Latest / Silent Sentinels- Protective Relays for A-C and D-C Systems / 012 - Westinghouse Protective and Control Relays Part 2

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012 - Westinghouse Protective and Control Relays Part 2 · Silent Sentinels- Protective Relays for A-C and D-C Systems

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  Speaker 1: Chapter nine, Part two of Silent Sentinels by Westinghouse Electric
• 0:08
  Speaker 1: and Manufacturing Company. This lipribox recording is in the public
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  Speaker 1: domain Westinghouse Protective and Control Relays two direct current relays.
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  Speaker 1: Installations where direct current is employed are so few and
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  Speaker 1: small in size as compared with the present day alternating
• 0:36
  Speaker 1: current installations that their importance is sometimes overlooked. It must
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  Speaker 1: be remembered that there are still many applications where alternating
• 0:46
  Speaker 1: current cannot be used, or at least where no means
• 0:50
  Speaker 1: have yet been devised for using it instead of direct current.
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  Speaker 1: On such installations. Therefore, it is important to have depend
• 1:00
  Speaker 1: relay service as protection against overcurrent, reverse current, and other
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  Speaker 1: sources of trouble. Type D overcurrent relay. This type serves
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  Speaker 1: to furnish protection against overcurrent in direct current circuits. The
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  Speaker 1: relay is of the moving coil type with an electro
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  Speaker 1: magnet energized by a voltage winding. The winding on the
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  Speaker 1: moving coil is connected across a shunt in series with
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  Speaker 1: the line, and in this way receives a current proportional
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  Speaker 1: to the current flowing in the circuit to be protected.
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  Speaker 1: The moving contact is carried by the moving coil and
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  Speaker 1: is held open by the action of a spring. The
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  Speaker 1: torque produced by current flowing in the coil opposes the
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  Speaker 1: action of this spring, and when the current reaches any
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  Speaker 1: predetermined value, the opposing action of the spring is overcome
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  Speaker 1: and the contacts are closed. The electromagnet field is highly saturated,
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  Speaker 1: and thus the action of the relay is unaffected by
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  Speaker 1: voltage changes. The overcurrent relay may be adjusted to operate
• 2:15
  Speaker 1: over a range with from forty to eighty millivolts impressed
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  Speaker 1: upon the winding type D reverse current relay conditions are
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  Speaker 1: often such that a reversal in the direction of current
• 2:30
  Speaker 1: flow may prove very disastrous. For example, it requires a
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  Speaker 1: very small percentage of normal folow current to cause a
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  Speaker 1: rotary converter to run away when running inverted. A slight
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  Speaker 1: modification of the D overcurrent relay makes its service a
• 2:49
  Speaker 1: highly sensitive reverse current relay applicable for protection against such conditions.
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  Speaker 1: The moving coil used in the D reverse current relay
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  Speaker 1: is such that approximately two millivolts will cause the contacts
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  Speaker 1: to close. This tripping value may be adjusted to a
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  Speaker 1: smaller amount by changing the relative position of the moving
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  Speaker 1: and stationary contacts. By using shunts of different capacities in
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  Speaker 1: series with the line to be protected, Almost any sensitivity
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  Speaker 1: required can be obtained. For example, suppose the relay is
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  Speaker 1: set to operate on one milli volt drop in a
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  Speaker 1: given direction and is connected to one hundred millivolte shunt.
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  Speaker 1: It will then trip when approximately one percent of bull
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  Speaker 1: load current is flowing in the reverse direction. Type TO
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  Speaker 1: overcurrent relay. The TO relay serves practically the same purpose
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  Speaker 1: as the T over current relay, except that its action
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  Speaker 1: is not as sensitive and its construction is such that
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  Speaker 1: it can be supplied at a lower price. The relay
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  Speaker 1: consists of a two pole electromagnet serving to attract a
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  Speaker 1: pivoted armature against the pool of a pelical spring. The
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  Speaker 1: tension of the spring determines the tripping point of the relay.
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  Speaker 1: The relay is suitable for use with a fifty millible
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  Speaker 1: shunt and may be adjusted to close contacts on from
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  Speaker 1: forty to eighty millivals Type m F flash relay. The
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  Speaker 1: flashing over of commutators on rotary converters has been the
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  Speaker 1: source of much trouble in the past, and although the
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  Speaker 1: improvement of modern design has eliminated the possibility of such occurrences,
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  Speaker 1: to some extent, the trouble still exists. The MF relay
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  Speaker 1: has been developed for the purpose of instantly disconnecting a
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  Speaker 1: machine upon the occurrence of a flash over. The MF
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  Speaker 1: relay operates by having an armature attraction close its contacts.
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  Speaker 1: The coil serving to attract the armature is connected directly
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  Speaker 1: between the frame of the machine and the ground. As
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  Speaker 1: flashovers usually occur between insulated circuits and the frame of
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  Speaker 1: the machine, this arrangement will give immediately a flow of
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  Speaker 1: current to ground through the relay coil, which acts almost
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  Speaker 1: instantaneously to disconnect the machine from the line. The action
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  Speaker 1: of the MF relay is so fast that with the
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  Speaker 1: ordinary flashover, the machine will be disconnected before other protective
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  Speaker 1: relays farther back on the system have time to operate,
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  Speaker 1: thus cutting out on the machine without disturbing the rest
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  Speaker 1: of the system. Its speed also aids in disconnecting the
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  Speaker 1: machine before any great damage has been done, type a
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  Speaker 1: polarity directional relay. In many electrochemical processes, a current reversal,
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  Speaker 1: even of small magnitude is serious, in many cases, serious
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  Speaker 1: enough to cause considerable damage. Such conditions give reasons for
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  Speaker 1: the development of a relay to prevent any reversal of polarity.
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  Speaker 1: The type A polarity directional relay fills the requirements for
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  Speaker 1: such protection and is applicable also to other uses where
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  Speaker 1: a check on the direction of polarity is desired. The
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  Speaker 1: relay consists of a polarized electromagnet serving to attract the
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  Speaker 1: soft iron armature the one polar The permanent magnet consists
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  Speaker 1: of two steps, upon which are placed the two coils
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  Speaker 1: of the relay. The relative action of the current flowing
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  Speaker 1: in these coils with respect to the pole of the
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  Speaker 1: permanent magnet on the soft armature determines the operation of
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  Speaker 1: the relay. Its sensitivity and design are such that the
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  Speaker 1: context will be closed upon any reversal polarity of the
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  Speaker 1: circuit to which it is connected, and upon the fall
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  Speaker 1: of the voltage to below twenty percent of normal upon
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  Speaker 1: the occurrence of an open circuit in the relay winding itself.
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  Speaker 1: Action of the relay is assured before any voltage has
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  Speaker 1: built up in the reverse direction. Type t V voltage relay,
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  Speaker 1: wherever it is desired to protect direct current circuits against
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  Speaker 1: excessive over voltage or under voltage a slight modification to
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  Speaker 1: the t V overcurrent relay may be used. The too
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  Speaker 1: overcurrent relay with the coils wound for voltage constitutes the
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  Speaker 1: TV voltage relay and is applicable for such voltage protection.
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  Speaker 1: Three temperature relays type h M bearing thermostat relays type
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  Speaker 1: HM relays are designed for use in protecting the bearings
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  Speaker 1: of rotating machinery from the disastrous effects of overheating. With
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  Speaker 1: this relay installed, it is unnecessary to have constant supervision
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  Speaker 1: of the bearings of rotating machinery. This relay is particularly
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  Speaker 1: valuable in automatic substation work. The action of the thermostat
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  Speaker 1: is largely mechanical. It consists of the operation of a
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  Speaker 1: toggle switch by means of the ex expansion of a bellos.
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  Speaker 1: The thermostat unit consists of a bulb which is to
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  Speaker 1: be embedded in the bearing, the connecting tube, and the
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  Speaker 1: expansion bellos. As the temperature of the material in which
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  Speaker 1: the bulb is embedded rises, the liquid enclosed in the
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  Speaker 1: bulb and bellows moollatizes and thus creates a pressure, causing
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  Speaker 1: the bellows to expand lengthwise. This expansion serves, in turn
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  Speaker 1: to operate the toggle switch thereby closing the contexts of
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  Speaker 1: the relay. The relay usually is made to operate at
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  Speaker 1: one hundred degrees, but different thermal elements having the temperature
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  Speaker 1: of operation seventy degrees, ninety degrees or one hundred degrees
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  Speaker 1: centigrade may be supplied Type H N grid thermostat. A
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  Speaker 1: slight modification of the HM thermostat is used for the
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  Speaker 1: protection of grid resistors from damage due to overload or
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  Speaker 1: to sustain short circuits on the system. The construction of
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  Speaker 1: this relay is largely the same as the HM, with
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  Speaker 1: the exception of the manner of resetting. This HN relay
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  Speaker 1: resets automatically, whereas the HM relay has to be reset
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  Speaker 1: by hand. The thermal element supplied with the HN relay
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  Speaker 1: is also somewhat different, giving operation at either one hundred
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  Speaker 1: and fifty degrees centigrade or three hundred degrees centigrade Type
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  Speaker 1: CT temperature relay. The problem of protecting electrical apparatus against
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  Speaker 1: over temperature presents many difficulties. The object in any such
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  Speaker 1: protective apparatus is to allow the protected machine to remain
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  Speaker 1: in service as long as it is safe to do so,
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  Speaker 1: and yet to disconnect it from the source of power
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  Speaker 1: as soon as the temperature becomes unsafe for further operation.
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  Speaker 1: In order to obtain the most efficient protection, a relay
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  Speaker 1: used for this purpose must take into consideration the ambient temperature,
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  Speaker 1: the speed with which the windings of the apparatus heat
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  Speaker 1: up when subjected to overload, and the conditions existing when
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  Speaker 1: the temperature of the machine becomes dangerously high. The CT
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  Speaker 1: temperature relay is applicable on alternating current circuits where the
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  Speaker 1: apparatus is so arranged that exploring coils can be installed
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  Speaker 1: in the windings. It operates on the wheatstone bridge principle,
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  Speaker 1: the moving part operating on the induction principle. The relay
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  Speaker 1: in its appearance is similar to the type co over
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  Speaker 1: current relay. The lower coil is directly connected to a
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  Speaker 1: current transformer in one lead of the machine which is
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  Speaker 1: to be protected. The upper coils are connected across the
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  Speaker 1: two points of the bridge arrangement to which the galvanometer
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  Speaker 1: is ordinarily connected. Two permanent resistance units mounted in the
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  Speaker 1: relay case serve for two arms of the bridge, while
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  Speaker 1: two copper exploring coils embedded in the winding of the
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  Speaker 1: apparatus to be protected served for the other two arms.
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  Speaker 1: The points of the bridge opposite those connected to the
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  Speaker 1: upper coils, are connected to the current transformer in parallel
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  Speaker 1: with the lower coil of the relay. The resistances of
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  Speaker 1: the different arms of the bridge are so arranged that
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  Speaker 1: at normal operating temperature, no current flows through the upper
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  Speaker 1: winding of the relay. When the apparatus becomes heated, however,
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  Speaker 1: the resist distance of the arm formed by the exploring
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  Speaker 1: coil changes, thus destroying the balance and causing current to
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  Speaker 1: flow through the upper coils of the relay. This produces
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  Speaker 1: a torque tending to rotate the disks and to close
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  Speaker 1: the contexts. As it is necessary to have a certain
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  Speaker 1: quantity of current flowing in both the upper and lower
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  Speaker 1: coils of the relay before the disc will rotate to
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  Speaker 1: close the contexts. The operation of the relay depends upon
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  Speaker 1: three conditions. One, the temperature of the material surrounding the
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  Speaker 1: coils must be such as to cause an unbalanced sufficient
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  Speaker 1: to send current through the upper coils of the relay. Two,
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  Speaker 1: the current flowing in the line at that time must
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  Speaker 1: be such as to give a sufficient current value in
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  Speaker 1: the lower coil of the relay. Three, heat that has
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  Speaker 1: been generated in previous overload but then has not yet
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  Speaker 1: been dissipated, tends to influence the temperature of the exploring
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  Speaker 1: coil type DT temperature relay. The DT temperature relay is
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  Speaker 1: simply a modification of the D over current relay used
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  Speaker 1: in connection with a wheatstone bridge. Its use is similar
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  Speaker 1: to that of the CT relay, except that the DT
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  Speaker 1: depends altogether on direct current for its operation and does
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  Speaker 1: not take into consideration the current flowing at the time
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  Speaker 1: when a critical temperature is attained, as in the case
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  Speaker 1: of the CT relay. The operating coil replaces the governometer
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  Speaker 1: connection in the bridge circuit. The two opposite points of
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  Speaker 1: the bridge are connected across the constant direct current source
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  Speaker 1: of voltage. The two opposite points of the bridge are
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  Speaker 1: connected across a constant direct current source of voltage. Three
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  Speaker 1: arms of the bridge are made up of fixed resistance,
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  Speaker 1: while a fourth arm consists of a copper exploring coil
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  Speaker 1: embedded in the winding of the apparatus to be protected.
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  Speaker 1: The resistance values of the arms of the bridge are
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  Speaker 1: so proportioned that when the temperature of the apparatus reaches
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  Speaker 1: a safe operating point, there is no appreciable current flowing
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  Speaker 1: through the relay moving coil winding. With a low temperature
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  Speaker 1: in the winding of the apparatus, current will flow through
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  Speaker 1: the relay coil in one direction, and with a high
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  Speaker 1: temperature current will flow in the other direction. Thus, with
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  Speaker 1: low temperature contact is made in one direction, while with
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  Speaker 1: high temperature contact is made in the opposite direction. From this,
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  Speaker 1: it is evident that the operation the relay depends solely
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  Speaker 1: on the temperature of the windings in the apparatus, leaving
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  Speaker 1: out the consideration of the current drawn by the apparatus
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  Speaker 1: at the time the critical temperature is reached. This relay,
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  Speaker 1: therefore is applicable wherever a constant source of direct current
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  Speaker 1: voltage is available and where the load conditions may be disregarded.
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  Speaker 1: Type B A and B D oil filled thermal relays.
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  Speaker 1: Another type of temperature relay which does not require the
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  Speaker 1: use of exploring coils embedded in the windings of the
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  Speaker 1: apparatus to be protected, has been developed. This type depends
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  Speaker 1: upon the expansion of a bimetal element. The element has
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  Speaker 1: characteristics such that it heats up at the same rate
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  Speaker 1: as the windings of the apparatus to be protected. In
• 16:58
  Speaker 1: order to further duplicate take the temperature rise of the
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  Speaker 1: protected apparatus. The bimetallic element is immersed in oil, and
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  Speaker 1: the walls of the container are such that the dissipation
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  Speaker 1: of heat will be approximately the same as in the
• 17:14
  Speaker 1: case of the apparatus to be protected. The operation of
• 17:18
  Speaker 1: the relay is simple. When the bimetallic element heats to
• 17:22
  Speaker 1: a certain temperature, it expands sufficiently to operate the relay,
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  Speaker 1: closing its contexts. The BA relay is suitable for use
• 17:33
  Speaker 1: on alternating current circuits. The BD relay is suitable for
• 17:39
  Speaker 1: use on direct current circuits. It is similar to the
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  Speaker 1: BA relay in construction and operation. A cartridge type of relay,
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  Speaker 1: which is not oil filled, is made suitable for either
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  Speaker 1: alternating current or direct current application where high precision is
• 17:59
  Speaker 1: unnecess The operation of the cartridge type relay is dependent
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  Speaker 1: on the expansion of a bimetallic element in the same
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  Speaker 1: way as that of the BA and BD relays, except
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  Speaker 1: that precautions are not taken in the relay to have
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  Speaker 1: its temperature rise identical in degree with that of the
• 18:19
  Speaker 1: rise in the protected apparatus. Four auxiliary relays. In the
• 18:26
  Speaker 1: design of relays, as with any other line of apparatus,
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  Speaker 1: it is desirable to adhere to the simplest plan possible.
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  Speaker 1: Many relay applications require only a single simple contact arrangement,
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  Speaker 1: while others require a more or less complex scheme of
• 18:45
  Speaker 1: interconnected contexts. Rather than complicate the design of any one
• 18:51
  Speaker 1: type of relay to take care of these more complex applications,
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  Speaker 1: several different relays are sometimes used to accomplish the purpose designed.
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  Speaker 1: In such applications, one relay is usually responsible for starting
• 19:06
  Speaker 1: a sequence of contact operations. This is termed the main
• 19:10
  Speaker 1: or primary relay of the application. The other relays simply
• 19:15
  Speaker 1: service contactors, their coil or coils being energized by the
• 19:20
  Speaker 1: action of the primary relay. These relays are termed auxiliary
• 19:25
  Speaker 1: control relays type BT transfer relay. In most relay applications,
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  Speaker 1: where the relay serves to energize the trip coil of
• 19:38
  Speaker 1: a circuit breaker, direct current is used as the source
• 19:41
  Speaker 1: of energy for the trip coil. In some cases, however,
• 19:46
  Speaker 1: it is desired to use alternating current taken from the
• 19:50
  Speaker 1: current transformer to which the relay windings are connected. In
• 19:54
  Speaker 1: such cases, it is necessary to provide some contact arrangement
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  Speaker 1: whereby the secondary circuit of the current transformer will be
• 20:04
  Speaker 1: closed at all times, and whereby the trip coil of
• 20:07
  Speaker 1: the circuit breaker will be simply inserted in series with
• 20:11
  Speaker 1: the transformer secondary when the relay operates. To energize the
• 20:15
  Speaker 1: trip coil, the BT transfer relay is used in connection
• 20:20
  Speaker 1: with the primary protective relays to accomplish this purpose. The
• 20:25
  Speaker 1: main winding of the relay is connected in series with
• 20:29
  Speaker 1: the secondary of the current transformer and the winding of
• 20:33
  Speaker 1: the primary relay and serves to hold the contacts in
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  Speaker 1: the normal position. When the primary relay closes, its contacts,
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  Speaker 1: the short circuit and auxiliary winding on the BT relay
• 20:47
  Speaker 1: and cause the contacts to operate and thereby cut the
• 20:50
  Speaker 1: trip coil of the breaker into the circuit. The design
• 20:53
  Speaker 1: of the contacts is such that when they are in
• 20:56
  Speaker 1: the normal position, the trip coil of the circuit breaker
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  Speaker 1: is mechanically and electrically isolated from the current transformer circuit.
• 21:06
  Speaker 1: The windings of the relay are designed to carry five
• 21:10
  Speaker 1: ampiers continuously, but during times of short circuit they may
• 21:16
  Speaker 1: be required to handle as much as one hundred or
• 21:19
  Speaker 1: two hundred ampiers. This can be done satisfactorily for a
• 21:24
  Speaker 1: short period of time type m C multi contact relay.
• 21:31
  Speaker 1: In the application of protective relays, it is often desirable
• 21:37
  Speaker 1: to have several circuits energized at the time the primary
• 21:42
  Speaker 1: relay operates. As most of the standard protective relays close
• 21:48
  Speaker 1: only one or two circuits when they operate, auxiliary relays
• 21:53
  Speaker 1: are necessary when it is essential to have more than
• 21:56
  Speaker 1: the two circuits closed. Another case one auxiliary relay is
• 22:02
  Speaker 1: needed is when the current required in the control circuit
• 22:06
  Speaker 1: which is to be closed by the action of the
• 22:08
  Speaker 1: primary relay is greater than the context of the primary
• 22:12
  Speaker 1: relay can safely handle, as in the case of the
• 22:16
  Speaker 1: multiple circuit requirements. Auxiliary relays are used to accomplish this purpose,
• 22:23
  Speaker 1: the relay winding being energized by the closure of the
• 22:26
  Speaker 1: primary relay contacts. The MC multiple contact relay fills either
• 22:33
  Speaker 1: of the purposes just described and is used also in
• 22:37
  Speaker 1: many other control installations where a simple multiple contactor is required.
• 22:43
  Speaker 1: Its design is simple and such that it is suitable
• 22:47
  Speaker 1: for operation either on alternating current or direct current circuits,
• 22:52
  Speaker 1: and may be allowed to remain energized continuously. The action
• 22:58
  Speaker 1: of the relay is positive and windings may be supplied
• 23:02
  Speaker 1: which are suitable for various values of alternating current or
• 23:06
  Speaker 1: direct current voltage. There are also a variety of contact
• 23:11
  Speaker 1: arrangements which may be supplied. Thus, standard contact arrangements are
• 23:16
  Speaker 1: first four independent makes second three makes one break all independent,
• 23:25
  Speaker 1: third two makes two breaks all independent, fourth one make
• 23:31
  Speaker 1: three breaks all independent, fifth five makes one brake all parallel,
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  Speaker 1: sixth one independent, make five parallel brakes, seventh four parallel
• 23:46
  Speaker 1: and one independent makes eighth six parallel makes Type M
• 23:53
  Speaker 1: multiple contact relay. The Type M relay is similar to them,
• 24:00
  Speaker 1: but is simpler. It is suitable for use only on
• 24:05
  Speaker 1: direct current and is intended only for intermitted service. This
• 24:10
  Speaker 1: relay is furnished with either two, four or six contacts,
• 24:15
  Speaker 1: the first having the independent and the last two the
• 24:18
  Speaker 1: parallel arrangement. Type MS banked Multi contact relay. The MS
• 24:27
  Speaker 1: relay consists of a group of ten different and distinct contactors,
• 24:32
  Speaker 1: similar to the MC assemblies, except that each contactor operates
• 24:38
  Speaker 1: only two contacts, or in other words, makes only two
• 24:43
  Speaker 1: complete circuits. The ten units are mounted in a neat case,
• 24:48
  Speaker 1: and the complete assembly is used on supervisory control systems
• 24:53
  Speaker 1: wherever it is necessary to insulate the low voltage telephone
• 24:57
  Speaker 1: equipment from the higher voltage power control circuit. The coils
• 25:03
  Speaker 1: of these contactors may be supplied for various values of voltage.
• 25:08
  Speaker 1: In the entire group of relays may be applied to
• 25:12
  Speaker 1: various applications wherever it is desirable to have a number
• 25:17
  Speaker 1: of contactors in as compact an arrangement as possible. Type
• 25:23
  Speaker 1: O line of auxiliary relays. The O line of auxiliary
• 25:29
  Speaker 1: relays is intended for miscellaneous switchboard and control use. Arrangement
• 25:35
  Speaker 1: usually is such that the auxiliary relays are energized by
• 25:40
  Speaker 1: protective or other primary relays, and they in turn energize
• 25:45
  Speaker 1: or deenergize any desired combination of circuits. They have instantaneous
• 25:51
  Speaker 1: time characteristics. The O relays are so designed that when
• 25:57
  Speaker 1: placed in a normal position and with the main coil deenergized,
• 26:02
  Speaker 1: they make a set of four contacts, and when in
• 26:06
  Speaker 1: the operated position, a second set of four contacts. The
• 26:11
  Speaker 1: interconnection between the four sets of contexts may be changed
• 26:16
  Speaker 1: so that a large number of circuit combinations are obtainable,
• 26:20
  Speaker 1: thus making the relay adaptable to a variety of applications.
• 26:26
  Speaker 1: There are four types of the O line of relays,
• 26:30
  Speaker 1: classified according to the method of resetting. Type OA. The
• 26:36
  Speaker 1: OA relay has a main operating coil only and resets
• 26:41
  Speaker 1: itself automatically as soon as the excitation is removed from
• 26:45
  Speaker 1: the main coil. Type OL. The OL relay has only
• 26:51
  Speaker 1: the main coil, but it has a latching mechanism which
• 26:55
  Speaker 1: latches the context in the operated position as soon as
• 27:00
  Speaker 1: the coil has been energized and holds them until the
• 27:04
  Speaker 1: latch mechanism is tripped by hand. Type OS. The OS
• 27:11
  Speaker 1: relay is equipped with a main coil to operate the relay,
• 27:16
  Speaker 1: and also an auxiliary coil which serves when energized, to
• 27:21
  Speaker 1: hold the context in the operated position after the main
• 27:26
  Speaker 1: coil has been deenergized. This type of relay resets automatically
• 27:32
  Speaker 1: if the holding coil is not energized, and otherwise resets
• 27:37
  Speaker 1: when the holding coil is deenergized. Type O X. The
• 27:43
  Speaker 1: OX relay is equipped with a maine coil and also
• 27:48
  Speaker 1: an auxiliary coil which is located similarly to that of
• 27:53
  Speaker 1: the OS relay. It has the latching mechanism so arranged
• 27:58
  Speaker 1: that when the relay operates, the contacts are locked in
• 28:02
  Speaker 1: the energized position until the latch is tripped either by
• 28:07
  Speaker 1: means of energizing the auxiliary coil or by hand coils,
• 28:13
  Speaker 1: which are suitable for operation on various alternating current and
• 28:17
  Speaker 1: direct current voltages may be supplied for the various types
• 28:21
  Speaker 1: of relays. On account of vibration, only the latching types
• 28:27
  Speaker 1: are satisfactory. On AC The contexts are of sturdy construction
• 28:33
  Speaker 1: and will carry ten ampiers continuously or will break five
• 28:38
  Speaker 1: ampiers at five hundred volts satisfactorily. Type g K long
• 28:45
  Speaker 1: time limit relay. It often is desirable to introduce a
• 28:51
  Speaker 1: time interval of considerable length between control switch operation, mechanical operation,
• 28:58
  Speaker 1: or factory process is where a series of operations occur
• 29:02
  Speaker 1: in sequence. A specific example of such application is in
• 29:07
  Speaker 1: the case of automatic railway substations, where various operations must
• 29:13
  Speaker 1: be correctly timed. The GK relay is used for this purpose.
• 29:20
  Speaker 1: It consists of a small motor driving a contact assembly
• 29:24
  Speaker 1: through a train of gears. The contacts of this relay
• 29:29
  Speaker 1: are carried on a drum connected to a worm gear.
• 29:33
  Speaker 1: This worm gear is engaged with the driving gear by
• 29:36
  Speaker 1: an electromagnet, either simultaneously with the starting of the motor
• 29:41
  Speaker 1: or at a certain definite interval after the motor has
• 29:45
  Speaker 1: been started. The GK relays may be supplied with a
• 29:50
  Speaker 1: time limit as high as forty minutes. Relays whose time
• 29:55
  Speaker 1: can be adjusted to from one to ten minutes can
• 29:58
  Speaker 1: be supplied on special orders. Type j M group nunciator.
• 30:06
  Speaker 1: Many features in electric service stations require operation indicators. To
• 30:12
  Speaker 1: satisfy this need, the Westinghouse Company has developed the Type
• 30:18
  Speaker 1: JM group annunciator, which comprises a group of twelve operation
• 30:23
  Speaker 1: indicators assembled in a glass covered case similar to that
• 30:27
  Speaker 1: of the Type MC relay. The twelve indicators are mounted
• 30:32
  Speaker 1: in four rows of three each and are all connected
• 30:36
  Speaker 1: in parallel. That is, each has one terminal stud for
• 30:41
  Speaker 1: one side of the line, and all the indicators are
• 30:44
  Speaker 1: connected to a thirteenth stud which goes on the other
• 30:48
  Speaker 1: side of the line. The indicators of this annunciator are
• 30:53
  Speaker 1: similar in appearance to the Type C operation indicators described
• 30:57
  Speaker 1: elsewhere in this book, but they differ for somewhat from
• 31:01
  Speaker 1: theasing construction. The target, which is made of non magnetic material,
• 31:06
  Speaker 1: is latched in place behind the front plate. When the
• 31:11
  Speaker 1: indicator coil is energized, the latch is pulled back, allowing
• 31:16
  Speaker 1: the operating spring to pull the target into view. All
• 31:20
  Speaker 1: indicators can be seen readily through the glass cover of
• 31:24
  Speaker 1: the relay. They are reset without removing the relay cover
• 31:29
  Speaker 1: by pulling a small knob which protrudes from the right
• 31:33
  Speaker 1: side front view of the relay case. There is a
• 31:37
  Speaker 1: separate reset knob for each roll of indicators, or four
• 31:41
  Speaker 1: for the relay. Portable phase indicator for use in making
• 31:47
  Speaker 1: relay connections in order to obtain correct operation. When connecting
• 31:54
  Speaker 1: a relay which requires both current and voltage connections to
• 31:59
  Speaker 1: a poly phase circuit, it is necessary to select the
• 32:03
  Speaker 1: current and voltage having a proper phase relation to each other.
• 32:08
  Speaker 1: One of the most convenient methods of checking such relay
• 32:12
  Speaker 1: connections is to use a Westinghouse phase indicator. The phase
• 32:17
  Speaker 1: indicator is a portable instrument built on the same principle
• 32:21
  Speaker 1: as is a power factor meter. However, the phase indicator
• 32:26
  Speaker 1: is calibrated to indicate degrees from zero to three hundred
• 32:31
  Speaker 1: and sixty instead of power factor percentages. It readily shows
• 32:37
  Speaker 1: the exact phase relation between any current and voltage to
• 32:41
  Speaker 1: which it may be connected. The phase indicator can also
• 32:46
  Speaker 1: be used to check the phase relation between two or
• 32:49
  Speaker 1: more currents. An example of such an application is the
• 32:54
  Speaker 1: checking of relay connections for differential protection. To select the
• 32:59
  Speaker 1: two current transformers, the secondaries of which should be connected together,
• 33:05
  Speaker 1: it is necessary only to select some voltage for uses
• 33:10
  Speaker 1: of reference, and then to measure the phase relation of
• 33:14
  Speaker 1: the different currents with respect to this reference voltage. End
• 33:20
  Speaker 1: of Chapter nine, Part two,