What are the fundamentals of medium voltage switchgears?

Switch gears are centralized collection of circuit breakers, switches and fuses to protect isolate and control electrical equipment. These devices are mounted in metal structures. The collection of the circuit protection devices are called as switchgear line up/assembly. Switchgears are found in electric utility transmission and distribution systems and in medium to large-sized industrial and commercial facilities. As of the best electrical switch gear companies in UAE, Al Taqah- ATS Generators’ range of switchgear and safety equipment is supplied by advanced technology and is manufactured by the finest brains.

Working of Switchgears

The circuit protection devices such as circuit breakers, fuses or switches distribute power to various sections of a facility and the electrical loads. The devices protects individuals and facility equipment but limiting the system current flow to safe levels.

Types of Medium- voltage Switchgear

  • Metal-clad switchgear

The device is medium- voltage electrical switchgear in which all the electrical components along with the incoming-outgoing bus, main circuit breaker, and instrumentation are all enclosed n separate metal compartments to provide ruggedness, easy maintenance and safety. The voltage levels of metal-clad switchgears ranges from 5 kV- 38 kV. It can be used in industrial facilities, electrical power generation and power transmission facilities.

  • Gas-insulated switchgear

This type of switchgears has sealed enclosures, filled with insulating gas like SF6 or SF6 with a mixture of other gases. This enclosure facilitates a compact and low profile installation. The gas insulating medium helps to reduce the distance between interrupting components.

  • Metal-enclosed switchgear

This device contains circuit protection devices like circuit breakers, fusible switches, power fuses and control & metering equipment. Metal-enclosed switchgears can be mounted in common compartments unlike metal-clad switchgear. These type of switchgears is used in industrial and commercial facilities where the electrical service is above 480/600V.

  • Vault/subsurface switchgear

This type of switchgears is used for electrical distribution systems of voltage range 15 kV- 38 kV, with the condition of requiring the switch and the accessories should be operated from below-grade location. The locations can be dry or wet. The vault switchgear allows the user to operate the switch manually from above ground and uses vacuum interrupters to isolate faults and protect loads. SF6, sold materials and solid-dielectric-in –air technology is used for insulation.

  • Pad-mounted switchgear

It is designed for underground distribution systems with a voltage range of 5 kV- 38 kV. This type of switchgears has the features of low profile, outdoor rating and tamper resistant construction which make them ideal for feeder sectionalizing, utility distribution and circuit protection applications. The fuses, switches and vacuum interrupters in the switchgear protect isolate faults, loads and minimize outages. Here, insulation includes fluid, SF6, solid-dielectric-in-air technology and old materials.

Switchgear Insulating Media

Insulating media is used to protect energized devises like bus, bushings etc from sudden arc faults. Air is the common insulator nut gas and fluid insulators provide higher dielectric strength and allow the switchgears to be smaller.

Switchgear Interrupting Devices

Switchgear interrupting devices include over current protection devices such as fuse, circuit breaker, switches and interrupt the flow of electricity.

  • Air Switch- It is a switching device which use air as dielectric and provide a visible means of disconnection. They have lower interrupt ratings than vacuum switches and are more economical.
  • Oil Switch- It is a device which is submerged in an oil-filled enclosure. They can be seen in pad-mounted switchgear where the oil insulation allows the construction of a low- profile enclosure.
  • Vacuum Switch- It is an electrical switch where the electricity is interrupted inside the vacuum bottles. The vacuum permits the arc produced to extinguish quickly. This type of switches requires less space and can be applied at higher voltages.
  • Vacuum circuit breaker- Here, in this device, the arc interruption and quenching takes place inside sealed vacuum bottles. The device permits the arc to extinguish quickly and thus reduce the arc energy. They can interrupt higher voltage faults and requires less space.
  • Fuse- This device interrupts excess current flow. It is achieved by the melting of an electrical wire. Fuses are paired with a switch in medium voltage switchgear applications to provide over current protection and give the ability to open and close the circuit.
  • Vacuum fault interrupter- This device functions as a load- break switch and also as an over current protection device to eliminate the need for a separate switch and fuse.

Interrupt Ratings

Interrupt ratings refers to the magnitude of current that a vacuum circuit breaker can safely interrupt without damaging the switchgear. The interrupting ratings for medium- voltage vacuum circuit breakers range from 25 kAIC – 60 kAIC symmetrical.

Short-circuit ratings

The maximum amount of current that the switchgear can withstand without causing equipment damage is called as short circuit current ratings/ withstanding ratings. It measures the support and bracing of the bus bars that allows them to remain intact and no damage when high current is passing due to faults in downstream equipments. For faults, the upstream switchgear must have a excess short- circuit current rating. That means the downstream faults do not damage the upstream equipments which is in the fault current path. The typical short-circuit current ratings range from 25kA to 63 kA symmetrical for the 2-second rating and 40 kA- 101 kA asymmetrical for the 10-cycle rating.

Continuous current

The amount of current that the main bus and over current protection device within the switchgear can carry without damaging the equipment is called as the continuous current rating of switchgear. For medium- voltage switchgear, the continuous current ratings can range from 600A- 4000A.

Medium voltage switch gears have voltage range of 600V- 230 kV and are classified by the maximum voltage it can service. The electrical switchgear companies in UAE offer the best quality as per market standard. It is a comprehensive inventory of switches, circuit breakers, switch fuse units, HRC fuses, offload isolators, contractors etc.

Al Taqah-ATS Generators is one among the best electrical switch gear companies in UAE, offering a significant variety of switchgears and safety equipment for generators. We manufacture and supply devices with latest and eco-friendly design and follow the European standards for RoHS compliance. Al Taqah Switchgears are one of the finest devices that can save on power and resources as our programming has contributed to a lower power usage and eventually lower costs.