Jul. 20, 2021
During the normal operation of generator, the excitation suddenly disappears completely or partially, which is called loss of excitation of generator.
Among the components of diesel generator set, the generator is very important. After a long time use of diesel generator set, the generator may lose excitation. This situation is normal. But this situation will affect the system. What are the impacts of excitation loass to generator?
1.Low-excitation and loss-of-excitation generators absorb reactive power from the system, causing the voltage of the power system to drop. If the reactive power reserve in the power system is insufficient, the voltage of some points in the power system will be lower than The allowable value destroys the stable operation between the load and each power source, and even causes the voltage of the power system to collapse.
2.When a generator loses its excitation, due to the voltage drop, other generators in the power system will increase their reactive power output under the action of the automatic adjustment of the excitation device, thereby causing some generators, transformers or lines to overcurrent , Its backup protection may malfunction due to overcurrent, which will expand the scope of the accident.
3.After a generator loses its magnetization, due to the swing of the generator's active power and the drop of the system voltage, it may cause the adjacent normal operating generators and the system, or between the various parts of the power system, to lose synchronization, causing the system to lose synchronization. Oscillation occurs.
4.The greater the rated capacity of the generator, the greater the reactive power deficit caused by low excitation and loss of excitation, and the smaller the capacity of the power system, the smaller the ability to compensate for this reactive power deficit. Therefore, the greater the ratio of the single generator capacity to the total capacity of the power system, the more serious the adverse impact on the power system.
What are the reason for the loss of excitation of generator?
(1) Symbol after the generator loses its excitation: the stator current and active power of the generator rise rapidly after an instant drop, and the ratio increases and starts to swing.
(2) The generator can still send a certain amount of active power after loss of excitation, and keep the direction of the active power sent out, but the pointer of the power meter periodically swings.
(3) As the stator current increases, its ammeter pointer also periodically swings.
(4) From the sent reactive power to the absorbed reactive power, the pointer also periodically swings. The amount of reactive power absorbed is approximately proportional to the amount of reactive power before loss of excitation.
(5) The rotor circuit induces alternating current and alternating magnetomotive force with slip frequency, so the pointer of the rotor voltmeter also periodically swings.
(6) The pointer of the rotor ammeter also oscillates periodically, and the current value is smaller than that before the loss of excitation.
(7) When the rotor circuit is open, a certain eddy current is induced on the surface of the rotor body to form a rotating magnetic field, which also generates a certain amount of asynchronous power.
How to deal with the problem of excitation loss of generator？
(1) After the loss of excitation protection is activated, the excitation mode is automatically switched, and the active load reduction is invalid and acts on the trip, it will be handled as an accident shutdown;
(2) If the de-excitation switch is tripped by mistake, the de-excitation switch should be reclosed immediately. If the reclose is unsuccessful, the generator will be de-loaded and stopped immediately;
(3) If the loss of excitation is due to a failure of the excitation regulator AVR, immediately switch the AVR from the working channel to the standby channel, and switch to manual operation if the automatic mode fails;
(4) After the generator loses excitation and the generator does not trip, the active load should be reduced to 120MW within 1.5min, and the allowable running time after the loss of magnetism is 15min;
(5) If the loss of excitation causes the generator to oscillate, the generator should be disconnected and shut down immediately, and then reconnected to the grid after the excitation is restored.
When generator occurs loss of excitation, we should find out the reason and solve the problem in time, to avoid impact to the generator. Dingbo Power not only provide technical support, but also produce diesel generator sets, if you have plan to purchase, welcome to contact us by email firstname.lastname@example.org.
Jan. 31, 2023
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