Active negative sequence cable monitor

Details Active negative sequence cable monitor Active negative sequence cable monitor

1975-02-05

1976-02-10

Trammell, James D.

Electricity: measuring and testing

Measuring, testing, or sensing electricity, per se

Frequency of cyclic current or voltage

317 27R, 317 45, 317 47, 324 51, H02H 316

Patent

active

039380068

ABSTRACT:
A ground conductor break in a polyphase A.C. cable having a separate power conductor and an equal number of symmetrically spaced ground conductors for each phase is detected by sensing negative-sequence current components being induced in the ground conductors. In response to two or more ground conductors of a three-phase cable being broken, the break is detected by sensing a current flow in one of the power conductors and an absence of positive sequence current components in the ground conductors. In response to the broken ground conductor being sensed, power conductors are open circuited. The sequence components are sensed with a network including a channel responsive to the current induced in each ground conductor. Each channel includes a current transformer for deriving an A.C. voltage that is a replica of the induced current for the conductor of the particular channel. The network includes operational amplifiers responsive to the voltages derived from the current transformers. Each operational amplifier includes an input circuit including a series resistor and capacitor, as well as a feedback resistor, to provide 240.degree. phase shift between its input and output voltages.

REFERENCES:
patent: 3699391 (1972-10-01), Eilts
patent: 3732464 (1973-05-01), Miki et al.
patent: 3848160 (1974-11-01), Boothman et al.
patent: 3891894 (1975-06-01), Scarpino

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