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Unusual cable?

AncientMariner
Some people collect stamps, I collect cable. Preferably as short encapsulated paperweights, although I do have others, such as a piece of TAT1 and a piece of the original transatlantic telegraph cable of 1866.


One of my paperweights is a 6-core lead covered cable, each core 0.125 sq. inches copper rated at 11,000 volts WP (which I guess is Working Pressure which translates to Working Voltage) It was produced for the City of Sheffield by the Western Electric Company London. No date given.


Why use a 6-core cable? Seems to be putting all ones eggs in one basket if used for a two circuit system. Had it been for a lower voltage, then perhaps an ac feed to a mercury arc rectifier, but surely not at 11 kV?

Clive
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    Sometimes such cables were used for sensitive and sophisticated fault detection. Two cores in parallel for each phase, should under normal circumstances share the current equally. The two cores for each phase were passed through the SAME current transformer but in OPPOSITE directions and thereby producing no output from the CT.

    Most faults or failures would upset this balance, and the CT output could be used to trip the feeder circuit breaker.


    Commonly used in coal mines, oil refineries, ordnance depots, and other places were any open arcing from a failed cable could have very serious consequences, a failure between any core and any other core should trip the feeder before open arcing results.


    Rather a costly and complicated system for an ordinary public supply though.
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    Sometimes such cables were used for sensitive and sophisticated fault detection. Two cores in parallel for each phase, should under normal circumstances share the current equally. The two cores for each phase were passed through the SAME current transformer but in OPPOSITE directions and thereby producing no output from the CT.

    Most faults or failures would upset this balance, and the CT output could be used to trip the feeder circuit breaker.


    Commonly used in coal mines, oil refineries, ordnance depots, and other places were any open arcing from a failed cable could have very serious consequences, a failure between any core and any other core should trip the feeder before open arcing results.


    Rather a costly and complicated system for an ordinary public supply though.
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