Generator protection knowledge

1. Generator demagnetization protection
Demagnetization protection is used as a demagnetization fault protection for abnormal drop or disappearance of the generator excitation current. It consists of criterion such as excitation low voltage Ufd(P), system low voltage, steady impedance, TV line disconnection and other criteria, and is respectively used to signal and de-column demagnetization. The excitation low voltage Ufd(P) criterion and the steady impedance criterion are both related to the steady boundary, which can detect whether the generator loses static stability due to loss of magnetism. Static impedance criteria act when the static boundary is demagnetized.
2. Generator overexcitation protection
Overexcitation protection is a protection that reacts to the excessive magnetic density of the core due to the decrease in frequency or the excessive voltage of the generator. Overexcitation protection is divided into two fixed values, high and low. The low fixed value sends a signal and reduces the excitation voltage after a fixed delay of 5 seconds (the function of reducing excitation voltage and excitation current is not used yet), and the high fixed value acts in de-column de-magnetization after the reverse time limit. The upper limit of the inverse time limit is 5 seconds, and the lower limit is 200 seconds.
3. Generator stator grounding protection
Generator stator grounding protection is a generator stator grounding fault protection. It consists of two parts: the fundamental zero-sequence voltage part and the third harmonic voltage. The fundamental zero-sequence voltage protects the single-phase grounding fault of the stator winding from the machine end to the machine end 95% of the machine end, which is composed of the principle of reflecting the zero-sequence voltage at the generator end, which is operated in de-rotation and de-magnetization after the time limit t1 (3s); the third harmonic voltage protects the single-phase grounding fault of the stator winding from the machine end to the machine end, which is composed of the neutral point of the generator and the third harmonic principle at the machine end, which is operated in the signal after the time limit t2 (5s). The two form the stator ground protection. The protection is equipped with PT disconnection lock.
4. The generator stator interturn
protection is composed of the longitudinal zero-sequence voltage and fault-partitioned negative-sequence direction criteria. PT line break locking measures are set as the main protection for the internal interturn, phase-to-phase short circuits and stator winding opening welding of the generator. The fault component negative-sequence direction criteria are realized by detecting the negative-sequence power flowing out of the generator by detecting the longitudinal zero-sequence voltage criteria output from the 3PT open triangular winding where the neutral point is directly connected to the generator neutral point but not grounded. Protective action is stopped at all.
5. The stepless
protection uses three-impedance elements to detect the number of slippery poles and determine the position of the oscillation center through the trajectory of the impedance. In the case of short circuit failure, system oscillation, voltage circuit disconnection, etc., the protection will not be erroneous. Protection generally operates on signals; when the oscillation center is inside the generator-transformer group, the protection section I starts to send a trip command via t1 (0.5s), and the protection section II starts to send a trip command via t1 (0.5s), and the de-column is to de-column; when the oscillation center is outside the generator-transformer group, the protection section II starts to send a signal via t2 (2s). The protection is equipped with a current locking device to ensure that the current does not exceed the rated circuit breaker breaking current when the circuit breaker is disconnected.
6. Low-frequency accumulation protection.
Low-frequency accumulation protection reflects the accumulated effect of the system frequency reduction on the turbine. The protection consists of a sensitive frequency relay and a counter, locked through the auxiliary contact of the exit circuit breaker (that is, the low-frequency accumulation protection also exits the operation when the generator exits the operation). The accumulated system frequency is lower than the frequency constant value of 47.5Hz. When the accumulated time reaches the set value of 3000 seconds, the signal is transmitted after a delay of 30 seconds. The device can monitor the display of fixed values, frequency f and accumulated time in real time during operation.
7. Excitation loop overload protection
Excitation loop overload protection is used as protection for the overcurrent or overload of the rotor excitation loop. It is connected into a three-phase type, consisting of two parts: time limit and reverse time limit. The operating current of the time limit is adjusted according to the conditions that can be reliably returned at the maximum rated current of normal operation. After the time limit t1 (5s), the signal is operated and the excitation current is reduced (the function of reducing the excitation current is not used); the operation characteristics of the anti-time limit are determined according to the overload capacity of the generator excitation winding, and the protection operation is carried out in de-column demagnetization, and the anti-time limit is 10 seconds.
8. Generator rotor point grounding protection.
Generator rotor point grounding protection is used to react to the generator rotor circuit grounding fault. The protection adopts the ping-pong switching principle, and takes turns sampling the positive and negative electrodes to ground voltages of the rotor circuit. By solving two different grounding loop equations, the rotor grounding resistance and grounding position are calculated in real time. Protect the signal to operate after 2 seconds of delay.
9. The generator symmetrical overload
protection device consists of two parts: time limit and reverse time limit, and the time limit part is operated on the signal after a time limit of 5 seconds. The reverse time limit action characteristics are determined according to the generator's ability to withstand overload current, and the action is in the de-list. The protection device can reflect the heat accumulation process of the generator stator.
10 The generator negative sequence overload protection
protection device consists of two parts: time limit and reverse time limit. The time limit operation current is adjusted according to the negative sequence current value that avoids the long-term allowable negative sequence current value of the generator and the current value that avoids the imbalance of the negative sequence current filter under the maximum load, and operates on the signal after a time limit of 3 seconds. The reverse time limit action characteristics are determined according to the generator's ability to withstand negative sequence current, and are operated in de-column demagnetization.