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AssigneeThe United States of America as represented by the Secretary of the Interior
InventorsGovind Rao Gadwal, Eldon Keith Stanek
Estimating the term…
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.
Apparatus for detecting a broken ground conductor in a polyphase A.C. cable having a separate power conductor for each phase and an equal number of ground conductors, said power conductors normally carrying a set of balanced positive-sequence currents, said conductors being reactively coupled together so that currents are induced in the ground conductors in response to currents flowing in the power conductors, positive-sequence currents normally being induced into the ground conductors by the power conductors, comprising means coupled to the ground conductors for sensing a negative-sequence current induced in the ground conductors and for deriving a first signal indicative of a negative-sequence current being sensed, means coupled to the conductors for deriving a second signal indicative of no current flowing in the ground conductors because a plurality of the ground conductors are open-circuited, and means responsive to either the first or second signal being derived for open circuiting the polyphase power conductors.
Apparatus for detecting a broken ground conductor in a polyphase A.C. cable having a separate power conductor for each phase and an equal number of ground conductors, said conductors being reactively coupled together so that currents are induced in the ground conductors in response to currents flowing in the power conductors, comprising means coupled to the ground conductors for sensing the sequence components of currents induced in the ground conductors, and means responsive to the sensed sequence components for controlling connections of the power conductors between a power source and a load.
Apparatus for enabling phase sequence components of polyphase currents to be derived comprising a network including a channel for each phase, each channel including means for monitoring each of the currents and for deriving a separate voltage that is a replica of each of the monitored currents, said network including means for deriving an output signal representing the vector sum of phase shifted voltages of the different channels, the voltage for channel K being phase shifted by 360.degree. .times. K, where ##EQU9## and N = the number of phases, said network including operational amplifier means responsive to the voltages and having input and feedback impedances, at least one of the impedances including a resistance and another of the impedances including a capacitor, the values of components included in the impedances being such that the phase shifted voltages are derived.
Dependencies are inferred from the claim text.