High Voltage Switchgear Meaning, Types and Maintenance

High voltage switchgear is a vital part of electrical grids or high tension power distribution networks. It enables the safe, efficient, and reliable transfer of electrical energy by providing a means to safely disconnect and isolate electrical equipment from the power supply. Here is more about this type of switchgear.

What is High Voltage Switchgear?

Switchgear makes an indispensable part of power distribution systems. When used with high voltage systems, this equipment must be able to match these voltage requirements. But what is high voltage switchgear in the first place and what parts make it?

To answer that, let’s start with the basics: High voltage switchgear is a combination of electrical components – switches, fuses, transformers, relays, and disconnectors – that are used in power networks carrying voltages above 36kV.

What is High Voltage Switchgear Used For?

The application of high voltage switchgear is seen in a wide variety of industries and electrical settings. These are typically systems that handle 36kV and higher, as we saw earlier. You will , therefore, usually find HV switchgear in these facilities and installations.

• In power plants to safely disconnect generators and other equipment from the grid
• On electricity transmission and distribution networks to connect or disconnect sections of the network
• In substations to connect or disconnect transformers, capacitor banks, and other equipment
• In large industrial and commercial premises to connect or disconnect equipment from the power supply or to turn large motors on and off

In these settings, the switchgear serves to protect equipment and personnel from the damaging effects of high current faults. High voltage switchgear is also used to control the flow of electricity within the grid, and to isolate equipment for maintenance or repair.

High voltage switchgear Components

In order to understand the working of high voltage switchgear, it’s first necessary to understand the components that make it. These are a sizeable number. However, we will only concern ourselves with the major parts. The main HV switchgear components found in indoor and outdoor switchgear include the following.

Circuit Breakers

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. In high voltage switchgear, the breaker is a complex device that acts within milliseconds to clear load and fault currents.

Instrument Transformers

These high voltage switchgear components act as measuring devices and include current and voltage transformers, commonly abbreviated as CTs and VTs. They reduce current and voltage levels so the amounts flowing through an electric system can be safely monitored. Instrument transformers activate the protective relays, or they may send the fault signal directly to the control center.

Earthing Switches

An earthing switch function is to connect an electrical circuit to earth when an isolator is opened or when the breaker opens during a fault. This is usually done to remove residual charges from a line that has been disconnected from the power supply. It ensures the protection of a power system as well as the safety of personnel.

Step Up/Down transformer

These are the largest (and most expensive) high voltage switchgear parts. The step-up transformer increases the voltage of an electrical signal so it can be transported over long distances with minimal power loss. The step-down transformer does the opposite, decreasing the voltage before it reaches equipment that can’t handle high voltages.

Disconnecting Switch

In high voltage switchgear, disconnectors are simple mechanical switches that can open and close an electrical circuit. They are used to connect or disconnect equipment from the power supply usually for maintenance purposes. These HV switchgear parts are also called isolators.

Relays

A relay is an electrically operated switch that can be used to turn on or turn off a circuit. Protective relays automatically detect faults in the electrical network and activate the circuit breaker. The breaker then disconnects the faulty equipment from the power supply while also helping to extinguish the resulting arc.

Busbars

Busbars are located all over a high voltage switchgear installation. They are, by definition, low impedance conductors that connect electrical equipment together. When used in high tension switchgear, busbars connect high voltage circuit breakers and other HV components, helping to deliver power from one point to another.

Surge Arresters

A surge arrester is a device used to protect equipment from damage caused by transient overvoltages, such as lightning strikes, and other causes such as switching surges. HV switchgear arresters help to protect equipment by dissipating the surge energy before it reaches the equipment.

Batteries

In many high voltage switchgear installations, batteries are used as a backup power source in case of a power outage. The batteries provide enough power to operate the circuit breaker and other HV components long enough to safely disconnect the equipment from the power supply.

Earthing Grid

This is a system of metal rods or plates buried in the ground that helps to dissipate electrical energy into the earth. The earthing grid protects equipment from damage caused by lightning strikes and other transient overvoltages.

How does High Voltage Switchgear work?

Now that we’ve covered the basics of high voltage switchgear and understand the individual components, let’s take a more in-depth look at how this type of switchgear works. Here is a brief description of the high voltage switchgear operation.

• As we’ve already covered, the main high voltage switchgear function is to provide a means to safely control the distribution of high voltage electricity.
• In order to do that, high voltage switchgear uses a series of devices that will automatically meter power flow, control it, or detect and break faulty circuits and isolate them to from the healthy ones.
• During the operation of a switchgear breaker, high voltage current is detected by the current transformer or protection relay, which activates the circuit breaker.
• The circuit breaker then breaks the circuit, interrupting the flow of current and preventing damage to the electrical equipment while quenching the generated arc.
• Some HV switchgear operations are manual, such as isolating equipment or lines using the disconnecting switch.

In the high voltage switchgear market, equipment is available with all sorts of mechanisms to allow the monitoring of the switchgear operation and help ensure a correctly working installation.

The high voltage switchgear and control gear includes various sensors and a control panel. The data collected by sensors is processed and analyzed in order to take preventive or corrective actions if necessary.

Types of High Voltage Switchgear

High voltage switchgear can be classified into two main types: air-insulated switchgear, AIS, and gas-insulated switchgear, GIS. AIS switchgear utilizes air as the primary insulating medium, while gas-insulated switchgear uses gas, typically sulfur hexafluoride (SF6). Here is more detail about the two HV switchgear types.

High Voltage Air Insulated Switchgear

High voltage, air insulated switchgear is mostly used outdoors, in substations, power plants, and other electricity distribution systems. This switchgear is less expensive – and easier to maintain. However, it’s more vulnerable to environmental conditions, such as dust, humidity, and salt air and, therefore, requires more regular maintenance than the gas insulated type.

High Voltage Gas Insulated Switchgear

High voltage, gas insulated switchgear is a more compact option than air insulated switchgear. It’s, therefore mostly used indoors where space is adequate. And although GIS switchgear is more expensive than AIS switchgear, it offers several benefits, such as a smaller footprint, increased reliability, and reduced maintenance requirements.

High Voltage switchgear Maintenance Requirements

High voltage switchgear is a critical part of many electrical installations. Once the preferred type of HV switchgear has been selected, the next step is to install it. After installation, the equipment must be maintained according to the manufacturer’s instructions.

High voltage switchgear manufacturers usually provide usage instructions and sometimes even training for maintenance personnel. These care instructions must be adhered to by users. That said, here is what high voltage switchgear maintenance typically entails:

HV Switchgear Preventive Maintenance

High voltage switchgear preventive maintenance refers to a scheduled program of activities that aim to keep the switchgear in good working condition. Its purpose is to help electricians identify any potential problems before they occur. Preventive maintenance includes:

• Inspections to check for loose bolts, signs of wear and tear, and other issues
• Cleaning of the high voltage switchgear parts to prevent any buildup of dirt or debris.
• Carrying out tests. The high voltage testing procedure must follow safety standards
• Adjustments as necessitated by the switchgear condition
• Calibrations to ensure the accuracy of various parts of the switchgear

HV Switchgear Corrective Maintenance

High voltage switchgear conditional maintenance is performed when there is evidence of a problem or when the results of preventive maintenance indicate that a problem may be developing. Conditional HV switchgear maintenance involves these activities:

• Troubleshooting to identify the root cause of the problem
• Repairs to fix any identified issues.
• Replacements of parts that are too damaged to be repaired
• Modifications to improve the switchgear’s performance or to address a design flaw

Conclusion

High voltage switchgear is an essential part of any electrical system. This guide has provided an overview of the different types of high voltage switchgear and the considerations that must be made when selecting, installing, and maintaining the equipment. With this information, you can make sure that your high voltage switchgear is up to the task of safely and reliably providing power to your electrical system.

When choosing high voltage switchgear for a particular application, it is important to consider the specific needs of the project. Factors such as cost, space constraints, maintenance requirements, and environmental conditions will all play a role in determining the best type of switchgear for the job.