7.14 Dielectric breakdown after gla

7.14 Dielectric breakdown after glancing impact
7.14.1 Scope
This test specifies the method for determining the retention of electrical breakdown voltage of conductor
insulation and/or covering after a glancing impact.
7.14.2 Apparatus
The apparatus shall consist of
a) an isolation transformer capable of supplying a test potential of 48 to 62 Hz, whose output
potential is continuously variable from near zero to the breakdown voltage;
b) a voltmeter having an accuracy of ±5% on the high voltage side of the transformer. If
analog, it shall have a response time that does not introduce a lagging error greater than 1% of
full scale at the specified rate of increase in voltage;
c) a fault current indicator;
d) a tank filled with tap water at ROOM TEMPERATURE;
e) a means of grounding with a maximum impedance of 15 W; and
f) an apparatus for applying a glancing impact to a wire specimen as shown in Figure 16,
having the following characteristics:
i) an oak wood anvil nominally 50 mm x 100 mm (2 in x 4 in) in cross-section and 250
mm (10 in) in length, rigidly supported 45 ±2° from the horizontal;
ii) a means of fastening the ends of the test specimen to the anvil;
iii) an impact mass 0.454 -0, +0.009 kg (1 -0, +0.02 lb), consisting of a solid steel
cylinder, 19 -1, +0 mm (0.75 -0.03, +0 in) in diameter having all surfaces smooth and
one end rounded to a radius of 9.5 -0.5, +0 mm (0.375 -0.015, +0 in); and
iv) a hollow tube to contain and guide the impact mass, having a 21 -0, +0.5 mm (0.82
-0, +0.02 in) inner diameter, mounted over the anvil in a vertical position.