Ultimate Guide To Switchgear High Voltage

What is range of HV & MV & LV? When discussing…

What is range of HV & MV & LV?

When discussing voltage range, the generic descriptors such as low-voltage, medium voltage, and high are contingent on the given context. In regards to power transmission and distribution systems, voltage can be divided into the following categories:

LV range encompasses voltages between 50 and 1000 volts. These include the 120, 220 and 230 volts that are available in our households. Even though these voltages are considered low, they can still be hazardous and may result in fatal mishaps. Consequently, caution must be taken when dealing with such voltage levels.

different voltage levels

Voltages between 1 kV and 100 kV are considered to be of medium voltage. Generally, electricity is distributed and secondary transmission are conducted in the medium-voltage range.

Voltages between 100 kV and 345 kV are referred to as high voltage (HV). Secondary transmission, and in certain parts of the world primary transmission, usually takes place in this range.

What is High Voltage (HV) switchgear?

KYN61 high voltage switchgear

High voltage switchgear (also called metal-clad switchgear) is indeed a power system that deals with voltages more than 36 kV. The arcing created during switching operation is likewise very high due to the high voltage level. As a result, more caution should be exercised while constructing high-voltage switchgear.

Because the high voltage circuit breaker (CB) is the most essential element of HV switchgear, it must have particular properties for safe and dependable operation. Defective high-voltage circuit breaking and switching are extremely infrequent. Such circuit breakers are frequently left in the ON position and can be used after a lengthy period of time.

As a result, CBs must be dependable enough to assure safe operation when needed. For high voltage electrical switchgear, minimum oil circuit breakers (MOCB), air blast circuit breakers, and SF6 circuit breakers are commonly utilized.

Types of High Voltage Switchgear

The two classifications of high voltage switchgear are gas-insulated indoor type switchgear and air-insulated outdoor type switchgear.

Gas-insulated indoor type switchgear is a type of high voltage switchgear that uses sulfur hexafluoride (SF6) gas as an insulating medium. It is typically used in power plants, substations, and other industrial sites where the equipment needs to be installed indoors.

Air-insulated outdoor type switchgear is a type of high voltage switchgear that uses air as an insulating medium. It is typically used in outdoor applications, such as transmission lines and distribution networks.

high voltage switchgear design

What Does High Voltage Switchgear Do?

High voltage switchgear is used to safely control, monitor, and protect the electrical equipment in power systems. It works by breaking the circuit when there is an overload or short circuit, or when maintenance is required.

High voltage switchgear also helps to reduce the amount of electricity that flows through a system by controlling the amount of current that goes through it. This helps to prevent large surges from damaging sensitive equipment and causing outages. In addition, it provides a safe way for technicians to disconnect. And isolate electrical components for maintenance or repair without compromising safety.

Overall, high voltage switchgear is an important part of any power system. As it ensures reliable operation while providing protection against faults and overloads.

Features of High Voltage Circuit Breakers

air circuit breaker structure

Electric switchgear must ensure safe operation of the electrical apparatus in scenarios such as:

1.Short-line faults-The short-circuit fault that occurs within 5km of the transmission network.

2.Terminal faults-The fault that occurs at the circuit breaker terminals. 

3.Capacitor bank charging-Capacitor bank charging is like an overvoltage condition and electrical system switchgear should allow the capacitor bank charging without interruption.

4.Transformer magnetizing currents-When a transformer is energized, there will be an inrush of current, which is around ten times the normal current rating of the transformer. 

5.Switching of the phase sequence-Phase sequence change particularly affects the rotating machines and the switchgear should take care of the safe operation of electrical rotating machines under such conditions.

6.Transmission line energizing-Switch gears should provide safe energizing and de-energizing of transmission lines. Keeping the equipment connected to the line without damage. 

Types of high-voltage circuit breaker

There are mainly three types of circuit breaker, as is well known, used in high voltage switchgear system. Such as air circuit breakers, SF6 circuit breaker, oil circuit breaker and vacuum circuit breaker.

Air Circuit Breaker (ACB) is an electrical device used to provide Overcurrent and short-circuit protection for electric circuits over 800 Amps to 10K Amps.

These are usually used in low voltage applications below 450V. We can find these systems in Distribution Panels (below 450V). 

types of high voltage circuit breaker

A circuit breaker in which SF6 under pressure gas is used to extinguish the arc is called SF6 circuit breaker. SF6 (sulphur hexafluoride) gas has excellent dielectric, arc quenching, chemical and other physical properties which have proved its superiority over other arc quenching mediums such as oil or air.

An Oil circuit breaker (OCB) is a type of circuit breaker that uses insulating oil as a dielectric medium to quench the arc and break the circuit safely. The oil used is insulating oil used usually transformer oil that has better dielectric strength than air. The heat produced by the arc vaporizes the oil, producing a hydrogen gas bubble surrounding the arc. The pressure of the oil compresses the gas bubble increasing its dielectric strength which extinguishes the arc during the zero-crossing.

A vacuum circuit breaker is a kind of circuit breaker where the arc quenching takes place in a vacuum medium. The operation of switching on and closing of current carrying contacts and interrelated arc interruption takes place in a vacuum chamber in the breaker which is called a vacuum interrupter.

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