What are the problems arising in differential protection in power transformer and how are they overcome? Difference in lengths of pilot wires on either sides of the relay. This is overcome by connecting adjustable resistors to pilot wires to get equipotential points on the pilot wires.
What are the problems encountered in differential protection of transformer?
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 differential protection of power transformer?
Differential protection is a unit-type protection for a specified zone or piece of equipment. It is based on the fact that it is only in the case of faults internal to the zone that the differential current (difference between input and output currents) will be high.
What are the limitation of differential protection when applied to Transformers?
There are some disadvantages in the voltage balance differential relay such as a multi tap transformer construction is required to accurate balance between current transformer pairs. The system is suitable for protection of cables of relatively short length otherwise capacitance of pilot wires disturbs the performance.
What is used to overcome the difficulty due to differences in length of pilot wires in differential protection?
To overcome this difficulty, the percentage differential relay or biased differential relay is used. (2) The difference in pilot wire lengths: The current transformer and machine to be protected are located at different sites and normally it is not possible to connect the relay coil to the equipotential points.
What are the shortcomings of differential protection scheme as applied to power transformer?
Simple differential protection system is inadequate because of its following inherent drawbacks:
- Difference in Length of Pilot Wires on Either Side of Relays: …
- Different CT Characteristics: …
- Tap Changing: …
- Magnetising Inrush Current:
What is differential protection in power system network?
Differential protection (ΔI) is a reliable and safe protection method, as well as the most important and most commonly used transformer protection. It is used for protecting the transformer with nominal power above 8 MVA. It is usually not used in the case of a transformer with lower nominal power up to 4 MVA.
What is the function of differential protection relay in transformer?
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.
How a differential protection scheme operates?
Working of Differential Protection System
When the internal fault occurs in the power transformer windings the balanced is disturbed and the operating coils of the differential relay carry current corresponding to the difference of the current among the two sides of the transformers.
Where is differential protection used?
The differential protection relay is used for the protection of the generator, transformer, feeder, large motor, bus-bars etc.
What are the different types of faults occur in power system?
There are mainly three types namely line to ground (L-G), line to line (L-L) and double line to ground (LL-G) faults. Line to ground fault (L-G) is most common fault and 65-70 percent of faults are of this type.