When the ground fault occurs to the generator in the diesel generator set configuration, it is characterized by loud noise, irregular jitter, temperature rise, unstable voltage, and similar excessive load. This fault is a ground fault caused by insulation damage between the generator winding and the iron core or the casing, also known as a winding ground fault. So, how should our users troubleshoot generator grounding faults? Here, Dingbo Power will share the following content with everyone for learning and reference in genset maintenance.
Ground fault phenomenon
The diesel generator set can not operate normally due to the electrification of the generator housing, control line out of control, and winding short circuit heating.
Cause of malfunction
Due to dampness in the generator winding, the insulation resistance decreases; Long term overload operation of the generator; Harmful gas corrosion; Metal foreign objects invading the inside of the winding damage the insulation; Insulation damage and iron core collision during rewinding of stator winding; The end of the winding touches the end cover base; Insulation burns caused by friction between stator and rotor; The insulation of the outgoing line is damaged and collides with the shell; Overvoltage causes insulation breakdown.
Fault detection method
(1) Observation method. By visually inspecting the insulation at the end of the winding and inside the wire slot, observe for any signs of damage or blackening, and if so, indicate the grounding point.
(2) Multimeter inspection method. Use a multimeter to check the low resistance range. If the reading is very small, it indicates grounding.
(3) Megohmmeter method. Select different megohmmeters according to different levels to measure the insulation resistance of each group of resistors. If the reading is zero, it indicates that the winding is grounded. However, for generator insulation that is damp or broken down due to accidents, it needs to be determined based on experience. Generally speaking, if the pointer swings irregularly at "0", it can be considered to have a certain resistance value.
(4) Lamp test method. If the test light is on, it indicates that the winding is grounded. If sparks or smoke are found at a certain location, it is the point of winding grounding fault. If the light is slightly on, there is a grounding breakdown in the insulation. If the light is not on, but there is also a spark when the test rod is grounded, it indicates that the winding has not been broken down yet, but is severely damp. You can also tap hard wood on the edge of the shell's mouth, and when it reaches a certain point, wait for one to turn off and one to turn on, indicating that the current is on and off, then that point is the grounding point.
(5) Current burning method. Use a voltage regulating transformer. After connecting to the power supply, the grounding point will soon heat up, and the place where the insulation smokes is the grounding point. Special attention should be paid to small generators not exceeding twice the rated current for a period of no more than half a minute; For large motors, the rated current should be 20% -50% or gradually increased, and the power should be cut off immediately when smoke comes from the grounding point.
(6) Group elimination method. For the grounding point inside the iron core and with severe burning, the burnt copper wire is fused with the iron core. The method used is to divide the grounded phase winding into two halves, and so on, and finally find the grounding point.
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