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Page 373

| Figure A-3 Polymer insulator showing fiberglass rod insulation and sealing (Courtesy Hubbell Power Systems). |

| ciated with porcelain insulators, that of providing a greater path for electric leakage between the energized conductors (terminals, buses, etc.) and the supporting structures. In inclement weather, this involves the shedding of rain water or sleet as readily as possible to maintain as much as possible the electric resistance between the energized element and the supporting structure, so that the leakage of electrical current between these two points be kept as low as possible to prevent flashover and possible damage or destruction of the insulator. Tables A-2a&b. |

| When the insulator becomes wet, and especially in a contaminated environment, leakage currents begin to flow on the surface; if the current becomes high enough, an external flashover takes place. The rate at which the |

Table A-2a

Polymer improvement over porcelain (Courtesy Hubbell Power Systems)

Watts Loss Reduction* (watts per insulator string)

Voltage | Relative Humidity

kV

30%

50%

70%

90%

100%

69

0.6

0.8

0.9

1.0

4.0

138

1.0

2.4

4.5

7.2

8.0

230

1.0

2.5

5.7

14.0

29.0

345

2.5

4.2

8.5

15.0

30.0

500

2.8

7.8

11.5

33.0

56.0

*Power loss measurements under dynamic humidity conditions on l-strings.

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