Neutral wire current monitoring for three-phase four-wire power

Communications: electrical – Condition responsive indicating system – Specific condition

Patent

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Details

340638, 324133, 324127, G08B 2100

Patent

active

051825473

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.

REFERENCES:
patent: 2736884 (1956-02-01), Yemomans
patent: 3771049 (1973-11-01), Piccione
patent: 3902168 (1975-08-01), Dola
patent: 3967257 (1976-06-01), Hager
patent: 4243982 (1981-01-01), Yarbrough
patent: 4263589 (1981-04-01), Lewiner et al.
patent: 4593276 (1986-06-01), Aida et al.
patent: 4691197 (1987-09-01), Damiano et al.
patent: 4714916 (1987-12-01), Schweitzer, Jr.
patent: 4725825 (1988-02-01), McKean
patent: 4808917 (1989-02-01), Fernandes et al.
patent: 4879626 (1989-11-01), Kim
patent: 5015944 (1991-05-01), Bubash
Nonlinear Loads Mean Trouble-Arthur Freund-Mar. 1988 EC&M p. 83, p. 90.
Double the Neutral and Derate the Transformer-Or Else- Arthur Freund-Dec. 1988-EC&M p. 81-p. 85.

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