Fully automatic dielectric strength breakdown voltage test method for insulating oil, the dielectric strength of transformer oil is not a criterion to assess the quality of the oil, but is used to indicate the degree of physical contamination of the oil by water and other suspended impurities, and to determine whether filtration and drying are required before and after injection into the product (equipment).

1、Transformer insulating oil test conditions

Test power supply should be an approximate sinusoidal waveform, its crest factor should be √2 ± 5% of the AC power supply (50Hz in China), by a special step-up transformer will be the low voltage of the power supply to 2kV / s rate of rise until the oil is breakdown, its capacity at 15kV voltage to produce a short-circuit current of not less than 20mA, the breakdown should be cut off within 0.02s.

Voltage regulation available regulator, resistor, etc., using automatic voltage regulation, manual voltage regulation is not easy to achieve uniformity. Voltage measurement is usually at the input side of the step-up transformer, can also be at the output side, such as the known power waveform approximates a sinusoidal waveform, then available ordinary AC voltmeter, such as waveform distortion, the application of peak voltage table, the peak voltage divided by √2 that is the breakdown voltage (i.e., rms voltage).

2、Transformer insulating oil cup and electrode

Oil cup should be a transparent container made of glass, plastic, or electrician made of ceramic, its volume in 300-500 mL, the height of 90mm, cross-section of 110 × 70mm, wall thickness of 5mm, electrodes on both sides of the long axis, the cup body sealed for appropriate.

The electrode should be made of polished copper, brass, bronze or stainless steel material. There are spherical (Φ12.5 - 13mm) hemispherical (spherical diameter Φ25mm, plane side diameter Φ36mm, thickness 13mm) and circular flat (Φ25mm) electrodes. Most of our hemispherical electrodes are used. The distance between the electrodes is 2.5mm±O.lmm, and the electrode shaft should be immersed in the oil about 40mm. Generally use Ding Sheng power transformer oil dielectric loss tester in the standard insulating oil test cup, also known as oil cup standard, standard test oil cup, oil pressure test cup.

3, transformer insulation oil sample preparation

Sampling bottle should be clean, and by dry grinding mouth bottle. Oil samples should be taken from the bottom of the transformer. Should first use the released oil to flush the oil sample valve, and release a certain amount of oil to prevent the deposition of debris in the inside of the oil sample valve to bring into the oil sample. When sampling the oil column of the oil flow should be along the inner wall of the bottle and down to prevent the air from being brought into the oil, and rinse the bottle with the released oil no less than twice, and then formally take the sample. Will obtain the oil sample gently shake, so that the oil in the debris evenly distributed, but does not form bubbles, and then use the oil sample rinse oil cup (the oil cup itself should be clean), at least twice. zui after the oil sample along the wall of the cup injection to the oil surface higher than the electrode not less than 10mm.

4、Transformer insulation oil test

Transformer insulation oil test can be used insulating oil dielectric strength tester, oil samples injected into the insulating oil standard oil cup to confirm that no air bubbles, you can boost the test (but zui not later than 10 minutes after loading oil). At this time, the humidity shall not exceed 75%. According to the insulating oil dielectric strength tester operating procedures to step up the pressure to oil breakdown. After breakdown between the electrodes with a clean, dry glass rod stirring shall not bring in air bubbles, wait one minute after the disappearance of bubbles, the second test, such as the disappearance of bubbles can not be seen, you must wait 5 minutes. Test a total of six times, * the breakdown voltage may deviate from the average, so take the average of the last five times as the test results.