In the electrical strength test of insulating oil, each cup of sample is tested six times, and the average value is taken as the electrical strength or
Dielectric strength
During the test, the spark discharge voltage changes in four ways:
(1) The secondary spark discharge voltage is particularly low. This test may be caused by the electrode gauge of the oil cup when filling the oil sample into the oil cup or before filling the oil cup
The surface roughness has brought in some external factors, making the secondary value low. At this time, the average value of 2 to 6 times can be taken
(2) The value of the spark discharge voltage gradually increased for six times. Generally, moisture is absorbed due to raw or insufficient treatment
Appears in the oil sample due to the improvement in the moisture level of the oil after the oil is discharged by sparks
(3) The value of the spark discharge voltage gradually decreases for the sixth time. It generally occurs in relatively pure oils tested because of the free radicals generated
The amount of charged particles, bubbles, and carbon chips increases in succession, damaging the insulation properties of the oil. In addition, there are automatic oil testers connected
During the six consecutive tests without stirring, the carbon particles between the electrodes gradually increased, resulting in a gradual decrease in the spark discharge voltage
(4) The spark discharge voltage is low at both ends and high in the middle. This is a normal phenomenon
