What is the principle of differential protection?
Principle of differential protection Differential protection is based on the fact that any fault within an electrical equipment would cause the current entering it, to be different, from the current leaving it.
How does line differential protection work?
Line differential relays basically operate on a difference in current into the line, compared to the current out of the line. For an internal fault, the current will flow into the line from both line terminals, with the polarity of the current transformers as shown in Figure.
How does transformer differential protection work?
Principle of Differential Protection The differential relay actually compares between primary current and secondary current of power transformer, if any unbalance found in between primary and secondary currents the relay will actuate and inter trip both the primary and secondary circuit breaker of the transformer.
Why is differential protection used?
Differential protection schemes are mainly used for protection against phase-to-phase fault and phase to earth faults. The differential protection used for power transformers is based on Merz-Prize circulating current principle. Such types of protection are generally used for transformers of rating exceeding 2 MVA.
What is differential protection of motor?
Motor overcurrent differential protection measures the current flow into a load and compares it to the current measured on the neutral side of the motor. A current difference is detected as a fault.
Why differential protection is called Unit protection?
Unit protection is designed to operate for abnormal conditions inside the protected zone while remaining stable for abnormal conditions outside the protected zone. This scheme requires current to be measured at each end of the zone. The current through the relay is zero if the two current transformers are identical.
Where is differential protection used?
What are the difficulties of differential protection?
The differential scheme described suffers from the following drawbacks: Unmatched characteristics of CTs. Ratio change as a result of tapping. Magnetizing inrush current.
What is core balance CT?
Concept: Core Balance Current Transformer (CBCT) : It is a ring-type current transformer through the center of which a three-core cable or three single-core cables of a three-phase system passes. This type of current transformer is normally used for earth fault protection for low and medium-voltage systems.
What is IS1 and IS2 in differential protection?
Relay Parameter Setting IS1: The basic differential current setting. K1: The lower percentage bias setting. IS2: The bias current threshold setting. K2: The higher percentage bias setting.
What is the difference between unit and non unit protection?
Non-unit protection consists of circuits that measure and compare the voltages and currents at the relaying point. This contrasts with unit protection which will not operate for a fault outside its zone. Examples of non-unit protection include fuses, overcurrent and distance relays, reclosers, and sectionalisers.
What is CBCT relay?
The CBCT, also known as a zero sequence CT, is used for earth leakage and earth fault protection. The concept is similar to the RVT. When there is an earth fault, the residual current (zero phase sequence current) of the system flows through the secondary of the CBCT and this operates the relay.