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When you want to buy switchgears, you should know some basic knowledge(part 2)
December 09 , 2020

When you want to buy switchgears, you should know some basic knowledge for "What? How? & Why?"(part 2)


complete set switchgear


14. What is the function of program lock? Where is it installed?

Cabinet and cabinet operation sequence according to the stipulated procedure linkage, plays the role of preventing misoperation.


15. What is the function of earth switch play?

The earth switch is installed at switchgear outlet, which can prevent the back-feed of high voltage during maintenance and ensure personal safety.


16. What is the function of a valve?

When the handcart is pulled away from the cabinet, prevent people or metal from contacting the static contact with high voltage.


17. Why should the bus be covered with rubber?

Play an insulating role, can reduce the air insulation distance, prevent small animals into the cabinet caused by short circuit accident.


18. What is the function of lightning arrester? Why does every group of switchgear have at least one lightning arrester?

The lightning arrester is designed according to the voltage class. Must be installed correctly. Some are also designed for different purposes. For example, power plant output, line operation, capacitance.

The lightning arrester is mainly used to absorb the high voltage in a section of the line to achieve the purpose of safe operation of the line. For example: there is a set of lightning arrester in the switchgear, which can protect the safety of the circuit inside the switchgear. When the outer power supply enters the switchgear, because of lightning arrester, if the outer power supply generates high voltage, it will be safe to enter the switchgear due to the protection of lightning arrester.

The lower end of the outlet cabinet is equipped with a lightning arrester. When the vacuum circuit breaker is broken, will course the over-voltage phenomenon, so It is necessary to install a lightning arrester in place of an overvoltage absorber.


19. What do the role of current transformer and zero sequence transformer.

The current transformer plays a measuring and protection role.

Zero sequence transformer plays a protective role.


20. What is the difference between VE cabinet and ring main unit?

VE cabinet (handcart type) is breaking with circuit breaker to protect the transformer for 0.2 seconds

Ring main unit (fixed type) Protect transformer for 0.02 seconds with high voltage fuse


21. What role does the humidity controller play?

The humidity is detected by the inductive probe. If it exceeds the normal humidity, it is adjusted by heating plate. There are two modes of operation: automatic and manual.


22. What does PT and CT represent?

PT - voltage transformer

CT - current transformer


23. What is the mean if AC and DC?

AC - alternating current

DC - direct current


24. How many operating mechanisms are there for circuit breaker?

Manual, automatic electric, magnetic, spring, contactor magnetic suction. For example, the low voltage air switch is manually operated,

High voltage vacuum switch use CD10 or CD17 (electromagnetic mechanism), CT8 or CT19 (spring mechanism).


25. What is the function of vacuum switchgear? How to protect the transformer?

Its function is vacuum arc extinguishing, It can open and close with load and transmit electricity. Protect the transformer by cutting off the current with current transformers and instruments. Other components can also be installed for other purposes.


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