What’s the matter with the oscillation and out-of-step of the generator?

Q: What is the generator’s oscillation and out-of-step?

Q: How to judge which generator is out of step and oscillate from the indication of the meter and what should the operator do when it is out of step?

Answer: When the synchronous generator is in normal operation, the rotational speed of the rotor and the synchronous rotational speed of the stator magnetic field are in a synchronous state. When the load changes suddenly, due to the inertia of the rotor, the displacement of the rotor cannot be stabilized at the new value immediately, and it will cause several times in the new value. This phenomenon is the oscillation of the synchronous generator. When the rotational speed of the oscillating unit is no longer consistent with the synchronous rotational speed of the stator magnetic field, the generator and the power system run asynchronously. This phenomenon is called synchronous power generation. Machine out of step.

From the indication of the meter, the oscillation or out-of-step has the following phenomena:

(1) The pointer of the stator ammeter swings violently, and the current may exceed the normal value.

(2) The pointers of the generator voltmeter and other bus voltmeters swing violently and often decrease.

(3) The pointer of the active power meter swings on the full scale.

(4) The pointer of the rotor ammeter swings around the normal value.

In the event of an accident, the meters of each motor running in parallel are often swinging, which can be distinguished from the following aspects:

(1) For the out-of-step caused by the accident in the factory, it is always possible to determine which related unit may be out of step from the operation reason or the fault location of the factory;

(2) Generally speaking, the swing amplitude of the meter of the out-of-step motor is stronger than that of other motors;

(3) The swing of the active power meter of the out-of-step motor is full scale, even hitting the needle bars on both sides, while other units swing around the normal load value, and when the needle of the active power meter of the out-of-step motor swings to zero or When it is negative, the needles of other motors swing to the side with the larger positive indication value, that is, the two swing in the opposite direction.

If there is an oscillation that tends to be stable, that is, the smaller the oscillation is, there is no need to do anything. After a few oscillations, it will pass, as long as you are mentally prepared to deal with the accident.

If it causes out of step, it is necessary to create conditions to restore the same period as soon as possible. Generally, the following measures can be taken:

(1) Increase the excitation of the generator.

(2) If a motor is out of step, its active power output can be appropriately reduced;

(3) According to the above method, if it still does not enter the synchronous state after 1–2 minutes, the out-of-step motor can be disconnected from the system.

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