Baker D30R, User'S Manual & Operating Instructions

Page: 44 / 142

D30R Users Manual
44
Do Not Touch Test Leads while test is in Progress!
71-023 Rev C 5/8/2007
IR(3min)
DA
=
IR(30s)
There are no accepted minimum or maximum values of the DA test. However,
the DA value is considered to be trendable. Any change in the DA value
indicates that something is changing in the ground wall insulation system. The
stator may be contaminated or wet. The stator may also be running hot and
burning insulation. Usually, changes in the DA will be accompanied by a change
in one of the other “recognized” tests such as the Megohm test, PI test or the DC
Over Voltage test.
The
HiPot
test demonstrates that the ground wall insulation system can
withstand a “high” applied voltage without exhibiting an extraordinarily high
leakage current or actually breaking down. The test consists of applying a DC
voltage to the windings of the machine, same as a Megohm test, but at a higher
voltage – usually more than twice the voltage of the machine’s operating
voltage. Therefore, the HiPot test is often called a “Proof” test. The insulation
resistance value at the high applied voltage is not of interest with the HiPot test.
However, the value of the leakage current is and, more specifically, whether or
not the observed leakage current is within acceptable limits.
The choice of test voltage depends on whether a new motor (or coil) is being
tested for acceptance or whether an existing motor is being tested for continued
service. Consult your organizations’ policies regarding the HiPot test voltage to
be used. The simple formula of “2V+1000” generally results in a good test
voltage for the HiPot test for motors already in service. Other recommended
HiPot test voltages can be found in IEEE 95, ANSI C50.10-1977, IEC 34.1 and
NEMA MG-1 (see chapter 2).
The HiPot test usually lasts one minute and the leakage current recorded at the
end of the minute. The leakage current at the end of this minute is to be recorded
for future comparisons. Between the time when the voltage is applied to the
motor and the time when the leakage current measurement is taken, the operator
should carefully observe the leakage current and watch for sporadically varying
leakage current that might indicate weak insulation. Such variations should be
considered a failure of the insulation.