Web address: www.hvinc.com

AC VOLTAGE WITHSTAND/HIPOT TESTING
With Very Low Frequency (VLF) AC Hipots

























Tan Delta testing is the easiest to perform, easiest to
interpret, and is a relatively inexpensive method of
performing a condition assessment test on a cable.
A TD test will show the level of degradation in a
cables insulation and accessories. By providing and
overall assessment of a cables insulation quality,
users can test many cables and comparatively rate
them by level of degradation, helping greatly to
prioritize cable replacement and/or injection. Now
available to 60kV peak: 200kV peak available
soon. Tan Delta testing is performed using sine
wave producing VLF instruments usually operating
at 0.1 Hz. Always buy a sine wave producing VLF.
TAN DELTA DIAGNOSTIC TESTING
Overall cable condition assessment
4/17/2008
7
0.1 Hz
phase 1
phase 2
phase 3
phase 1
phase 2
phase 3
x Vo
tgdelta L1
tgdelta L2
tgdelta L3
0.5
0.0018
0.0008
0.0013
(2Uo-Uo)
(2Uo-Uo) (2Uo-Uo)
1.0
0.0019
0.0009
0.0014
0.0035
0.0018
0.0025
1.5
0.0026
0.0011
0.0019
0.0019
0.0009
0.0014
2.0
0.0035
0.0018
0.0025
2.5
0.0044
0.0026
0.0032
0.0016
0.0009
0.0011
0.000
0.002
0.004
0.006
0.0
1.0
2.0
3.0
Voltage x Vo
ta
n
d
e
l
ta
L2: tg delta 0.1Hz
L3: tg delta 0,1Hz
L1: tg delta 0.1Hz
200 kVdc @ 5 mA
80 kVdc @ 10 mA
Just now becoming available are products for field testing cables for partial discharge using an HVI VLF hipot to supply the test voltage.
This off-line PD testing is an excellent method of revealing the location and severity of partial discharge disturbances in a cables insulation
and accessories. Performing elevated voltage PD testing (soon up to 200 kV), using a sine wave output HVI VLF and PD detectors from
various companies worldwide, offers a detailed picture of a cables health, especially when compared to on-line PD testing, which is an un-
calibrated test that misses PD present above operating voltage. Off-line PD field testing is performed using sine wave producing VLF
instruments usually operating at 0.1Hz. Although PD testing can of course be performed at 50/60 Hz, at this frequency it is prohibitively
expensive and overly cumbersome due to the large size and high weight of the equipment. Using VLF solves these problems.
PARTIAL DISCHARGE TESTING OFF LINE Using any HVI VLF and third party PD products
TAN DELTA NUMBERS VERSUS INCREASING VOLTAGE
& RATIO OF 2Vo/Vo
60 kV TD
Most of the world has switched from DC voltage testing of solid
dielectric cables to AC testing using VLF hipots. The VLF hipot
enables users to perform AC stress tests to long cables in the field
with a portable and affordable AC hipot. HVI offers VLF models
from 28 kV 200 kV capable of testing cables miles long. If a cable
defect cant hold the test voltage, the VLF test causes failure at the
defect location. A VLF test is the best way to check the AC
integrity of a cable. Pass/fail: the ultimate diagnostic tool.
28 kVac peak
0.1 Hz @ 1.0 uF
60 kVac peak
0.1 0.02 Hz @ 5.5 uF
Using DC voltage to test aged solid dielectric cable is no longer
recommended and used by few. Although much of the world has
switched to AC cable testing using VLF, VLF TD, and/or VLF PD,
many still use DC. DC is often used for testing oil insulated cable and
new solid dielectric cable. HVI offers DC hipots from 37 kVdc 600
kVdc. All HVI DC hipots are also HV Megohmmeters, permitting
both insulation resistance measurements as well as leakage current
readings to be taken.
DC LEAKAGE CURRENT ASSESSMENT

VLF Proof Test VLF TD VLF PD It all starts with a VLF Hipot