10 Best Medium Voltage Switchgear Manufacturers

Location Considerations

Switchgear is categorized as either indoor switchgear or outdoor switchgear depending on whether it is used for an indoor or outdoor location.

Indoor Switchgear

Indoor switchgear is designed specifically to be installed within buildings or other enclosures, where it is shielded from elements like wind, rain, snow, or unusual dust accumulations, aberrant condensations, ice, and hoary frost.
Typically, indoor switchgear has a metal-clad construction. The switchgear’s numerous parts are organized into compartments and divided by earthed metal walls. As a result, we have compartments for breakers, CT/PT, cable termination, busbars, surge suppressors, LT busbars, instrument panel chambers, etc.
Certain devices may be merged into one compartment depending on the design, for example, some manufacturers may combine CTs, VTs, and the cable termination arrangement in one compartment. Surge suppressors or VTs are positioned in the breaker box in certain other designs (on the truck carriage base).

Outdoor switchgear

Outdoor switchgear is designed to be installed in areas that are exposed to the elements, including rain, dust, and other environmental factors. Depending on the application, these can be mounted on a structure (porcelain-dad switchgear or pole-mounted) or inside a metal enclosure in the form of kiosks for accepting HT connections. The enclosure needs to be weatherproof when installing metal-clad switchgear outside.

Rating Considerations

Circuit breakers are rated at both the maximum operational voltage and the usual rated voltage. The power system to which the circuit breaker is connected shouldn’t go over this maximum operational voltage. The continuous current that a circuit breaker can handle without surpassing the rate of temperature rise is known as the rated current. This is crucial for the major power conducting parts’ insulation’s longevity!
Based on the fault level of the system and location/application, such as whether it is positioned at the generating point/source, far away, or located after other electrical equipment like transformers, the circuit breaker’s breaking capacity and short-time rating should be chosen.

Ambient Considerations

MV switchgear is made to function properly at the ratings listed on the rating plate in a typical environment. An altitude of up to 1000 meters and a temperature of 40°C are considered standard ambient conditions. The switchgear must be derated when these conditions change. For all such high altitude installations, surge suppressor use should also be taken into consideration.

Atmospheric air is utilized in circuit breakers for insulation and cooling. The less dense air at high elevations makes for poor cooling and insulation. Therefore, it is important to think about derating circuit breakers.

System Earthing Considerations

Systems are earthed using both firmly grounded and ineffectively grounded systems. A system that is securely grounded generates ground fault currents that are powerful enough to activate the afflicted feeder’s earth fault relay.

As a result, the right circuit breaker trips, isolating the malfunctioning part of the system without cutting off power to the working part.

Potential transformers with open delta secondary winding used in conjunction with neutral voltage displacement relays or core balance current transformers (often referred to as CBCTs) in conjunction with sensitive earth leakage relays aid in the prompt discovery of these issues.

Seismic Considerations

The idea of seismic withstand criterion was initially developed for machinery utilized in nuclear power generating units. However, massive earthquakes that occurred in many different places of the world caused significant property damage, including severe electrical equipment damage, which drew attention to the necessity for good seismic design of equipment.

Based on the seismic intensity at each of these locations, the various locations are divided into five zones. Seismic testing is used for verification and is carried out on a shaker table, testbed, or other appropriately built test fixture.

Overvoltage Considerations

Surge suppressors, also known as surge arrestors, are used to guard against system overvoltages or over-voltages brought on by a certain kind of switching medium used in electrical equipment like transformers, motors, and capacitor banks.

Surge suppressors using a capacitance-resistance combination and gapless zine oxide surge suppressors are also often employed.

Interrupt and short-circuit ratings

Overcurrent protective device interrupt ratings

The amount of current that an overcurrent protective device, which is commonly a vacuum circuit breaker, can safely interrupt without causing damage to the device itself or the switchgear, is referred to as the interrupt rating. This rating is typically provided on a symmetrical current basis. In medium-voltage overcurrent protection devices, specified parameters such as peak and asymmetrical ratings are also typical. The switchgear assembly itself is not subject to interrupt ratings; rather, they only apply to the actual overcurrent safeguard devices that interrupt the circuit in the event of a fault. For medium-voltage vacuum circuit breakers, typical interrupt values vary from 25 kAIC to 63 kAIC symmetrical. (This rating is frequently referred to as breaking current for IEC equipment.)

Switchgear short-circuit or withstand ratings

The highest amount of current that switchgear can safely sustain (i.e., permit to travel through it) without being damaged is known as the short circuit current rating of the switchgear. This is a measurement of the bracing and support of the busbars, which enables them to pass large currents owing to faults that happen downstream of the switchgear while remaining undamaged and unharmed. The upstream switchgear must have a short circuit current rating greater than the worst-case currents that will be traveling through it to protect against faults in downstream equipment. This makes sure that the equipment upstream that is in the fault current path is protected from harm caused by downstream faults. According to ANSI standards, typical short circuit current (or withstand) ratings range from 25 kA to 63 kA for the 2-second rating and from 40 kA to 101 kA for the 10-cycle rating. This rating is also known as a short-circuit rating, short-circuit withstand rating, or withstand rating when applied to electrical switchgear.

Continuous current

The amount of current that the primary overcurrent protection device and main bus within the switchgear can constantly carry without causing a trip or harming the equipment is known as the continuous current rating of the switchgear. For medium-voltage switchgear, continuous current ratings can commonly range from 600A to 4000A.