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Shields Scotty

May 21, 2013
Inquiry

What impacts do rejuvenation fluids have on the conductor and insulation shields?

Response

With Star Trek Into Darkness in the theaters it was appropriate to revisit the question of shields. Not the shields that deflect Klingon disrupter blasts, but the conductor and insulation shields used to smooth electrical stress in underground power cable. When rejuvenation technology was first introduced about 25 years ago, that was one of the first questions that had to be resolved.

The table below provides some publically available data from a report prepared by Cable Technology Laboratories titled “Testing of VEPCO 35kV cable 5 Years After Upgrading,” dated May 28, 1999. The data examined the impact of a 70:30 mixture of phenylmethyldimethoxysilane and trimethylmethoxysilane (the white phase) and dimethyldimethoxysilane (the blue phase) in an application at Virginia Electric Power, compared to the untreated control (the green phase).

In short, both rejuvenation fluids show slight, but insignificant increases in volume resistivities of the conductor and insulation shields, four year after treatment at both 22°C and 90°C. In all cases, the increase is well below the limit set for cables of that vintage. The more modern limit is even more forgiving than the 1971 values. Dozens of such measurements were made in the last century, but they ceased to be interesting, because the impact was repeatedly insignificant.

Volume Resistivity of Semiconducting Shields

Temperature (°C)

Volume resistivity (Ω-m)

AEIC CS5- 1971 Limits

Green

White

Blue

Conductor Shield

22

0.17

0.81

0.9

≤50

90

1.2

61

40

≤500

Insulation Shield

22

0.04

0.06

0.064

≤50

90

0.14

0.25

0.22

≤500

CTL – Testing of VEPCO 35kV cable 5 Years After Upgrading, Tables 14-15 (Provided by Tacoma Public Utilities)