Symbol of generator after magnetic loss:
(1) The stator current and active power of the generator rise rapidly after an instant decline, and the ratio increases, and begins to swing.
(2) After the generator loses magnetism, it can also produce a certain amount of active power, and keep the direction of the sent active power unchanged, but the pointer of the power meter periodically swings.
(3) The stator current increases, and the ammeter pointer also oscillates periodically.
(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 the magnetic loss.
(5) The rotor loop induces alternating current and alternating magnetomotive force of slip frequency, so the rotor voltmeter pointer also oscillates periodically.
(6) The rotor ammeter pointer also oscillates periodically, and the value of the current is smaller than that before the magnetic loss.
(7) When the rotor circuit is open, a certain eddy current is induced by the surface of the rotor body to form a rotating magnetic field, and a certain asynchronous power is generated.
Process:
(1) After the loss of magnetic protection action, the automatic switching of excitation mode, reducing active load is ineffective and acting on the trip, according to the accident stop treatment;
(2) If the loss of magnetism is caused by the wrong trip of the magnetic switch, the magnetic switch should be immediately coincided, and the coincidence is unsuccessful, the generator will be disconnected immediately.
(3) If the loss of magnetism is due to the failure of the excitation regulator AVR, the AVR should be immediately switched from the working channel to the standby channel, and the automatic mode is switched to the manual mode of operation;
(4) After the generator loses magnetism 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 magnetism causes the generator to oscillate, the generator should be unlined and shut down immediately, and re-connected to the grid after the excitation recovery.
When the generator loses magnetism and runs asynchronously, the general treatment principles are as follows:
(1) Generators that are not allowed to operate without excitation should be removed from the grid immediately to avoid damaging the equipment or causing system accidents.
For generators that allow unexcited operation, the following operations should be performed according to the unexcited operation regulations:
1, quickly reduce the active power to the allowable value (the power value specified by the factory’s magnetic loss is consistent with the average value of the meter swing), at this time the stator current will swing around the rated current.
2, manually disconnect the magnetic switch, exit the automatic voltage regulation device and generator forced excitation device.
3, pay attention to other normal operation of the generator stator current and reactive power value is beyond the provisions, if necessary, according to the generator allowed overload provisions.
4, the excitation system for a quick and careful inspection, such as the problem of the working exciter, should quickly start the standby exciter to restore excitation.
5, pay attention to the voltage level of the factory branch, if necessary, can be poured to the standby power supply connection.
6, in the specified time of no excitation operation, still can not make the unit to restore excitation, the generator should be separated from the system. The loss of magnetic field of large capacity generator has great influence on the system. Therefore, the generator is generally not allowed to operate without excitation before the test is determined. The domestic 300MW generator set is equipped with undermagnetic protection and loss of magnetic protection devices. In order to ensure that the protection device word system does not mismove when it oscillates, the loss of magnetic protection time limit is set to 1S. When the generator loses magnetism, after 0.5S, the magnetic protection action is insufficient, the generator is switched from automatic excitation to manual excitation, and the standby excitation power is put into operation. If the excitation circuit of the generator is not faulty, the generator can still be pulled into synchronization and resume normal work.
If the generator’s magnetic loss is not eliminated after the standby excitation is put into operation, then after S, the magnetic loss protection action will detach the generator from the system. Generator magnetic loss will have an adverse effect on the generator and the system, the impact on the system is:
1, make the system reactive power difference;
2, cause other generators to overcurrent; The impact on the generator itself is: (1). The loss of rotor increases resulting in local heating of rotor. (2). The generator vibrates under the impact of alternating asynchronous power.
For more questions about the generator set, please call the Beidou Power team. More than ten years of professional production and sales of power generation equipment experience, more professional engineer team to serve you, choose Beidou power is to choose rest assured, welcome on-site factory inspection.
Post time: Nov-25-2024