× Home MCQ Videos Basic Electrical Circuit Theories Electrical Laws Materials Batteries Illumination Generation Transmission Distribution Switchgear Protection Measurement Control System Utilities Safety Transformer Motor Generator Electrical Drives Electronics Devices Power Electronics Digital Electronics Biomedical Instrumentation

Low Voltage Switchgear or LV Switchgear

on 24/2/2012 & Updated on Wednesday 16th of May 2018 at 06:06:14 PM
Generally electrical switchgear rated upto 1KV is termed as low voltage switchgear. The term LV Switchgear includes low voltage circuit breakers, switches, off load electrical isolators, HRC fuses, earth leakage circuit breaker, miniature circuit breakers (MCB) and molded case circuit breakers (MCCB) etc i.e. all the accessories required to protect the LV system. The most common use of LV switchgear is in LV distribution board. This system has the following parts

Incomer

The incomer feeds incoming electrical power to the incomer bus. The switchgear used in the incomer should have a main switching device. The switchgear devices attached with incomer should be capable of withstanding abnormal current for a short specific duration in order to allow downstream devices to operate. But it should be cable of interrupting maximum value of the fault current generated in the system. It must have interlocking arrangement with downstream devices. Generally air circuit breakers are preferably used as interrupting device. Low voltage air circuit breaker is preferable for this purpose because of the following features

Related pages
Low Voltage Switchgear or LV Switchgear

  1. Simplicity
  2. Efficient performance
  3. High normal current rating up to 600 A
  4. High fault withstanding capacity upto 63 kA
Although air circuit breakers have long tripping time, big size, high cost but still they are most suitable for low voltage switchgear for the above mentioned features.

Sub - Incomer

Next downstream part of the LV Distribution board is sub - incomer. These sub - incomers draw power from main incomer bus and feed this power to feeder bus. The devices installed as parts of a sub - incomer should have the following features
  1. Ability to achieve economy without sacrificing protection and safety
  2. Need for relatively less number of inter - locking since it cover limited are of network.

ACBs (Air Circuit Breakers) and switch fuse units are generally used as sub - incomers along with molted case circuit breakers (MCCB).

Feeders

Different feeders are connected to the feeder bus to feeds different loads like, motor loads, lighting loads, industrial machinery loads, air conditioner loads, transformer cooling system loads etc. All feeders are primarily protected by switch fuse unit and in addition to that, depending upon the types of load connected to the feeders, the different switchgear devices are chosen for different feeders. Let's discuss in details

In LV switchgear system, electrical appliances are protected against short circuit and over load conditions by electrical fuses or electrical circuit breaker. However, the human operator is not adequately protected against the faults occurs inside the appliances. The problem can be overcome by using earth leakage circuit breaker. This operates on low leakage current. The earth leakage circuit breaker can detect leakage current as low as 100 mA and is capable of disconnecting the appliance in less than 100 msec. low A typical diagram of low voltage switchgear is shown above. Here the main incomer comes from LV side of an electrical transformer. This incomer through an electrical isolator as well as an MCCB (not shown in the figure) feeds the incomer bus. Two sub-incomers are connected to the incomer bus these sub incomers are protected by means of either switch fuse unit or air circuit breaker. These switches are so interlocked along with bus section switch or bus coupler that only one incomer switch can be put on if bus section switch is in on position and both sub incomer switches can be put on only if bus section switch is at off position. This arrangement is fruitful for preventing any mismatch of phase sequence between the sub - incomers. The different load feeders are connected to any of the both sections of the feeder bus. Here motor feeder is protected by thermal overload device along with conventional switch fuse unit. Heater feeder is protected only by conventional switch fuse unit. The domestic lighting and AC loads are separately protected by miniature circuit breaker along with common conventional switch fuse unit. This is most basic and simple scheme for low voltage switchgear or LV distribution board.

Rate the page.

Rating = 4.2 & Total votes = 5


New Articles
Articles on Switchgear
Electrical Power DistributionSwitchgear ProtectionIsolatorLV SwitchgearMV SwitchgearHV SwitchgearGas Insulated SwitchgearMetal Enclosed SwitchgearLightning ArresterIndoor SwitchgearBasic Insulation Level
More Articles on Switchgear
Circuit BreakerMCBArcingVacuum SwitchgearTransducer
Articles Categories
Home
Basic Electrical
Electric Transformer
Electric Generator
Electric Motor
Electrical MCQ
Tools
Video Lectures
Electrical Generation
Electric Transmission
Switchgear
Electric Protection
Electrical Measurement
Electronics Devices
Power Electronics
Digital Electronics