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What Are the Causes of Sudden Short Circuit of Diesel Generator Set


Because magnetic circuit and magnetic resistance for direct axis of synchronous generator is different from that of variable axis, the stator and rotor are in relative motion, so the mutual inductance coefficient and self-inductance coefficient of stator and rotor are not constant. It is difficult to analyze and solve by using differential equations, based on the principle of flux conservation in superconducting closed loop, explain from the physical concept, and derives the short circuit current in each winding when sudden short circuit occurs.

Characteristics of sudden short circuit for diesel generators

1.In the case of steady-state short-circuit, the steady-state short-circuit current is not large because of the large synchronous reactance, while in the case of sudden short-circuit, the sudden short-circuit current is large because the super-transient reactance limiting its current is very small and contains DC component. The peak value of the sudden short-circuit current can reach more than ten times of the rated current.

2.With the emergence of this impulse current, the winding of the electric motor will be affected by a great impulse electromagnetic force, which may cause the winding to be deformed or even the insulation of the winding to be damaged.

3.In the process of sudden short-circuit, the electric motor is affected by strong short-circuit torque, which can cause vibration.

4. Overvoltage occurs in stator and rotor windings of motors.



Characteristics of physical phenomena in generators during sudden short circuit

1.When in steady-state short circuit, the armature current is constant, and the corresponding armature magnetic potential is a constant amplitude rotating magnetic field rotating at synchronous speed, therefore, it will not induce electromotive force and generate current in the rotor winding. From the current relationship, it is equivalent to the open circuit state of transformer.

2.When short circuit occurs suddenly, the magnitude of armature current varies, and the corresponding magnitude of armature magnetic field varies. Therefore, the transformer between stator and rotor can induce potential and current in the rotor winding, and then affect the change of current in the stator winding. From the point of view of electromagnetic relationship, it is equivalent to the sudden short-circuit state of transformer.
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