Everything About Medium Voltage Switchgear Explained

Medium voltage switchgear
Medium voltage switchgear
Resource: http://emadrlc.blogspot.com

With the increasing demand for higher voltage systems across different industries, medium voltage switchgear is becoming more common today—and attracting the attention of specifiers than ever before. As a result, many people are seeking to understand the product in more detail. In order to shed light on MV switchgear, we compiled this in-depth post to explain its design, types, and application.

What is Medium Voltage Switchgear?

According to industry standards, medium switchgear is defined as electrical equipment that uses voltages between 1 kV and 52 kV. This encompasses a large portion of the power distribution spectrum, which helps explain why the medium voltage switchgear range is so wide.

  • But electrical systems where this type of switchgear is used rarely reach 52 kV. So the medium voltage switchgear definition is commonly altered to mean switchgear that controls voltages up to 36 kV.

That said, every MV switchgear is designed for a specific system. So the voltage it can handle will vary depending on the application. Speaking of application, let’s see hoe the medium voltage switchgear operation helps to ensure the smooth working of power distribution networks.

Medium Voltage Switchgear Function

Just like any other type of the equipment, the main medium voltage switchgear function is to protect electrical equipment and circuits. It does this by automatically disconnecting specific parts from the power supply when there is a problem, such as an electrical fault.

Other functions include disconnecting power to allow electricians to work on a circuit without being electrocuted, controlling the amount of power that flows through a system, and providing isolation so that one circuit can be worked on without affecting another.

Medium voltage switchgear diagram showing the various parts
Medium voltage switchgear diagram showing the various parts
Resource: https://www.semanticscholar.org

Medium Voltage Switchgear Components

As mentioned above, MV switchgear is meant to protect electrical equipment and circuits using a variety of switching and safety devices. Depending on the particular equipment, these may be housed inside an enclosure or without enclosure. Here is a look at the main medium voltage components or devices.

1. Circuit breakers

The switchgear circuit breaker disconnects equipment from the power supply. There are two main types of circuit breakers used in MV switchgear: air, oil, and vacuum circuit breakers. These can be either manually or automatically operated.

2. Fuses

A switchgear fuse helps to protect against overloads by melting strip of material (metal) to break an electrical path. They work by “blowing” when too much current flows through them. This interrupts the circuit and prevents further damage.

3. Switches

Switchgear switches include electrical devices that make, carry, and break currents under normal circuit conditions and also meet the specified requirements when making, carrying, and breaking specified abnormal circuit conditions.

4. Relays

A switchgear relay is an electrically operated switch. During an electrical fault, its contacts close to send a signal to the circuit breaker. The signal causes the breaker to stop power transmission to a circuit or load. As such, it’s often called a protective relay.

5. Grounding Switches

As the name suggests, grounding switches are used to connect equipment to a ground. This is done to dissipate any static electricity that may have built up on the equipment. Grounding switches are typically manually operated.

6. Isolators

The switchgear isolator or disconnector switch connects or disconnect an electrical circuit. It effectively isolates a faulty circuit from the healthy ones, or it can be used when a circuit has to be isolated for maintenance purposes.

7. Surge Arresters

A surge arrester is a device that helps to protect electrical equipment from voltage spikes. A voltage spike is a sudden increase in voltage that can damage equipment. The arrester works by diverting the extra voltage away from equipment and into the ground.

8. Instrument Transformers

These include current and voltage transformers. A switchgear transformer can act as a metering and protection device, enabling switchgear to perform its function. Current transformers lower current, while voltage transformers, also called potential transformers, lower voltage.

9. Auto Reclosers and Sectionalizers

An auto-recloser in medium voltage switchgear automatically reconnects a power line or circuit after an electrical fault has been cleared. A sectionalizer’s function, on the other hand, is to isolate a section of a circuit so that it can be repaired without affecting the rest of the circuit.

Pad-mount medium voltage switchgear
Pad-mount medium voltage switchgear
Resource: ttp://electricalengineeringtour.blogspot.com

Types of Medium Voltage Switchgear

Medium voltage switchgear design can take many forms, with features varying from insulation medium to whether an enclosure is used or not. That, in turn, means a variety of different types of medium voltage switchgear on the market. Here is a list of the most common.

1. Gas Insulated Switchgear (GIS)

GIS is insulated using gas, such as SF6 or a combination of SF6 and other gases. This switchgear comes in the form of fully enclosed devices with gas as the insulating medium. Gas insulation allows the gap between breakers to be much smaller. This makes gas insulated, medium voltage switchgear more compact and installable in tighter spaces.

2. Air Insulated Switchgear (AIS)

Air insulated switchgear uses air as the insulating medium, which is why it is often referred to as “air-break” switchgear. The switchgear is less expensive than the gas type. However, the breaker gap must increase, seeing that air is not as good an insulator as gas. These types of equipment are, therefore, normally installed outdoors.

3. Solid Dielectric Switchgear

As the name suggests, this type of MV switchgear is insulated using solid materials, such as porcelain or glass. This makes it more robust 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 good insulator— and relatively inexpensive. However, it is flammable and can be damaging to the environment. As a result, oil insulated MV switchgear is not as common today.

5. Metal Enclosed Switchgear

This medium voltage switchgear uses an external metal enclosure to provide mechanical protection. The internal components are, therefore, not exposed. This makes it more resistant to the environment and tampering. Metal enclosed switchgear is often used in industrial and commercial applications.

6. Metal Clad Switchgear

Metal clad switchgear is similar to metal enclosed switchgear, except that the internal components are also enclosed in metal enclosures. The enclosed compartments are further grounded and designed to be draw out cabinets.

7. Pad Mounted Switchgear

Pad mounted switchgear is a type of metal-clad switchgear that is mounted on a concrete or other pad and mostly installed underground, in outdoor conditions. The switchgear is often used in industrial and commercial applications.

8. Arc Resistant Switchgear

Arc resistant switchgear is designed to contain and extinguish an electrical arc flash. This type of switchgear is normally used in applications where there is a risk of an arc flash, such as those with high short-circuit currents. It’s also normally designed as 4 different types, in accordance with ANSI/IEEE medium voltage switchgear standards.

  • Type 1: only arc resistant from the front
  • Type 2: entire switchgear assembly arc resistant; front, side and rear
  • Type 2B: arc resistant all around even when the control compartment doors are open
  • Type 2C: arc resistant both around its perimeter and between compartments
Switchgear maintenance
Switchgear maintenance
Resource: https://www.mdpi.com

Medium Voltage Switchgear Installation

Medium voltage switchgear installation must be done by qualified personnel. This is usually a team of experienced electricians. Because of the higher voltages involved, medium voltage switchgear training is also a common practice by many manufacturers. The training helps to ensure their products are correctly installed.

The first step in the installation of MV switchgear is to determine the voltage and amperage of the power supply. This information is used to select the appropriate type of switchgear rating for the application. Once the MV switchgear has been selected, the electricians will need to ensure these rules during the installation process.

  • That the installation site is level and well-ventilated.
  • All drawings and technical information is correct
  • All materials required for MV switchgear installation are available
  • All electrical connections are made by qualified personnel.

After the MV switchgear installation procedure is completed, the equipment will need to be tested. This is done using various methods and tools. The results of these tests should be within the manufacturer’s specified data based on the particular medium voltage switchgear specifications.

Medium Voltage Switchgear Maintenance

MV switchgear requires periodic maintenance. This usually involves checking the components for signs of wear or damage. The frequency of these checks will vary depending on the type of MV switchgear and the application.

Generally, medium voltage switchgear preventive maintenance involves the following:

  • Inspecting components for corrosion or dirt
  • Checking the switchgear’s interlock operations
  • Checking if there are overheating signs
  • Testing the various components
  • Testing the switchgear insulation for resistance

In some cases, the switchgear may need to be replaced due to age or damage. Medium voltage switchgear manufacturers usually provide the necessary direction for their products. That said, every electrician overseeing a MV installation will usually keep a maintenance checklist.

Conclusion

Medium voltage switchgear is an important part of most power systems today, helping to control power distribution while also protecting electrical equipment and system. There are a variety of types of MV switchgear available on the market. When installing or replacing MV switchgear, it is important to follow the manufacturer’s instructions for the specific product. This will help to ensure that the new switchgear works as intended.

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