DIELECTRICWITHSTANDTEST..docVIP

DIELECTRIC WITHSTAND TEST The DielectricWithstand Test is the third test required by the electrical safety testing standards. The Dielectric Withstand Testconsists in measuring the current leak of a device under test, while phase and neutral are short circuited together. The measure result of a Dielectric Withstand Testis a current value, which has to be lower than the indicated limit from the international standards. A Dielectric Withstand Tester (also called hipot tester, dielectric strength tester, flash tester, high voltage tester) is then used to measure this current. DIELECTRIC WITHSTAND TEST VOLTAGES It is performed in AC or DC with voltages varying from some hundred volts to several tens of kilovolts. The choice of the nature and value of the test voltage is determined by standards which apply to the product tested. In the absence of standards, the following rule of thumb is used : the test is always performed with a voltage of same nature than that under which the sample operates. Example: Direct for a battery. Alternating for a transformer.The maximum value is given by the formula: U test = 2 x U operating +1000 V.A manufacturer of laundry-iron will therefore perform the test under a voltage:Utest = 2x230VAC + 1000VAC = 1460 VAC. The dielectric strength test can be made to be destructive or non-destructive. DESTRUCTIVE TESTS Certain standardized tests require the application of a high power source to the sample to which the dielectric strength test is applied. This entails the destruction of the equipment tested, through carbonization of the insulating material. These tests are above all used to test components or equipment employed in electricity or electro-technology of medium and high power (circuit-breakers, switches, transformers, insulators, etc...). NON-DESTRUCTIVE TESTS Diagram 1: Evolution of leakage current as a function of test voltage. It is in this area that the hipot tester evolved most and obtained increasingly higher performa