Instructions For Testing Insulators - Textron HDE HI-TEST IT-4 Operating Instructions Manual

INSTRUCTIONS FOR TESTING INSULATORS

Important Points of Information:
1) Insulators can be tested energized at any line voltage or de-energized using the Hi-Test
Insulator Tester, subject to the limitations described in the LIMITATIONS TO THE USE OF
THE HI-TEST INSULATOR TESTER section, page 4.
2) The types of physical damage usually seen during the visual examination of porcelain
insulators (cracks, chips, broken skirts, flash burns, dried and flaking cement around
the pins) are very poor predictors of the dielectric condition of these insulators. Such
types of damage affect the flash over withstand capability and/or the gross mechanical
strength of the insulators. However, they often do not affect the resistance value of
the insulators. The type of damage that does affect resistance value is an internal
crack, through the porcelain which is often non-visible (and, in the case of suspension
insulators, always non-visible).
3) Insulators, by definition, should have infinite resistance. When they have less than
infinite resistance there are only two paths for this loss of resistance: a) through the
body of the insulator due to an internal crack which presents an opportunity for
electric current to flow; and b) across the external surface of the insulator due to
the presence of moisture on that surface. (NOTE: There are some insulators which
are resistance graded and have conductive glazes making them surface conductive
and the user should be aware of the possibility of their presence).
4) There are a wide variety of insulator shapes, sizes, and materials. They can all be tested
with the Hi-Test Insulator Tester. However, the following points should be used as a
guideline on where to focus testing efforts and attention:
A GLASS INSULATORS - are all pre-stressed when manufactured so that any failure of
the glass results in the entire skirt being shed. In this way, they are self identifying for
failure of their resistance value and do not need to be tested for non-visible defects.
B COMPOSITE/POLYMER/NON CERAMIC INSULATORS - failure of these types
typically begins on the external surface and visible signs of potential failure include
extensive evidence of surface tracking and/or color or consistency changes in
the shed material. They can be tested using the procedure set out on page 9 for
testing insulators; however, the visible signs described above rarely coincide
with dielectric failure.
C PORCELAIN INSULATORS - virtually every shape and style is capable of sustaining
non-visible failure and they should all be routinely tested for such failures prior to
being recycled.
NOTE: Several types of porcelain insulators appear to be single piece insulators but
are, in fact, assemblies of two or more pieces of porcelain bonded together with cement.
Such insulators can be readily identified by turning them upside down and looking for
a cement bead between the skirts. If such a bead is located, each skirt must be tested
separately (see test procedure on page 9).
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