What Is percent differential protection?
What Is percent differential protection?
The percentage differential relay is designed to operate the differential current in terms of its fractional relation with actual current flowing through the circuit. It is used to protect the system under Current transformer saturation, unequal CT ratios, nuisance trip etc.
What is line differential protection?
Line differential protection is one of the most popular forms of transmission line protection. This type of protection is based on Kirchoff’s current law, which states that the current flowing into a line must be equal to the current flowing out of the line.
Which CT is used for differential protection?
The PS class CTs are used for differential protection. The differential protection is also called the zone or unit protection.
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.
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.
Why Is percent differential protection superior to simple differential protection?
So generally the percentage differential relay scheme is more stable than a simple differential relay scheme. And stable means that the relay will operate only for real internal fault in the protected zone, and it will never operate for through faults or due to any other mismatch.
Where 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 biased differential protection?
The purpose of biased differential protection is to detect faults with high selectivity and sensitivity. This means that it can trip with no intentional time delay for faults within its zone of protection, the reason why differential protection is often applied on high value equipment such as transformers.
Why PS class CT used for differential protection?
The PS class CT is special protection class CT. Both the PS class CTs used for differential protection have the identical saturation characteristics and their knee point voltage are the same. The designer takes the data like lead resistance,relay burden and system fault level from user before design of PS class CT.
What are the drawbacks of differential relay?
Disadvantages of Current Differential Relay:
- The impedance of the pilot cables generally causes a slight difference between the currents at the two ends of the section to be protected.
- Pilot cable capacitance causes incorrect operation of the relay when a large through-current.
What is a differential relay 87?
87 Differential protective relay A protective relay that functions on a percentage, phase angle, or other quantitative difference between two currents or some other electrical quantities.
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.
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