Atec High-Voltage-VLF-28CMF - Manual (Page 3)

PEAK
KILOVOLTS
0
60
CABLE CAPACITANCE
MICROFARADS
0
60
0 6.0
OUTPUT PEAK MILLIAMPERES
SCOPE
POS
NEG
START
TIMER
60
30
10
METER
μF
mA
CAPACITANCE
SCALE X10
PUSH TO READ
X1
CAP
ZERO
53
What is VLF?
VLF stands for Very Low Frequency. A VLF hipot
is an AC output high voltage instrument. HVI VLF
products provide sinusoidal AC voltage but at 0.1
Hz - 0.01 Hz, compared to the 50/60 Hz output of
conventional AC test sets. It is still an AC voltage
with sinusoidal polarity reversals every half cycle.
The VLF instrument is used to provide a simple go/
no-go, or pass/fail, withstand test. Also, HVI VLF
instruments can be used as the voltage source for
performing off-line Partial Discharge and Tan
Delta cable diagnostic testing.
Why VLF?
VLF test sets are used to field test high capacitance
loads like cables and motors/generators. The lower
the frequency of an AC source, the lower the cur-
rent and power required to apply a voltage to a ca-
pacitive load like a cable. At 0.1Hz, it requires 600
times less power to test a cable than at 60Hz. The
HVI VLF instruments permit users to field test
long cables and large generators with a portable
and affordable test set. A 100 lb VLF instrument
can do the job of a multi-ton 60Hz AC test set.
Cables should be tested with AC voltage. With the
HVI VLF products, it can be down with a practical,
economical, and easy to use package.
When and Where Is VLF Used –
Cable & Rotating Machinery
The principal use of VLF is testing medium and
high voltage shielded power cables. A long cable
may have many microfarads of capacitance. To AC
high voltage test this cable requires the use of VLF
technology. An AC voltage test is the best way to
verify the AC integrity of a cable. If a cable can’t
hold 2 – 3 times normal voltage, it is not healthy and
an in-service failure is likely. Use the VLF to cause
defects to fail during the test. Find the fault, make
the repair or replacement, and be left with a better
cable. It is especially valuable for verifying a cable
after installation or repair: far better than using
a DC hipot, 5kV megohmmeter, hot stick adaptor,
or soak test, none of which provide meaningful
information about a cables ability to withstand
several times normal AC voltage. IEEE 400, IEEE
400.2, VDE 0276, CENELEC HD 620/621, and IEC
60060-3 standards define VLF cable testing.
VLF is also very useful for testing large rotating
machinery, since it provides a portable and affordable
method of field testing coils and is sanctioned by the
IEEE 433 standard.
Partial Discharge & Tan Delta
VLF Cable Diagnostic Testing
The VLF hipot by itself provides a withstand, or
proof test. It can also be used as the voltage source
for off-line partial discharge and tan delta cable
diagnostic testing. HVI can serve the needs of the
industry for cable testing better than any other.
Contact HVI for additional information on other
cable testing methods and products available.
Why Buy HVI VLF Products?
The HVI Design – Portable, Affordable, Rugged, Reliable, Proven
Benefits of HVI VLF AC Hipots
For more information on VLF testing, download our
VLF FAQ from our website: www.hvinc.com
• Portable and affordable
• All models feature a true sinewave output
• Waveform is independent of load
capacitance between 0.01 mF and
maximum load
• Highest load ratings available
• Highest voltage models available
• Simple and easy operation
• AC testing does not degrade good
cable insulation
• Harmful space charges are not injected
into the cable insulation
• No traveling waves are generated during
testing
• BNC scope output for waveform viewing
• Rugged and reliable design less prone
to failure from transients
• Much easier to service compared to
units with solid state design