What is Switchgear?
The apparatus used for switching, controlling and protecting the electrical circuits and equipment is known as switchgear.
Components of Switchgear
Some equipments are designed to operate under both normal and abnormal conditions. Some equipments are meant for switching and not sensing the fault.
On the other hand, when a failure (e.g. short circuit) occurs on any part of power system, a heavy current flows through the equipment, threatening damage to the equipment and interruption of service to the customers.
However, the switchgear detects the fault and disconnects the unhealthy section from the system. For more details visit working of circuit breaker and protective relays.
Read more about Components of Switchgear
Evolution of Switchgear
The tumbler switch with ordinary fuse is the simplest form of switchgear and is used to control and protect lights and other equipment in homes, offices etc.
For circuits of higher rating, a high-rupturing capacity (H.R.C.) fuse in conjunction with a switch may serve the purpose of controlling and protecting the circuit. However, such a switchgear cannot be used profitably on high voltage system (33 kV) for two reasons.
- Firstly, when a fuse blows, it takes sometime to replace it and consequently there is interruption of service to the customers.
- Secondly, the fuse cannot successfully interrupt large fault currents that result from the faults on high voltage system.
- A circuit breaker is a switchgear which can open or close an electrical circuit under both normal and abnormal conditions. Even in instances where a fuse is adequate, as regards to breaking capacity, a circuit breaker may be preferable. For more details, go through this article on What is fuse and How it Works?
- It is because a circuit breaker can close circuits, as well as break them without replacement and thus has wider range of use altogether than a fuse.
Essential Features of Switchgear
- Complete reliability: With the continued trend of interconnection and the increasing capacity of generating stations, the need for a reliable switchgear has become of paramount importance. This is not surprising because it is added to the power system to improve the reliability. When fault occurs on any part of the power system, they must operate to isolate the faulty section from the remainder circuit.
- Absolutely certain discrimination: When fault occurs on any section of the power system, the switchgear must be able to discriminate between the faulty section and the healthy section. It should isolate the faulty section from the system without affecting the healthy section. This will ensure continuity of supply.
- Quick operation: When fault occurs on any part of the power system, the switchgear must operate quickly so that no damage is done to generators, transformers and other equipment by the short-circuit currents. If fault is not cleared quickly, it is likely to spread into healthy parts, thus endangering complete shut down of the system
- Provision for manual control: A switchgear must have provision for manual control. In case the electrical (or electronics) control fails, the necessary operation can be carried out through manual control.
Classification of Switchgear
Switchgear can be classified on the basis of voltage level in to the following
- Low voltage (LV) Switchgear
- Medium voltage (MV) Switchgear
- High voltage (HV) Switchgear
1. Low Voltage Switchgear
They are generally rated upto 1 kV (1000 V).
2. Medium Voltage Switchgear
- Normal ON/OFF switching operation.
- Short circuit current interruption.
- Switching of capacitive currents.
- Switching of inductive currents.
- Some special application.
3. High Voltage Switchgear
Read more about Types of High Voltage Circuit Breakers
- air switches
- oil switches.
Read more about fuse here What is a FUSE and How it Works?
3. Circuit Breakers
Read more about Circuit Breaker – Operating Principle and Arcing Phenomenon
Read in detail How Protective Relays Work?