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Transformer Oil Test

This document describes a procedure to determine the dielectric strength of transformer oil. The apparatus required includes a transformer oil test kit and transformer oil. The test involves placing polished brass spheres 4mm apart in oil inside a test cell. The voltage is gradually increased until a flashover occurs, recording this rapidly applied voltage. It is then increased to the previously recorded value and held for one minute to determine the breakdown voltage, which should be at least 30kV. Repeating measurements and taking the average provides the dielectric strength of the oil sample.

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ROYAL GAMING
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415 views3 pages

Transformer Oil Test

This document describes a procedure to determine the dielectric strength of transformer oil. The apparatus required includes a transformer oil test kit and transformer oil. The test involves placing polished brass spheres 4mm apart in oil inside a test cell. The voltage is gradually increased until a flashover occurs, recording this rapidly applied voltage. It is then increased to the previously recorded value and held for one minute to determine the breakdown voltage, which should be at least 30kV. Repeating measurements and taking the average provides the dielectric strength of the oil sample.

Uploaded by

ROYAL GAMING
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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AIM:- Determine dielectric strength of transformer oil.

APPARATUS REQUIRED:-Transformer oil test kit, Transformer oil.

THEORY:- The oil is poured in a container known as test-cell which has internal dimensions of 55mm
X 90mm X 100mm high. The electrodes are polished spheres of 12.7 to 13mm diameter, preferably
of brass, arranged horizontally with their axis not less than 48mm above the bottom of the cell. For
the test, the distance between the spheres shall be 4+0.02mm. A suitable gauge is used to adjust
the gap. While preparing the oil sample, the test-cell should be thoroughly cleaned and the moisture
and suspended particles should be avoided. Fig. shows an experimental set-up for finding out the
dielectric strength of the given sample of oil. The voltmeter is connected on to the primary side of
the high voltage transformer but calibrated on the high voltage side.

The gap between the sphere is adjusted


to 4mm with the help of a gauge and the spheres are immersed in oil to a depth as mentioned
earlier. The voltage is increased gradually and continuously till a flash over of the gap is seen or the
MCB operates . Note down the voltage. This voltage is known as rapidly- applied voltage. The
breakdown of the gap has taken place mainly due to Field effect. Next bring the voltage back to with
zero voltage and increase the voltage to a value just obtained in the previous step and wait for a
minute. It is expected that the breakdown will take place. A few trials around this point will give us
the breakdown value of the dielectric strength. The acceptable value is 30 kV for 4 mm applied for
one minute. In fact these days transformer oils with 65 kV for 4 mm 1 minute value are available. If it
is less than 30 kV, the oil should be sent for reconditioning. It is to be noted that if the electrodes are
immersed vertically in the oil, the dielectric strength measured may turn out to be lower than what
we obtained by placing the electrodes in horizontal position which is the normal configuration.

PROCEDURE:-

1. Study the enclose 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 30kV for one minute. If it fails earlier, note the time it stood, 30kV. If it
fails at a voltage lower than 30kV record that voltage as breakdown voltage.
4. Then raise the voltage till such time there is a break down, and record the breakdown
voltage. At 40kV the sparks between two electrodes immersed in the oil separated by a
specific gap or distance. All the time take care not to exceed the maximum voltage of 60kV.
5. Remove the suspended particles due to breakdown with the help of glass tube provided.
6. Wait for 5 minutes.
7. Repeat steps 3 to 6, five times given a total of six observations.
8. Switch off the test kit.

9. OBSERVATION:- The dielectric strength of transformer oil is also known as the breakdown
voltage of the transformer oil. Breakdown voltage (BDV) is measured by observing at which
voltage, sparking strands between two electrodes immersed in the, separated by a specific
gap. We observed that at 40kV the breakdown voltage immersed.
PRECAUTION:-
1. Transformer oil should be free from moisture content.
2. Gap should be premise.
3. Nobody should go near the H.T bushing.
4. The equipment must be grounded firmly.
5. Electrodes must be cleaned properly before and after the use.
6. Before starting the experiment, make sure the electrodes are properly aligned and
zero reading is adjusted.

Prepared by: Sneha Majumder


Roll no. 46/EE/22/12

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