MV/HV Cable Testing VLF Technology

VLF Withstand VLF Tan Delta VLF Partial Discharge

High Voltage, Inc. offers VLF test equipment for all medium and high voltage cables up to 161 kV.
Diagnostic field testing of cables is now here. All three technologies shown above are very well proven for testing MV cables.
Any VLF model from HVI can be used to perform the three tests described. Our 200 kV VLF tests HV cables.

Withstand and Diagnostic field testing of medium and high voltage cable is now practical using HVI VLF technology along
with commercially available Tan Delta and Partial Discharge measuring devices. The use of multi-ton, very expensive power
frequency resonant equipment is no longer necessary. VLF products from HVI are far smaller, lighter, easier to transport,
and less expensive: everything needed to bring factory cable testing methods to the field. These tests are performed off-line,
providing the most information possible. Test procedures and test specifications are within IEEE and other Standards.

VLF Withstand Testing

The most basic use of the VLF is to perform a go/no-go withstand test
to expose defects that cannot hold the test voltage. If a cable cant hold
~1.5 3 times normal voltage, depending on cable class, find out now.
Let failure occur during downtime, make the repair, and not worry about
that cable for many years. It is very useful following installation, repair,
or to insure critical cables are sound. In situations where the user can
tolerate a failure during the test, it is the simplest and most certain way to
test a cable. Any defect severe enough to be driven to partial discharge
is allowed to fail. Lesser defects and good insulation are unaffected. It is
the ultimate diagnostic test.

Tangent Delta/Dissipation Factor/Loss Angle Testing

When a non destructive diagnostic test is preferred over a
withstand test, there are proven options. The first technique and
the most common is a Tan Delta test. This is a global test of the
Tan Delta 15 kV EPR
cable, providing the condition from end to end. Using a VLF as the 20.00

voltage source and a separate divider to make the measurements, 18.00

the voltage is raised while measuring the Tan Delta of the cable. If 16.00
Test stopped to prevent cable failure.
a cable is perfect, it behaves like a capacitor where there is a phase Phase B is Highly Degraded.
14.00
shift of 90 between the voltage and current. The more degraded the
Tan Delta x10-3

12.00
insulation and accessories are, the more this angle becomes less
10.00
than 90, as resistive leakage current is added. This change in the
8.00
angle is easily measured and assumptions can be made about the
6.00
degree of degradation. The absolute TD number is important, but Phases A & C are Good with little rise in TD
more indicative is if the curve trends sharply upward as the voltage is 4.00
numbers with increasing voltage.
raised, the cable is highly degraded. Test many cables and rate them 2.00

as Highly or Moderately Degraded, or Good. This data is used to help 0.00

0 5 10 15 20
prioritize cable replacement, injection, and/or to determine what other Voltage kV
tests may be of value. TD testing is easily performed and interpreted.

HIGH VOLTAGE, INC. 31 County Rt. 7A, Copake, NY 12516 (518) 329-3275 Fax: (518) 329-3271
E-Mail: sales@hvinc.com Web: www.hvinc.com
High Voltage, Inc. designs and manufactures high voltage test equipment for utility and industrial applications. Also available are Very Low
Frequency (VLF) high voltage AC test sets, oil dielectric test sets, AC and DC instrumented test sets, cable fault locators and other products.
 MV/HV Cable Testing VLF Technology
Partial Discharge Testing
Partial Discharge testing is fairly new using VLF, yet proven and
accepted. The obvious advantage to using VLF rather than power
frequency systems is the smaller size, lower weight, far less power
consumed, and price. PD testing attempts to locate defects and
their severity along the cable path. While TD testing provides the
overall health of the cable, PD testing finds individual locations
of electrical discharge. The operator then makes a determination
whether the level of PD is worrisome or acceptable. Any PD in
the insulation at levels near or slightly above operating voltage is
unacceptable, whereas accessories can survive with rather high
levels of PD. This is where the interpretive nature of PD testing
comes in. With no real guide as to what is and isnt acceptable PD
and at what voltage level, particularly in accessories, interpretation
can be difficult. Also measured are the Partial Discharge Inception
Voltage (PDIV) and the PD Extinction Voltage (PDEV). Knowing Sample PD Screen Shot: Location and Amplitude
where PD begins relative to applied voltage compared to normal Power Diagnostix Systems GmbH
operating voltage, and where the PD extinguishes when voltage
is lowered, provides valuable data used in the interpretation. PD testing is of great value, although the most expensive

Conclusion

All three methods of testing provide useful information, but different information. None are suited for every situation.
None can provide all the information needed about a cable system. Ideally, all three technologies with the data they
provide should be performed before making a decision. The cost of the test, the cost to buy the equipment, the ease
of the test, the ease of interpretation, the skill of the operator necessary, the availability of the equipment, the cable
design, age, ease of repair, the data needed to make cable maintenance decisions, and whether cable failure during
the test is permissible are all vital in selecting what tests are best for your cable system.
No other company can offer as much as HVI. All three methods have been used for years and are
well proven for testing cables. Select one or more to learn as much as possible about your cables

40 kV
28 kV

90 kV

120 kV

200kV VLF Withstand, VLF TD & VLF PD Test Truck Not shown: 50 kV, 60 kV, 65 kV & 200 kV
Inducor Ingenieria S.A. Argentina Load ratings from 0.4 mF 50 mF

HIGH VOLTAGE, INC. 31 County Rt. 7A, Copake, NY 12516 (518) 329-3275 Fax: (518) 329-3271
E-Mail: sales@hvinc.com Web: www.hvinc.com
High Voltage, Inc. designs and manufactures high voltage test equipment for utility and industrial applications. Also available are Very Low
Frequency (VLF) high voltage AC test sets, oil dielectric test sets, AC and DC instrumented test sets, cable fault locators and other products.

MAY2013-1M