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The effect of generator loss of magnetism on the generator itself
1. Due to the slip after the engine loses magnetism, the difference frequency current occurs in the rotor circuit of the generator, and the difference frequency current causes loss in the rotor circuit. If the allowable value is exceeded, the rotor will be overheated. In particular, high-capacity large-scale units with direct cooling have a relatively low heat capacity margin and the rotor is more susceptible to overheating. The difference frequency current of the surface layer of the rotor can also cause severe local overheating or even burns on the contact surface of the rotor body wedge and the guard ring.
2. After the loss-generating generator enters the asynchronous operation, the equivalent reactance of the generator is reduced, and the reactive power is absorbed from the power system. The greater the active power before the demagnetization, the larger the slip and the smaller the equivalent reactance. The greater the reactive power absorbed. After the loss of magnetism under heavy load, the generator stator will overheat due to overcurrent.
3. For large steam turbine generators with direct cooling high force rate, the maximum value of the average asynchronous torque is small, the inertia constant is also relatively reduced, and the rotor is also obviously asymmetrical in terms of the vertical axis and the horizontal axis. For these reasons, after the loss of magnetism under heavy load, the generator torque and active power are subject to severe periodic oscillation. For hydro-generators, a similar situation will occur when the average value of the average asynchronous torque is small and the rotor is asymmetrical in terms of the longitudinal and transverse axes. In this case, the motor torque, which has a large or even exceeding the rated value, is periodically applied to the shafting of the generator and transmitted to the base through the stator. At this time, the slip is also periodically changed, and its maximum value may reach 4% to 5%, and the generator periodically overspeeds. These situations directly threaten the safety of the crew.
4. When the demagnetization is running, the leakage at the end of the stator is enhanced, which will overheat the components at the end and the core of the edge.