Standard device Function numbers:
1. master element. The initiating device,
such as a control switch, etc., that serves,
either directly or through such permissive
devices as protective and time-delay
relays, to place equipment in or out of
operation.
NOTE: This number in normally used for
a hand-operated device, although it may
also be used for an electrical or mechanical
device for which no other function
number is suitable.
2. time-delay starting or closing relay. A
device that functions to give a desired
amount of time delay before or after any
point of operation in a switching
sequence or protective relay system, except
as specifically provided by device
functions 48, 62, and 79.
3. checking or interlocking relay. A relay
that operates in response to the position of
a number of other devices (or to a number
of predetermined conditions) in equipment
to allow an operating sequence to
proceed, stop, or provide a check of the
position of these devices or conditions for
any purpose.
4. master contactor. A device, generally
controlled by device function 1 or the
equivalent and the required permissive
and protective devices, that serves to
make and break the necessary control circuits
to place equipment into operation
under the desired conditions and to take it
out of operation under abnormal conditions.
5. stopping device. A control device used
primarily to shut down equipment and
hold it out of operation. (This device may
be manually or electrically actuated, but it
excludes the function of electrical lockout
[see device function 86] on abnormal
conditions.)
6. starting circuit breaker. A device whose
principal function is to connect a machine
to its source of starting voltage.
7. rate-of-rise relay. A relay that functions
on an excessive rate-of-rise of current.
8. control power disconnecting device. A
disconnecting device, such as a knife
switch, circuit breaker, or pull-out fuse
block, used for the purpose of respectively
connecting and disconnecting the
source of control power to and from the
control bus or equipment.
NOTE: Control power is considered to
include auxiliary power that supplies such
apparatus as small motors and heaters.
9. reversing device. A device that is used
for the purpose of reversing a machine
field or for performing any other reversing
functions.
10. unit sequence switch. A switch that is
used to change the sequence in which
units may be placed in and out of service
in multiple-unit equipment.
11. multifunction device. A device that performs
three or more comparatively
important functions that could only be
designated by combining several of these
device function numbers. All of the functions
performed by device 11 shall be
defined in the drawing legend or device
function definition list.
12. overspeed device. Usually, a direct-connected
speed switch that functions on
machine overspeed.
13. synchronous-speed device. A device
such as a centrifugal-speed switch, a slipfrequency
relay, a voltage relay, an undercurrent
relay, or any other type of device
that operates at approximately the synchronous
speed of a machine.
14. underspeed device. A device that functions
when the speed of a machine falls
below a pre-determined value.
15. speed or frequency matching device. A
device that functions to match and hold
the speed or frequency of a machine or a
system equal to, or approximately equal
to, that of another machine, source, or
system.
16. Reserved for future application.
17. shunting or discharge switch. A switch
that serves to open or close a shunting circuit
around any piece of apparatus
(except a resistor), such as a machine
field, a machine armature, a capacitor, or
a reactor.
NOTE: This excludes devices that perform
such shunting operations as may be
necessary in the process of starting a
machine by devices 6 or 42 (or their
equivalent) and also excludes device
function 73 that serves for the switching
of resistors.
18. accelerating or decelerating device. A
device that is used to close or cause the
closing of circuits that are used to
increase or decrease the speed of a Machine.
19. starting-to-running transition contactor.
A device that operates to initiate or
cause the automatic transfer of a machine
from the starting to the running power
connection.
20. electrically operated valve. An electrically
operated, controlled, or monitored
valve used in a fluid, air, gas, or vacuum
line.
NOTE: The function of the valve may be
more completely indicated by the use of
suffixes as discussed in 3.2.
21. distance relay. A relay that functions
when the circuit admittance, impedance,
or reactance increases or decreases
beyond a predetermined value.
22. equalizer circuit breaker. A breaker that
serves to control or make and break the
equalizer or the current-balancing connections
for a machine field, or for regulating
equipment, in a multiple-unit
installation.
23. temperature control device. A device
that functions to raise or lower the temperature
of a machine or other apparatus,
or of any medium, when its temperature
falls below or rises above a predetermined
value.
NOTE: An example is a thermostat that
switches on a space heater in a switchgear
assembly when the temperature falls to a
desired value. This should be distinguished
from a device that is used to provide
automatic temperature regulation
between close limits and would be designated
as device function 90T.
24. volts per hertz relay. A relay that functions
when the ratio of voltage to frequency
exceeds a preset value. The relay
may have an instantaneous or a time characteristic
25. synchronizing or synchronism-check
device. A device that operates when two
ac circuits are within the desired limits of
frequency, phase angle, and voltage to
permit or cause the paralleling of these
two circuits.
26. apparatus thermal device. A device that
functions when the temperature of the
protected apparatus (other than the loadcarrying
windings of machines and transformers
as covered by device function
number 49) or of a liquid or other
medium exceeds a predetermined value;
or when the temperature of the protected
apparatus or of any medium decreases
below a predetermined value.
27. undervoltage relay. A relay that operates
when its input voltage is less than a predetermined
value.
28. flame detector. A device that monitors
the presence of the pilot or main flame in
such apparatus as a gas turbine or a steam
boiler.
29. isolating contactor. A device that is used
expressly for disconnecting one circuit
from another for the purposes of emergency
operation, maintenance, or test.
30. annunciator relay. A nonautomatically
reset device that gives a number of separate
visual indications upon the functioning
of protective devices and that may
also be arranged to perform a lockout
function.
31. separate excitation device. A device that
connects a circuit, such as the shunt field
of a synchronous converter, to a source of
separate excitation during the starting
sequence.
32. directional power relay. A relay that
operates on a predetermined value of
power flow in a given direction or upon
reverse power flow such as that resulting
from the motoring of a generator upon
loss of its prime mover.
33. position switch. A switch that makes or
breaks contact when the main device or
piece of apparatus that has no device
function number reaches a given position.
34. master sequence device. A device such
as a motor-operated multicontact switch,
or the equivalent, or a programming
device, such as a computer, that establishes
or determines the operating
sequence of the major devices in equipment
during starting and stopping or during
other sequential switching operations.
35. brush-operating or slip-ring short-circuiting
device. A device for raising, lowering,
or shifting the brushes of a
machine; short-circuiting its slip rings; or
engaging or disengaging the contacts of a
mechanical rectifier.
36. polarity or polarizing voltage device. A
device that operates, or permits the operation
of, another device on a predetermined
polarity only or that verifies the
presence of a polarizing voltage in equipment.
37. undercurrent or underpower relay. A
relay that functions when the current or
power flow decreases below a predetermined
value.
38. bearing protective device. A device that
functions on excessive bearing temperature
or on other abnormal mechanical
conditions associated with the bearing,
such as undue wear, which may eventually
result in excessive bearing temperature
or failure.
39. mechanical condition monitor. A device
that functions upon the occurrence of an
abnormal mechanical condition (except
that associated with bearings as covered
under device function 38), such as exces
sive vibration, eccentricity, expansion,
shock, tilting, or seal failure.
40. field relay. A relay that functions on a
given or abnormally low value or failure
of machine field current, or on an excessive
value of the reactive component of
armature current in an ac machine indicating
abnormally low field excitation.
41. field circuit breaker. A device that functions
to apply or remove the field excitation
of a machine.
42. running circuit breaker. A device whose
principal function is to connect a machine
to its source of running or operating voltage.
This function may also be used for a
device, such as a contactor, that is used in
series with a circuit breaker or other faultprotecting
means, primarily for frequent
opening and closing of the circuit.
43. manual transfer or selector device. A
manually operated device that transfers
the control circuits in order to modify the
plan of operation of the switching equipment
or of some of the devices.
44. unit sequence starting relay. A relay
that functions to start the next available
unit in multiple-unit equipment upon the
failure or nonavailability of the normally
preceding unit.
45. atmospheric condition monitor. A
device that functions upon the occurrence
of an abnormal atmospheric condition,
such as damaging fumes, explosive mixtures,
smoke, or fire.
46. reverse-phase or phase-balance current
relay. A relay that functions when the
polyphase currents are of reverse-phase
sequence or when the polyphase currents
are unbalanced or contain negative phasesequence
components above a given amount.
47. phase-sequence or phase-balance voltage
relay. A relay that functions upon a
predetermined value of polyphase voltage
in the desired phase sequence, when the
polyphase voltages are unbalanced, or
when the negative phase-sequence voltage
exceeds a given amount.
48. incomplete sequence relay. A relay that
generally returns the equipment to the
normal, or off, position and locks it out if
the normal starting, operating, or stopping
sequence is not properly completed within
a predetermined time.
49. machine or transformer thermal relay.
A relay that functions when the temperature
of a machine armature winding or
other load-carrying winding or element of
a machine or power transformer exceeds
a predetermined value.
50. instantaneous overcurrent relay. A
relay that functions instantaneously on an
excessive value of current.
51. ac time overcurrent relay. A relay that
functions when the ac input current
exceeds a predetermined value, and in
which the input current and operating
time are inversely related through a substantial
portion of the performance range.
52. ac circuit breaker. A device that is used
to close and interrupt an ac power circuit
under normal conditions or to interrupt
this circuit under fault or emergency conditions.
53. exciter or dc generator relay. A relay
that forces the dc machine field excitation
to build up during starting or that functions
when the machine voltage has built
up to a given value.
54. turning gear engaging device. An electrically
operated, controlled, or monitored
device that functions to cause the turning
gear to engage (or disengage) the
machine shaft.
55. power factor relay. A relay that operates
when the power factor in an ac circuit
rises above or falls below a predetermined
value.
56. field application relay. A relay that automatically
controls the application of the
feld excitation to an ac motor at some predetermined
point in the slip cycle.
57. short-circuiting or grounding device. A
primary circuit switching device that
functions to short-circuit or ground a circuit
in response to automatic or manual
means.
58. rectification failure relay. A device that
functions if a power rectifier fails to conduct
or block properly.
59. overvoltage relay. A relay that operates
when its input voltage is more than a predetermined
value.
60. voltage or current balance relay. A
relay that operates on a given difference
in voltage, or current input or output, of
two circuits.
61. density switch or sensor. A device that
operates on a given value, or a given rate
of change, of gas density.
62. time-delay stopping or opening relay. A
time-delay relay that serves in conjunction
with the device that initiates the shutdown,
stopping, or opening operation in
an automatic sequence or protective relay
system.
63. pressure switch. A switch that operates
on given values, or on a given rate of
change, of pressure.
64. ground detector relay. A relay that operates
upon failure of machine or other
apparatus insulation to ground.
NOTE: This function is not applied to a
device connected in the secondary circuit
of current transformers in a normally
grounded power system, where other
device numbers with the suffix G or N
should be used; that is, 51N for an ac time
overurrent relay connected in the secondary
neutral of the current transformers.
65. governor. The assembly of fluid, electrical,
or mechanical control equipment
used for regulating the flow of water,
steam, or other media to the prime mover
for such purposes as starting, holding
speed or load, or stopping.
66. notching or jogging device. A device
that functions to allow only a specifed
number of operations of a given device or
equipment, or a specified number of successive
operations within a given time of
each other. It is also a device that functions
to energize a circuit periodically or
for fractions of specified time intervals, or
that is used to permit intermittent acceleration
or jogging of a machine at low
speeds for mechanical positioning.
67. ac directional overcurrent relay. A
relay that functions on a desired value of
ac overcurrent flowing in a predetermined
direction.
68. blocking relay. A relay that initiates a
pilot signal for blocking of tripping on
external faults in a transmission line or in
other apparatus under predetermined conditions,
or that cooperates with other
devices to block tripping or to block
reclosing on an out-of-step condition or
on power swings.
69. permissive control device. Generally, a
two-position device that in one position
permits the closing of a circuit breaker, or
the placing of an equipment into operation,
and in the other position prevents the
circuit breaker or the equipment from
being operated.
70. rheostat. A variable resistance device
used in an electric circuit when the device
is electrically operated or has other electrical
accessories, such as auxiliary, position,
or limit switches.
71. level switch. A switch that operates on
given values, or on a given rate of change,
of level.
72. dc circuit breaker. A circuit breaker that
is used to close and interrupt a dc power
circuit under normal conditions or to
interrupt this circuit under fault or emergency
conditions.
73. load-resistor contactor. A contactor that
is used to shunt or insert a step of load
limiting, shifting, or indicating resistance
in a power circuit; to switch a space
heater in circuit; or to switch a light or
regenerative load resistor of a power rectifier
or other machine in and out of circuit.
74. alarm relay. A relay other than an
annunciator, as covered under device
function 30, that is used to operate, or that
operates in connection with, a visual or
audible alarm.
75. position changing mechanism. A mechanism
that is used for moving a main
device from one position to another in
equipment; for example, shifting a
removable circuit breaker unit to and
from the connected, disconnected, and
test positions.
76. dc overcurrent relay. A relay that functions
when the current in a dc circuit
exceeds a given value.
77. telemetering device. A transmitter used
to generate and transmit to a remote location
an electrical signal representing a
measured quantity, or a receiver used to
receive the electrical signal from a remote
transmitter and convert the signal to represent
the original measured quantity.
78 phase-angle measuring or out-of-step
protective relay. A relay that functions at
a predetermined phase angle between two
voltages, between two currents, or
between voltage and current.
79. ac reclosing relay. A relay that controls
the automatic reclosing and locking out of
an ac circuit interrupter.
80. flow switch. A switch that operates on
given values, or on a given rate of change,
of flow.
81. frequency relay. A relay that responds to
the frequency of an electrical quantity,
operating when the frequency or rate of
change of frequency exceeds or is less
than a predetermined value.
82. dc load-measuring reclosing relay. A
relay that controls the automatic closing
and reclosing of a dc circuit interrupter,
generally in response to load circuit conditions.
83. automatic selective control or transfer
relay. A relay that operates to select automatically
between certain sources or conditions
in equipment or that performs a
transfer operation automatically.
84. operating mechanism. The complete
electrical mechanism or servo mechanism,
including the operating motor, solenoids,
position switches, etc., for a tap
changer, induction regulator, or any similar
piece of apparatus that otherwise has
no device function numher.
85. carrier or pilot-wire receiver relay. A
relay that is operated or restrained by a
signal used in connection with carriercurrent
or dc pilot-wire fault relaying.
86. lockout relay. A hand or electrically reset
auxiliary relay that is operated upon the
occurrence of abnormal conditions to
maintain associated equipment or devices
inoperative until it is reset.
87. differential protective relay. A protective
relay that functions on a percentage,
phase angle, or other quantitative difference
between two currents or some other
electrical quantities.
88. auxiliary motor or motor generator. A
device used for operating auxiliary equipment,
such as pumps, blowers, exciters,
rotating magnetic amplifiers, etc.
89. line switch. A switch used as a disconnecting,
load-interrupter, or isolating
switch in an ac or dc power circuit. (This
device function number is normally not
necessary unless the switch is electrically
operated or has electrical accessories,
such as an auxiliary switch, a magnetic
lock, etc.)
90. regulating device. A device that functions
to regulate a quantity or quantities,
such as voltage, current, power, speed,
frequency, temperature, and load, at a certain
value or between certain (generally
close) limits for machines, tie lines, or
other apparatus.
91. voltage directional relay. A relay that
operates when the voltage across an open
circuit breaker or contactor exceeds a
given value in a given direction.
92. voltage and power directional relay. A
relay that permits or causes the connection
of two circuits when the voltage difference
between them exceeds a given
value in a predetermined direction and
causes these two circuits to be disconnected
from each other when the power
flowing between them exceeds a given
value in the opposite direction.
93. field-changing contactor. A contactor
that functions to increase or decrease, in
one step, the value of field excitation on a
machine.
94. tripping or trip-free relay. A relay that
functions to trip a circuit breaker, contactor,
or equipment; to permit immediate
tripping by other devices; or to prevent
immediate reclosing of a circuit interrupter
if it should open automatically,
even though its closing circuit is maintained
closed.
95-99.Used only for specific applications in
individual installations if none of the
functions assigned to the numbers
from 1 to 94 is suitable.
1. master element. The initiating device,
such as a control switch, etc., that serves,
either directly or through such permissive
devices as protective and time-delay
relays, to place equipment in or out of
operation.
NOTE: This number in normally used for
a hand-operated device, although it may
also be used for an electrical or mechanical
device for which no other function
number is suitable.
2. time-delay starting or closing relay. A
device that functions to give a desired
amount of time delay before or after any
point of operation in a switching
sequence or protective relay system, except
as specifically provided by device
functions 48, 62, and 79.
3. checking or interlocking relay. A relay
that operates in response to the position of
a number of other devices (or to a number
of predetermined conditions) in equipment
to allow an operating sequence to
proceed, stop, or provide a check of the
position of these devices or conditions for
any purpose.
4. master contactor. A device, generally
controlled by device function 1 or the
equivalent and the required permissive
and protective devices, that serves to
make and break the necessary control circuits
to place equipment into operation
under the desired conditions and to take it
out of operation under abnormal conditions.
5. stopping device. A control device used
primarily to shut down equipment and
hold it out of operation. (This device may
be manually or electrically actuated, but it
excludes the function of electrical lockout
[see device function 86] on abnormal
conditions.)
6. starting circuit breaker. A device whose
principal function is to connect a machine
to its source of starting voltage.
7. rate-of-rise relay. A relay that functions
on an excessive rate-of-rise of current.
8. control power disconnecting device. A
disconnecting device, such as a knife
switch, circuit breaker, or pull-out fuse
block, used for the purpose of respectively
connecting and disconnecting the
source of control power to and from the
control bus or equipment.
NOTE: Control power is considered to
include auxiliary power that supplies such
apparatus as small motors and heaters.
9. reversing device. A device that is used
for the purpose of reversing a machine
field or for performing any other reversing
functions.
10. unit sequence switch. A switch that is
used to change the sequence in which
units may be placed in and out of service
in multiple-unit equipment.
11. multifunction device. A device that performs
three or more comparatively
important functions that could only be
designated by combining several of these
device function numbers. All of the functions
performed by device 11 shall be
defined in the drawing legend or device
function definition list.
12. overspeed device. Usually, a direct-connected
speed switch that functions on
machine overspeed.
13. synchronous-speed device. A device
such as a centrifugal-speed switch, a slipfrequency
relay, a voltage relay, an undercurrent
relay, or any other type of device
that operates at approximately the synchronous
speed of a machine.
14. underspeed device. A device that functions
when the speed of a machine falls
below a pre-determined value.
15. speed or frequency matching device. A
device that functions to match and hold
the speed or frequency of a machine or a
system equal to, or approximately equal
to, that of another machine, source, or
system.
16. Reserved for future application.
17. shunting or discharge switch. A switch
that serves to open or close a shunting circuit
around any piece of apparatus
(except a resistor), such as a machine
field, a machine armature, a capacitor, or
a reactor.
NOTE: This excludes devices that perform
such shunting operations as may be
necessary in the process of starting a
machine by devices 6 or 42 (or their
equivalent) and also excludes device
function 73 that serves for the switching
of resistors.
18. accelerating or decelerating device. A
device that is used to close or cause the
closing of circuits that are used to
increase or decrease the speed of a Machine.
19. starting-to-running transition contactor.
A device that operates to initiate or
cause the automatic transfer of a machine
from the starting to the running power
connection.
20. electrically operated valve. An electrically
operated, controlled, or monitored
valve used in a fluid, air, gas, or vacuum
line.
NOTE: The function of the valve may be
more completely indicated by the use of
suffixes as discussed in 3.2.
21. distance relay. A relay that functions
when the circuit admittance, impedance,
or reactance increases or decreases
beyond a predetermined value.
22. equalizer circuit breaker. A breaker that
serves to control or make and break the
equalizer or the current-balancing connections
for a machine field, or for regulating
equipment, in a multiple-unit
installation.
23. temperature control device. A device
that functions to raise or lower the temperature
of a machine or other apparatus,
or of any medium, when its temperature
falls below or rises above a predetermined
value.
NOTE: An example is a thermostat that
switches on a space heater in a switchgear
assembly when the temperature falls to a
desired value. This should be distinguished
from a device that is used to provide
automatic temperature regulation
between close limits and would be designated
as device function 90T.
24. volts per hertz relay. A relay that functions
when the ratio of voltage to frequency
exceeds a preset value. The relay
may have an instantaneous or a time characteristic
25. synchronizing or synchronism-check
device. A device that operates when two
ac circuits are within the desired limits of
frequency, phase angle, and voltage to
permit or cause the paralleling of these
two circuits.
26. apparatus thermal device. A device that
functions when the temperature of the
protected apparatus (other than the loadcarrying
windings of machines and transformers
as covered by device function
number 49) or of a liquid or other
medium exceeds a predetermined value;
or when the temperature of the protected
apparatus or of any medium decreases
below a predetermined value.
27. undervoltage relay. A relay that operates
when its input voltage is less than a predetermined
value.
28. flame detector. A device that monitors
the presence of the pilot or main flame in
such apparatus as a gas turbine or a steam
boiler.
29. isolating contactor. A device that is used
expressly for disconnecting one circuit
from another for the purposes of emergency
operation, maintenance, or test.
30. annunciator relay. A nonautomatically
reset device that gives a number of separate
visual indications upon the functioning
of protective devices and that may
also be arranged to perform a lockout
function.
31. separate excitation device. A device that
connects a circuit, such as the shunt field
of a synchronous converter, to a source of
separate excitation during the starting
sequence.
32. directional power relay. A relay that
operates on a predetermined value of
power flow in a given direction or upon
reverse power flow such as that resulting
from the motoring of a generator upon
loss of its prime mover.
33. position switch. A switch that makes or
breaks contact when the main device or
piece of apparatus that has no device
function number reaches a given position.
34. master sequence device. A device such
as a motor-operated multicontact switch,
or the equivalent, or a programming
device, such as a computer, that establishes
or determines the operating
sequence of the major devices in equipment
during starting and stopping or during
other sequential switching operations.
35. brush-operating or slip-ring short-circuiting
device. A device for raising, lowering,
or shifting the brushes of a
machine; short-circuiting its slip rings; or
engaging or disengaging the contacts of a
mechanical rectifier.
36. polarity or polarizing voltage device. A
device that operates, or permits the operation
of, another device on a predetermined
polarity only or that verifies the
presence of a polarizing voltage in equipment.
37. undercurrent or underpower relay. A
relay that functions when the current or
power flow decreases below a predetermined
value.
38. bearing protective device. A device that
functions on excessive bearing temperature
or on other abnormal mechanical
conditions associated with the bearing,
such as undue wear, which may eventually
result in excessive bearing temperature
or failure.
39. mechanical condition monitor. A device
that functions upon the occurrence of an
abnormal mechanical condition (except
that associated with bearings as covered
under device function 38), such as exces
sive vibration, eccentricity, expansion,
shock, tilting, or seal failure.
40. field relay. A relay that functions on a
given or abnormally low value or failure
of machine field current, or on an excessive
value of the reactive component of
armature current in an ac machine indicating
abnormally low field excitation.
41. field circuit breaker. A device that functions
to apply or remove the field excitation
of a machine.
42. running circuit breaker. A device whose
principal function is to connect a machine
to its source of running or operating voltage.
This function may also be used for a
device, such as a contactor, that is used in
series with a circuit breaker or other faultprotecting
means, primarily for frequent
opening and closing of the circuit.
43. manual transfer or selector device. A
manually operated device that transfers
the control circuits in order to modify the
plan of operation of the switching equipment
or of some of the devices.
44. unit sequence starting relay. A relay
that functions to start the next available
unit in multiple-unit equipment upon the
failure or nonavailability of the normally
preceding unit.
45. atmospheric condition monitor. A
device that functions upon the occurrence
of an abnormal atmospheric condition,
such as damaging fumes, explosive mixtures,
smoke, or fire.
46. reverse-phase or phase-balance current
relay. A relay that functions when the
polyphase currents are of reverse-phase
sequence or when the polyphase currents
are unbalanced or contain negative phasesequence
components above a given amount.
47. phase-sequence or phase-balance voltage
relay. A relay that functions upon a
predetermined value of polyphase voltage
in the desired phase sequence, when the
polyphase voltages are unbalanced, or
when the negative phase-sequence voltage
exceeds a given amount.
48. incomplete sequence relay. A relay that
generally returns the equipment to the
normal, or off, position and locks it out if
the normal starting, operating, or stopping
sequence is not properly completed within
a predetermined time.
49. machine or transformer thermal relay.
A relay that functions when the temperature
of a machine armature winding or
other load-carrying winding or element of
a machine or power transformer exceeds
a predetermined value.
50. instantaneous overcurrent relay. A
relay that functions instantaneously on an
excessive value of current.
51. ac time overcurrent relay. A relay that
functions when the ac input current
exceeds a predetermined value, and in
which the input current and operating
time are inversely related through a substantial
portion of the performance range.
52. ac circuit breaker. A device that is used
to close and interrupt an ac power circuit
under normal conditions or to interrupt
this circuit under fault or emergency conditions.
53. exciter or dc generator relay. A relay
that forces the dc machine field excitation
to build up during starting or that functions
when the machine voltage has built
up to a given value.
54. turning gear engaging device. An electrically
operated, controlled, or monitored
device that functions to cause the turning
gear to engage (or disengage) the
machine shaft.
55. power factor relay. A relay that operates
when the power factor in an ac circuit
rises above or falls below a predetermined
value.
56. field application relay. A relay that automatically
controls the application of the
feld excitation to an ac motor at some predetermined
point in the slip cycle.
57. short-circuiting or grounding device. A
primary circuit switching device that
functions to short-circuit or ground a circuit
in response to automatic or manual
means.
58. rectification failure relay. A device that
functions if a power rectifier fails to conduct
or block properly.
59. overvoltage relay. A relay that operates
when its input voltage is more than a predetermined
value.
60. voltage or current balance relay. A
relay that operates on a given difference
in voltage, or current input or output, of
two circuits.
61. density switch or sensor. A device that
operates on a given value, or a given rate
of change, of gas density.
62. time-delay stopping or opening relay. A
time-delay relay that serves in conjunction
with the device that initiates the shutdown,
stopping, or opening operation in
an automatic sequence or protective relay
system.
63. pressure switch. A switch that operates
on given values, or on a given rate of
change, of pressure.
64. ground detector relay. A relay that operates
upon failure of machine or other
apparatus insulation to ground.
NOTE: This function is not applied to a
device connected in the secondary circuit
of current transformers in a normally
grounded power system, where other
device numbers with the suffix G or N
should be used; that is, 51N for an ac time
overurrent relay connected in the secondary
neutral of the current transformers.
65. governor. The assembly of fluid, electrical,
or mechanical control equipment
used for regulating the flow of water,
steam, or other media to the prime mover
for such purposes as starting, holding
speed or load, or stopping.
66. notching or jogging device. A device
that functions to allow only a specifed
number of operations of a given device or
equipment, or a specified number of successive
operations within a given time of
each other. It is also a device that functions
to energize a circuit periodically or
for fractions of specified time intervals, or
that is used to permit intermittent acceleration
or jogging of a machine at low
speeds for mechanical positioning.
67. ac directional overcurrent relay. A
relay that functions on a desired value of
ac overcurrent flowing in a predetermined
direction.
68. blocking relay. A relay that initiates a
pilot signal for blocking of tripping on
external faults in a transmission line or in
other apparatus under predetermined conditions,
or that cooperates with other
devices to block tripping or to block
reclosing on an out-of-step condition or
on power swings.
69. permissive control device. Generally, a
two-position device that in one position
permits the closing of a circuit breaker, or
the placing of an equipment into operation,
and in the other position prevents the
circuit breaker or the equipment from
being operated.
70. rheostat. A variable resistance device
used in an electric circuit when the device
is electrically operated or has other electrical
accessories, such as auxiliary, position,
or limit switches.
71. level switch. A switch that operates on
given values, or on a given rate of change,
of level.
72. dc circuit breaker. A circuit breaker that
is used to close and interrupt a dc power
circuit under normal conditions or to
interrupt this circuit under fault or emergency
conditions.
73. load-resistor contactor. A contactor that
is used to shunt or insert a step of load
limiting, shifting, or indicating resistance
in a power circuit; to switch a space
heater in circuit; or to switch a light or
regenerative load resistor of a power rectifier
or other machine in and out of circuit.
74. alarm relay. A relay other than an
annunciator, as covered under device
function 30, that is used to operate, or that
operates in connection with, a visual or
audible alarm.
75. position changing mechanism. A mechanism
that is used for moving a main
device from one position to another in
equipment; for example, shifting a
removable circuit breaker unit to and
from the connected, disconnected, and
test positions.
76. dc overcurrent relay. A relay that functions
when the current in a dc circuit
exceeds a given value.
77. telemetering device. A transmitter used
to generate and transmit to a remote location
an electrical signal representing a
measured quantity, or a receiver used to
receive the electrical signal from a remote
transmitter and convert the signal to represent
the original measured quantity.
78 phase-angle measuring or out-of-step
protective relay. A relay that functions at
a predetermined phase angle between two
voltages, between two currents, or
between voltage and current.
79. ac reclosing relay. A relay that controls
the automatic reclosing and locking out of
an ac circuit interrupter.
80. flow switch. A switch that operates on
given values, or on a given rate of change,
of flow.
81. frequency relay. A relay that responds to
the frequency of an electrical quantity,
operating when the frequency or rate of
change of frequency exceeds or is less
than a predetermined value.
82. dc load-measuring reclosing relay. A
relay that controls the automatic closing
and reclosing of a dc circuit interrupter,
generally in response to load circuit conditions.
83. automatic selective control or transfer
relay. A relay that operates to select automatically
between certain sources or conditions
in equipment or that performs a
transfer operation automatically.
84. operating mechanism. The complete
electrical mechanism or servo mechanism,
including the operating motor, solenoids,
position switches, etc., for a tap
changer, induction regulator, or any similar
piece of apparatus that otherwise has
no device function numher.
85. carrier or pilot-wire receiver relay. A
relay that is operated or restrained by a
signal used in connection with carriercurrent
or dc pilot-wire fault relaying.
86. lockout relay. A hand or electrically reset
auxiliary relay that is operated upon the
occurrence of abnormal conditions to
maintain associated equipment or devices
inoperative until it is reset.
87. differential protective relay. A protective
relay that functions on a percentage,
phase angle, or other quantitative difference
between two currents or some other
electrical quantities.
88. auxiliary motor or motor generator. A
device used for operating auxiliary equipment,
such as pumps, blowers, exciters,
rotating magnetic amplifiers, etc.
89. line switch. A switch used as a disconnecting,
load-interrupter, or isolating
switch in an ac or dc power circuit. (This
device function number is normally not
necessary unless the switch is electrically
operated or has electrical accessories,
such as an auxiliary switch, a magnetic
lock, etc.)
90. regulating device. A device that functions
to regulate a quantity or quantities,
such as voltage, current, power, speed,
frequency, temperature, and load, at a certain
value or between certain (generally
close) limits for machines, tie lines, or
other apparatus.
91. voltage directional relay. A relay that
operates when the voltage across an open
circuit breaker or contactor exceeds a
given value in a given direction.
92. voltage and power directional relay. A
relay that permits or causes the connection
of two circuits when the voltage difference
between them exceeds a given
value in a predetermined direction and
causes these two circuits to be disconnected
from each other when the power
flowing between them exceeds a given
value in the opposite direction.
93. field-changing contactor. A contactor
that functions to increase or decrease, in
one step, the value of field excitation on a
machine.
94. tripping or trip-free relay. A relay that
functions to trip a circuit breaker, contactor,
or equipment; to permit immediate
tripping by other devices; or to prevent
immediate reclosing of a circuit interrupter
if it should open automatically,
even though its closing circuit is maintained
closed.
95-99.Used only for specific applications in
individual installations if none of the
functions assigned to the numbers
from 1 to 94 is suitable.
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