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Sudden Short Circuit of 500kw Diesel Generator Set

Sep. 20, 2019

When we use diesel generator set, maybe there is a sudden short circuit problem, do you know how to deal with this problem? Today Starlight manufacturer will shares with you.


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.

Yuchai generator


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.


What is the harm of sudden short circuit of diesel generator set?

1.When the diesel generator is short-circuit suddenly, the end of the generator winding will be greatly impacted by electrodynamic force, which may cause the end of the coil to be deformed or even damage the insulation.

2.Overvoltage in stator and rotor windings of diesel generators is harmful to generator insulation. Powerful impulse current in stator winding, combined with overvoltage, may lead to breakdown of weak insulation links.

3.Diesel generators may produce violent vibration, which may cause strong and destructive mechanical stress on some structural components.

4.Sudden short circuit on the secondary side will damage the transformer.

When the secondary side of transformer is short-circuited suddenly, a huge short-circuited current will be generated in the winding, whose value can reach 20-30 times of the rated current. The harm to transformer at so large current is as follows:

1.Under the action of huge short circuit current, huge electromagnetic force will be produced in the winding, whose value can reach 400-900 times of rated electromagnetic force, which will destroy the mechanical strength of the winding.

2.Huge short-circuit current will heat the winding, produce high temperature, and may burn the winding.


Therefore, the transformer must have reliable short circuit protection device, so that the transformer can operate safely and normally.

If the short-circuit phenomenon occurs in diesel generating sets, corresponding measures can be taken.

1.After checking the fuse, it was found that the fuse had been burned out. The phenomenon of burning of the components in the control box was observed. During the checking, it was found that the two-stage tube with limited current had been burned out.

2.Six rectifier diodes were measured with a multimeter, and no abnormality was found from the test results.

3.After replacing the current limiting diode and fuse, start up the diesel engine, when the rated speed is reached, the generator is not generate electricity.

All above faults indicates that the fault may be that the residual magnetic voltage inside the exciter is too low (in the process of normal power generation, a sudden short circuit of the electrical equipment and a large fireball will result in the disappearance of the residual magnetic voltage inside the exciter).

4.After charging the exciter with a battery, start the diesel engine to the rated speed, and the generator starts to generate electricity and meets the required requirements.


Sudden short circuit is a serious problems for diesel generator sets, we need to deal with it in time, so that can make diesel genset service life longer. Starlight power generator manufacturer will provide support for you all the time if you have any generator question or need to purchase diesel generators.

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