MRM3-2 – Motor Protection Relay
MRM3-2 – Motor Protection RelayManual MRM3-2 (Revision A)
WoodwardManual MRM3-2 GBWoodward Governor Company reserves the right to update any portion of this publication at any time .Informationprovided by Woodward Governor Company is believed to be correct and reliable .However no responsibility is assumed by Woodward Governor Company unless otherwise expressly undertaken Woodward 1994-20082DOK-TD-MRM3 Rev.A
Manual MRM3-2 GBWoodwardContents1.Introduction and Application . 62.Characteristics and Features . 73.Design . 83.1Connections .83.1.1 Analog Inputs .93.1.2 Output Relays.93.1.3 Digital Inputs.103.1.4 Low/High Range of the Digital Inputs .103.2Front plate .113.2.1 Indicating LEDs .123.2.2 Adjusting LEDs .123.3Analog part .123.4Digital part .134.Working Principle . 144.1Start Recognition .144.1.1 Criteria for Blocking the Start .164.2Starting time .184.3Thermal Image .184.4Requirement on the Main Current Transformers .195.Operation and Adjustments . 205.1Displayed text for parameter settings .205.2Setting Procedure .215.3System parameters .215.3.1 Presentation of Measuring Values as Primary Quantities on the Display (Iprim Phase) 215.3.2 Rated -Frequency .215.3.3 Operating Hour Meter (h) .215.3.4 Number of Motor Starts (No.) .215.3.5 Indication of pickup .215.3.6 Parameter Set Changeover Switch (P2) .225.4Protection Parameters .225.4.1 Thermal Overload Protection (k x IB) .225.4.2 Warning/Tripping with thermal Overload .225.4.3 Tripping Delay for Thermal Overload .225.4.4 Heating Period Constant W and Cooling-Down Time Factor C .225.4.5 t2x and t6x Minimal Trip Time During the Starting Process. .235.4.6 Phase Undercurrent Element (I ) .235.4.7 Phase Over current Element (I ) .235.4.8 Trip Characteristics for the Phase Over current Element (I CHAR) .235.4.9 Tripping Time or Time Factor for the Phase Over current Element (I t ) .245.4.10Reset Mode for the Trip Characteristics in the Phase Current Path (I CHAR t ) .245.4.11Phase Short-Circuit Trip (I ) and (I Start) .245.4.12Negative Phase Sequence.255.4.13Earth Fault Element (IE ).255.4.14Switching Over Warning/Tripping.255.4.15Trip Characteristics for the Earth-Fault Element (IE CHAR) .255.4.16Tripping Time or Time Factor for the Earth Fault Element (IE t ) .265.4.17Reset Time for the Earth Fault Element (IE CHAR t ) .265.4.18Tripping Time for the CB Failure-Protection (CB t ) .265.4.19External Trip (delayed)(Trip t ) .265.4.20Trip Blocking in case of Excessive Phase Current (Trip Block) .265.5Start Supervision .275.5.1 Duration of a Start Cycle (No. Start) .275.5.2 Number of Starts per Cycle (No. Start) .275.5.3 Start Blocking Time (Start Block t ) .275.5.4 Characteristic for the Starting Time.275.5.5 Rated starting current I Start .275.5.6 Maximal Start Time (Start t ) .28DOK-TD-MRM3 Rev.A3
WoodwardManual MRM3-2 GB5.5.7 Start-up recognition time or Motor Running time . 285.5.8 Stopping time . 285.6Interface Parameters . 285.6.1 Adjustment of the Slave-Address (RS) . 285.6.2 Adjustment of the Baud-Rate (only for Modbus Protocol) . 285.6.3 Adjustment of the Parity (only for Modbus-Protocol) . 285.7Recorder (FR) . 295.7.1 Fault Recorder or Disturbance Recorder. 295.7.2 Number of Fault Recordings . 305.7.3 Adjustment of the Trigger Event . 305.7.4 Pre-Trigger Time (Tvor) . 305.8Setting of the Clock. 315.9Additional Functions . 325.9.1 Blocking of the Protective Functions . 325.9.2 Allocation of the Reset Functions . 335.9.3 Allocation of the Output Relays . 345.10 Measuring Value and Fault Indications . 365.10.1Measuring Value Indications. 365.10.2Units of the Displayed Measuring Values . 365.10.3Indication of the Fault Data . 365.10.4Fault Memory . 375.11 Reset. 385.11.1Erasure of the Fault Memory . 385.11.2Reset of the Thermal Memory . 385.12 Digital Inputs . 395.12.1Parameter Set Changeover Switch . 395.12.2External Trigger of the Fault Recorder . 395.12.3Recognition of “Motor Running” Condition . 395.12.4Undelayed External Trip . 395.12.5Delayed External Trip . 396.Notes on Relay Tests and Commissioning . 406.1Connection of the auxiliary voltage . 406.2Testing of Output Relays and LEDs . 406.3Test circuit for MRM3-2 . 416.3.1 Checking of Input Circuits and of the Measuring Values. 416.3.2 Testing the START-STOP-RUNNING Recognition . 416.3.3 Testing the Pick-Up and Disengaging Values . 426.3.4 Testing the maximum starting time . 426.3.5 Testing the thermal image . 426.3.6 Testing the Control Inputs. 426.3.7 Testing the CB Failure Protection . 426.4Primary Test. 436.5Maintenance . 437.Technical Data. 447.1Measuring input . 447.2Common data . 447.3Setting ranges and steps . 457.3.1 System parameter . 457.3.2 Time over current protection . 467.3.3 Load Unbalance Protection . 487.3.4 Earth fault protection. 497.3.5 Circuit breaker failure protection . 507.3.6 External trip delay . 507.3.7 Trip blocking beginning with the adjusted rated current . 507.3.8 Start parameter . 517.3.9 Interface parameter . 527.3.10Fault recorder parameter . 527.4Tripping characteristics . 537.4.1 Tripping characteristic for max. starting time . 537.4.2 Thermal image . 544DOK-TD-MRM3 Rev.A
Manual MRM3-2 GBWoodward7.4.3 Initial load factor .547.4.4 Tripping of t2x and t6x - times .557.4.5 Inverse time over current protection .567.4.6 Trip characteristics .577.4.7 Inverse Time Characteristic for Load Unbalance .617.5Output relays .618.Order form . 62DOK-TD-MRM3 Rev.A5
WoodwardManual MRM3-2 GB1. Introduction and ApplicationThe motor protection relay MRM3-2 offers reliable protection for LV and MV motors which are either operated via power contactors or power circuit breakers.The following functions are integrated into this relay: Overload protection acc. to IEC 255-8 in consideration of the initial load factor(thermal image)Definite undercurrent protectionDefinite time over current protection (DMT)Inverse time over current protection (IMT) with select-able trip characteristicsShort-circuit protectionLoad unbalance supervision with definite or inverse trip characteristicsEarth-fault detection with suppression of harmonicsThe MRM3-2 recognizes the “Start-Up“ and “Motor Running“ phase.Motors with a limited number of starts can be controlled by the start limiting function of the relay.The earth-fault supervision is either realized in Holm-green connection or by means of a core-typecurrent transformer.The motor can be stopped in delayed or undelayed mode via digital inputs.The MRM3-2 is available with rated currents of 1A or 5A.Important:For additional common data of all MR-relays please refer to manual "MR - Digital Multifunctional relays". On page 45 of this manual you can find the valid software versions.6DOK-TD-MRM3 Rev.A
Manual MRM3-2 GBWoodward2. Characteristics and Features Microprocessor technology with self-supervision,Measuring of phase currents as RMS value,Digital filtering of the earth current with discrete Fourier analysis, by which the influence ofinterference signals, such as harmonics and transient DC components during an earthfault are suppressed.Two sets of parameters,Operating hour meter,Complies with the requirements of IEC 255-8, VDE435, part 301-1 for overload relays,Definite time undercurrent protection,Selectable protective functions : Definite time over-current protection (DMT) and inversetime over current protection (IMT)Selectable IMT trip characteristics of IEC 255-4:- Normal inverse (Type A)- Very inverse (Type B)- Extremely inverse (Type C)- Special-purpose characteristicsReset mode for DMT/IMT trip characteristics is selectable,Definite element for short-circuit high-speed tripSingle-step earth fault supervision,Load unbalance protection with inverse or definite trip characteristics (NPS),CB failure protection,Display of the measuring values as primary quantities,Measuring of the phase currents during short-circuit free operation,Blocking of the individual protective elements or the trip elements can be set freely,The protective functions can be freely allocated to the output relays. (Relay Matrix),Suppression of an LED indication after activation (LED flash),„Manual/Automatic“ reset function of the trip elements adjustable via the configurationmatrix,Saving of trip values and the switch-off times (tCBFP) of 25 fault events (voltage fail-safe)Recording of up to 8 fault events with time stamp,Display of date and time,Trip via digital inputs,Rack mounting, with self-acting short-circuit mechanism for CT circuits,Possibility of serial data exchange via the RS485 interface, optionally with WoodwardRS485 Pro-Open-Data Protocol or Modbus Protocol.DOK-TD-MRM3 Rev.A7
WoodwardManual MRM3-2 GB3. Design3.1ConnectionsFigure 3.1: Connection Diagram MRM3-2Figure 3.2: Measuring of phase currents and earth current detection in Holmgreen connection (IE)This kind of connection can be used where three phase CTs are available and a combination ofphase and earth current measuring is required.8DOK-TD-MRM3 Rev.A
Manual MRM3-2 GBWoodwardFigure 3.3: Measuring of earth current with core-type CT (IE)With the combination of phase and earth current measuring, CTs to be connected according toFigure 3.2. and Figure 3.3.3.1.1 Analog InputsThe analog input signals of the phase currents IL1 (B3 - B4), IL2 (B5 - B6), IL3 (B7 - B8) and the earthcurrent IE (B1 - B2) are fed to the protection device via separate input CTs.The current measuring quantities are galvanic decoupled, analogously filtered, and then fed to theanalog/digital converter.3.1.2 Output RelaysThe MRM3-2 has 5 output relays. Two of these relays with two change-over contacts and three relays with one change-over contact each are used for signaling. The protective functions can befreely allocated except of those for the self-supervision relay. Relay 1: C1, D1, E1 and C2, D2, E2Relay 2: C3, D3, E3 and C4, D4, E4Relay 3: C5, D5, E5Relay 4: C6, D6, E6Relay 5: Self-supervision C7, D7, E7All relays are operating according to the n. o. principle with the exception of the self-supervision relay, which operates acc. to the n. c. principle.DOK-TD-MRM3 Rev.A9
WoodwardManual MRM3-2 GB3.1.3 Digital InputsThe MRM3-2 has 7 digital inputs with fixed functions. All inputs have a common reference point :Terminal D8. (See Chapter l resetExternal blockingParameter set change-over switchExternal trigger for the fault recorderIdentification „Motor Running“Ext. trigger, undelayedExt. trigger, delayedCoding Plug21347653.1.4 Low/High Range of the Digital InputsThe MRM3-2 is equipped with a wide-range power supply unit and hence the supply voltage isfreely selectable. The switching threshold of the digital inputs, however, has to be fixed in compliance with the supply voltage. Two different switching thresholds can be adjusted:RangeLowHighPlugPlugged inOpenU not active 8V 60VU active 10V 80VFigure 3.4: Coding Plug10DOK-TD-MRM3 Rev.A
Manual MRM3-2 GB3.2WoodwardFront plateFigure 3.5: Front plate MRM3-2-IEFigure 3.6: Front plate MRM3-2-IDOK-TD-MRM3 Rev.A11
WoodwardManual MRM3-2 GBThe LEDs , h, RS and FR on the MRM3-2 emit a yellow light, all other LEDs are bi-colored. TheLEDs at the left next to the alphanumerical display give a green light during measuring and a redone when a fault signal occurs.The LEDs underneath the SELECT/RESET - push but-ton emit a green light during adjustmentand inquiry of the setting quantities left to the LEDs. They show a red light if the printed settingquantities right to the LEDs are activated.3.2.1 Indicating LEDsL1, L2, L3EI2 h Indication of the phase currentsIndication of the earth currentIndication of the unbalanced loadcurrent (NPS)Indication of the temperature equivalentOperating hour meterDate and time3.2.2 Adjusting LEDsIB K W Ct No.CHARI I I2 I IE CBBlock0StartTripFRRSP2S/R3.3Rated motor currentConstant quantity (k*IB 100% thermal load)Heating period constantCooling down factorTripping times, generallySwitching threshold of the thermal overload alarmNumber of motor startsCharacteristics settingUndercurrent settingOver current settingLoad unbalance setting (NPS)Short-circuit settingEarth current settingCB failure protectionStart blocking/Protective blockingCurrent 0/ 0 START/STOP recognitionStart blocking/Start timeExternal tripParameter for the fault recorderSetting of the relay addressParameter set 2 is activeMotor starting/Motor runningAnalog partThe alternating currents injected by the CTs are converted into galvanical isolated voltages via input transmitters and burden in the analog part.The effect of inductive and capacitive coupled interferences are suppressed by RC analog filters.The measuring voltages are fed to the analog inputs (A/D trans-former) of the micro-processor andthen converted into digital signals by means of sample and hold circuits. These digitized values arethen used for further processing. The measuring values are acquired at fn 50 Hz (fn 60 Hz) witha sampling frequency of 800 Hz (960 Hz), and thus the instantaneous values of the measuredquantities are acquired every 1.25 ms (1.04 ms).12DOK-TD-MRM3 Rev.A
Manual MRM3-2 GB3.4WoodwardDigital partThe protection relay is equipped with a powerful micro-controller, being the core element of the protection unit. With this micro-controller all tasks are completely digitally processed, from discretisation of the measuring quantities to protective tripping.With the protection program, stored in the program storage (EPROM), the micro-processorprocesses the voltages applied to the analog inputs and from this calculates the fundamental harmonics of the current. Digital filtering (DFFT-Discrete Fast-Fourier-Transformation) for suppressionof harmonics as well as suppression of DC components during the short-circuit is used in theprocess.The micro-processor compares the existing current with the threshold value (setting value) storedin the parameter storage (EEPROM) and up-dates the thermal image. If a current exceeds thethreshold value for longer than the trip delay or if the thermal image exceeds its rated value, a faultsignal occurs. Dependent on their settings, the output relays pick up as well. When setting the parameters, all setting values are read-in by the micro-processor and saved in the parameter storage.The program flow is continuously monitored by the incorporated "Hardware-Watchdog". Processorfailure is signaled by the “Self supervision” output relay.Figure 3.7: Block Diagram of Protective FunctionsDOK-TD-MRM3 Rev.A13
WoodwardManual MRM3-2 GB4. Working Principle4.1Start RecognitionThe MRM3-2 monitors the flow of the current from which the following operational conditions of themotor are gathered. STOP START RUNNINGFigure 4.1: Different Start-Up Behavior of MotorsSTOP - Condition:If no current can be measured (I Stop threshold), STOP conditions are recognized after expiration of the stop time.Start/Stop ThresholdThis threshold is fixed at 2% of INStop time:The Stop time is adjustable in order to tolerate a brief off-time of the current flow (e.g. change-overStar/Delta) from the START or RUNNING conditions. STOP is only indicated if the current was under 2% IN for longer than the stop time. Based on this time the running down period can be considered in a certain way for the LED indication.START-Condition:START is only recognized if the previous condition was STOP and the motor current has exceededthe start threshold. If the STOP or RUNNING conditions are recognized, the START condition isterminated.14DOK-TD-MRM3 Rev.A
Manual MRM3-2 GBWoodwardOverload Threshold:This corresponds to the permissible thermal continuous current k x IB and is adjusted by theparameter of the thermal image.Starter Recognition Time:This adjustable time has only to be extended for special start procedures in order to prevent thatthe RUNNING conditions are indicated too early in advance. No exceeding of the start threshold during pony motor start-up or when soft starters areused.Multistage resistance start where the start threshold is either exceeded several times or notat all.The time is running from the instance the start threshold is exceeded. RUNNING is only acceptedby the supervision after the time has elapsed or the overload threshold is undershot. If the overloadthreshold is not a clear criterion, the time has to be set at least for so long that the longest regularstart procedure is covered.RUNNING can be recognized in different ways: If the START has been successfully completed. This is the case when the motor currenthas dropped below k x IB and the start recognition time has elapsed. (direct start)or if the motor is connected across several resistance steps, it is possible that the start threshold is passed through repeatedly. RUNNING conditions are recognized when the startrecognition time has run out after the last step and a current has settled between 2% INand k x IB t. (Resistance start). if after STOP a motor current has settled between 2% IN and k x IB and the start recognition time has elapsed. The overload threshold has not necessarily to be exceeded.(soft start) If the «Motor Running» input was activated but the overload threshold is not (or not anylonger) exceeded. (See Chapter 5.12.3 )With the recognition of STOP, the RUNNING conditions have ceased to exist.Figure 4.2: Flow Diagram of the Start ConditionsDOK-TD-MRM3 Rev.A15
WoodwardManual MRM3-2 GB4.1.1 Criteria for Blocking the StartNumber of monitored starts :The MRM3-2 is equipped with a flexible supervision element which can limit the sequence of possible starts.A start should be prevented if it is obvious that it is likely to be interrupted due to overload so that intotal the down-time can be curtailed. If a start is not recommendable at a certain time (with the motor switched off), the MRM3-2 activates an allocated output relay until the waiting time has elapsed.Irrespectively of the adjustment of this element, the thermal image is always activated and shutsthe motor down as soon as the thermal overload threshold is reached (due to a start or overload).The protective element can either be tied to the thermal image or be manually defined by the number of starts and cycle duration.Number of Starts/Cycle DurationThese two are defined as parameters.Example:The motor should be allowed to be started three times an hour:This means that in theory the motor can be started every 20 minutes ( 60 min/3).From this it can be concluded that the load generated by the start procedure has decayed afterthese 20 minutes. If the motor would be successfully started three time in quick succession, animmediate fourth start would overload the motor. The start blocking relay would be activated andthe next start would only be advisable after about 20 minutes. The protective element ensures thatthe start sequence is kept within safe intervals but that at least three starts are allowed during thegiven time frame. If the intervals between each start are long enough then even more than threestarts an hour might be possible because the motor was able to cool down in the mean time. Thedelay can be firmly defined (through start blocking time) or be automatically ascertained (VARI )until the 20 minutes given in the example are over. The state of the thermal image has no influence.on the delayFigure 4.3: Relation Start Period/Start Blocking Time16DOK-TD-MRM3 Rev.A
Manual MRM3-2 GBWoodwardFigure 4.4: Relation Start Period/Start Blocking Time with firm Start Blocking TimeThermal ImageA start is always possible as long as there is enough thermal reserve for a start. This start limitationis a dynamic one and is orientated on the data the thermal ima
Relay 2: C3, D3, E3 and C4, D4, E4 Relay 3: C5, D5, E5 Relay 4: C6, D6, E6 Relay 5: Self-supervision C7, D7, E7 All relays are operating according to the n. o. principle with the exception of the self-superv
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