What are the the limitations in the differential protection of a transformer?
The differential scheme described suffers from the following drawbacks: Unmatched characteristics of CTs. Ratio change as a result of tapping. Magnetizing inrush current.
Why do bus bar faults occur?
The causes of busbar faults can be ; Failure of support insulator resulting in earth faults. Flash over across support insulator, causing flash over due to over-voltage. Heavily polluted insulator, causing flash-over due to overvoltage.
What are the different faults in bus bar?
The bus zone fault occurs because of various reasons likes failure of support insulators, failure of circuit breakers, foreign object accidentally falling across the bus bar, etc., For removing the bus fault, all the circuits connecting to the faulty section needs to be open.
What is bus zone protection?
Bus Zone Protection includes, besides the bus itself the apparatus such as circuit breakers, disconnecting switches, instrument transformers and bus sectionalizing reactors, etc. Although bus zone faults are rare, experience shows that bus zone protection is highly desirable in large and important stations.
What are the difficulties of differential protection?
Difficulties of differential protection:
(1) Saturation of CT magnetic circuit during short circuit condition: Due to these causes the relay may operate even for external faults, the relay may lose its stability for through faults.
What are the difficulties associated with circulating current in differential protection when applied to power transformers how we can overcome these difficulties?
Tap changing will cause differential current to flow through the relay even under normal operating conditions. The above difficulty is overcome by adjusting the turn-ratio of CTs on the side of the power transformer provided with taps.
What is bus differential protection?
Bus differential protection is based on Kirchhoff’s current law, which states that the sum of currents entering a node is zero. A bus is treated as a node, and current measurements are taken from all terminals connected to the bus. Under normal conditions, the currents sum to zero.
Which protection is used for bus bar?
The system that is used to cover busbar protection consists of overcurrent or distance protection. Making use of this system the busbar will be inherently protected. This technique or method is applied to simple distribution systems by implementing overcurrent protection.