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Insulation Inspection of Generator Bearings

Aug. 03, 2023

Due to the unequal air gap around the rotor and between the stator, the configuration of each seam of the effective iron core around the stator is asymmetric. This results in uneven distribution of magnetic flux and unbalanced magnetic beam when the generator is running. The cutting of an unbalanced magnetic beam with a rotating axis generates an axial electromotive force. The shaft current generated under the action of shaft electromotive force can damage the rotor shaft collar, bearing bush tungsten, etc. For this reason, insulation should be applied between the exciter and the foundation plate of the unit for the generator with a horizontal axis.

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For suspended hydro generators, both the upper guide bearing and thrust bearing should be insulated with insulation pads and the stator casing. An additional layer of insulation pad can also be added between the thrust head and the mirror plate to strengthen insulation. This can avoid damage accidents caused by shaft current. For vertical axis hydro generators, before installing the bearing pads, a 1000 volt megohmmeter should be used to check the insulation resistance of each pad of the upper guide bearing and thrust bearing, with a value not less than 100 megohms. After installation, connect the insulation pads of the bearing shells with each other, and then measure the insulation resistance. When the thrust bearing and upper and lower guide bearings are all installed and before oil injection, the rotor can be lifted and the entire insulation resistance of the generator thrust bearing can be measured. The value should not be less than 5 megohms. If you want to measure the insulation resistance of the bearing after injecting oil into the oil groove, you can connect a wire on the bearing seat to the outside of the oil groove for measurement. When the rotor is jacked up and the oil tank is filled with oil, the total insulation resistance value should not be less than 0.3 megaohms.

When the generator is running, the bearing insulation can be checked by measuring the Shaft voltage. During the measurement, an AC Voltmeter with high internal resistance and small range should be used. One end should be grounded (generator housing), and the other end can be connected to the shaft of the generator rotor (exciter side) through a copper mesh brush. Due to the rotation of the rotor, special care and safety should be taken during measurement to prevent the shaft mouth, wires, hair, etc. from being entangled in the motor. Jiangsu Defeng Power Generation Equipment Co., Ltd. is mainly engaged in generators, generator sets, mobile trailers, mobile generators, small generators, household generators, silencers, low-noise generators, diesel generator, diesel generator sets, low-noise generators, etc.

Dingbo Power has advanced testing equipment, modern production technology, professional manufacturing technology, perfect quality management system, and strong technical research and development capabilities. It can provide 3KW~2500KW various specifications of ordinary, automatic, four protection, automatic switching, low noise and mobile generator sets, high quality and low energy consumption to meet the diverse power needs of customers, and can also meet users with different voltages and different frequencies. It is required to create a parallel power supply system for multiple units. If you are interested in our product or any question on generator, welcome to send email to sales@dieselgeneratortech.com.

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