The differential scheme described suffers from the following drawbacks: Unmatched characteristics of CTs. Ratio change as a result of tapping. Magnetizing inrush current.
What are the drawbacks of the simple differential protection?
Answer : Limitations of differential protection of transformer: 1) Due to the magnetization characteristics of the CTs used, the ratio errors change with respect to the circulating currents. 2) The pilot wires … current (higher imbalance) due to which accuracy of sensing & operation is decreased.
What are the problems arising in differential protection in power transformer and how are they overcome?
What are the problems arising in differential protection in power transformer and how are they overcome? 1. 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 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 purpose of backup protection?
The backup protection provides the back up to the main protection whenever it fails in operation or its cut out for repairs. The backup protection is essential for the proper working of the electrical system.
What is percentage differential protection?
Percentage restrained differential relays measure the individual branch currents and quantify the through current in the zone of protection. The percentage restraint characteristic requires that the differential current be greater than a percentage of the through (restraint) current.
How do you protect a transformer?
The protection of a transformer against the overloads is performed by a dedicated protection usually called thermal overload relay. This type of protection simulates the temperature of the transformer’s windings. The simulation is based on the measure of the current and on the thermal time constant of the transformer.
On which principle differential protection is based?
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.
What happens in differential relay when saturation is too high?
The effect of CT saturation on transformer differential protection is double-edged. Although, the percentage restraint reduce the effect of the unbalanced differential current, in the case of an external faults, the resulting differential current which may be of very high magnitude can lead to a relay male-operation!