Within a substation, or any other facility containing high voltage electrical apparatus, there are many types of electrical gear that require some form of high voltage testing, whether it’s Withstand/Proof testing, Insulation Resistance measurement, hipot leakage current testing, Tan Delta/Power Factor and Partial Discharge measurement, and other tests that do not require high voltage AC or DC. Some of the mentioned tests require AC high voltage, some use DC voltage and some can use either. Most HV testing of electrical substation apparatus should be done with AC voltage, although there are several tests where DC voltage is suitable. Users should check with their vendors’ Maintenance Manuals and established standards for the recommended testing methods. This application guide will describe the over-voltage tests performed using high voltage AC or DC Dielectric test sets, or Hipots.
Over Voltage Testing
There are many tests to perform to the electrical apparatus used for the Generation, Transmission, and Distribution of electricity. Here we cover over-voltage AC Dielectric testing, commonly called hipoting. These include simple pass/fail stress tests and more complicated diagnostic tests to measure the quality of the insulation tested, without risking flash over. It is presumed that AC voltage is to be used.
AC Withstand Acceptance Testing: An Acceptance test is usually performed on all new installations and a similar Maintenance test (but at a reduced voltage) in later years. Apply the test voltage for the required length of time. The load either holds the voltage and is passed or it flashes over and is failed: a go/no-go test. The test voltage is defined by the IEEE or other standards followed. The test current is a function of the capacitance of the load, necessary to know to properly size the kVA of the hipot needed.
For high voltage testing electrical apparatus and cable, many types of testers are needed. Some are for general use that can be applied to many testing applications and some that are designed for specific test requirements, although may also be useful elsewhere. These products include:
Portable AC Hipots: up to ~3 kVA
Portable DC Hipots: up to ~1 kW
Portable Insulation Resistance (IR) instruments: up to ~25 kVdc
Transportable AC Hipots for higher uF loads: up to ~15 kVA
Large AC Dielectric Test sets: up to ~40 kVA
Parallel Resonant Test Sets: up to 300 kVA
Oil Dielectric Test sets: up to ~100 kVac
VLF 0.10 – 0.01 Hz. AC Hipots: Up to ~200 kVac & 10 uF
Accessory Instruments: Partial Discharge Detection Measurement, ~200 kVac
Tan Delta/Power Factor Measurement, ~200 kVac