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008 - Relay Settings · Silent Sentinels- Protective Relays for A-C and D-C Systems

• 0:01
  Speaker 1: Chapter six of Silent Sentinels by Westinghouse Electric and Manufacturing Company.
• 0:09
  Speaker 1: This LibriVox recording is in the public domain. Relay settings,
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  Speaker 1: the selection of the proper current tap in time index,
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  Speaker 1: lever setting, or induction type over current relays demands a
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  Speaker 1: knowledge of the load conditions in the circuit or portion
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  Speaker 1: of the circuit to be protected, and the amount of
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  Speaker 1: short circuit current available under minimum generating capacity conditions. It
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  Speaker 1: is also desirable to know the amount of short circuit
• 0:43
  Speaker 1: current available under maximum generating conditions, but in case the
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  Speaker 1: data is not available, the interrupting ability of the oil
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  Speaker 1: circuit breaker will service a first approximation. While there are
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  Speaker 1: minor modifications in the actual set of the relays dependent
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  Speaker 1: on the particular type of protection employed. The following remarks
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  Speaker 1: will outline the general considerations with reference to the simpler
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  Speaker 1: cases current tap settings on radio and loop feeders, the
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  Speaker 1: proper current tap is determined largely by the current transformer
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  Speaker 1: ratio and the full load current in the feeder. In general,
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  Speaker 1: the current tap is so chosen to be at least
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  Speaker 1: two hundred percent of the secondary current from the current
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  Speaker 1: transformers when carrying full load in the line. In cases
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  Speaker 1: where the load is subject to violent fluctuations, it may
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  Speaker 1: be necessary to make normal operating current for the relay
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  Speaker 1: three hundred percent of the secondary current corresponding to normal
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  Speaker 1: full load. The current tap should not, however, be chosen
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  Speaker 1: so high that the wheels delay winding receives less than
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  Speaker 1: three hundred percent of its current setting under short circuit
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  Speaker 1: with minimum generating capacity on the system, as otherwise, the
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  Speaker 1: time of operation will be so long as to completely
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  Speaker 1: disrupt service. Time settings on radial feeders, the proper time
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  Speaker 1: of operation of the relay is determined by its location
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  Speaker 1: with respect to the source of power and other relays
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  Speaker 1: on the same circuit. For a radio feeder system, the
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  Speaker 1: outermost relay is set for the shortest time, and the
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  Speaker 1: relays towards the generating station for successively longer times. The
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  Speaker 1: relays at the source of power must be set sufficiently
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  Speaker 1: long to allow any outlying faulty section to be cleared.
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  Speaker 1: With induction type relays and direct current operated circuit breakers,
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  Speaker 1: it is common practice to set successive relays for time
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  Speaker 1: intervals zero point five seconds apart, with the outermost relay
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  Speaker 1: set for zero point one second, adopting a maximum of
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  Speaker 1: two point one seconds, as the longest time of fault
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  Speaker 1: should remain on this system. We therefore find that five
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  Speaker 1: sections is about the most that should be protected by
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  Speaker 1: selective timing alone. Although some systems are operating satisfactorily with
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  Speaker 1: relays set zero point three or zero point four seconds apart,
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  Speaker 1: such systems achieve success only by extreme care in the
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  Speaker 1: maintenance of the oil circuit breaker mechanism and careful adjustment
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  Speaker 1: of relays in trip circuit mechanisms. Time intervals closer together
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  Speaker 1: than zero point five second are not to be recommended
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  Speaker 1: for average systems. The time of operation should be that
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  Speaker 1: required when the relay is operating on the flat or
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  Speaker 1: minimum time interval of the time current curve i e.
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  Speaker 1: When the second current is five hundred percent or more
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  Speaker 1: of the relay current tap setting time settings on loop
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  Speaker 1: feeders for the simple loop system involving only one source
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  Speaker 1: of power, the relay time settings are described in the
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  Speaker 1: paragraph on time settings on radio feeders. The loop is
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  Speaker 1: opened at one of the generating station breakers and the
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  Speaker 1: relays on the outgoing sides of the substations set for
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  Speaker 1: successively higher times of operation from the outermost substation. Considering
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  Speaker 1: the feeder as straight radio to the generating station. The
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  Speaker 1: loop is then closed up and the other generating station
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  Speaker 1: breaker opened. The time settings on the remaining relays being
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  Speaker 1: determined is already outlined. Starting on the loop at any
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  Speaker 1: point and approaching the generating station, it will then be
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  Speaker 1: observed that the relays set to trip for power flowing
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  Speaker 1: from the generating station will be set for increasingly longer
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  Speaker 1: times of operation, whereas the relays set to trip for
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  Speaker 1: power flowing towards the generating station will be set for
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  Speaker 1: increasingly shorter times of operation. The loop system, which receives
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  Speaker 1: power at two or more points in the ring, is
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  Speaker 1: especially difficult to relay. If the various substation relays are
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  Speaker 1: timed for one source of power, as outlined in the
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  Speaker 1: preceding paragraph, the timing is wrong when considering the other
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  Speaker 1: source or sources of power. Parallel lines between any two
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  Speaker 1: points can of course use some form of balanced protection
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  Speaker 1: for parallel operation, but this is not a place likable
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  Speaker 1: when the lines are operating singly. In applying a series
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  Speaker 1: of time settings to such a system, it is generally
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  Speaker 1: necessary to consider both the amountain source of short circuit
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  Speaker 1: current available. Selection usually can be obtained by working on
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  Speaker 1: the inverse portion of the time current curve of the relay.
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  Speaker 1: Parallel feeders protected by type CD relays four lines protected
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  Speaker 1: by Type CD relays, It is usual to set the
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  Speaker 1: relay to operate on a differential current of three ampers.
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  Speaker 1: For through short circuits, the current in the two equal
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  Speaker 1: lines will be balanced so that there will be a
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  Speaker 1: very slight amount of differential current tending to trip the relays.
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  Speaker 1: For the somewhat infrequent case where type CD relays protect
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  Speaker 1: two parallel lines of unequal impedance, but equipped with current
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  Speaker 1: transformers of the same ratio type, a current balance auto
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  Speaker 1: transformers should be used to make equal the currents flowing
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  Speaker 1: through the relay windings. The time setting is generally on
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  Speaker 1: the order of zero point one or zero point two
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  Speaker 1: second settings for ground relays. Ground relays are set the
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  Speaker 1: same as line relays, except that ground current flow differs
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  Speaker 1: in magnitude from the current flow for a line to
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  Speaker 1: line short circuit. End of Chapter six