How to Solve Reduction of Insulation Resistance of 250kw Generator

Why is the insulation resistance of 200kw diesel generator reduced?

Faults: under thermal stability, insulation resistance of 200kw diesel generator is lower than 0.5m Ω, lower than 2m Ω in cold state.

Reason:

1)Diesel generator set is stored in humid environment or the alternator winding is affected by moisture during transportation.

2)During maintenance and cleaning working, the insulation of motor winding is damaged., or the insulation is damaged in the process of alternator overhaul and wire embedding.

3)Conductive dust in the surrounding air (e.g. metallurgical or coal industrial areas) or acid and alkaline vapors (such as chemical industrial areas) invade the alternator and corrode the alternator insulation.

4)Natural aging of generator winding insulation.

How to solve the reduction of insulation resistance of 200kw generator?

1)AC synchronous generator affected with damp must be dried, otherwise the generator may be burnt out due to insulation damage. Meanwhile, the ventilation conditions of the generator storage environment must be improved and good ventilation equipment should be provided.

2)In the cold season, the warehouse must be equipped with heating equipment to ensure that the temperature in the warehouse is not lower than 5 ℃, and it is forbidden to drop water from nearby into the alternator. For the generator with semiconductor excitation mode, when measuring the insulation resistance of excitation circuit, the excitation device should be disconnected, or each silicon rectifier element should be short circuited with wire to prevent breakdown during measurement.

Details of dry method: Short circuit the two-phase outlet wire of generator stator winding, and connect it firmly. Adjust the voltage regulator in the field excitation return circuit to the maximum resistance position. If the resistance value is not large enough, another resistor should be connected in series to increase the resistance value, and then start the generator. Pay attention to slowly accelerating to the rated speed, and then slowly adjust the excitation current.

The excitation current is determined according to the damp condition of generator, but the short-circuit current of stator winding shall not exceed the rated current. This short-circuit current is used to dry the generator. The drying time of short circuit depends on the short circuit current and the damp condition of generator.

3)Replace winding or slot insulation with damaged insulation.

4)The surrounding environment of AC synchronous generator should be improved or the installation site of generator should be transferred so that there is no conductive dust or acid or alkaline steam in the surrounding environment.

5)If the winding insulation of AC synchronous generator is naturally aging, it must be replaced with a new generator or overhauled, and the winding and insulation materials must be replaced.

How to measure insulation resistance of 200KW emergency generator?

The state of the generator during the test. When measuring the insulation resistance of generator winding, it should be carried out under actual cold state and hot state respectively. The inspection test can only be carried out in the actual cold state.

Measurement method. For different windings of the generator, such as the stator winding and excitation winding of synchronous generator, as well as the windings of reactor and current transformer in the excitation system of some self-excited generators. If both ends of their wires have been led out of the motor casing, the insulation resistance of each winding to the shell and the insulation resistance between each winding shall be measured respectively.

When measuring, the rotational speed of the hand-operated megohmmeter should be kept at about 120rmp, and the reading should be read after the pointer of the meter reaches stable.

After measurement, the measured winding should be discharged to the ground and then the measuring line should be removed.

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