What Is High Voltage Switchgear?
High-voltage switchgear is any switch used to connect or disconnect a component of a high-voltage power system that operates at voltages more than 36 kV. This equipment is critical for the protection and uninterrupted functioning of a high voltage power system since it is directly related to the quality of the electrical supply.
The high voltage circuit breaker (CB), which is the most important component of HV switchgear, needs specific characteristics in order to operate safely and dependably. High-voltage circuit breakage and switching defects are quite rare. These circuit breakers can be utilized after a long period of time and are often kept in the ON state.
CBS must therefore be trustworthy enough to guarantee safe functioning when required. The technology of high-voltage circuit breakers has advanced significantly during the past 15 years. Minimum oil circuit breakers (MOCB), air blast circuit breakers, and SF6 circuit breakers are often used for high-voltage switchgear.

Electrical Switchgear Types
There are three different classes of switchgear systems: low-voltage, medium-voltage, and high-voltage.
- High Voltage Switchgears: High-voltage switchgears(HV) are those that control 75KV of power or more. Because these breakers are designed for high-voltage use, they often include improved safety features.
- Medium Voltage Switchgear: Medium-voltage switchgear(MV) is utilized in systems ranging from 1 KV to 75 KV. This switchgear is commonly found in systems that include motors, feeder circuits, generators, and transmission and distribution lines.
- Low Voltage Switchgear: Low-voltage switchgear (LV) is designed to regulate systems up to 1KV. These are often found on the low-voltage sides of power distribution transformers and are employed in a wide range of industries.
High voltage switchgear Components
Understanding the operation of high-voltage switchgear requires familiarity with its basic elements. Although there are various components, we will concentrate on the essential ones. The basic components of high-voltage switchgear, present in both indoor and outdoor forms are:
Circuit Breakers
The circuit breaker, a critical component in high-voltage switchgear systems, is an electrical switch that automatically protects a circuit from damage caused by overload or short circuits. Its innovative design enables it to function in milliseconds, rapidly reducing excessive and fault currents and therefore protecting the entire system.
Instrument transformers
Instrument transformers are critical measuring equipment that are built into high-voltage switchgear systems. The basic function of current transformers (CTs) and voltage transformers (VTs) is to reduce current and voltage levels. This decrease allows for the safe monitoring of electrical system flows, the activation of protection relays, and the transmission of fault signals to the control center.
Earthing Switches
The earthing switch, a safety-essential component in a power system, is important to the system’s and operators’ safety. When the isolator or breaker is opened, it establishes a ground connection. This operation dissipates any remaining electrical charges in the line that has been removed from the power source, preventing dangerous circumstances.
Step-Up/Down Transformer
The largest and most expensive components of high-voltage switchgear are the step-up transformer, which increases the voltage of an electrical signal for efficient long-distance transport with minimal power loss, and the step-down transformer, which reduces the voltage before it reaches equipment that cannot handle high voltages.
Disconnecting Switch
Disconnectors are simple mechanical switches used in high-voltage switchgear systems to stop or restart electrical circuits. They are commonly used to connect or detach equipment from a power supply, primarily for maintenance or repair purposes. These components are also known as isolators.
Relays
A relay is a switch powered by electricity that may be used to activate or deactivate circuits. Protective relays are intended to detect problems in the electrical system and trip the circuit breaker. This breaker then disconnects the malfunctioning equipment from the power supply and helps to dissipate any ensuing electrical sparks.
Busbars
Busbars are low-impedance cables that connect electrical devices. Busbars in high-voltage switchgear link high-voltage circuit breakers and other components, allowing electricity to be sent between places.
Surge Arresters
A surge arrester is a gadget that protects equipment from damage caused by unexpected high voltages, such as lightning strikes and switching surges. High-voltage switchgear arresters operate by collecting surge energy before it may damage the equipment.
Earthing Grid
An earthing grid, made up of metal rods or plates placed in the ground, is used to route electrical energy into the earth. This protects equipment from lightning strikes and abrupt voltage surges.
Transformer
Simply described, a transformer is a device that employs alternating electromagnetic fields to convert various voltage levels (really electrical energy), with the voltage before and after the conversion being constant in frequency. It is classified into several types based on its application, including power transformers, rectifier transformers, voltage regulators, isolation transformers, and CT, PT, among others. A power transformer is something we frequently see on the project site.
Contactor
A contactor is an electrical device that is used to routinely turn on and off AC and DC main circuits, as well as large-capacity control circuits over long distances. The major control objects are motors, lights, capacitor banks, and contactors, which are classified as AC or DC. Compared to the circuit breaker, the difference is that the frequency of action is extremely high (so the electrical and mechanical life must be long enough); it has a larger breaking and making capacity, but it is often utilized at voltage levels of 1kV and lower. It cannot be compared to circuit breakers that have tens or hundreds of kilovolts of voltage.
Types of High Voltage Switchgear
There are two primary categories of high voltage switchgear: gas-insulated switchgear (GIS) and air-insulated switchgear (AIS). Whereas gas-insulated switchgear employs gas—typically sulfur hexafluoride (SF6)—AIS switchgear uses air as its principal insulating medium. Here are some details on the two types of HV switchgear.
AIS Air Insulated Switchgear)
Air-insulated Switchgear (AIS) uses air as the primary insulation medium to isolate and control the electrical power system. AIS is typically used for lower voltage applications and is known for its simple design, low cost, and ease of maintenance.
GIS (Gas Insulated Switchgear)
Gas-insulated Switchgear (GIS) uses sulfur hexafluoride (SF6) gas as the primary insulation medium. GIS is designed for high-voltage applications and is known for its compact design, high reliability, and superior performance.
How do you Troubleshoot High Voltage Switchgear?
Troubleshooting a high voltage switchgear is dependent on the source of the issue. Common troubleshooting techniques for high-voltage switchgear include:
You cannot lock the handle.
- This issue is caused by the internal locking mechanism rusting or malfunctioning.
- It’s also possible that you’re using the wrong key to open it.
- To resolve this issue, confirm that you are using the right key.
- You need to grease or replace the locking mechanism.
Internal noise
- Your switchgear’s internal noise is caused by the electromagnetic induction screws on the dividing plates.
- Cables contacting gland plates are another source of internal noise.
- Tighten the screws on the portioning plates and apply a coating of sealant on the cable.
Overheated connectors
- This is the effect of having overhead and loose bolts.
- To remedy this, make sure you use the rated current value.
- Also, tighten any loose bolts and replace the busbar as needed.
The switchgear fails the dielectric test or has a ground fault.
- Switchgear with cracked insulators fails the dielectric test or develops a ground fault.
- Such insulators are susceptible to moisture and other pollutants.
- To remedy this, replace the insulators.
- You can also use an appropriate cleaning chemical and dry the wet areas.
Shutters are not shutting.
- The major reason the shutters are not shutting is because they are damaged.
- To resolve this issue, fix the shutters and clean the adjustable components.
- You may also use lubricating oil to help these pieces close.
Indicates light extinction
- Light extinction can be indicated by the following:
- Fuse or resistor burned. Broken bulb filament, broken limit switch contactor, or inadequate contact with the auxiliary switches.
- To solve this, examine the following: change the bulb, replace the fuse or resistor, clean the auxiliary contacts, or monitor the MCCB of the fuse terminal.
Poor control unit operation
- Poor control unit operation may be due to unsecured terminal block screws.
- It might also be because the control connector is not properly connected.
- Tighten the screws for the terminal blocks.
- You may also connect the control plugs properly.
The shutters are not opening
- If your shutters do not open, it might be due to improper adjustment of the moving components or a lack of lubrication in these parts.
- It is also possible that the shutters are distorted.
- To resolve this, adjust and oil the moving parts, and inspect the shutters to verify they are in the proper shape.
Protection Functions Of High Voltage Switchgear
- Prevent closing with load: Once the vacuum circuit breaker trolley inside the high voltage switchgear is closed in the test position, the trolley circuit breaker cannot be moved into the working position.
- Prevent closing with grounding line: When the high voltage switchgear cabinet’s grounding knife is in the closing position, the trolley circuit breaker cannot close.
- Keep from accidentally entering the charged interval: When the vacuum circuit breaker within the high voltage switchgear is in the closed position, the mechanism on the grounding knife locks the rear door of the panel cabinet to the cabinet door.
- To avoid blocking the grounding line with electricity, ensure that the vacuum circuit breaker in the high voltage switchgear is closed while working and that the grounding knife is not in use.
- Prevent drawing the knife with a load: The high voltage switchgear within the vacuum circuit breaker cannot be removed from the trolley circuit breaker’s operational position during the closing process.
High Voltage Switchgear FAQs
What Are The Types Of Switchgear Used in HV?
There are two primary categories of high-voltage switchgear: gas-insulated switchgear (GIS) and air-insulated switchgear (AIS). Whereas gas-insulated switchgear employs gas—typically sulfur hexafluoride (SF6)—AIS switchgear uses air as its principal insulating medium.
What is the purpose of a switchgear?
A switchgear in an electric power system consists of electrical disconnect switches, fuses, or circuit breakers that regulate, protect, and isolate electrical equipment. Switchgear is used to deenergize equipment so that work may be done and to remove problems downstream.
Is A Switchgear A Transformer?
Transformers adjust the voltage level to enable power transmission and distribution. Switchgear protects and disconnects electrical circuits. UPSs safeguard equipment from voltage fluctuations and outages by supplying backup and conditioned power.