High Voltage VT33 Combination VLF AC Hipot and Thumper 13kV

With cable diagnostic testing becoming more common, the need for fault locating will rise. If a cable cannot withstand the test voltage, failure will occur, requiring fault locating. If you’re in the market for a thumper, why not get one with a VLF hipot built-in to test the AC integrity of the cable following repair. The VT33 incorporates a powerful VLF hipot, a VLF Burner that rapidly reduces a faults impedance (arc-over voltage), TDR/radar capability, and continuous discharge for pinpointing the fault. Suitable for cables up to 25 kV. HVI puts all the tools needed in one box.

HVI produces some of the most powerful and full featured fault locators available. All the features needed for efficient fault finding can be found in our thumpers,  don’t settle for less:

• Three full joule output voltage settings
• Three fully variable hipot output voltages
• The highest Burn current available
• Internal Arc Reflection and Current Impulse filter
• Compatable with nearly all TDR/radar models
• The most rugged and reliable design
• World’s only VLF Thumper combination

5 kV – 25 kV Cable Systems
The VT33 VLF Thumper Combination is the best approach: VLF test cables, use VLF output for diagnostic cable testing, use VLF Cable Burner to reduce fault voltage, fault locate with 13 kV @ 760 joules, use TDR/radar for sectionalizing and for pre-locating faults.

• VLF test cables per IEEE400.2, VDE 0276, CENELEC, etc.
• Pre-locate faults using a connected TDR/radar
• VLF Burn faults to lower arc-over voltage
• Pinpoint fault with continuous thumping

VLF stands for Very Low Frequency. VLF is generally considered to be 0.1 Hz and lower. VLF testing is used for any application requiring AC testing of high capacitance loads. The major application is for testing solid dielectric cable (per IEEE400.2), followed by testing large rotating machinery (per IEEE 433-1974), and occasionally for testing large insulators, arrestors, and the like. One of the best reasons to use VLF is to check installation quality and accessories, like splices. Many failures are due to damage during installation and/or defective workmanship. At the very least, every newly installed or repaired cable should be VLF tested before re-energizing.

The IEEE/EPRI/CEA and other world engineering bodies recommended test level for solid dielectric cable is up to three times (3Vo) line to ground voltage for 15 + minutes. For a 15 kV cable, which ordinarily carries from 7.2 to 8 kV line-ground voltage, the test is usually performed at 22 kV. A 25 kV system is tested up to 33 kV and a 69 kV cable system is VLF tested up to 120 kV. VLF hipoting is not destructive to good  insulation and does not lead to premature failures like with DC voltage testing. Using VLF does not cause  degradation of the insulation. It does cause existing cable defects, like water trees and splice defects, to break through during the test. If a cable can’t hold 2 – 3 times normal voltage, it is not a good situation.  Cause failure at defect locations during a controlled outage or prior to energizing newly installed or repaired cables, find the fault, make the repair, and be left with a good cable. It is AC voltage; what the cable is designed for and experiences during service. Cable is factory tested with AC voltage at levels higher than the field test voltage.

VLF testing is not a diagnostic test. It is an AC stress test. There are no leakage current readings to take. (DC leakage currents tell little about the cable quality.) A cable either holds the test voltage or fails. If a cable can’t hold 2 – 3 times normal voltage, it’s not going to last long. You want it to fail during the test, when you are ready to repair or replace it. The surest way to weed out bad cables and accessories is to just perform a simple AC hipot test, just like we do with vacuum bottles, arrestors, hot sticks, switchgear bus and insulators, etc. Yes the cable may fail under test if it has a severe defect, but that’s the point of the test. If a cable can’t withstand three times normal voltage for 10 or 15 minutes, it’s bound to soon fail. Fail it when convenient, rather than waiting for it to fail on its own, often at the worst possible time.