Various kinds of electrode were used for this test is to obtain test results in case of failure of transformer oil pressure oil volume, uniform and non-uniform field.
1) Transformer Oil Processing
Dielectric strength of the transformer oil is strongly influenced by processing and testing conditions, as it determines the quality of transformer oil during testing. The nature of the oil will be lost through moisture, gases, impurities, and charging into testing tank.
Oil quality should be checked periodically with oil cup tester, so as to obtain information that the reduction electric strength of transformer oil is ignored if the tank closed 4 days. If the oil dielectric strength decreases from the initial value KV/25 65 mm to 55 kV / 2.5 mm, or if more than 4 days after filled with oil, the oil must be replaced.
2) Application of Voltage
AC voltage and impulse voltage is usually used in testing, testing with AC voltage can be obtained by raising method Steady voltage and withstand voltage method, with increased from 5 to 10% step, from 60% of the expected breakdown voltage. Impulse voltage created by the up and down method from 5 to 10% of the expected breakdown voltage step.
Test probability of failure can be obtained in two ways:
」AC voltage riding at a constant speed 3kV/sec failure. This procedure is repeated up to 500 times in 1 minute intervals.
」Voltage band between 0 to 100% breakdown voltage, which, divided in several levels. AC voltage was applied for 1 minute 20 times each voltage level, while the impulse voltage was applied 20 times for each voltage level.
Failure Analysis of Transformer Oil
Some factors affecting the dielectric strength of the transformer oil, among others, the phenomenon of stabilization, treatment before the use of oil and electrodes, the effect of the speed of the oil, the effect of parallel capacity of the test cell, and the effect of the electrode area and gap distance.
1) Equipment trial
To understand the analysis done first glimpse of reviewing the experimental procedures and tools used in transformer oil failure. There are 3 types of electrodes are commonly used in the experiment, namely mild steel electrodes and a small (10 mm diameter), brass electrode-Bruce profile with broad flat areas and coaxial cylindrical steel electrodes with a gap distance over a wide range.
2) The cleaning procedure
First electrode preparation was washed with trichlorethylene, penggosongan surfaces are standard with 1000 grade silicon carbide paper, then washed in a mixture of water hot and soapy solution, drying and removal of dust with synthetic rubber foam, rinse with hot water and distilled water.
The electrodes were dried in air different cabinet sectional and finally rubbed with lens tissue lint with acetone wear after wear trichlorethylene. Rest connection electrode is washed with hot water and soap solution and rinsed in accordance with the above procedure each time after testing
3) Electrical Testing
All testing is done with a sine wave ac voltage with a frequency of 5 Hz. Applied voltage is increased uniform in all tests with an average price of 2 kV / sec. A CB is connected to the primary side of the transformer with a purpose to decide if the fault current is allowed to flow disturbances too long will cause carbonization and will perforate electrodes.