Application Description
If you are Acceptance testing dozens of long 35 kVac cables, maybe will also need to locate cable and accessory faults, and maybe even need to perform AC high voltage dielectric testing to all the new substation apparatus installed, there is only one vendor you need that can offer all the equipment, decades of experience and knowledge to help you through, and has the industry’s best reputation for customer support and availability, then you are home. HVI is your one stop for all that is needed to make your job go smoothly and easily. HVI – your source for all your high voltage test equipment needs.
The most common test is the VLF AC Withstand test. This is a pass/fail over voltage stress test performed to ensure that the cable insulation, attached accessories, and the terminations are all sound with no damage from installation errors or factory material defects. Since the whole system is new, it can be assumed that all components are healthy except for those that were not installed correctly or damaged during installation. If there is a defective splice or cut in the cable, the test voltage level and the test duration are designed to cause the defect to fail during the test, while not adversely affecting the rest of the healthy cable installation.
Usually the IEEE 400.2-2012 Standard for VLF and Tan Delta Cable testing is referenced. This standard dictates that for Acceptance testing cable rated for 35 kVac, a peak sinusoidal VLF voltage of 62 kVac be applied for 30 – 60 minutes. Based on the known electrical tree growth rate under these VLF voltage conditions, any defect severe enough to be driven into a partial discharge condition will have enough time to grow and penetrate through the insulation, causing a failure. Find the fault, fix it, and retest.
HVI Product Solutions
- VLF Withstand Testing
- VLF Tan Delta Testing
- VLF Partial Discharge Testing
- Cable Fault Locating
- Concentric Neutral Corrosion Testing
HVI produces products for VLF Withstand, Tan Delta, and Partial Discharge testing. HVI also offers high voltage, high energy thumpers needed for efficient fault finding, and the Ohm Check for on line testing of neutral corrosion. HVI can supply these devices separately or designed as a custom package ready to mount in your van. All the accessories to the above are also available to offer a complete package of the equipment needed to test and/or fault locate your cables.
Order your custom engineered and fabricated Cable Testing & Fault Locating Van Package. Everything needed and ready to go.
The VLF Withstand Test
A VLF AC hipot is needed, rated for the test voltage requirements and the µF capacitance of the load. The voltage needed is readily available, but the µF rating of the VLF, especially if 0.1 Hz. is the only permissible test frequency specified, can be a problem. As a practical matter, a maximum of perhaps 10 – 20 miles of cable can be VLF Withstand tested.
More Testing Options
Diagnostic testing is also often performed, especially on older installations, to learn of the cables’ insulation health but without the risk of a possible failure that a Withstand test poses. The two commonly performed tests apply slight over voltage for short duration to gather results. Both tests are useful and measure different data sets about the cable.
A Tan ẟ (delta) test measures the degree of insulation deterioration over the entire cable length. This offers an excellent way of comparing many cables to help prioritize injection/rejuvenation, replacement, or other testing methods that may be beneficial.
A Partial Discharge test locates specific places of troublesome electrical discharges and their severity. IEEE 400.3-2012 Standard for VLF Partial Discharge testing is referenced Both of these tests are limited to perhaps 2 miles or 3 – 4 km.
