Relays: Function

Field-changing contactor

A contactor that functions *to increase or decrease, in one step, the value of field excitation* on a machine.

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.

Stopping device

A control device *shuts down equipment* and hold it out of operation. (This device may be manually or electrically actuated, but excludes the function of electrical lockout [see device function 86] on abnormal conditions.)

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.

Synchronous-speed device

A device such as a centrifugal-speed switch, a slip-frequency relay, a voltage relay, an undercurrent relay, or any other type of device that operates at approximately the *synchronous speed* of a machine.

Master Sequence device

A device such as a motor-operated multi-contact 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.

Multi-function device

A single, microprocessor-based product which has the capabilities to support *three or more* protection and control elements.

Permissive control device

Generally, a *two-position device* that in one position *permits* the closing of a circuit breaker, or the placing of equipment into operation, and in the other position *prevents* the circuit breaker or the equipment from being operated.

Manual transfer or selector device 43

A *manually operated* device that *transfers* the control circuits to modify the plan of operation of the switching equipment or of some of the devices.

Time-delay stopping or opening relay

A *time-delay* relay that serves with the device that initiates the shutdown, *stopping or opening* operation in an automatic sequence or protective relay system.

Rheostat

A *variable resistance device* that is used in an electric circuit when the device is electrically operated or has other electrical accessories such as auxiliary, position, or limit switches.

Equalizer circuit breaker

A breaker that serves to control or to make and break the *equalizer* or the current-balancing connections for a machine field, or for regulating equipment, in a multiple-unit installation.

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.

Bearing protective device

A device that *functions on excessive bearing temperature* or on other abnormal mechanical conditions that are associated with the bearing, such as undue wear, which may eventually result in excessive bearing temperature or failure.

Mechanical condition monitor

A device that *functions upon the occurrence of an abnormal mechanical condition*, such as excessive vibration, eccentricity, expansion, shock, tilting, or seal failure.

Apparatus thermal device

A device that *functions when the temperature of the protected apparatus or of a liquid or other medium *exceeds* or *decreases* below a predetermined value.

Flame detector

A device that *monitors the presence of the pilot or main flame* as in such apparatus as a gas turbine or a steam boiler.

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.

Notching or jogging device

A device that functions *to allow only a specified 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.

Field circuit breaker

A device that functions *to apply or remove the field excitation* of a machine.

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.

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 (close) limits for machines, tie lines, or other apparatus.

Speed or frequency matching device

A device that functions to *match and hold the speed or the frequency* of a machine or of a system equal to, or approximately equal to, that of another machine, source, or system.

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 provided by device functions 48, 62, and 79.

Atmospheric condition monitor

A device that functions upon the occurrence of an abnormal *atmospheric condition*, such as damaging fumes, explosive mixtures, smoke, or fire.

Underspeed device

A device that functions when the *speed of a machine falls below* a predetermined value.

AC circuit breaker 52

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.

Isolating switch or contactor

A device that is used expressly for *disconnecting one circuit from another* for the purposes of emergency operation, maintenance, or test.

Reversing device

A device that is used for *reversing a machine field* or for performing any other reversing functions.

Auxiliary motor or motor generator

A device that is used for operating *auxiliary equipment*, such as pumps, blowers, exciters, or *rotating* magnetic amplifiers.

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.

Density switch or sensor

A device that operates on a given value, or a given rate of change, of *gas density*.

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.

Synchronizing or synchronism-check device 25

A device that operates when two AC circuits are within the desired limits of frequency, phase angle and voltage to permit or to cause the *paralleling* of these two circuits.

Polarity or polarizing voltage device

A device that operates, or permits the operation of, another device on a predetermined polarity only, or *verifies the presence of a polarizing voltage* in equipment.

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 fault-protecting means, primarily for frequent opening and closing of the circuit.

Starting circuit breaker

A device whose principal function is to *connect a machine to its source of starting voltage*.

Master contactor

A device, which is controlled by device function 1 or the equivalent, and the required permissive and protective devices which serve *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.

Control power disconnecting device

A disconnecting device, such as a knife switch, circuit breaker, or pull-out fuse block that is used for *connecting and disconnecting the source of control power* to and from the control bus or equipment.

Lockout relay or device 86

A hand or electrically reset auxiliary or electronic device relay that is operated upon the occurrence of abnormal conditions *to maintain associated equipment or devices inoperative* until it is reset

Positioning 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.

Annunciator relay 30

A non-automatically reset device that gives a number of separate *visual indications* upon the functioning of protective devices, and which may also be arranged to perform a lockout function.

Short-circuiting or grounding device

A primary circuit switching device that functions to *short circuit or to ground* a circuit in response to automatic or manual means.

Differential protective relay 87

A protective relay that functions on a percentage, phase angle, or other *quantitative difference between two currents* or some other electrical quantities.

Alarm relay

A relay other than an annunciator, as covered under device function 30, that is used to operate, or that operates with a visual or *audible alarm*.

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.

Field application relay

A relay that automatically *controls the application of the field excitation* to an AC motor at some predetermined point in the slip cycle.

AC reclosing relay 79

A relay that controls the automatic *reclosing* and locking out of an *AC* circuit interrupter.

Exciter or DC generator relay

A relay that forces the *DC machine field excitation* to build up during startup, or that functions when the machine voltage has built up to a given value.

Unit sequence starting relay

A relay that functions *to start the next available unit* in multiple-unit equipment upon the failure or non-availability of the normally preceding unit.

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.

Phase-angle measuring or out-of-step protective relay

A relay that functions at a *predetermined phase angle* between two voltages or between two currents, or between voltage and current.

Rectification failure relay

A relay that functions if a *power rectifier fails* to conduct or block properly.

Instantaneous overcurrent relay 50

A relay that functions instantaneously on an *excessive value of current*.

AC directional overcurrent relay 67

A relay that functions on a desired value of *AC overcurrent flowing in a predetermined direction*.

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.

Rate-of-rise relay

A relay that functions on an *excessive rate-of-rise of current*.

Phase-sequence voltage relay 47

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

AC time overcurrent relay 51

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.

Distance Relay 21

A relay that functions when the *circuit admittance, impedance, or reactance increases or decreases* beyond a predetermined value.

DC overcurrent relay

A relay that functions when the *current in a DC circuit exceeds* a given value.

Undercurrent or underpower relay

A relay that functions when the *current or power flow decreases* below a predetermined value.

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.

Machine or transformer thermal relay 49

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.

Reverse-phase current relay 46

A relay that functions when the polyphase currents are of *reverse-phase* sequence, or when the polyphase *currents* are unbalanced or contain negative phase-sequence components above a given amount.

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*.

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.

Carrier or pilot-wire receiver relay

A relay that is operated or restrained by a signal that is used with *carrier-current* or DC *pilot-wire* fault relaying.

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, to stop, or to provide a check of the position of these devices or conditions for any purpose.

Voltage or current balance relay

A relay that operates on a given *difference in voltage, or current* input or output, of two circuits.

Directional power relay 32

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.

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*.

Ground protective relay 64

A relay that operates upon failure of machine or other apparatus *insulation to ground*.

Undervoltage relay 27

A relay that operates when its *input voltage is less than* a predetermined value.

Overvoltage relay 59

A relay that operates when its *input voltage is more than* a predetermined value.

Power factor relay

A relay that operates when the *power factor* in an AC circuit rises above or falls below a predetermined value.

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*.

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.

Frequency relay 81

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.

Line switch 89

A switch that is used as a disconnecting, load-interrupter, or *isolating switch* in an AC or DC power circuit.

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.

Position switch

A switch that makes or breaks contact* when the main device or piece of apparatus, which has no device function number, reaches a *given position*.

Flow switch

A switch that operates on given values, or on a given *rate of change of flow*.

Pressure switch

A switch that operates on given values, or on a given rate of change of *pressure*.

Level switch

A switch that operates on given values, or on a given rate of change, of *level*.

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. 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.

Telemetering device

A transmitter that is used to *generate* and *transmit* to a remote location an electrical signal representing a measured quantity, or a receiver that is used to *receive* the *electrical signal* from a remote transmitter and *convert* the signal *to represent the original measured quantity*.

Electrically operated valve

An *electrically operated*, controlled, or monitored *valve* in a fluid, air, gas, or vacuum line.

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.

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.

Operating mechanism 84

The complete electrical *mechanism* or servomechanism, 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 number.

Master Element

The initiating device, such as a control switch, that directly or indirectly *places equipment in or out of operation*.

Data Communications device

Used to label *Communication Networking Devices*. This element also uses a unique set of suffixes that are applicable only to Device 16. The first suffix letter is to be either S for serial devices or E for Ethernet devices.

Overspeed device

Usually, a direct-connected speed switch that functions on *machine overspeed*.