Neutral wire current monitoring for three-phase four-wire power distribution system
First Claim
1. Current monitoring apparatus for detecting at least one defined current level in a neutral circuit of a three-phase four-wire electric power distribution system, said current monitoring apparatus comprising:
- current transformer means coupled to said neutral circuit for generating a current signal representative of current flowing through said neutral circuit;
fuse means connected in shunt across said current transformer means for conducting current signals up to a current rating of said fuse means; and
alarm means connected in shunt across said fuse means for alerting personnel operating said power distribution system upon operation of said fuse means in response to current signals exceeding the current rating of said fuse means.
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Accused Products
Abstract
A neutral circuit current monitoring device detects at least one current level, which includes harmonic currents, flowing in a neutral circuit of a power distribution system such that preliminary warnings can be given to personnel operating the system before serious overload problems exist. Warnings can be given via audible and/or visual alarms and/or by electrical contacts which can be used to operate auxiliary devices. Preferably, two current levels defined by interchangeable secondary fuses within the monitoring circuit are detected with a first or low current level in the neutral circuit being calculated to also indirectly monitor for overheating of the distribution transformer caused mainly by circulating third harmonic currents in the transformer primary. The low current level permits personnel to investigate and correct a developing problem before it occurs. Preferably, a second or high current level of the current sensor can be set at a value less than 100% of the phase current rating. The monitoring device may be set up such that when the high current level is exceeded the monitor once again activates an alarm and/or trips a protecting circuit breaker located at the input or output of a distribution transformer to protect the transformer as well as the neutral circuit.
105 Citations
20 Claims
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1. Current monitoring apparatus for detecting at least one defined current level in a neutral circuit of a three-phase four-wire electric power distribution system, said current monitoring apparatus comprising:
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current transformer means coupled to said neutral circuit for generating a current signal representative of current flowing through said neutral circuit; fuse means connected in shunt across said current transformer means for conducting current signals up to a current rating of said fuse means; and alarm means connected in shunt across said fuse means for alerting personnel operating said power distribution system upon operation of said fuse means in response to current signals exceeding the current rating of said fuse means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of monitoring current in a neutral circuit of a three-phase four-wire electric power distribution system for detecting at least one defined current level therein comprising the steps of:
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coupling a current transformer to said neutral circuit; connecting first fuse means across said current transformer to shunt current signals generated by said transformer up to a first current rating of said first fuse means; and connecting alarm means across said first fuse means, said alarm means being activated to generate an alarm signal upon operation of said first fuse means by current signals exceeding the rating of said first fuse means. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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Specification