- What is switchgear
- Functions of switchgear
- components of switchgear
- Essential features of switchgear
- Types of switchgear
What is switchgear
Switchgear is an apparatus which is used for switching, controlling and protecting electrical circuits and equipment. The requirement of electric power has increased a lot, so in order to get a continuous power supply. Power system must be protected from large faults and provide protection to machinery and devices. For the continuity of the power supply machinery such as generators and motors are switched on and off many times and the means provide to achieve this is called switchgear.
In general, switchgear is the term including the entire range of switching devices and their combination with associated control, measuring, protecting, and regulating equipment.
What are the functions of switchgear
- Carrying the normal load current
- Making or breaking the normal load current
- Clearing the fault current
Components of switchgear
- Circuit breaker
- Current transformer and potential transformer
- Protective relays
- Measuring instruments
- Switches
- fuses
- Surge arrestors
- Isolators
- Miniature circuit breaker
What is the consideration which must be done while using switchgear in the power system
- Location of the equipment if it is indoor or outdoor
- System parameters such as system earthing, frequency, insulation level, ambient conditions,
- Erection of switchgear – mechanical and electrical interconnections, placing the equipment on foundation, assembly of loose supplied parts, connections of controls and power circuits
- Switchgear commissioning – Testing must be done to ensure if the installation meets the requirements
What are the essential features of switchgear
- Reliability – switchgear is used in a power system to improve the reliability when a fault occurs in system switchgear must isolate the faulty section from the remainder circuit
- Absolutely certain discrimination – if fault occurs in a power system then switchgear must be able to discriminate between the faulty section and healthy section.
- Quick operation – if any fault occurs in a power system then switchgear must be able to act quickly so that no damage is done to the equipment
- Provision for manual control – switchgear must have manual control in case of any electrical or electronic control fail
- Provision for instruments – provisions for the instruments is needed this may be in the form of ammeter, voltmeter…
Types and classification of switchgear
Classification of switchgear can be done by
- The current rating
- Interrupting rating
- Voltage class- low voltage (less than 1000volts)
Medium voltage (1000 – 35000 volts)
High voltage (more than 35000 volts)
- Insulating medium – air, gas, oil, vacuum
- Construction type – indoor, outdoor, industrial, metal-enclosed, metal-clad…
- Type of current – AC, DC
- By application – transmission system, distribution
- Operating method – manually, motor or solenoid/stored energy
Different switch gears
Switchgear has a lot of equipment which is related to switching and interrupting current under normal and abnormal conditions. It includes equipments such as fuses, relay, circuit breakers, and other equipment
High voltage switchgear
Air-insulated switchgear
Air circuit breakers are used for high voltage system it is mostly used in high voltage sub-station for voltage range up to 800Kv, these circuit breakers are used where space restriction and environment circumstances are not severe. Electrical and mechanical components of AIS installation are assembled on site. AIS which is used for industrial operation is not safe to touch and it will be affected by the environment and climatic change.
Gas-insulated switchgear
Its design is really compact and it would really be an advantage for installation it is used in a substation where the voltage range up to 550Kv. It is installed in the middle of the load center of an urban or industrial area. This type of switchgear is insensitive to contamination and it provides safety from electric shocks
Highly integrated switchgear
HIS switchgear has the advantages of air-insulated installation and the technology of gas-insulated switchgear it is used in voltage range up to 550Kv. This type of switchgear are suited for new substations in a limited space and in places where environmental conditions are extreme and it can also be used in places where the maintenance cost is high
Low voltage switchgear
Contactors
Contactors are load breaking devices with a limited short circuit breaking and making capacity and they are used for high switching rates, it can be divided into two types they are air-insulated and vacuum contactor.
Circuit breakers
They make and break all currents within the scope of their rating, from small inductive capacitive load currents to full short circuit current and this is done under all fault conditions in the power supply system such as earth faults, phase opposition… it can be used to control the input from the transformer.
Molded case and miniature circuit breaker
These circuit breakers are light weight compact circuit breakers for mounting onto or behind the panels, they are designed for hand operation but it also has a built-in protective tripping arrangements
Fuses
Fuses are used with low voltage switchgear as a backup for distribution contractors or for various control and instrumentation circuits. They are composed of fuse base and fuse-link with the fuse base an isolated distance can be established and with the fuse link one single breaking of short circuit current can be done
