METHOD OF AND DEVICE
FOR PROTECTING ELECTRICAL POWER SYSTEM
United States Patent No. 5,305,174, Apr. 19, 1994
An electrical power system protection device includes a circuit breaker and a switch connected in series to a power line. The protection device also has a current limiting element connected in parallel to the circuit breaker. When the level of electrical current flowing in the power line, detected by a current detector, has exceeded a predetermined first set level, a first over-current detector delivers immediately a trip command to the circuit breaker. As a consequence, fault current is commutated to the current limiting element so that any drop of voltage in the power line upstream of the circuit breaker is greatly suppressed.
When a state in which a predetermined second set level is exceeded by the detected current level is continued beyond predetermined period, a second over-current detector delivers an off command to the switch, thus protecting the upstream portion of the power line against the fault in this power line. The current level is set to fall within a range which activates a momentary element of an over-current relay of a receiving end breaker of a downstream sub-system connected to the power line. In the event of a failure in the downstream power line, the receiving end breaker is tripped immediately so that the sound portion of the power line is reset to a normal state of operation. ( 24 Claims, 10 Drawing Sheets)
Inventors:
Masao Morita, Aichi
Toshiaki Ueda, Nagoya
Yukio Kurosawa, Hitachi
Hiroshi Arita, Mito
Tokio Yamagiwa, Hitachi
all of Japan
Reference Paper:
Solid-state Current Limiter for Power Distribution System
Summary’ń‹ź Ari-Enterprise
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