Switchgear is an electrical device that connects and disconnects electrical equipment or circuit from the power supply. It conducts interrupts the flow of electrical power. In its initial design, it was a mechanical switch that physically separated or joined two or more conductors. Development over time has made switch gears offer control, protection, and isolation, or electrical equipment or circuit. They comprise more than one device to form a system that collective work together.
Types of switchgear
There exist different devices that can be integrated into switchgear depending on the need. The most common ones include;
- Circuit breaker
- Potential transformer
- Current transformer
- Lightning arrestor
Operation Modes of Switchgears
A fuse is used to protect against overcurrent that may be due to overload or short-circuit fault. It breaks the circuit by blowing away the thin wire. The fuse is replaced after fault finding and fixing are done. A circuit breaker is the most common type, it serves two purposes at the same time. It offers overcurrent protection, whereby it trips, and also it can be operated manually to connect or disconnect equipment/circuits. Unlike a fuse, a breaker can be reset to on state after tripping. Current and voltage/potential transformers are used in medium to high voltage switchgear to measure line voltage and current. Should the measured values exceed the set parameters a motorized breaker is actuated and trips to interrupt power flow? Relays are electrical switches used in protection, remote and automatic control of switchgear. Lighting arrestor de-energizes the circuit whenever lightning-caused surges exceed set allowable limits. They trigger contactors and circuit breakers to make or break.
There are three main modes of operation as outlined below.
- Manual- this is human-operated. They have a handheld lever that is moved to either make or break the switch. They are the earliest to be invented and requires an operator to be adequately clothed with personal protective equipment.
- Automatic – it’s self-operated. It has electrical sensors and actuators that are triggered whenever circuit parameters exceed set limits. The sensor and send the error signal to technicians for attention as well as keep checking whether the error is cleared and triggers a reconnection action. Automatic systems employ relays, contactors, and motors.
- Remote-controlled switchgear- the system is controlled as the name suggests from a remote location. The system sensors send their status to monitors in a far-off location. From the remote point, a command signal can be sent to switch the device as the operator so wishes.
Factors to consider in design and installation of a switch gear
- Voltage rating- the magnitude of voltage, low, medium, or high determines insulation needed.
- Current rating – determines the sizes of busbar used, circuit breaker and quenching medium
- Operation method- manual, remote or automatic
- Insulation medium- air, gas or oil
- Installation- outdoor or indoor
- Type of current- is it direct or alternating
- Application- transmission, distribution or industrial
- Nature of interruption – fuse of circuit breaker
- Purpose – to disconnect equipment or circuit, overcurrent protection or earthing switch
In the electrical engineering system between the generator and load are conductors, measuring instruments and switch gears. The switchgear monitoring and control comprise most of the work electrical engineers do. Whether its regional or national grid, transmission and distribution network, industrial, commercial and residential electrical system switch gears and conductors are the most encountered. It is therefore quite important than all electrical and electronic engineering professionals understand these devices from where they can design proper switchgear.