Tank Discharge of Diesel Generator Set

When the discharge electrode of the diesel generator set is grounded and the non discharge electrode is connected to high voltage, more discharges occur in the positive half cycle of the applied voltage; And the negative half cycle discharge frequency is less. This is because in the positive half cycle of the applied voltage, the conductor is negative. At this time, no positive ions accumulate and hit the cathode to produce secondary electrons emission, so the initial discharge voltage is high. The discharge waveform is characterized by large discharge capacity and many discharges; In the negative half cycle of the applied voltage, because the conductor is a positive pole, it is not easy to emit electrons, so the number of discharges is small. When the electrons are emitted, the positive ions generated at the same time will hit the cathode to generate secondary electrons emissions, so the initial discharge voltage is lower than that in the positive half cycle of the applied voltage, so the discharge waveform is characterized by small discharge amount and fewer times.

High voltage motor slot discharge refers to the discharge between the insulation surface of the coil and the iron core. The reason for its occurrence is that the surface of the coil slot cannot fully contact the wall of the iron core slot, and there is always a gap during this period. The electric field distribution at the ventilation slot is uneven. When the local electric field strength reaches a certain value, the gas in the air gap undergoes local ionization and generates slot discharge.

The main prevention method for slot discharge is to use a low resistance anti-corona layer for treatment. On the one hand, to evenly distribute the electric field at the ventilation slot to reduce the axial field strength; On the other hand, the contact between the low resistance layer and the groove wall is at a low potential, which shortens the gap and prevents the generation of corona. However, it is not entirely possible to prevent slot discharge by using a low resistance layer treatment. If the contact between the anti-corona layer and the groove wall is poor or unstable, the contact point may be indistinguishable under the action of electromagnetic vibration; Or due to stator core vibration during operation. Causing looseness of fixed components of the wire rod, such as slot wedges and cushion strips, and damage to the low resistance layer; The stress caused by the overheating of the contact point of the iron core of the wire rod results in the loss of the low resistance layer of the wire rod, which can lead to slot discharge.

Slot discharge is a gap spark discharge with energy hundreds of times greater than that of corona discharge. The local temperature can reach hundreds to thousands of degrees celsius, causing the insulation surface to come into contact with the stator core slot wall in the urban area. It is a high-energy capacitive discharge. The accelerating electrons generated by this high-energy discharge will exert thermal and mechanical forces on the surface of the coil. Discharge ionizes the air and produces oxides of ozone and nitrogen. The oxides react chemically with the water in the air gap, causing damage and corrosion to the coil surface's anti-corona layer, main insulation, and gasket. The gasket under the interlayer machine wedge burns into a nibble like state. In the actual operation of the motor, it was found that the electrical corrosion caused by this condition rapidly damages the insulation of the motor. The prevention method is to make the coil firmly fixed in the slot, not loose, and in good contact with the slot wall.

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