Power System Protection is a branch of electrical engineering that deals with the protection of electrical equipment (or component) in a power system network by removing the faulty part.
In a power system, there are various equipments such as alternators, busbar, transmission line, transformers, etc. connected in between the generation side and distribution side. All such equipment undergo abnormal conditions or faults in their lifetime due to various reasons.
For example, a tree falling or touching an overhead transmission line may cause a fault. There will be overloading of a motor due to worn out of the bearing. A lightning strike on overhead insulator can cause insulation failure. Pollution may result in degradation in the performance of insulators which may lead to a breakdown. Under frequency or over frequency of an alternator may result in mechanical damage to its turbine requiring tripping of an alternator. Even otherwise, the low-frequency operation will reduce the life of a turbine and hence it should be avoided.
The function of the protection system is to protect the system from abnormal conditions and faults by isolating the faulty element as quickly as possible. This will ensure the working of a healthy section of the network.
A protection system consists of Current & Voltage Transformers, protective relays, circuit breakers, and batteries.
1. Current transformers (CTs) & Potential Transformers (PTs): The purpose of these transformers is to reduce the current and voltage so that it could be used by relays for operation.
2. Protective Relays: The purpose of relays is to detect the fault and initiate a trip sequence when an electrical quantity (example, voltage, current, frequency, phase-angle, etc.) goes beyond the normal range. Hence it will send a command to the circuit breaker to disconnect the faulty part.
3. Circuit Breakers: The purpose of the circuit breakers is to operate on the trip sequence initiated by the relays in order to open the circuit.
4. Batteries: The batteries are used as back up power supply in the event of mains supply failure.