Protection Relay Considerations
The advent of programmable microprocessor-based relays (also called numeric relays) has provided some flexibility in the use of protective relays. However, a large part of protection relays still in use are electromechanical/or simply thermal-magnetic relays with no electronic component at all.
Cost wise, digital relays are much affordable than electromechanical relays. Old protection specialists who trudged the long and rigorous path to bring us the present state of advanced protective relaying technique consider employment of affordable digital relay devices is not the primary concern, but how the “art of protective relaying” is preserved with the entry of programmable microprocessor-based relays.
Microprocessor based relays is considered a big leap for a great number of protection specialists in big or small engineering firms. It is a big leap, too, most especially for digital relay manufacturers, since the massive investment in precision equipment needed to build electromechanical relay components, such as precision balance beams, polarizing coils, induction disks, is no longer a big concern. All these complicated components have all been replaced by a simple easy to manufacture printed boards that can be mass produced with minimum time.
The advent of the digital relay has one big disadvantage: a big number of engineers now almost always ignore symmetrical component theory and application.
Probably the most onerous practice today is A/E firms’ passing the responsibility of short-circuit calculations and system protection to electrical contractors or testing specialist freelance which is creating a legal liability environment. Only the protection specialist employed or maintained by A/E firms MUST perform all the complex calculations for the protection system.
Device #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.
Device #2 – Time-delay Starting or Closing Relay A device which functions to give the 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.
Typical uses: For providing a time-delay for re-transfer back to the normal source in an automatic transfer scheme
Device #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.
Device #5 – Stopping Device. 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. 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.)
Device #6 – Starting Circuit Breaker. A device whose principal function is to connect a machine to its source of starting voltage.
Device #7 – Rate of Change Relay. A relay that functions on an excessive rate-of-rise of current.
Device #8 – Control Power Disconnecting Device. 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.
Device #9 – Reversing Device. 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. A device that is used for the purpose of reversing a machine field or for performing any other reversing functions.
Device #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.
Device #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.
NOTE: If only two relatively important functions are performed by the device, it is preferred that both function numbers be used.
Device #12 -Overspeed Device. 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. Usually, a direct-connected speed switch that functions on a machine over speed.
Device #13 – 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.
Device #14 – Underspeed Device. A device that functions when the speed of a machine falls below a predetermined value.
Device #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.
Device #16 – Data Communications Device. For communication system application.
Device #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.
Device #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.
Device #19 – Starting to Running Transition Timer. A device which operates to initiate or cause the automatic transfer of a machine from the starting to the running power connection.
Typical uses: Used to transfer a reduced voltage starter from starting to running.
Device #20 – Electrically Operated Valve (solenoid valve). An electrically operated, controlled or monitored valve used in a fluid, air, gas, or vacuum line.
Device #21 – Distance Relay. A device which functions when the circuit admittance, impedance or reactance increases or decreases beyond predetermined limits. It has three (3) zones of protection, Zone-1, Zone-2 and Zone-3.
Typical uses: For transmission line protection.
Device #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.
Device #23 – Temperature Control Device. A device which functions to raise or to lower the temperature of a machine or other apparatus, or of any medium, when its temperature falls below or rises above, a predetermined level.
Typical uses: Used thermostat control space heaters in outdoor equipment.
Device #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.
Device #25 – Synchronizing or synchronism check device. 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. A device which operates when two AC circuits are within the desired limits of frequency, phase angle or voltage, to permit or cause the paralleling of these two circuits.
Typical uses: In a closed transition breaker transfer, a device #25 relay is used to ensure two-sources are synchronized before paralleling. Use for feeder protection.
Device #26 – Apparatus Thermal Device. A device that functions when the temperature of the protected apparatus (other than the load carrying windings of machines and transformers as covered by device function #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.
Device #27 – Under Voltage Relay. A device which functions on a given value of under voltage.
Typical uses: Used to initiate an automatic transfer when a primary source of power is lost.
Device #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.
Device #29 – Isolating Contactor. A device that is used expressly for disconnecting one circuit from another for the purposes of emergency operation, maintenance, or test.
Device #30 – Annunciator Relay. 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.
Typical uses: Used to remotely indicate that a protective relay has functioned, or that a circuit breaker has tripped. Typically, a mechanical “drop” type annunciator panel is used.
Device #31 – Separate Excitation Device. A device that connects a circuit, such as a shunt field of a synchronous converter, to a source of separate excitation during the starting sequence.
Device #32 – Directional Power Relay. A relay which functions on the desired value of power flow in a given direction, or upon reverse power resulting from arc back in the anode or cathode circuits of a power rectifier.
Typical uses: Used to prevent reverse power from feeding an upstream fault. Often used when primary backup generation is utilized in a facility.
Device #33 – Position Switch. A device which makes or breaks contact when the main device or piece of apparatus, which has no device function number, reaches a given point. TYPICAL USES: Used to indicate the position of a draw out circuit breaker (TOC switch).
Typical uses: Used to indicate the position of a draw out circuit breaker (TOC switch).
Device #34 – 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.
Device #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.
Device #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.
Device #37 – Undercurrent or Underpower Relay. A relay which functions when the current or power flow decreases below a predetermined value.
Typical uses: Motor protection relay.
Device #38 – Bearing Protective Device. A device which functions on excessive bearing temperature, or on other abnormal mechanical conditions, such as undue wear, which may eventually result in excessive bearing temperature.
Typical uses: Motor or generator protection relay.
Device #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 excessive vibration, eccentricity, expansion, shock, tilting, or seal failure.
Device #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.
Device #41 – Field Circuit Breaker. A device which functions to apply, or to remove, the field excitation of a machine.
Typical uses: Generator applications.
Device #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 fault protecting means, primarily for frequent opening and closing of the circuit.
Device #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.
Device #44 – 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.
Device #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.
Device #46 – Reverse-phase, or Phase Balance, Current Relay. A relay which functions when the polyphase currents are of reverse-phase sequence, or when the polyphase currents are unbalanced or contain the negative phase-sequence components above a given amount.
Typical uses: Motor protection relay.
Device #47 – Phase-sequence Voltage Relay. A relay which functions upon a predetermined value of polyphase voltage in the desired phase sequence.
Typical uses: Feeder protection.
Device #48 – Incomplete Sequence Relay. A relay that generally returns the equipment to the normal, or off, position and locks it out of the normal starting, or operating or stopping sequence s not properly completed within a predetermined amount of time. If the device is used for alarm purposes only, it should preferably be designated as 48A (alarm)
Device #49 – Machine, or Transformer, Thermal Relay. A relay that functions when the temperature of a machine armature, or other load carrying winding or element of a machine, or the temperature of a power rectifier or power transformer (including a power rectifier transformer) exceeds a predetermined value.
Typical uses: Motor or transformer thermal relay application.
Device #50 -Instantaneous Overcurrent, or Rate-of-Rise Relay. A relay that functions instantaneously on an excessive value of current, or an excessive rate of current rise, thus indicating a fault in the apparatus of the circuit being protected.
Typical uses: Use for tripping circuit breakers instantaneously during a high-level short circuit. Can trip on phase – phase (50), phase-neutral (50N), phase-ground (50G) faults.
Device #51 – AC Time Overcurrent Relay. A relay with either a definite or inverse time characteristic that functions when the current in an AC circuit exceeds a predetermined value.
– For tripping a circuit breaker after a time delay during a sustained overcurrent.
– For tripping a circuit breaker instantaneously during a high level short circuit.
– Trips on phase (51), neutral (51N) or ground (51G) overcurrents.
Device #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.
Typical uses: A term applied typically to high and medium voltage circuit breakers or low voltage power circuit breakers.
Device #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.
Device #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.
Device #55 – Power Factor Relay. A relay that operates when the power factor in an AC circuit rises above or below a predetermined value.
Typical uses: Under or over frequency application used in generating plants.
Device #56- 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.
Device #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.
Device #58 – Rectification Failure Relay. A device that functions if a power rectifier fails to conduct or block properly.
Device #59 – Over Voltage Relay. A relay that functions on a given value of overvoltage.
Typical uses: Used to trip a circuit breaker, protecting downstream equipment from sustained overvoltages.
Device #60 – Voltage or Current Balance Relay. A relay that operates on a given difference in voltage, or current input or output of two circuits.
Device #61 – Density Switch or Sensor. A device that operates on a given value, or a given rate of change, of gas density.
Device #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.
Typical uses: Used in conjunction with a 27 device to delay tripping of a circuit breaker during a brief loss of primary voltage, to prevent nuisance tripping.
Device #63 – Pressure Switch. A switch which operates on given values or on a given rate of change of pressure.
Typical uses: Use to protect a transformer during a rapid pressure rise during a short circuit. This device will typically act to open the protective devices above and below the transformer. Typically used with a 63-X auxiliary relay to trip the circuit breaker.
Device #64 – Ground Protective Relay. A relay that functions on a failure of the insulation of a machine, transformer, or of other apparatus to the ground, or on flashover of a DC machine to the 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 overcurrent relay connected in the secondary neutral of the current transformers.
Typical uses: Used to detect and act on a ground-fault condition. In a pulsing high resistance grounding system, a device #64 will initiate the alarm.
Device #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.
Device #66 – 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 also 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.
Typical uses: Motor protection applications.
Device #67 – AC Directional Overcurrent Relay. A relay that functions on the desired value of AC overcurrent flowing in a predetermined direction.
Device #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.
Device #69 – Permissive Control Device. A device that is generally a two-position manually operated switch 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 to the equipment from being operated.
Typical uses: Used as a remote-local switch for circuit breaker control.
Device #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.
Device #71 – Level Switch. A switch that operates on given values, or on a given rate of change of level.
Typical uses: Used to indicate a low liquid level within a transformer tank in order to save transformers from loss-of-insulation failure. An alarm contact is available as a standard option on a liquid level gauge. It is set to close before an unsafe condition actually occurs.
Device #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.
Device #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 a circuit, or to switch a light or regenerative load resistor of a power rectifier or other machine in and out of the circuit.
Device #74 – Alarm Relay. A device other than an annunciator, as covered under device number 30, which is used to operate, or to operate in connection with, a visible or audible alarm.
Device #75 – Position Changing Mechanism. A mechanism that is used for moving the 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.
Device #76 – DC Overcurrent Relay. A relay that functions when the current in a dc circuit exceeds a given value.
Device #77 – 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.
Device #78 – 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.
Device #79 – AC Reclosing Relay. A relay that controls the automatic closing and locking out of an AC circuit interrupter.
Typical uses: Used to automatically reclose a circuit breaker after a trip, assuming the fault has been cleared after the power was removed from the circuit. The recloser will lock-out after a predetermined amount of failed attempts to reclose.
Device #80 – Flow Switch. A switch that operates on given values, or on a given rate of change, of flow.
Device #81 – Frequency Relay. A relay that functions on a predetermined value of frequency either under or over, or on a normal system, frequency or rate of change frequency. TYPICAL USES: Used to trip a generator circuit breaker in the event the frequency drifts above or below a given value.
Device #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.
Device #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.
Device #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 number.
Device #85 – Carrier or Pilot-Wire Receiver Relay. A relay that is operated or restrained by a signal used in connection with carrier current or DC Pilot-Wire fault relaying.
Device #86 – Locking-out Relay. An electrically operated hand, or electrically, reset relay that functions to shut down and hold an equipment out of service on the occurrence of abnormal conditions.
Typical uses: Used in conjunction with protective relays to lock-out a circuit breaker (or multiple circuit breakers) after a trip. Typically required to be manually reset by an operator before the breaker can be reclosed.
Device #87 – Differential protective Relay. A protective relay that functions on a percentage or phase angle or other quantitative difference of two currents or of some other electrical quantities.
Typical uses: Use to protect static equipment, such as cable, bus, transformers by measuring the current differential between two points. Typically the upstream and/or downstream circuit breaker will be incorporated into the “zone of protection”.
Device #88 – Auxiliary Motor or Motor Generator. A device used for operating auxiliary equipment, such as pumps, blowers, exciters, rotating magnetic amplifiers, etc.
Device #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.)
Device #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.
Device #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.
Device #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.
Device #93 – Field-changing Contactor. A contactor that functions to increase or decrease, in one step, the value of field excitation on a machine.
Device #94 – Tripping or Trip-free Relay. A relay that functions to trip a circuit breaker, contactor, or equipment, or to permit immediate tripping by other devices, or to prevent immediate reclosure of a circuit interrupter, in case it should open automatically even though its closing circuit is maintained closed.
Device #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.
B – Bus F – Field G – Ground or generator N – Neutral T – Transformer
Sources and References:
– IEEE Standard C37.2-2008
– ABB Device Function Numbers according to IEEE C.37.2-1991
– EATON Sheet 0017 Jan, 2005