Power Frequency Tests of Bushing

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Power Frequency Tests of Bushing

  1. Power Factor Test
  2. Partial Discharge Test
  3. Wet Power Frequency Voltage withstand Test
  4. Momentary Power Frequency Voltage Withstand Test
  5. Visible Discharge Test

Power Factor Test
  1. High voltage Schering bridge is used for this test. The test setup is shown in Figure A.
  2. The conductor coming from bushing is connected to HV source and transformer tank is connected to detector (D) side as shown.
  3. The Schering bridge is balanced by usual procedure.
  4. The observations are taken with increasing, and decreasing values of voltages.
  5. The power factor (cos Φ), capacitance of bushing (C2) is evaluated for each observation.
  6. The loss factor (tan 𝛿) is calculated.
Power Factor Test on Bushing using Schering Bridge
Figure A
The characteristics of tan 𝛿 and applied voltage is plotted.
Graph of test voltage Vs tan 𝛿
Figure B
Potential Discharge Test
The test setup is shown in Figure C.
Partial Discharge Test on Bushings
Figure C
    1. The bushing to be tested is connected across sphere gap.
    2. The cascade transformer produces high voltage which is applied to bushings.
    3. If any partial discharge activity takes place, in bushing due to voids, cracks etc, it is recorded by PD measurement circuit.
    Wet Power Frequency Voltage Withstand Test
    1. These tests are applicable to outdoor, indoor and outdoor immersed bushings up to 245 kV ratings.
    2. Duration of test is 60 seconds.
    3. The test is conducted in accordance with 1.5.2071 (Part 2) 1976. Before the commencement of the test, the bushings is exposed to the atmospheric condition specified in I.S.
    4. The bushings is considered to have passed the test if no flashover or puncture occurs.
    5. If there is puncture the bushing is considered to failed the test.
    6. If flashover occurs the test is repeated only once.
    7. If during the repetition of the test, no flashover or puncture occurs the bushing is considered to have passed the test.
    Momentary Power Frequency Voltage Withstand Test

    1. The test voltage as mentioned in IS is applied to bushing for 30 seconds.
    2. The bushing has to withstand this voltage without flashover or puncture.
    Visible Discharge Test
    1. This test is performed in dark room because the discharge taking place is not visible in light.
    2. Standard test voltage is applied to the bushing.
    3. No discharge should take place on the bushings.
    4. The discharge taking place on arcing horns, grading rings of bushing is permitted.
    5. The radio interference occurring due to this is also measured using suitable arrangement.

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