The Use Of A Hipot Tester

By Paul Olson

The term hipot is usually used as an abbreviation for high potential. It is a term that is used to refer to a certain class of electrical safety testing instruments referred to as a hipot tester. These instruments are used in the verification of the electrical insulation in finished cables, appliances, and other wired assemblies. Such assemblies include electric motors, transformers, and printed circuit boards just to mention a few.

In many cases, after the assembling/manufacturing of an appliance/product some current leakage of some level occurs. The interior of the product contains internal capacitance and voltages that often cause this minimal current leakage. It is normal for all devices to experience this leakage. However, in some scenarios, the current leakage may too high that it should be due to certain reasons.

Several causes lead to the excessive current leakage, including flaws in design and break down of internal insulation. Anyone that gets exposed to such faulty devices may be electrocuted from the excessive current leakage. To protect the operator from shock, it is important to conduct a hipot test for verification purposes to ensure that the product has sufficient insulation.

Dielectric Withstanding Voltage, DWV, is another term used in reference to the hipot test. At the time of the test, a high voltage is applied between the conductors that carry current in the product and its metallic shielding. Upon completion, there will exist a resultant current that makes its way through the insulator material. The term used for this current is leakage current and is tested using a high potential tester.

This process of testing has its basis on a major assumption. The assumption is that if the device works safely without its insulation breaking after being exposed to high voltage, then it can work fine under normal working conditions. During normal operation, the device should be able to withstand standard voltage application. This assumption is the source of the term Dielectric Withstanding Voltage.

The aim of the test is to stress the insulation used in the product. However, besides stressing the insulation, the test is also used to detect defects in workmanship. The most important aspects of workmanship that are monitored are the small gap spacings that occur between current-carrying conductors and earth ground. Under normal operating environment, these small gaps can be closed by contaminants, shock, vibration, humidity, and dirt.

When the gaps are closed, current is allowed to flow. Such conditions can be a major electrical hazard that must be corrected at the factory before the product is released into the market. Such defects cannot be detected by any other method besides DWV. Even though other methods may be used to attempt to resolve these problems, but they cannot be as effective as DWV.

Manufacturers use high potential testers to do the verification of electrical insulation. Often, this simple electric device comprises of a switching matrix, current meter, and a source for the high voltage. All the points located on the cable are connected to the high-voltage source and the current meter through the matrix. Including a display and a microcontroller helps to automate the testing process.

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