Limitations To The Use Of The Hi Test® Insulator Tester - Textron HDE HI-TEST IT-4 Operating Instructions Manual

LIMITATIONS TO THE USE OF THE HI-TEST® INSULATOR TESTER
Three factors limit the use of the Hi-Test Insulator Tester under energized conditions and
they must be understood prior to its use:
1) On a 69 kVAC phase-to-phase nominal circuit the phase-to-ground voltage is
approximately 40 kVAC. The tester has an operating frequency of 50/60Hz. The
tester was designed and constructed to withstand 60 kVAC low impedance, phase-
to-ground voltage across the probes of the tester. This gives an additional 50% safety
margin above 40 kVAC before flashover will occur. CAUTION: The 60 kVAC flashover
voltage was tested in clean, dry conditions. To further increase safety to the operator
and to the tester, the tester is externally "shunted" on the back of the housing to limit
the flashover voltage to 50 kVAC. This shunt ensures that should the tester be placed
across a circuit in which the voltage exceeds 50 kVAC phase-to-ground, the tester
will flash across its external surface first. The shunt is located behind the DO NOT
REMOVE label (see Figure One below). The flashover voltage may be reduced by
the moisture and/or contamination on the tester surface. ALWAYS be sure the tester
is clean and dry before use. This means the tester is capable of withstanding the
phase-to-ground voltage on any circuit up to and including 69 kVAC phase-to-phase
nominal while testing insulators (i.e. the voltage on the line is directly across the
probes of the tester with no other insulators in the string working).
2) One side of any insulator under test must be isolated from the circuit in order to be
able to test that insulator. If the user attempts to test an insulator going directly from
phase-to-ground: the probe placed in contact with the conductor side of the insulator
will be common with all insulators connected to that conductor; the probe placed in
contact with the ground side of the insulator will be common with all insulators on
that circuit sharing ground. The tester will then try to test the resistance of all parallel
insulation paths it can reach simultaneously.
FURTHERMORE, placing the tester across a single insulator going directly from phase-
to-ground at line voltages greater than 69 kVAC phase-to-phase nominal will result in
externally flashing the tester and a line-to-ground fault!
NOTE: Users of the tester report some success testing pin and cap insulators on distribution
circuits when the insulators are mounted on wooden cross-arms, which are not bonded to
ground and when the cross-arms are dry. In these circumstances, the cross-arms provide
isolation of the insulator under test to the common ground side.
3) WHEN TESTING INSULATORS IN SUB STATIONS, such testing must be done DE-ENERGIZED
unless the user recognizes and understands the limitations set out above and uses the
tester in accordance with those limitations.
READ ALL OPERATING INSTRUCTIONS PRIOR TO USING THE TESTER
4
Figure One