With the increasing demand for higher voltage systems across various industries, medium voltage switchgear is becoming more common today and attracting the attention of specifiers more than ever. Therefore, many people are looking for a more detailed understanding of the product. To shed light on medium voltage switchgear, we have written this in-depth article explaining its design, types, and applications.
1. What is a medium voltage switchgear?
According to industry standards, medium-sized switchgear is defined as electrical equipment operating at voltages between 1 kV and 52 kV. As a result, medium voltage switchgear ranges cover a large portion of the distribution spectrum.
- But electrical systems using such switchgear rarely reach 52 kV. Therefore, the definition of medium voltage switchgear is usually changed to switchgear controlling voltages up to 36 kV.
That is, each medium voltage switchgear is designed for a specific system. So the voltage it can handle will vary by application. The operation of medium voltage switchgear helps ensure the smooth operation of power distribution networks.
2. Medium voltage switchgear function
In the same way as any other type of equipment, medium voltage switchgear protects electrical equipment and circuits. It does this by automatically disconnecting specific components from the power source in the event of a problem, such as an electrical failure.
Other functions include disconnecting power to allow electricians to work on circuits without getting electrocuted, controlling the amount of electricity flowing through a system, and providing isolation so that one circuit can work without affecting another.
3. Medium voltage switchgear components
As mentioned above, medium voltage switchgear is designed to protect electrical equipment and circuits using various switches and safety devices. Depending on the specific device, these devices may be housed within an enclosure or without an enclosure. Below are the main medium voltage components or equipment.
1) Circuit breaker
The switchgear circuit breaker disconnects the equipment from the mains. There are two main types of circuit breakers used in medium voltage switchgear: air circuit breakers, oil circuit breakers, and vacuum circuit breakers. It is possible to operate these manually or automatically.
Switchgear fuses help protect against overloads by melting strips of material (metal) to break electrical paths. They work by “blowing” when too much current flows through them. In this way, the circuit is interrupted and further damage is prevented.
Switchgear switches include electrical devices that make, carry, and break current under normal circuit conditions, and that make, carry, and break current under specified abnormal circuit conditions that also meet the specified requirements.
A switchgear relay is a type of electrical switch. During an electrical fault, its contacts close to sending a signal to the circuit breaker. This signal causes the circuit breaker to stop delivering power to the circuit or load. Therefore, it is often called a protective relay.
5) Grounding switch
As the name suggests, a grounding switch is used to ground equipment. This is done to remove any static electricity that may build up on the device. Earthing switches are usually manually operated.
A switchgear isolator or disconnector connects or disconnects an electrical circuit. It is effective in isolating a faulty circuit from a normal circuit or is used when a circuit must be isolated for maintenance purposes.
7) Lightning arrester
A surge arrester is a device that helps protect electrical equipment from voltage spikes. Voltage spikes can damage equipment due to a sudden increase in voltage. Surge arresters work by diverting extra voltage from the device to the ground.
These include current transformers and voltage transformers. A switchgear transformer acts as a metering and protection device, enabling the switchgear to perform its function. Current transformers step down current, while voltage transformers, also known as voltage transformers, step down voltage.
9) Automatic recloser and segmenter
Automatic reclosers in medium voltage switchgear automatically reconnect power lines or circuits after an electrical fault has cleared. On the other hand, the function of a segmenter is to isolate a part of a circuit so that it can be repaired without affecting the rest of the circuit.
4. Types of medium voltage switchgear
The design of medium voltage switchgear can take many forms, with different characteristics from the insulating medium to the use of enclosures. In turn, this means that there are various different types of medium-voltage switchgear on the market. The most common ones are listed below.
1) Gas-insulated switchgear (GIS)
GIS uses gases for insulation, such as SF6 or a combination of SF6 and other gases. The switchgear adopts the form of a fully enclosed device and uses gas as the insulating medium. Gas insulation allows for much smaller gaps between circuit breakers. This makes gas-insulated medium-voltage switchgear more compact and can be installed in tighter spaces.
2) Air-insulated switchgear (AIS)
Air-insulated switchgear uses air as the insulating medium, so it is often called “air-break” switchgear. Switchgear is less expensive than gas types. However, breaker clearances must be increased because air is less insulator than gas. Therefore, these types of devices are usually installed outdoors.
3) Solid medium switchgear
As the name suggests, this type of medium voltage switchgear uses solid materials such as ceramic or glass for insulation. This makes it stronger than other types of MV switchgear and resistant to weather and environmental conditions. However, it also makes it more expensive and less flexible than other types of switchgear.
4) Oil-insulated switchgear
Oil-insulated switchgear utilizes oil as the insulating medium. Oil is a great insulator — and relatively cheap. However, it is flammable and potentially damaging to the environment. Therefore, oil-insulated medium voltage switchgear is not common today.
5) Metal-enclosed switchgear
Mechanical protection is provided by an external metal enclosure on this medium-voltage switchgear. Therefore, internal components are not exposed. This makes it more resistant to the environment and tampering. Metal-enclosed switchgear is commonly used in industrial and commercial applications.
6) Metal composite switchgear
Metal composite switchgear is similar to metal-enclosed switchgear, except that the internal components are also enclosed in a metal shell. The closed compartments are further grounded and designed as extraction cabinets.
7) Pad-mounted switchgear
Pad-mounted switchgear is metal-clad switchgear mounted on a concrete or other pad, primarily underground, in outdoor conditions. Industrial and commercial applications commonly use switchgear.
8) Arc-resistant switchgear
Arc-resistant switchgear is designed to control and extinguish arc flashes. This type of switchgear is often used in applications where there is a risk of arc flash, such as those with high short-circuit currents. According to the ANSI/IEEE medium voltage switchgear standard, it is also usually designed into 4 different types.
- Type 1: arc resistant only from the front
- Type 2: The entire switchgear assembly is arc resistant; front, side, and rear
- Type 2B: Fully arc resistant even with the control room door open
- Type 2C: arc resistant both at its perimeter and between compartments
5. Installation of medium voltage switchgear
Installation of medium voltage switchgear must be carried out by qualified personnel. Usually, this is a team of experienced electricians. Due to the higher voltages involved, medium voltage switchgear training is also a common practice for many manufacturers. Training helps ensure their products are installed correctly.
The first step in installing medium voltage switchgear is to determine the voltage and amperage of the power supply. A switchgear rating is selected based on this information. During installation, the electrician must follow these rules once the MV switchgear has been selected.
- The installation site is level and well-ventilated.
- All drawings and technical information are correct
- All materials required for medium voltage switchgear installation are available
- Qualified personnel should make all electrical connections.
After the medium voltage switchgear installation procedure is complete, the equipment needs to be tested. Various methods and tools are used to accomplish this. The results of these tests should be within the data specified by the manufacturer according to the specific medium voltage switchgear specification.
6. Maintenance of medium voltage switchgear
Medium voltage switchgear requires regular maintenance. This usually includes inspecting components for signs of wear or damage. The frequency of these inspections will vary depending on the type and application of the MV switchgear.
Typically, preventive maintenance for medium-voltage switchgear includes the following:
- Check parts for corrosion or dirt
- Check the interlock operation of the switchgear
- Check for signs of overheating
- Test various components
- Testing the insulation resistance of switchgear
In some cases, switchgear may need to be replaced due to age or damage. Manufacturers of medium voltage switchgear usually provide the necessary guidance for their products. That said, each electrician who oversees MV installations usually keeps a maintenance checklist.
Medium voltage switchgear is an essential part of most power systems today, helping to control power distribution while protecting electrical equipment and systems. There are various types of medium-voltage switchgear on the market. Always follow the product-specific manufacturer’s instructions when installing or replacing MV switchgear. This will help ensure that the new switchgear works as expected.