The time-honored methods of proof testing in the field involve high potential direct current (dc). The advantage of the dc test is obvious. Yet due to design flaws or other factors, the insulation in a product can break down, resulting in excessive leakage current flow. This failure condition can cause shock or death to anyone that comes into contact with the faulty product.
High-voltage cable testing, sometimes known as HiPot (High Potential), is a method of testing used to ensure adequate insulation in a myriad of applications ranging from electric motors and printed circuit boards to transformers and industrial cables.
Under normal conditions, any electrical device will produce a minimal amount of leakage current due to the voltages and internal capacitance present within the product. Yet due to design flaws or other factors, the insulation in a product can break down, resulting in excessive leakage current flow. This heavier than normal current flow through the diodes will cause them to overheat and fail.
Users of this system may select dual-polarity DC and cable jacket or sheath output modes. Testing the insulation is vital in determining the safety of cables, reducing the chance of electrocution. Meggar testing equipment is therefore a valuable investment for any business in the power services industry.
These testing devices maximize the dependability of motors, generators, and transformers by utilizing variable frequency (VLF) output, enabling technicians to locate weak cables. Locating problems in an electrical problem before it becomes out-of-control can minimize maintenance costs and extend the life of the equipment being tested. Like any system, an electrical system needs the TLC that HiPot testing affords.
A HiPot tester generally consists of three parts: a high-voltage source, a switching matrix used to connect all points in a circuit, and an amp meter (that measures the current in a circuit). When the high-voltage is applied, an ideally insulated device leaks only a minimal amount of current, keeping the device safe. When there is a breakdown in the dielectric, a material very resistant to electric flow, however, a dangerous amount of current escapes through the insulating material and presents a potentially fatal situation for a service technician.
Insulation resistance is not a definite measure of the voltage an insulation will withstand, but when properly interpreted affords a useful indication of the suitability of the winding for continued service. It should be remembered that values of insulation resistance, even on identical machines and for identical conditions, may vary over a wide range. Insulators spark-over at the lowest voltage when the cap, or electrode surrounded by the denser field, is (+). The (+) spark-over voltage generally corresponds closely to the maximum a-c.
This process is equally important in regulating quality control in the factory. When applied to brand-new cables, this test provides important information on how much voltage can be delivered without damaging the product and causing dielectric breakdown, as well as the resistance of the cable insulation.
A VLF hipot test is a go/no-go test and is not a diagnostic test, but is one of the best ways to check the AC integrity of an electrical asset to determine a pass or fail result. Similar to offline partial discharge testing, the challenge of this test is that the equipment must be taken out of service. Instruments for multi-point Hipot, resistance, continuity and capacitance measurement Multi-point Hipot high voltage cable testers verify the electrical connections in a cable.
Ensuring safety and increasing the dependability and lifetime of electrical devices is vital to any power services company's success. With the many benefits of using high-voltage cable testing and the need to ensure safety, many would argue that using a HiPot testing system is just as important as seeing their doctor for a check-up.
