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How to Test The Insulation Level of Diesel Generator Sets

Nov. 07, 2018

In electrical equipment such as generators, insulating materials are the weakest link and are often susceptible to high temperature and accelerated aging. By conducting insulation level test on the diesel generator set and judging whether the insulation performance meets the equipment requirements, it can greatly avoid the leakage or short circuit accident caused by the aging of the insulation material. So how do you test the insulation level of a diesel generator set?


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1. Electrical measurement

 

The electrical measurement method is divided into two types: the pulse current method and the radio interference method. The pulse current method is a parameter for detecting partial discharge is the generated pulse current, the radio interference voltage method is to detect the electromagnetic radiation wave generated when the generator is partially discharged. Since the pulse current method can calibrate the discharge cell according to the equivalent circuit of the partial discharge, the detection sensitivity is high, which is a commonly used method.

 

 

2. Non-electrical measurement

 

The non-electrical measurement method is a method of detecting partial discharge of the generator set by acoustics and special gas without detecting the electric quantity parameter. There are two commonly used non-electrical detection methods: one is ultrasonic detection. When the generator is partially discharged, it generates pulses with a spectrum of about 1 HM, but its acoustic signal is very Microsoft. Ultrasonic testing converts its signal into an electrical signal and amplifies the output. The other is ozone, the concentration detection method, because ozone is the characteristic gas of generator dizziness. An ozone detecting device is arranged in the generator set, and by determining the state of the genset voltage by detecting the ozone concentration, the intensity of the partial discharge state of the generator during operation can be determined, thereby effectively monitoring the insulation of the generator.

 

Reasons for the reduction of generator insulation resistance and treatment methods

 

The reduction of the insulation resistance of the generator is manifested by the insulation resistance of the generator below 0.5 MΩ in the thermal state and less than 2 MΩ in the cold state. What causes the insulation resistance to decrease, and what are the corresponding treatment methods?

 

cause of issue

 

1. The diesel generator set is stored in a humid environment for a long time or the motor windings are wet during transportation.

2. During maintenance, the insulation of the motor winding is damaged or the insulation is damaged when the motor is overhauled.

3. Conductive dust in the air (such as metallurgical industrial areas) or acid/alkaline vapors (such as chemical industrial areas) enter the motor and corrode the motor insulation.

4. Generator winding insulation is naturally aged.

 

Corresponding processing method

 

1. Improve the ventilation conditions of the generator storage environment, dry the humidified generator, and directly short the three-phase outlet of the generator stator winding, and connect firmly. Adjust the voltage regulator varistor in the excitation circuit to the maximum resistance position, start the generator, slowly accelerate to the rated speed, and then adjust the excitation current. The stator winding short-circuit current must not exceed the rated current. The drying time depends on the magnitude of the short-circuit current and the dampness of the generator.

2. Replace insulated insulation or slot insulation.

3. Improve the surrounding environment of the generator or transfer the generator installation site.

4. Overhaul the generator, replace the windings and insulation or replace the generator with a new one.

 

 

Check the insulation of the generator and each winding

 

Thoroughly check the insulation of the generator and each winding, and check the electrical and mechanical connections.

 

After maintenance and overhaul, check the electrical connection and mechanical installation of the motor correctly and firmly, and use dry compressed air to blow the inside of the motor. Finally, under normal start and run requirements, it is tested for no-load and load to determine if it is intact.

 

Beware of dust damage to the insulation of diesel generator sets

 

During the use of diesel generator sets, attention should be paid to the cleanliness of the environment to avoid dust, because the dust will damage the insulation of the diesel generator set, thus causing adverse effects on the unit.

 

1. Due to the influence of dust, the dielectric loss angle of motor increases and the leakage current increases, which shortens the climbing distance of insulation meter.

 

2. The dust on the insulation surface combines with oil, steam and moisture for a long time, forming a hard shell, which cracks gradually under the action of thermal stress, and makes the insulation film of the motor also produce cracks, which can easily cause the breakdown of the motor’s interturn, interphase and ground insulation.

3. The dust immersed in the insulation gap acts as a "abrasive agent" for electromagnetic vibration conductor insulation, resulting in inter-turn short circuit fault.

4. The dust falling on the surface of winding and iron core and casing makes the heat dissipation condition of the motor worse and reduces the effect of ventilation cooling.

5. The mechanical and chemical action of dust erodes the insulation of windings and is the main factor to destroy the insulation layer.

 

 


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