Latest / Silent Sentinels- Protective Relays for A-C and D-C Systems / 011 - Westinghouse Protective and Control Relays Part 1

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011 - Westinghouse Protective and Control Relays Part 1 · Silent Sentinels- Protective Relays for A-C and D-C Systems

• 0:01
  Speaker 1: Chapter nine, Part one of Silent Sentinels by Westinghouse Electric
• 0:09
  Speaker 1: and Manufacturing Company. This LibriVox recording is in the public domain.
• 0:17
  Speaker 1: Westinghouse Protective and Control Relays, Part one one. Alternating current
• 0:26
  Speaker 1: Relays type COO over current relay. The protective relay now
• 0:35
  Speaker 1: having the most universal application, is one that may be
• 0:40
  Speaker 1: used to disconnect circuits or apparatus when the current flowing
• 0:45
  Speaker 1: in the circuits or apparatus succeeds any given value. Such
• 0:50
  Speaker 1: a relay has a wide variety of uses. The most
• 0:55
  Speaker 1: common uses are applications to outgoing feeders, transmission lines generating
• 1:01
  Speaker 1: the substations, distribution feeders at substations, and to motor and
• 1:08
  Speaker 1: transformer circuits. A relay designed for such a diversity of
• 1:13
  Speaker 1: applications must have very reliable characteristics which will allow a
• 1:20
  Speaker 1: flexible adjustment for operation under all circumstances and conditions. In
• 1:27
  Speaker 1: verse time characteristics, the co over current relay embodies characteristics
• 1:36
  Speaker 1: which make it applicable to the widest variety of uses.
• 1:40
  Speaker 1: For over current protection. The relay is similar in operation
• 1:46
  Speaker 1: to thea watt hour meter. It operates on the induction principle,
• 1:52
  Speaker 1: the contacts being closed by the rotation of a disc.
• 1:57
  Speaker 1: It is necessary to have a certain quantity of current
• 2:01
  Speaker 1: flowing in the relay winding before the disc will begin
• 2:05
  Speaker 1: to rotate. After it once has been started. The speed
• 2:09
  Speaker 1: of rotation is proportional to the current flowing in the
• 2:13
  Speaker 1: winding until such current reaches an excessively high value. This
• 2:19
  Speaker 1: gives the relay an inverse time characteristic, or in other words,
• 2:24
  Speaker 1: the greater the current flowing in the relay winding, the
• 2:28
  Speaker 1: sooner the relay contexts will close. The design of the
• 2:33
  Speaker 1: relay and the action of the damping magnet are such
• 2:37
  Speaker 1: that the time of action is definite for any given
• 2:41
  Speaker 1: current value. Definite minimum time characteristics conditions arise in over
• 2:49
  Speaker 1: current protection, which demand that a relay used for such
• 2:55
  Speaker 1: a purpose should never close its contacts instantaneously. Because of
• 3:01
  Speaker 1: the inverse characteristics of the COO relay, it is evident
• 3:06
  Speaker 1: that upon excessive overcurrent, the action of the relay would
• 3:11
  Speaker 1: become almost instantaneous. A small torque compensator is added in
• 3:17
  Speaker 1: the relay winding for the purpose of placing a definite
• 3:21
  Speaker 1: limit to the inverse time characteristic. This compensator becomes saturated
• 3:29
  Speaker 1: at excessively high currents and acts upon the relay in
• 3:34
  Speaker 1: such a way that a definite minimum time must elapse
• 3:38
  Speaker 1: before the context will close, regardless of the value of
• 3:43
  Speaker 1: current flowing in the winding. This is termed the definite
• 3:48
  Speaker 1: minimum time characteristic of the relay current settings. Conditions very
• 3:56
  Speaker 1: often arise where the current supply uses for operating an
• 4:01
  Speaker 1: overcurrent relay varies widely due to different current transformer ratios,
• 4:07
  Speaker 1: different conditions under which the relay is desired to act,
• 4:12
  Speaker 1: and different degrees of sensitivity required in the relay. Such
• 4:18
  Speaker 1: an adjustment of operating current is obtained in the co
• 4:23
  Speaker 1: relay by varying the number of active terms in the
• 4:27
  Speaker 1: main coil winding. This is accomplished by means of a
• 4:32
  Speaker 1: screw in the terminal block at the top of the
• 4:36
  Speaker 1: relay element. The numbers on this terminal block represent the
• 4:41
  Speaker 1: minimum current which will operate the relay time settings. It
• 4:47
  Speaker 1: is also very often desired to vary the time in
• 4:51
  Speaker 1: which the contexts will close when any given amount of
• 4:55
  Speaker 1: current is flowing in the relay winding. This adjustment is
• 5:00
  Speaker 1: accomplished in the co relay by varying the distance through
• 5:04
  Speaker 1: which the disc must rotate before the contacts are closed.
• 5:09
  Speaker 1: This distance through which the disc must travel is adjusted
• 5:13
  Speaker 1: by means of the scale and hand lever located directly
• 5:18
  Speaker 1: above the disc. The time current curve shown on the
• 5:22
  Speaker 1: name plate of each relay gives the time required for
• 5:27
  Speaker 1: the context to close with different values of current flowing
• 5:32
  Speaker 1: in the relay winding with the time lever set on
• 5:35
  Speaker 1: the number ten graduation. It will be noted from this
• 5:40
  Speaker 1: curve that two seconds is the minimum time in which
• 5:44
  Speaker 1: the relay will close its contexts for any given value
• 5:48
  Speaker 1: of current, regardless of how great it may be. This
• 5:52
  Speaker 1: definite minimum time may be reduced, of course, by placing
• 5:58
  Speaker 1: the time lever on a smaller setting. For instance, if
• 6:02
  Speaker 1: the lever is placed on the number one graduation, the
• 6:07
  Speaker 1: action of the relay will be almost instantaneous, because the
• 6:12
  Speaker 1: disc has practically no distance through which it must rotate
• 6:16
  Speaker 1: before the contacts are closed. Contact troubles have always been
• 6:22
  Speaker 1: plentiful in relay operation. This source of trouble has been
• 6:27
  Speaker 1: largely eliminated from the co relay by introducing an auxiliary
• 6:33
  Speaker 1: contactor switch interconnected with the tripping contacts so that it
• 6:38
  Speaker 1: closes the instant the main relay contacts close. This arrangement
• 6:44
  Speaker 1: relieves the relay main contacts from carrying the tripping current,
• 6:49
  Speaker 1: and also assures good contact even though barely enough current
• 6:55
  Speaker 1: is flowing in the relay. Winding to close the main contacts.
• 7:00
  Speaker 1: The action of the contexts responsible for making the tripping
• 7:05
  Speaker 1: circuit is therefore made positive, and a tripping current of
• 7:11
  Speaker 1: its high as thirty ampiers may be safely handled without
• 7:16
  Speaker 1: fear of contact trouble type ca over current relay. In
• 7:25
  Speaker 1: many power plants and substations, the space for mounting instruments
• 7:31
  Speaker 1: and other switchboard apparatus is limited. In such stations, it
• 7:37
  Speaker 1: is often very essential also to have supervision over the
• 7:42
  Speaker 1: current flowing in each circuit leading out from the station.
• 7:46
  Speaker 1: A means of providing this current supervision and also relay
• 7:51
  Speaker 1: protection for each circuit without the necessity of supplying and
• 7:56
  Speaker 1: providing room for mounting both ammeters and relays, is provided
• 8:01
  Speaker 1: by the CoA relay. This relay consists of the co
• 8:08
  Speaker 1: relay with the addition of a current indicator, which serves
• 8:13
  Speaker 1: to show at all times the value of the current
• 8:16
  Speaker 1: flowing in the circuit. The current indicator consists of a
• 8:21
  Speaker 1: thin copper segment mounted on a separate shaft directly above
• 8:26
  Speaker 1: the main disc of the relay in such a way
• 8:29
  Speaker 1: that it is actuated by the same flux that passes
• 8:33
  Speaker 1: through the relay disc. As the relay winding is connected
• 8:38
  Speaker 1: directly in the circuit to be protected by means of
• 8:41
  Speaker 1: a current transformer, the current indicating element shows at all
• 8:47
  Speaker 1: times the quantity of current flowing in the line. The
• 8:51
  Speaker 1: current indicating element also gives a double protective assurance, inasmuch
• 8:58
  Speaker 1: as any accident which a curves either within or without
• 9:03
  Speaker 1: the relay to prevent the main electromagnet from operating the
• 9:07
  Speaker 1: relay disc will also keep the indicating disk from operating.
• 9:13
  Speaker 1: Low energy type COO relay. Certain relay applications are such
• 9:21
  Speaker 1: that only very little energy is available for operating the relay.
• 9:27
  Speaker 1: This is especially the case on high voltage lines, where
• 9:30
  Speaker 1: low ratio bushing type current transformers are the only convenient
• 9:35
  Speaker 1: means for supplying energy for the operation of relays or instruments.
• 9:42
  Speaker 1: A modification of the COO relay has been designed to
• 9:47
  Speaker 1: fit such conditions. This low energy co relay requires approximately
• 9:54
  Speaker 1: two volt ampiers for tripping. In construction and operation, it
• 10:00
  Speaker 1: is very similar to the standard COO relay, except that
• 10:05
  Speaker 1: the contacts are not closed directly by the action of
• 10:09
  Speaker 1: the disk, but through a train of gears. This train
• 10:13
  Speaker 1: of gears also supplies the definite minimum time characteristics, thus
• 10:19
  Speaker 1: eliminating the torque compensator. Due to the construction of the relay,
• 10:25
  Speaker 1: it is somewhat more sensitive than the other COO relays
• 10:30
  Speaker 1: and is therefore suitable for use on applications requiring great sensitivity.
• 10:36
  Speaker 1: The differential protection of generators is an example of this
• 10:41
  Speaker 1: type of application. Type c R directional relay. All relays
• 10:49
  Speaker 1: dependent on current alone for their operation function when sufficient
• 10:54
  Speaker 1: current is flowing in the winding regardless of the direction
• 10:58
  Speaker 1: of the flaw. In protecting transmission lines and in making
• 11:04
  Speaker 1: possible the sectionalizing of such lines on the occurrence of trouble,
• 11:10
  Speaker 1: it is often necessary to have protective relays which will
• 11:14
  Speaker 1: close their contacts only when current is flowing in one
• 11:18
  Speaker 1: certain direction. The CR relay has been developed to fill
• 11:23
  Speaker 1: these requirements. The CR directional relay is a combination of
• 11:30
  Speaker 1: the COO overcurrent relay and a watt element. The current
• 11:36
  Speaker 1: element is the same as that of the standard COO
• 11:40
  Speaker 1: overcurrent relay and has identical operating characteristics. The watt element
• 11:47
  Speaker 1: is similar to the CW power relay, except that it
• 11:51
  Speaker 1: operates on a very small percentage of normal voltage. The
• 11:56
  Speaker 1: contexts of the overcurrent element are connected in series with
• 12:00
  Speaker 1: the contexts of the watt element, and as this element
• 12:04
  Speaker 1: will close its contacts only when the power flows in
• 12:08
  Speaker 1: one direction, the relay as a unit operates only when
• 12:13
  Speaker 1: current is flowing in any given direction. As the relay
• 12:17
  Speaker 1: has all the characteristics of the COO relay, the following
• 12:22
  Speaker 1: conditions must exist before the tripping circuit is completed. One
• 12:28
  Speaker 1: access current must be flowing. Two current must be flowing
• 12:33
  Speaker 1: away from the bus bars or in the direction for
• 12:36
  Speaker 1: which the relay is connected. Three current must be flowing
• 12:41
  Speaker 1: for a sufficient length of time. Thus, the directional element
• 12:47
  Speaker 1: may close its contacts upon momentary surges of current in
• 12:53
  Speaker 1: the reverse direction, or the overcurrent element may close its
• 12:58
  Speaker 1: contacts on the flow of access current in the normal direction,
• 13:03
  Speaker 1: But the tripping circuit is completed only when both elements
• 13:07
  Speaker 1: close their contacts. Low energy type CR directional relay. The
• 13:15
  Speaker 1: low energy CR directional relay has been developed to be
• 13:20
  Speaker 1: used in the same way as the standard CR relay,
• 13:24
  Speaker 1: except that it is suitable where only a small quantity
• 13:28
  Speaker 1: of energy is available for the operation of the relay.
• 13:34
  Speaker 1: The low energy characteristic of the relay has been obtained
• 13:39
  Speaker 1: by substituting the low energy CO overcurrent element for the
• 13:44
  Speaker 1: standard CO overcurrent element. Thus, the low energy CR relay
• 13:50
  Speaker 1: has over current characteristics similar to those of the low
• 13:54
  Speaker 1: energy CO relay and directional element characteristics similar to those
• 14:00
  Speaker 1: of the standard CR relay type CRA relay. In cases
• 14:09
  Speaker 1: where it is desired to have an indication of the
• 14:12
  Speaker 1: current flowing in the circuit, the CoA overcurrent element has
• 14:17
  Speaker 1: been used in the CR relay in place of the
• 14:20
  Speaker 1: standard COO element. This makes a compact, convenient arrangement serving
• 14:27
  Speaker 1: the purpose of an AM meter without adding greatly to
• 14:30
  Speaker 1: the expense of installation or detracting it all from the
• 14:34
  Speaker 1: operating characteristics of the relay. Type c Z impedance distance relay.
• 14:43
  Speaker 1: On large complicated transmission systems, the method of sectionalizing by
• 14:49
  Speaker 1: means of overcurrent and directional relays is often difficult to
• 14:54
  Speaker 1: apply and sometimes even impossible. This is due to the
• 14:59
  Speaker 1: necessity have enpoint such a large number of relays that
• 15:04
  Speaker 1: it is impossible to keep the timing sequence within safe limits.
• 15:09
  Speaker 1: At times, it is impossible to secure proper discrimination at all,
• 15:16
  Speaker 1: especially in the case of a complicated loop which is
• 15:20
  Speaker 1: fed at several points and where the points of feed
• 15:24
  Speaker 1: change with load conditions. The Westinghouse Company has recently developed
• 15:31
  Speaker 1: a relay which overcomes all such difficulties experienced on large
• 15:37
  Speaker 1: and complicated systems. Its application does not supplant that of
• 15:43
  Speaker 1: the standard COO and CR relays, but makes protection possible
• 15:48
  Speaker 1: where otherwise it would be difficult or even impossible. The
• 15:53
  Speaker 1: only requisite is that with a short at the far
• 15:58
  Speaker 1: end of the line, the headen's drop in the line
• 16:01
  Speaker 1: should be at least three point zero percent of the
• 16:05
  Speaker 1: normal voltage. That is, the line must be of sufficient
• 16:10
  Speaker 1: length to give this drop. The c Z relay consists
• 16:15
  Speaker 1: of an overcurrent element and a voltage element. The overcurrent
• 16:21
  Speaker 1: element is similar to that of the CO relay. The
• 16:26
  Speaker 1: special feature of this relay is the construction of the
• 16:30
  Speaker 1: voltage element. The voltage element is so constructed that its
• 16:35
  Speaker 1: action in relation to the closing of the relay contexts
• 16:39
  Speaker 1: depends on the distance the relay is away from the fault.
• 16:44
  Speaker 1: In other words, the voltage element acts in opposition to
• 16:48
  Speaker 1: the overcurrent element, and when the relay is a considerable
• 16:53
  Speaker 1: distance from the fault, the voltage on the element is
• 16:57
  Speaker 1: comparatively high, thus lengthening the time required for the relay
• 17:03
  Speaker 1: to close its contacts. On the other hand, the relays
• 17:08
  Speaker 1: near the fault will have a very low voltage imposed
• 17:12
  Speaker 1: on the voltage element, thus causing the relay to operate
• 17:16
  Speaker 1: in much less time due to less opposition being offered
• 17:20
  Speaker 1: to the action of the overload element by the voltage element. Thus,
• 17:26
  Speaker 1: the relay that is nearest to the fault operates first,
• 17:31
  Speaker 1: and at no time does the time exceed zero point
• 17:35
  Speaker 1: seven five to one point zero second. For some applications,
• 17:41
  Speaker 1: it is necessary to restrain the relay from operating unless
• 17:47
  Speaker 1: the power is flowing in a given direction. To fill
• 17:51
  Speaker 1: such needs, a directional element similar to that of the
• 17:55
  Speaker 1: CR relay is added to the c Z relay. Type
• 18:00
  Speaker 1: CA ratio differential relay. The type CA ratio differential relay
• 18:09
  Speaker 1: is a current operated induction relay similar in appearance to
• 18:14
  Speaker 1: the type CO relay. As the name implies, it operates differentially,
• 18:22
  Speaker 1: but it differs from the relays usually used in that
• 18:25
  Speaker 1: the tripping current varies with the load. The current required
• 18:30
  Speaker 1: to trip the relay increases in proportion to the line
• 18:34
  Speaker 1: current instead of remaining constant for all load conditions. This
• 18:40
  Speaker 1: feature of the relay provides against faulty tripping due to
• 18:45
  Speaker 1: a combination of through short circuits and variations of current
• 18:50
  Speaker 1: transformer ratio, and allows the relay to be set for
• 18:54
  Speaker 1: close protection at normal loads. Other methods of differential protection
• 19:00
  Speaker 1: generally act on a difference of two currents, so that
• 19:04
  Speaker 1: a slight difference in current transformer ratios increased by heavy
• 19:09
  Speaker 1: loads or by through short circuits is often sufficient to
• 19:15
  Speaker 1: cause enough circulating current to operate the relay. The CA
• 19:20
  Speaker 1: relay is designed to avoid this trouble and will trip
• 19:25
  Speaker 1: out generators and motors on a trouble circuit as slow
• 19:29
  Speaker 1: as two point five percent of the line current without
• 19:34
  Speaker 1: danger of tripping them out on system troubles. For protection
• 19:39
  Speaker 1: of star delta transformer banks, Scott connected banks, or in
• 19:44
  Speaker 1: any case where the currents in the circuits to be
• 19:47
  Speaker 1: balanced are unequal, the relay is provided with taps so
• 19:53
  Speaker 1: that balancing auto transformers are unnecessary, as saving any expense
• 19:59
  Speaker 1: and in one switchboard space is made possible by the
• 20:03
  Speaker 1: provision of these taps. This relay is less sensitive than
• 20:09
  Speaker 1: that used for generator protection in order to get the
• 20:14
  Speaker 1: ratio feature of the relay. Both of the secondary currents
• 20:18
  Speaker 1: to be balanced, as well as the differential current are
• 20:22
  Speaker 1: used in the relay. A field proportional to the sum
• 20:27
  Speaker 1: of the currents reacts with the field proportional to their difference,
• 20:31
  Speaker 1: and the resultant field acts to produce rotation. The quadrature
• 20:36
  Speaker 1: flux is supplied to the upper poles by transformer windings
• 20:41
  Speaker 1: on each of the lower poles. Figure eighty seven show
• 20:45
  Speaker 1: schematically the connections of the CAA relay for the protection
• 20:49
  Speaker 1: of a generator. The arrows show the relative instantaneous directions
• 20:54
  Speaker 1: of current flow under normal conditions. If the currents supplied
• 20:59
  Speaker 1: by each tree transformer are equal, there will be no
• 21:02
  Speaker 1: current flowing Coil A. If the current transformers supply unequal currents,
• 21:08
  Speaker 1: the difference flows through coil A. The direction of current
• 21:13
  Speaker 1: in Coil A with respect to coil B does not
• 21:16
  Speaker 1: affect the tripping direction of the relay. The flux produced
• 21:21
  Speaker 1: by coil B tends to hold the relay open, and
• 21:25
  Speaker 1: that due to Coil A tends to trip the relay.
• 21:28
  Speaker 1: As the line currents increase, the torque holding the relay
• 21:32
  Speaker 1: open increases, and more torque and consequently, more current is
• 21:37
  Speaker 1: required to close it. The relay for generator protection is
• 21:42
  Speaker 1: provided with a tapped difference coil winding so that the
• 21:46
  Speaker 1: sensitivity may be varied readily. On the transformer relay, the
• 21:52
  Speaker 1: conditions are very similar, except that both the sum coil
• 21:56
  Speaker 1: and the difference coil windings are tapped in order to
• 22:00
  Speaker 1: compensate for the effect of unbalanced currents. The sensitivity cannot
• 22:06
  Speaker 1: be varied on this relay. The energy required to operate
• 22:11
  Speaker 1: the relays, particularly the transformer relay, is very small. This,
• 22:17
  Speaker 1: combined with the fact that the operating current increases in
• 22:21
  Speaker 1: proportion to the line currents, makes the relays very adaptable
• 22:26
  Speaker 1: to conditions requiring the use of bushing type current transformers.
• 22:32
  Speaker 1: When greater sensitivity is required, as in the case of
• 22:37
  Speaker 1: the generator relay, the burden of the relay is somewhat greater,
• 22:42
  Speaker 1: but under these conditions the current transformers used are of
• 22:46
  Speaker 1: higher grade and the load is well within the capacity
• 22:50
  Speaker 1: of the current transformers. The relay is very rugged. There
• 22:55
  Speaker 1: are no adjustments to get out of order and no
• 22:59
  Speaker 1: delicateche panical parts to give trouble. The contexts are set
• 23:04
  Speaker 1: well out in front where they can be seen through
• 23:06
  Speaker 1: the glass cover and where they are easily accessible for
• 23:11
  Speaker 1: adjustments or repair. All the relays are provided with two
• 23:15
  Speaker 1: trip circuits and an operation indicator and contact or switch.
• 23:20
  Speaker 1: As in the CO relay type C B over current relays.
• 23:27
  Speaker 1: The cost of the current transformers used with relays often
• 23:32
  Speaker 1: forms a considerable part of the entire cost. Where the
• 23:37
  Speaker 1: current transformers must be connected to high voltage circuits, they
• 23:42
  Speaker 1: must be insulated for the high voltages and their cost
• 23:46
  Speaker 1: is high. The CB relay has been designed for use
• 23:50
  Speaker 1: on high voltage installations. It is a combination of the
• 23:55
  Speaker 1: CO overcurrent relay and the BT transfer relay with the
• 24:00
  Speaker 1: addition of a special contactor switch. A standard transformer is
• 24:05
  Speaker 1: used without regard to insulation for the high voltage line,
• 24:10
  Speaker 1: and the CO relay element is connected in the usual manner.
• 24:14
  Speaker 1: The COO and BT relays, however, with the current transformer
• 24:20
  Speaker 1: are mounted on a slate base which is mounted on
• 24:24
  Speaker 1: an insulator. The contactor switch is separate from this assembly
• 24:29
  Speaker 1: and is connected to the BT relay by means of
• 24:33
  Speaker 1: a Makarta chain. Thus, the tripping circuit is insulated from
• 24:37
  Speaker 1: the high voltage circuit, which is to be protected when
• 24:41
  Speaker 1: the CO relay contacts close they serve to operate the
• 24:45
  Speaker 1: BT transfer relay. This relay, in turn, by means of
• 24:50
  Speaker 1: the Macarta chain, closes the tripping circuit contactor switch. The
• 24:55
  Speaker 1: operating characteristics of the CB relay are the same as
• 25:00
  Speaker 1: those of the standard CO relay type CD selective differential relay.
• 25:08
  Speaker 1: Balanced current protection is very often desired where two or
• 25:13
  Speaker 1: more similar transmission lines are used to connect two stations
• 25:18
  Speaker 1: or two different points in a system. Balance current protection
• 25:22
  Speaker 1: on such lines means that each line normally carries approximately
• 25:27
  Speaker 1: the same current, and if this condition does not exist,
• 25:31
  Speaker 1: the line carrying the greater current must be in fault.
• 25:35
  Speaker 1: The CD relay furnishes a simple method of securing such protection.
• 25:42
  Speaker 1: It avoids the necessity for any special apparatus such as
• 25:47
  Speaker 1: split conductor cable, and as it operates on current alone,
• 25:52
  Speaker 1: potential connections or potential transformers are not required. The relay
• 25:58
  Speaker 1: operates on the induction principle and is in reality two
• 26:02
  Speaker 1: overload elements so located that they act in opposition upon
• 26:07
  Speaker 1: a common disc through a common magnetic circuit. Each element
• 26:12
  Speaker 1: is connected separately to its own current transformer and to
• 26:16
  Speaker 1: corresponding phases of the two lines that are to be protected.
• 26:21
  Speaker 1: These two elements are electrically opposed and under conditions a
• 26:26
  Speaker 1: balanced line load, which will give approximately the same current
• 26:31
  Speaker 1: in each element. The fluxes in the magnetic circuit of
• 26:35
  Speaker 1: the relay are equal and opposite, giving a resultant zero
• 26:39
  Speaker 1: torque in the relay disc. When a fault occurs in
• 26:43
  Speaker 1: either line, however, the current in that line will become greater,
• 26:48
  Speaker 1: and the unbalanced will cause the relay to operate, tripping
• 26:52
  Speaker 1: out the line in which the greater current is flowing.
• 26:56
  Speaker 1: The CD relay has inverse time time characteristics and also
• 27:02
  Speaker 1: a definite minimum time of operation with excessive overcurrent. The
• 27:07
  Speaker 1: inherent characteristics of the relay are such that when one
• 27:11
  Speaker 1: line of a pair is tripped out, double the normal
• 27:14
  Speaker 1: current is required in the other line before it will
• 27:18
  Speaker 1: be tripped out, thus making it possible for one of
• 27:21
  Speaker 1: a pair of protected lines to be open and the
• 27:25
  Speaker 1: other line to carry its load without interference from the relay.
• 27:30
  Speaker 1: Any number of lines may be balanced against one another,
• 27:34
  Speaker 1: but the tripping out of certain lines in a group
• 27:38
  Speaker 1: will necessarily destroy the balance connection between the remaining lines.
• 27:44
  Speaker 1: The CD relay has the same current adjustment and time
• 27:47
  Speaker 1: adjustment as that of the CO relay. The time adjustment is, however,
• 27:53
  Speaker 1: seldom of importance inasmuch as the relays usually are designed
• 27:58
  Speaker 1: to operate almost instantaneous. Yes type CW power relay. In
• 28:05
  Speaker 1: many instances, a motor is so connected to its load that,
• 28:09
  Speaker 1: under certain conditions, the load may drive the motor, causing
• 28:13
  Speaker 1: it to act as a generator. A mine hoist driven
• 28:17
  Speaker 1: by an induction motor is a good example of such
• 28:20
  Speaker 1: an installation. In such cases, it is sometimes necessary to
• 28:26
  Speaker 1: provide some sort of protection to ensure against having the
• 28:30
  Speaker 1: motor return too much power to the line when it
• 28:33
  Speaker 1: is being driven as a generator. The CW power relay
• 28:38
  Speaker 1: serves this purpose. It is also often used to prevent
• 28:42
  Speaker 1: undesirable or excessive interchange of power between parts of a system,
• 28:48
  Speaker 1: as in the case of a small plant connected in
• 28:51
  Speaker 1: parallel with a larger plant, where some means must be
• 28:55
  Speaker 1: provided to prevent the small plant from being subjected to
• 28:58
  Speaker 1: the entire load of the system should the larger plant
• 29:02
  Speaker 1: be suddenly disconnected. The CW relay is essentially a contact
• 29:08
  Speaker 1: making watt meter. It operates on the induction principle and
• 29:13
  Speaker 1: is similar to the CO relay, except that it requires
• 29:17
  Speaker 1: both current and potential connections. It closes its context in
• 29:22
  Speaker 1: but one direction and only after a predetermined time when
• 29:27
  Speaker 1: a predetermined quantity of power is flowing in a predetermined direction.
• 29:32
  Speaker 1: Which direction may be either the normal or the reverse
• 29:35
  Speaker 1: according to the way the relay is connected. The relay
• 29:40
  Speaker 1: has a standard time adjustment in also taps for changing
• 29:43
  Speaker 1: the wattage values necessary to trip the relay type CV
• 29:49
  Speaker 1: voltage relay. The CV relay is designed for general use
• 29:55
  Speaker 1: when it is desired to have circuits or apparatus protected
• 29:59
  Speaker 1: against voltage changes of any predetermined value. It operates to
• 30:04
  Speaker 1: close a circuit, either for the purpose of disconnecting the
• 30:07
  Speaker 1: apparatus or of actuating a signal. The time delay characteristic
• 30:13
  Speaker 1: of the relay is used also in many applications where
• 30:17
  Speaker 1: a timing device is desired. In these applications, the relay
• 30:22
  Speaker 1: is used to close the circuit after a predetermined interval
• 30:26
  Speaker 1: when the relay winding is energized. This relay is similar
• 30:31
  Speaker 1: in appearance to the CO relay and operates on the
• 30:35
  Speaker 1: same principle. The chief difference between the two types is
• 30:39
  Speaker 1: that the CVE relay operates on voltage, whereas the CO
• 30:44
  Speaker 1: relay operates on current. The latest design of the CVE
• 30:49
  Speaker 1: relay is provided with a voltage adjustment by means of
• 30:53
  Speaker 1: which the operating voltage can be adjusted over a wide range.
• 31:00
  Speaker 1: Justment consists of a slide wire resistor connected in the
• 31:04
  Speaker 1: upper pole circuit of the relay. The resistor is provided
• 31:09
  Speaker 1: with a calibrated scale so that the relay can be
• 31:12
  Speaker 1: readily set to close its contexts at the desired voltage value.
• 31:17
  Speaker 1: The time adjustment of the relay is identical with that
• 31:21
  Speaker 1: of the CO relay. One form of the CV relay
• 31:26
  Speaker 1: closes its context only when the voltage is raised to
• 31:30
  Speaker 1: the operating point or above, and another form closes its
• 31:35
  Speaker 1: context only when the voltage is lowered to the operating
• 31:39
  Speaker 1: point or below that value. These two forms are called
• 31:44
  Speaker 1: over voltage and under voltage relays, respectively. A third form
• 31:50
  Speaker 1: is equipped with the front and rear contexts, the front
• 31:53
  Speaker 1: context closed when the voltage is raised above the operating value,
• 31:58
  Speaker 1: and the rear context close when the voltage is lowered
• 32:02
  Speaker 1: somewhat below that point. When a relay having a long
• 32:06
  Speaker 1: time delay is desired, it is possible to supply a
• 32:11
  Speaker 1: CV relay with a geared element similar to that of
• 32:15
  Speaker 1: the low energy CO relay. With this relay, a time
• 32:21
  Speaker 1: delay of as much as sixty seconds can be obtained
• 32:25
  Speaker 1: type CP reverse phase relay. In many motor installations, it
• 32:32
  Speaker 1: is very essential that the direction of rotation of the
• 32:35
  Speaker 1: motor always be in a given direction. This applies particularly
• 32:40
  Speaker 1: to motors used in connection with control equipment, or for
• 32:44
  Speaker 1: motors used for operating elevators, pulleys, conveyors, cranes, machine tools,
• 32:51
  Speaker 1: et cetera. The reversal of phase rotation in a polyphase
• 32:55
  Speaker 1: system caused by the reversal of two wires, although not
• 33:00
  Speaker 1: of frequent occurrence yet, is liable to happen at any
• 33:04
  Speaker 1: time when lines are being changed or repaired. Such a
• 33:09
  Speaker 1: reversal a phase rotation means a reversal in the direction
• 33:13
  Speaker 1: of rotation of all polyphase motors connected to the line.
• 33:18
  Speaker 1: The CP reverse phase relay serves to protect against such occurrences.
• 33:24
  Speaker 1: It operates upon phase reversal or when any one phase
• 33:28
  Speaker 1: of a polyphase circuit opens. In case of a phase reversal,
• 33:33
  Speaker 1: the relay may serve to disconnect the motors from the circuit. However,
• 33:39
  Speaker 1: in case of one phase opening, with polyphase motors operating
• 33:43
  Speaker 1: on the system, the relay will not operate until the
• 33:46
  Speaker 1: motors have been stopped. Due to the fact that practically
• 33:50
  Speaker 1: normal voltage is maintained on all phases by the motor.
• 33:54
  Speaker 1: The relay will operate, however, as soon as the machines
• 33:58
  Speaker 1: are stopped, thus prem from being again started. The CP
• 34:04
  Speaker 1: relay operates on the induction principle and has two windings,
• 34:10
  Speaker 1: each of which is energized from a separate phase. The
• 34:14
  Speaker 1: construction of the moving element is such that the disc
• 34:18
  Speaker 1: is maintained in its normal position, with the contexts opened
• 34:22
  Speaker 1: by the torque produced by the two windings. In case
• 34:27
  Speaker 1: either winding is deenergized or the direction of current in
• 34:31
  Speaker 1: one winding is reversed, the torque becomes zero or is reversed,
• 34:36
  Speaker 1: and the context are closed by the reversed torque or
• 34:40
  Speaker 1: the action of a spring. As the relay operates on
• 34:44
  Speaker 1: the induction principle and the closing of the context depends
• 34:48
  Speaker 1: on the rotation of the disc, a time delay action
• 34:52
  Speaker 1: is produced when the relay operates on low or unbalanced voltage.
• 34:58
  Speaker 1: This time delay action is a very important characteristic of
• 35:02
  Speaker 1: the relay because it prevents the relay from tripping upon
• 35:06
  Speaker 1: the occurrence of momentary voltage disturbances in the line to
• 35:11
  Speaker 1: which the relay is connected. Type C M phase balance
• 35:18
  Speaker 1: current relay. In installations where polyphase machinery such as rotary
• 35:24
  Speaker 1: converters and motors, is used, it is necessary to have
• 35:29
  Speaker 1: some protective means available whereby the machine will be disconnected
• 35:33
  Speaker 1: from the source of power in case of an unbalanced
• 35:36
  Speaker 1: condition of the current flowing in the phases, or in
• 35:40
  Speaker 1: case of a phase failure where the apparatus would be
• 35:44
  Speaker 1: compelled to operate on single phase. This protection is necessary
• 35:49
  Speaker 1: because a polyphase machine operating on a system with unbalanced
• 35:54
  Speaker 1: faces or on single phase draws excessive current and may
• 35:59
  Speaker 1: over heat. The CM phase balance current relay is used
• 36:04
  Speaker 1: to prevent such occurrences. The CM relay operates on the
• 36:10
  Speaker 1: induction principle and consists of four single phase current elements
• 36:16
  Speaker 1: mounted in a single case. The four elements are mounted
• 36:20
  Speaker 1: in pairs, one pair being in the upper part of
• 36:23
  Speaker 1: the case with its own disc, and the other pair
• 36:26
  Speaker 1: in the lower part of the case with its disc.
• 36:30
  Speaker 1: Each disk carries its own set of contacts, the two
• 36:33
  Speaker 1: sets being connected in parallel in order that either disc
• 36:37
  Speaker 1: may close the tripping circuit. The two current elements in
• 36:42
  Speaker 1: each pair are mounted on opposite sides of the disk
• 36:45
  Speaker 1: and are so connected that the torque produced by one
• 36:49
  Speaker 1: bus that produced by the other. Therefore, when balanced conditions
• 36:55
  Speaker 1: exist on the system, there is no movement of the disc,
• 36:59
  Speaker 1: but with an unbalanced or opened phase, the balanced condition
• 37:03
  Speaker 1: of the disc is destroyed and the tripping circuit is closed.
• 37:08
  Speaker 1: The relay has inverse and definite minimum time characteristics, and
• 37:14
  Speaker 1: it gives protection for each phase because all phases are
• 37:17
  Speaker 1: represented in the winding. The value of the unbalanced current
• 37:22
  Speaker 1: necessary to trip the relay may be adjusted by means
• 37:26
  Speaker 1: of current taps, as in the CO relay type CQ
• 37:32
  Speaker 1: phase balance relay. The CQ relay is designed to protect
• 37:39
  Speaker 1: polyphase motors and rotary converters against running in case of
• 37:43
  Speaker 1: an open phase, the reversal of phases, or in case
• 37:48
  Speaker 1: of a three phase unbalanced such as is caused by
• 37:51
  Speaker 1: a single phase short circuit. This is necessary because operation
• 37:57
  Speaker 1: with any of these conditions existing for considerable time will
• 38:01
  Speaker 1: cause serious overheating. It is generally desirable to have machines
• 38:07
  Speaker 1: disconnected from the line on as small and unbalanced condition
• 38:12
  Speaker 1: as possible, and they should not operate on single phase
• 38:16
  Speaker 1: currents at all with machines in isolated locations. However, it
• 38:22
  Speaker 1: is sometimes desirable to have the machines kept on the
• 38:26
  Speaker 1: line running on single phase or unbalanced current if the
• 38:30
  Speaker 1: load to be carried is not high enough to cause
• 38:33
  Speaker 1: serious overheating or vibration in the machine. The CQ relay
• 38:39
  Speaker 1: has current and time adjustments which make this operation possible
• 38:44
  Speaker 1: wherever it is desired. The relay operates on the induction principle,
• 38:51
  Speaker 1: the operating element being very similar to that of the
• 38:54
  Speaker 1: CO relay. The winding of this element is so connected
• 38:59
  Speaker 1: that under normal conditions of operation, no current is flowing
• 39:04
  Speaker 1: in it. However, with any unbalanced condition, current will flow
• 39:10
  Speaker 1: through the winding, operate the element and close the contact,
• 39:14
  Speaker 1: which may either actuate an alarm or disconnect the protected
• 39:18
  Speaker 1: machine from its source of power. The CQ relay has
• 39:23
  Speaker 1: an inverse time characteristic. Its construction is such that it
• 39:29
  Speaker 1: is extremely sensitive to small quantities of unbalanced current. The
• 39:35
  Speaker 1: current necessary for operation may be adjusted, and the time
• 39:40
  Speaker 1: required for the contact to close may also be changed.
• 39:45
  Speaker 1: Its application is practically the same as that of the CM,
• 39:50
  Speaker 1: but it is a much more sensitive and a later
• 39:53
  Speaker 1: designed relay and should be used unless the CM is
• 39:57
  Speaker 1: desired for some good reason. Type r F frequency relay.
• 40:05
  Speaker 1: Sometimes it is desired to have the frequency of a
• 40:08
  Speaker 1: circuit or system maintained at a given value, or to
• 40:12
  Speaker 1: have some means whereby a signal is given if the
• 40:16
  Speaker 1: frequency varies from the given value. The F frequency relay
• 40:22
  Speaker 1: is designed to take care of such applications and may
• 40:26
  Speaker 1: be used either to disconnect the circuit or to simply
• 40:30
  Speaker 1: actuate a signal when the frequency changes above or below
• 40:34
  Speaker 1: the normal value. The relay consists of two coils operating
• 40:40
  Speaker 1: on a balanced lever. The coils are connected across the
• 40:44
  Speaker 1: same source, one with a reactance and the other with
• 40:48
  Speaker 1: a resistance in series. As long as normal conditions exist,
• 40:54
  Speaker 1: a balance is maintained on the lever and the contacts
• 40:58
  Speaker 1: remain open. A change in the frequency causes a change
• 41:02
  Speaker 1: in the current flowing in the coil that has the
• 41:05
  Speaker 1: reactance in series, whereas the current flowing in the other
• 41:09
  Speaker 1: and resistance coil remains practically the same. This condition causes
• 41:15
  Speaker 1: an unbalance, which closes the contacts and serves to perform
• 41:19
  Speaker 1: the required operation. The relay can be made very sensitive
• 41:25
  Speaker 1: and is adaptable to a variety of applications. Type C
• 41:31
  Speaker 1: operation indicator. In many installations where a number of relays
• 41:37
  Speaker 1: are in service, a circuit breaker may be tripped by
• 41:41
  Speaker 1: one of several protective relays. As each relay affords protection
• 41:47
  Speaker 1: against some special kind of fault in the line, it
• 41:50
  Speaker 1: is highly desirable to know which relay has tripped the
• 41:54
  Speaker 1: breaker in order to be able more easily to locate
• 41:58
  Speaker 1: the trouble. As most protective relay is reset automatically as
• 42:03
  Speaker 1: soon as the circuit breaker opens, it is difficult to
• 42:07
  Speaker 1: determine which relay has operated without some auxiliary means. The
• 42:12
  Speaker 1: operation indicator is the small coil serving to attract a
• 42:17
  Speaker 1: semaphore into a visible position when the coil is energized.
• 42:22
  Speaker 1: This operation indicator may be installed within the case of
• 42:26
  Speaker 1: all the standard types of protective relays and is connected
• 42:30
  Speaker 1: in series with the tripping circuit. As soon as the
• 42:34
  Speaker 1: relay closes its contacts, thereby closing the tripping circuit, the
• 42:39
  Speaker 1: operation indicator is energized and attracts the indicator to the
• 42:45
  Speaker 1: operated position. The indicator remains in this position until reset.
• 42:51
  Speaker 1: The hand reset of the indicator is so arranged that
• 42:54
  Speaker 1: it may be actuated without removing the cover of the
• 42:58
  Speaker 1: relay Chapter nine, Part one