What is the principle of differential protection of generators

Differential protection. It is the main protection of the transformer, which is installed according to the principle of circulating current. It is mainly used to protect various phase-to-phase short-circuit faults that occur inside the winding of double-winding or three-winding transformers and their lead-out lines, and can also be used to protect transformers from single-phase inter-turn short-circuit faults.

The basic principle of differential protection is to detect the current at the beginning and end of the motor, and compare the phase and amplitude of the current at the beginning and the end of the current and the principle of composition, under normal circumstances, the difference between the two is 0, that is, the current flowing into the motor is equal to the current flowing out of the motor. When a short circuit fault occurs inside the motor, a differential current is generated between the two, and the protection function is activated, and the circuit breaker of the exit tripping motor is launched.

Differential protection. The principle is utilizationKirchhoffWhen the transformer works normally or when it is faulty outside the area, it is regarded as an ideal transformer, then the current flowing into the transformer and the outflow current (converted current) are equal, and the differential relay does not operate. When there is an internal fault in the transformer, two (or three) sides are provided to the fault pointShort-circuit current, the differential quietly brother protects the secondary current felt andProportionalAt the point of fault, the current is current, and the differential relay acts.

The function of differential protection is that the differential protection of the transformer is the main protection of the transformer, which is mainly used to protect the various interphase short-circuit faults that occur inside the double-winding or three-winding transformer winding and its lead line, and can also be used to protect the single-phase inter-turn short-circuit fault of the transformer.

Advantages and disadvantages of differential protection.

The advantage of differential protection is that it can quickly and selectively remove faults within the protection range, the wiring is correct, the adjustment is appropriate, and there will be no misoperation.

The disadvantage is that it cannot react to the inside of the internal transformer, such as the overheating of the iron core.

Faults such as oil level reduction, such as a short circuit between turns of a few turns in the transformer winding, although the short circuit current in the short circuit turn is very large, which will cause serious overheating of the local winding and produce a strong impact of oil flow in the direction of the oil pillow, but the phase current is not large, and the differential protection will not respond. Therefore, differential protection is not a substitute for gas protection.

The phenomenon is that two (or three) sides (or three) supply short-circuit current to the point of fault.

The sum of the secondary currents felt by differential protection is proportional.

current at the point of fault; The measure is to reduce the unbalanced current in the steady-state condition.

The differential protection works using Kirchhoff's current theorem, when the transformer is often working or has an out-of-area fault, it is regarded as an ideal transformer, then the current flowing into the transformer and the outflow current are equal, and the differential relay does not operate. When the internal fault of the transformer is made, the two beats (or three sides) provide short-circuit current to the fault point, and the sum of the secondary current felt by the differential protection is proportional to the fault point current, and the differential relay acts.

To reduce the unbalanced current in the steady-state condition, the transformer differential protects the current transformers on each side.

D-class current transformer for transformer differential protection is selected; When the external maximum steady-state short-circuit current is passed, the secondary load of the differential protection circuit should be able to meet the requirement of 10% error.

1. Principle of differential protection.

Differential protection is the use of Kirchhoff.

When the current theorem works, when the transformer is working normally or when it is faulty outside the area, it is regarded as an ideal transformer, then the current flowing into the transformer and the outflow current (converted current) are equal, and the differential relay does not operate.

When there is an internal fault in the transformer, two (or three) sides provide short-circuit current to the fault point.

The secondary current is proportional to the difference between the impact and the difference.

At the point of fault, the current is current, and the differential relay acts.

Second, the role of differential protection.

The transformer differential protection is the main protection of the transformer, which is mainly used to protect various interphase short-circuit faults that occur in the winding of the double-winding or three-winding transformer and its lead line, and can also be used to protect the transformer from single-phase inter-turn short-circuit faults.

Generators are star-shaped, under normal circumstances, each phase of the stator coil inlet and tail (star) current is the same, when the stator coil fails, inter-turn short circuit, interphase short circuit, poor insulation and other faults, stator coil inlet and tail (star) current is not the same, connected to the inlet and tail (star) current transformer will produce a current difference, causing the differential relay to trip, this is differential protection.

The current transformer on the outlet side is generally connected to the generator outlet switch, and the other is connected to the place close to the star point, and the protection range is the generator outlet switch to the star point.

The outlet and tail end of the three-phase winding of the generator are equipped with a hand transformer with the same parameters, and the current at the end of each phase head and tail is subtracted, which should be zero under normal conditions (the output hall is equal to the input).

When there is a leakage inside the generator, the fault current flows back to the tail end of the winding through the fault point, so that the output current of the generator and the input current are not zero, so the protection is acted.

Differential protection is the difference between the CT current vectors at both ends of the input, and the action element is activated when the set operating value is reached. The protection range is between the CT at both ends of the input, and the disadvantage of differential protection is that the short-circuit fault cannot be reflected, etc.