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009 - Typical Relay Application · Silent Sentinels- Protective Relays for A-C and D-C Systems

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  Speaker 1: Chapter seven of Silent Sentinels by Westinghouse Electric and Manufacturing Company.
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  Speaker 1: This LibriVox recording is in the public domain. Typical relay application.
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  Speaker 1: When it is desired to relay a power transmission system,
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  Speaker 1: there are many factors which enter into the problem, all
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  Speaker 1: of which must be given consideration. In most systems, so
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  Speaker 1: many complications are present that it is almost impossible to
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  Speaker 1: secure an ideal application of relay protection. However, in most
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  Speaker 1: cases it is possible to arrange the relay setting so
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  Speaker 1: that certain lines in case of a fault may be
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  Speaker 1: disconnected without disturbing the service, and the disconnecting of these
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  Speaker 1: lines leaves conditions such that ideal selective action is secure.
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  Speaker 1: You're on the rest of the system where distance between
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  Speaker 1: stations is great enough to give the necessary three percent drop,
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  Speaker 1: and it is convenient to use the type c Z relay,
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  Speaker 1: these complications may be eliminated. Figure sixty four shows a
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  Speaker 1: schematic sketch of a typical network system which will be
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  Speaker 1: used as the basis for illustrating one method of making
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  Speaker 1: an initial relay application. Figure sixty four is described here
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  Speaker 1: in order to facilitate understanding the remainder of the chapter.
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  Speaker 1: It is suggested to copy this down to paper to
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  Speaker 1: facilitate understanding. The Crichton Generating Station is connected via a
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  Speaker 1: loop system to seven substations. Line one connects Relay twenty
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  Speaker 1: two at Kryme Generating Station with relay one at Woodward Sub.
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  Speaker 1: Line two connects Relay twenty one at Crichton Generating Station
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  Speaker 1: with relay two at Woodward Sub. The distance is three miles.
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  Speaker 1: Fault location A is located on line one. Line three
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  Speaker 1: connects relay three at Woodward Sub two Relay four at
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  Speaker 1: Parsons Sub over a distance of three miles. Fault location
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  Speaker 1: B is on this line. Line four connects Relay six
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  Speaker 1: at Parsons Sub with relay seven at bryce Ki Sub.
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  Speaker 1: Fault location C is on this line. The distance is six.
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  Speaker 1: Line five connects relay eight at brice Key Sub with
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  Speaker 1: relay nine at Feldman Sub. Fault location D is on
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  Speaker 1: this line. Line six connects Relay ten at Feldman Sub
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  Speaker 1: with relay eleven at Goldsboro Sub. Fault location E is
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  Speaker 1: on this line. The distance is one mile. Line seven
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  Speaker 1: connects relay twelve at Goldsboro Sub with relay thirteen at
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  Speaker 1: Kubiak Sub. Fault location F is on this line, the
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  Speaker 1: distance is three miles. Tie Line eight connects relay five
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  Speaker 1: at Parsons Sub with relay fourteen at Kubiak Sub. Fault
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  Speaker 1: location G is on this line, the distance is five miles.
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  Speaker 1: Tie Line nine connects relay fifteen at Kubiak Sub with
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  Speaker 1: relay twenty at Crichton Generating Station. Fault location H is
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  Speaker 1: on this line, the distance is five miles. Line ten
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  Speaker 1: connects relay sixteen at Kubiak sub with relay seventeen at
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  Speaker 1: Anderson's Sub. Fault location I is on this line, the
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  Speaker 1: distance is four miles. Line eleven connects relay eighteen at
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  Speaker 1: Anderson Sub with relay nineteen at Crichton Generating Station. Fault
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  Speaker 1: location J is on this line. The distance is two
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  Speaker 1: miles end of figure sixty four description. Upon analysis, the
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  Speaker 1: network is found to be really a loop system, with
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  Speaker 1: tie line number eight connecting Parsons and Kubiak substations, and
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  Speaker 1: number nine connecting the generating station with the Kubiak sub.
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  Speaker 1: This loop, without these ties connects seven substations with a
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  Speaker 1: generating station. Either the co CR or the CZ relay
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  Speaker 1: scheme will be the typical one to use. Therefore, the
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  Speaker 1: COOCR scheme will be chosen with the CZ scheme S
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  Speaker 1: an alternative. Standard CO overcurrent relays are therefore allotted to
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  Speaker 1: each outgoing line numbers one qu nine eleven at the
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  Speaker 1: generating station, and standard CR directional overcurrent relays on each
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  Speaker 1: line of the loop. At each substation. The type CR
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  Speaker 1: relays are connected so that the directional element contacts will
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  Speaker 1: close only when power is flowing away from the substation
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  Speaker 1: bus s bars. It should be remembered throughout this discussion
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  Speaker 1: that access current flowing in this direction is necessary to
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  Speaker 1: complete the tripping circuit. After assigning relays to the various lines,
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  Speaker 1: the next problem is to assign time settings to the
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  Speaker 1: relays and then check out to determine if the proper
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  Speaker 1: time intervals necessary for selective action can be allowed without
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  Speaker 1: having excessive type settings on any of the relays. A
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  Speaker 1: five tenths second interval between relay settings is commonly used
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  Speaker 1: in present day press. This value allowing zero point three
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  Speaker 1: five second for the breaker to open after the trip
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  Speaker 1: circuit has been made, and zero point one five second margin.
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  Speaker 1: The maximum allowable setting, of course depends on the system,
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  Speaker 1: but three point one seconds is considered the highest time setting,
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  Speaker 1: which it is safe to use, and a maximum of
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  Speaker 1: two point six seconds is adhere to whenever possible. Referring
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  Speaker 1: to the system in question, there are seven substations in
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  Speaker 1: the loop which would require a maximum time setting of
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  Speaker 1: three point six seconds for the relays at the generating station.
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  Speaker 1: This value is rather high, therefore some way must be
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  Speaker 1: found to lower it. When checking the distance between stations,
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  Speaker 1: it is found that line six is comparatively short. Hence
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  Speaker 1: a pilot wire scheme may be used to protect this secondction.
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  Speaker 1: That makes one less section to be counted in adding
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  Speaker 1: the successive time intervals, but three point one seconds is
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  Speaker 1: still higher than is desirable. Trying to find some means
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  Speaker 1: of eliminating one more section, it is observed that the
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  Speaker 1: Anderson sub might be eliminated from the loop for the
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  Speaker 1: first trial application, making tie line number nine a part
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  Speaker 1: of the loop. This will make it possible to obtain
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  Speaker 1: the proper intervals between successive relays with a maximum setting
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  Speaker 1: of approximately two point six seconds. Definite time settings may
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  Speaker 1: now be assigned to the successive relays in the following manner.
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  Speaker 1: Beginning at the Woodward sub, the cr relays numbers one
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  Speaker 1: and two on lines one and two set to trip
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  Speaker 1: with power flowing from the sub to the generating station
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  Speaker 1: may be set to trip almost instantly, because a fault
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  Speaker 1: online number one or two is the only circumstance to
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  Speaker 1: cause excess current to flow in this direction, and therefore
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  Speaker 1: the relays may be set to clear as soon as possible.
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  Speaker 1: It is customary to make this setting zero point one second.
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  Speaker 1: Going on to the next sub persons, we find that
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  Speaker 1: Relay four online number three at this sub is set
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  Speaker 1: to trip with power flow in the same direction, namely
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  Speaker 1: away from the bus bars towards woodward sub. This relay
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  Speaker 1: must accordingly be given a higher time setting because a
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  Speaker 1: fault online one or two will draw current through Relay four,
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  Speaker 1: and therefore it is essential to have Relay one trip first.
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  Speaker 1: A definite setting of zero point six second is therefore
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  Speaker 1: assigned to it. In like manner, each successive relay connected
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  Speaker 1: to trip with the power flow in this direction is
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  Speaker 1: given a setting of zero point five second higher than
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  Speaker 1: the next preceding one, which leads to a setting of
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  Speaker 1: two point six seconds on Relay twenty at the generating station.
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  Speaker 1: Relay number eleven at Goldsborough's sub may be ignored because
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  Speaker 1: it can be set to trip almost instantly when a
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  Speaker 1: fault occurs in line six, but a fault on any
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  Speaker 1: other part of the system will not affect it. A
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  Speaker 1: similar procedure is followed out for the relays set to
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  Speaker 1: trip with the power flow in the other direction, or
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  Speaker 1: clockwise as it might be considered. Beginning at Kubiak sub
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  Speaker 1: relay fifteen is assigned to zero point one second, setting
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  Speaker 1: Reulay twelve zero point six second, Relay eight one point
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  Speaker 1: one second, and so on until relays twenty one and
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  Speaker 1: twenty two at the generating station are reached. The next
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  Speaker 1: problem which must be met and solved is the time
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  Speaker 1: setting for relays five and fourteen on line eight and
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  Speaker 1: relays six, sixteen, seventeen, eighteen, nineteen on lines ten and eleven.
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  Speaker 1: No definite rule can be followed for making the settings
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  Speaker 1: on relays five and fourteen. Very often the relays on
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  Speaker 1: a tie line are set to trip in a short
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  Speaker 1: time whenever excess current flows, because this action makes the
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  Speaker 1: relay operation on the rest of the system simpler and
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  Speaker 1: does not injure the service. In this case, however, by
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  Speaker 1: assigning a setting of one point six seconds to relay
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  Speaker 1: five and two point one seconds on relay fourteen. Comparatively
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  Speaker 1: good protection is secured for line eight, and neither relay
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  Speaker 1: will trip with a fault elsewhere on the system, except
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  Speaker 1: in one or two cases as well be shown later.
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  Speaker 1: The lines ten and eleven may be considered as completing
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  Speaker 1: the loop from substation Kubiak rather than line nine, and
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  Speaker 1: the settings a de signed to fit in with the
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  Speaker 1: rest of the loop as already described. A check can
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  Speaker 1: now be made assuming a fault in each line in turn,
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  Speaker 1: and then determining whether the proper relay operation will take place.
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  Speaker 1: Assuming a fault on line one at a current will
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  Speaker 1: flow to the fault from the generator station and from
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  Speaker 1: woodward sub Thus Relay one will clear within zero point
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  Speaker 1: one second, cutting off all flow from that direction, and
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  Speaker 1: Relay twenty two will clear within two point six seconds.
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  Speaker 1: Assuming a fault at B on line three, current will
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  Speaker 1: flow in from both directions, tending to trip relay's seven
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  Speaker 1: at brice Ski fourteen at Kubiak in twenty one and
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  Speaker 1: twenty two in addition to three and four at the
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  Speaker 1: immediate ends of the line. Relay three will be twenty
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  Speaker 1: two and twenty one out, thus clearing the fault inn
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  Speaker 1: in that direction. And relay four will trip in zero
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  Speaker 1: point six second, which is a shorter period than that
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  Speaker 1: of any of the others that will be likely to trip.
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  Speaker 1: Assuming fault sets C on line four, D on five,
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  Speaker 1: G on eight, E on line six, H on line nine,
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  Speaker 1: J on line eleven, and I online ten, the action
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  Speaker 1: may be checked out in the same way. Assuming of
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  Speaker 1: fault online seven et F. We find that current may
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  Speaker 1: be drawn from both directions that coming from sub kubiak
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  Speaker 1: being possibly drawn from lines eight, nine, and ten. In
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  Speaker 1: case enough current is drawn from line eight to give
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  Speaker 1: relay five its definite minimum time of tripping, it may
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  Speaker 1: trip before relay thirteen clears. However, relay thirteen will trip
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  Speaker 1: before any other relays in the system. Therefore the opening
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  Speaker 1: of the tie line is not serious. There is also
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  Speaker 1: a possibility of setting the current taps on relay five
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  Speaker 1: so that it will be operating on the inverse part
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  Speaker 1: of the curve under such a condition, and thus increase
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  Speaker 1: its time of tripping to the extent that Relay thirteen
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  Speaker 1: will trip first if it is desired. And an analysis
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  Speaker 1: of short circuit current values shows that sufficient unbalanced will
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  Speaker 1: exist between lines one and two with a fault in
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  Speaker 1: either one. Additional current balance CD relays may be installed
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  Speaker 1: at each end. These will provide a means for clearing
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  Speaker 1: either line almost instantly when they are both in service
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  Speaker 1: and one develops a fault. Type CO relays should be
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  Speaker 1: used on each outgoing feeder from the several substations. TYPEZA
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  Speaker 1: relays should be used for the differential protection of the
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  Speaker 1: three banks of transformers in the generating station. The transformers
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  Speaker 1: in the substations elseh may be supplied with differential protection
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  Speaker 1: if their size and location justify it. In most cases, however,
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  Speaker 1: where the transformers are relatively small less than two thousand
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  Speaker 1: kilovote ampiers, and where the overload relays may be given
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  Speaker 1: a low time setting, the overload relays serve also as
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  Speaker 1: sufficient transformer fault protection. On complicated systems employing COO and
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  Speaker 1: CR relays for protection, the time required to trip sometimes
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  Speaker 1: becomes excessive in some parts of the system. This subjectionable
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  Speaker 1: feature is entirely absent in a CZ installation, as all
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  Speaker 1: lines have their relays set to clear the line in
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  Speaker 1: a maximum time of zero point seven five second with
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  Speaker 1: a short at the far end. If the short takes
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  Speaker 1: place add or near the relay, the short is cleared
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  Speaker 1: almost instantaneously since the voltage restrained action is zero. The
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  Speaker 1: other relays on the system are restrained in proportion to
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  Speaker 1: their distance from the short and accordingly do not open
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  Speaker 1: their breakers. Type CA relays should be used for the
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  Speaker 1: differential protection of the three generators. It should be understood
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  Speaker 1: that definite current in time settings and final checks on
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  Speaker 1: the relay operation can be made only after a short
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  Speaker 1: circuit study of the system has been made, thus determining
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  Speaker 1: the actual currents which will flow in different lines with
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  Speaker 1: faults at the different locations. After this information is available,
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  Speaker 1: the proper current transformer ratios in current taps on the
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  Speaker 1: relays may be specified, and with the time setting assumed,
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  Speaker 1: the exact time of operation may be found from the
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  Speaker 1: relay time current curve. End of Chapter seven