Friday, September 7, 2018

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.

Upon the manufacture or assembly of an appliance or product, it is usual for some degree of electrical leakage to occur. However, the leakage is usually very low and is brought about by internal capacitance and voltages inside the appliance. It is normal for such leakage to occur and it needs to be expected of every device. There exist a number of instances where the leakage, for some reason, may be excess.

Faults in the design or disintegration of product insulation among many other reasons may be the cause of the excessive leakage. These flaws often cause excessive leaking of current and may give rise to electrical shock for any individual that comes into contact with the defective appliance. The essence of a hipot test is to ensure and verify that the product has enough insulation so that the user of the device may not be electrocuted.

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 testing process makes one major assumption. The assumption is that if the insulation of the device is not broken by the deliberate application of excess voltage, then it should be safe for normal operation. The device should be able to withstand application of normal voltage, which is applied during normal use. The name Dielectric Withstanding Voltage comes from this assumption.

The objective during testing is to stress the insulation in the product. However, apart from inducing stress on insulation, the test detects any workmanship defects that may be present. The workmanship monitoring focuses on the tiny gap spaces occurring between the earth ground and conductors that carry current in the device. In normal working environment, these small gaps can be closed by dirt, humidity, vibration, shock, or contaminants.

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.

An electric device that manufacturers use in verification of electrical insulation is a high potential tester. It is made of a source of high voltage, a switching matrix and a current meter. Connection of the source of voltage and the current meter is done by the matrix switch. Including a display and a microcontroller automates the process of testing.




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