. When such a large current passes through the switch cabinet, a large electrical dynamic force will be generated between phases and between the same-phase buses. At this time, we need to rely on the support of support insulators to prevent the bus from generating significant displacement. Generally, the distance between two insulators should not exceed 800mm, and certain weak links should be strengthened.

The contact surfaces and current-carrying capacity of the moving and static knives of the disconnector should be reasonably designed to prevent them from sticking.

Temperature rise parameter of medium voltage VCB:

Reasonably design the ventilation and heat dissipation structure to control the temperature rise of the internal components of the switch cabinet within the allowable range. Ensure good heat exchange to avoid equipment failure and shortened lifespan due to overheating.

We can take various measures such as applying vaseline, conductive paste, tin plating, silver plating, etc. on the electrical connection surfaces. In the structural design, what we should pay attention to is to try our best to avoid the occurrence of eddy current phenomenon. When it is truly unavoidable, materials with high magnetic resistivity (such as stainless steel materials) can be used.

Lightning impulse test of medium voltage VCB:

The switch cabinet should have a certain lightning impulse withstand capacity to cope with the influence of lightning overvoltage. This is achieved through reasonable insulation coordination and the configuration of lightning arresters.

The following are the parameter requirements for the lightning impulse of the 10kV high-voltage switch cabinet body:

• Lightning impulse withstand voltage:
• To ground: 75kV
• Between phases: 75kV
• Circuit breaker port: 75kV
• Isolation port: 85kV

Partial discharge test of medium voltage VCB:

Control the level of partial discharge inside the switch cabinet, select high-quality insulation materials, optimize the electric field distribution, reduce the occurrence of partial discharge, and improve the reliability of the equipment.

The general partial discharge quantity is usually required to be no more than 5pC, and the leakage current is generally not more than 1mA.

During the design process of the 10kV medium voltage switchgear body, all the above key points need to be comprehensively considered, relevant standards and specifications should be followed, and rigorous design and calculation should be carried out to ensure the safe and reliable operation of the switchgear.

Thanks for reading :)