General Order 95
Section V
Detailed Construction Requirements for Supply Lines
(Class H, L and T Circuits)
55.3 Voltage Requirements
Insulators used on supply lines shall be so designed that their
dry flash–over voltage is not more than 75% of their puncture voltage at
operating frequencies.
A. Pin Type
All pin type insulators used on supply lines shall have
a dry flash–over voltage as specified in Rule 55.3–C
for the nominal line voltage at which they are used.
B. Suspension, Bracket Mounted and Strain Types
Suspension, bracket mounted and strain type insulators
used on supply lines shall have a dry flashover voltage as specified in
Rule 55.3–C
for the nominal line voltage at which they are used when tested with their
attaching fittings or harness and under the mechanical loading to which they
are to be subjected.
Note: Revised January 6, 1968 by
Decision No. 73455.
C. Flashover Voltage
The insulator flashover voltages required by
Rules 55.3–A
and 55.3–B
shall be not less than as shown in Table 12
and shall be determined in accordance with the Standards of the American
Institute of Electrical Engineers for Insulator Tests, Standard Number 41
dated March 1930.
|
Table 12: Insulator Flashover
Voltages
|
|||
|
Nominal Line Voltage |
Dry Flashover Voltage |
Nominal Line Voltage |
Dry Flashover Voltage |
|
750 |
5,000 |
55,000 |
140,000 |
|
2,300 |
20,000 |
66,000 |
170,000 |
|
4,000 |
30,000 |
88,000 |
220,000 |
|
6,600 |
40,000 |
110,000 |
315,000 |
|
11,000 |
50,000 |
132,000 |
390,000 |
|
22,000 |
75,000 |
150,000 |
420,000 |
|
33,000 |
100,000 |
200,000 |
560,000 |
|
44,000 |
125,000 |
||
For intermediate voltages above 750 volts
the value for flashover voltages may be obtained by interpolation.
D. Additional Insulation
Insulators used in territories
where fog or lightning conditions prevail should be given more liberal factors
of safety than those indicated in Table 12
.
In partial underground distribution,
the primary transformer bushings shall have ratings of not less than 95
kV BIL and a dry flashover of not less than 60 kV; line conductor insulators,
either post clamp or dead–end type, shall have a dry flashover rating of
not less than 80 kV.
Insulators used at crossings
or conflicts shall conform to Rules 104
and 114
.