Partial Discharge Monitoring of a Distribution Transformer

EXPERIMENT NO. 11 Condition Monitoring of a distribution Transformer

1: Partial Discharge Monitoring of a distribution transformer

OBJECTIVE:

PARTIAL DISCHARGE MEASUREMENT ON A 11kV, 25kVA DISTRIBUTION TRANSFORMER

PROCEDURE: • Read the enclosed instructions on PD measurement. • PD meter is pre-calibrated. Do not disturb any controls of the PD meter. • Switch on the power to the PD meter. • Note the initial indication. This is the ambient discharge level. • Switch on the mains to the Distribution Transformer. • Slowly increase the applied voltage in steps of 10% (as read from the Auto-transformer scale) with the help of the Autotransformer. • Maintain the potential for 5 minutes at each level and the steady indication on the meter by choosing a suitable range. • Upon reaching 100% start reducing the voltage level again in steps of 10% noting the steady PD level at each of the applied voltage. • Switch off the mains. • Switch off the PD meter. • Ground the coupling capacitor. • Plot the variation of discharge level with the actual applied voltage on the H.V side of transformer.

Find Out:

1] What is PD? 2] Apparent charge? 3] Different type of PD?

Further Reading:

i ] Kuffel & Zaengel : High Voltage Engineering , Pergamom Press ii] M. Khalifa : High Voltage Engineering , Mercel Deckker . iii] Naidu & Kamraju : High voltage Engineering , Tata McGraw Hill iv] Dieter Kind & Feser. High Voltage Test Techniques, SBA Publications.

1 Star/Delta r 50Hz Auto-Trans. Transformer 3 ph 400V 400 V/ 11kV, y 3ph, 28 A ,50 Hz 400A / 1.31 A b Coupling 440V 25 kVA, 50 Hz Capacitor 1000pf, 100kV

Coupling Quadripole

Partial Discharge Meter

II: Dielectric Test on Transformer Oil.

OBJECTIVES:

TO FIND THE DIELECTRIC STRENGTH OF THE GIVEN TRANSFORMER OIL SAMPLE.

PROCEDURE:

1. Study the enclosed instructions on Transformer oil testing. 2. Switch on the test kit. 3. Slowly raise the voltage, and keep it at 30kV for one minute. At the end, record whether the oil sample with stood 30 kV for one minute. If it fails earlier, note the time it stood, 30 kV. If it Fails at a voltage lower than 30 kV, record that voltage as breakdown voltage. 4. Then raise the voltage till such time there is a breakdown, and record the breakdown voltage. All time take care not to exceed the maximum voltage of 60 kV. 5. Remove the suspended particles due to breakdown with the help of the glass tube provided. 6. Wait for five minutes. 7. Repeat steps 3 to 6, five times giving a total of six observations. 8. Switch off the test kit.