Motor Protection ApplicationConsiderations

About the Authors

Paul Lerley has 28 years of utility and electronics experience, including 15 years at Central MainePower Co. He is a graduate of the University of New Hampshire and was Director of SubstationsElectrical Systems at Central Maine Power prior to joining Basler Electric Company. Mr. Lerley is aSenior Member of the IEEE and a member of four working groups of the Power System RelayingCommittee. He has authored articles on testing for the Doble Engineering Conference and Transmis-sion and Distribution magazine. He was previously very active in the Electric Council of New England.Mr. Lerley was a Regional Application Engineer for Basler Electric from 1994 to 1999.

Mike Young of Sanford, Florida, received his MBA from Rollins College in 1983 and BSET fromPurdue University in 1971. He worked for Wisconsin Electric Power Company as a Relay Engineerfor two years, and for Florida Power Corporation as a Field Relay Supervisor for 21 years. Heauthored the text "Protective Relaying for Technicians" and co-authored papers for the Georgia TechProtective Relaying Conference. Mr. Young has been a Regional Application Engineer for BaslerElectric since 1994 and is a member of the IEEE.

This document contains a summary of information for the protection of various types of electricalequipment. Neither Basler Electric Company nor anyone acting on its behalf makes any warranty orrepresentation, express or implied, as to the accuracy or completeness of the information containedherein, nor assumes any responsibility or liability for the use or consequences of use of any of thisinformation.

First printing 4/98

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Motor Protection ApplicationConsiderations

1. INTRODUCTION

When applying protective relays to motors orany other equipment, we always ask how muchprotection is enough. The answer depends onrewind cost, loss of production, effect ondowntime, new versus old installation, need forcommunication, metering, control and theconsequences of a motor failure on the electri-cal system and process.

This publication presents an overview of motorhazards and a discussion of detection andprotection options. Basler relay models areoffered with typical setting value ranges andconsiderations to help designers and usersselect Basler relays for motor protection. Mostof the protection functions apply to squirrelcage, wound induction motors and synchro-nous motors. Additional protection is usuallyprovided for synchronous motors and will bementioned in this document.

2. OVERVIEW OF MOTOR HAZARDS

Motor protection is a challenge because thereare so many different things that can go wrongwith a motor and its associated load:

Motor induced• Insulation failure (within the motor)• Bearing failure• Mechanical failure• Synchronous motors-loss of field

Load induced• Overload and underload• Jamming• High inertia

Environment induced• High ambient temperature• High contaminant level or blocked

ventilation• Cold or wet ambient conditions

Source induced• Loss of phase or phases• Voltage unbalance• Overvoltage• Undervoltage• Phase reversal• Out of step condition resulting from system

disturbance

Operation induced• Synchronizing or closing out of phase• High duty cycle• Jogging• Rapid reversing

3. PROTECTION

3.1 Stator Faults

3.1.1 Phase Fault Overcurrent Protection

Phase to phase and three phase faults areusually detected with nondirectional

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instantaneous or definite time overcurrentrelays. If the available 3-phase fault current is alow multiple of the relay setting (weak system),quick pickup is not assured. Differential relayingshould then be considered. Instantaneousrelays are typically applicable when the motorrating is less than one-half of the supply trans-former KVA rating.

The instantaneous phase relay should be set atno less than 1.6 times the locked rotor currentusing the value of locked rotor current atmaximum starting voltage. This setting alsoassumes the relay is sensitive to the transientoverreach (DC offset) of an asymmetrical fault.Lower settings are possible if the relay disre-gards the transient component or if a time delaylonger than the transient time (6-15cy) is added.Verify that the minimum 3-phase fault current atthe motor terminals is at least 3 times the relaysetting. Fig. 1 illustrates the relay settings inrelation to the starting current and the minimumshort circuit current.

FIGURE 1. Stator short circuit protection with 50 or 50Pelement.

3.1.2 Differential Protection

Differential protection is used on motors wherethe available short circuit current is close to thevalue of locked rotor current. It is also frequentlyused on very large motors because of itsgreater sensitivity. Differential protection isalways preferred; however, it is generally morecostly than instantaneous relaying because allsix leads must be brought out of the motor andadditional relays may be required.

SELF BALANCINGThe most economical approach is self-balanc-ing differential as shown in Fig. 2. Both ends ofthe winding are passed through a toroidalcurrent transformer and connected to a 50device. This CT has a maximum openingaround 8 inches that may preclude its use onlarger motors.

FIGURE 2. Self balancing differential.

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With a fixed ratio of 50:5 and a sensitive instan-taneous overcurrent, the self-balancing differen-tial provides a pickup around 5 amps of primarycurrent. This scheme is self-balancing andproduces no current for starting or load varia-tion and, because there is only one CT perphase, there is no concern about matching CTperformance to eliminate unequal CT saturation.CT saturation is likely for large fault currents butis slow enough to allow the instantaneous relaysto operate.

PERCENTAGE RESTRAINT DIFFERENTIALWhen the toroidal CT cannot be used, thepercentage restraint differential circuit (Fig. 3)must be applied. Typically, all 6 CTs are thesame ratio and accuracy class. A 2-windingdifferential relay can be applied with equalcurrents flowing in the restraint windings fornormal load, starting, and external faults. Forinternal phase or ground faults, all of the currentwill flow through the operate windings. Thescheme will also protect for cable faults be-tween the motor and the motor breaker (52) byusing the line side CTs of the breaker. If themotor and motor breaker are supplied sepa-rately, be certain to match the CT ratios andaccuracy classes when specifying the equip-ment.

FIGURE 3. Conventional percent differential relay.

3.1.3 Ground Fault Protection GroundSensor 50G

The preferred and most sensitive method todetect stator ground faults is with a groundsensor CT. All three phase leads from the motorare passed through the opening of a toroidalcurrent transformer supplying the instantaneousovercurrent 50G relay shown in Fig. 4. Thisarrangement leaves only the ground fault zerosequence currents in the CT. The typicalapplication calls for a 50:5 CT ratio regardlessof the size of the motor. Primary pickup valuesin the range of 4-12 amps are typical. If moresensitive settings are required, time delay maybe necessary to avoid nuisance trips due tozero-sequence cable capacitance current flowduring external faults.

The ground fault sensor connection may be theonly scheme providing sufficient sensitivitywhen the supply system is high-impedancegrounded. If a large ground fault current isavailable in a solidly grounded system, the 50Grelay must operate before the low ratio CTsaturates. Fortunately, the low impedance ofsolid state relays reduces the CT burden.

FIGURE 4. Ground sensor relay and residual groundconnection.

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RESIDUAL CONNECTION 51NFor larger motors, where the conductors will notfit through a ground sensor CT, the residualground connection, shown in Fig. 4, must beused. The ground fault relay sensitivity is limitedby the phase CT ratio. Since unequal CTperformance must be expected, a 51 relay isused to avoid tripping on false residual current.

This 51N relay must be coordinated against the51G system ground protection relay (typically inthe supply transformer neutral). In solidlygrounded feeder applications, where theground fault is usually high and the CT qualitygood, an instantaneous relay (50N) can beadded to accelerate the tripping. This relayshould be set at 4 x Full Load Current or higherto avoid tripping on starting.

3.2 Thermal Damage

3.2.1 Locked Rotor Protection

When a motor stator winding is energized withthe rotor stationary, stator winding currents mayrange from three to seven times rated full-loadvalue depending on motor design and supplysystem impedance. Actual values of lockedrotor currents are part of the motor data sup-plied by the motor manufacturer. Heating in thestator winding, proportional to I2t, is 10 to 50times rated conditions and the winding iswithout benefit of the ventilation normallyproduced by rotation of the rotor.

Depending on the design, a motor may bestator limited (thermally) or rotor limited (ther-mally) during locked-rotor conditions. Themotor manufacturer can furnish the allowablelocked-rotor time only after the motor design iscompleted. This is given as time at rated locked-rotor current starting from either rated ambienttemperature or rated operating temperature alsoreferred to as cold stall time or hot stall time. Italso is given as part of the motor time-currentcurve defined by IEEE Standard 620-1996.

Starting times depend on motor design andload torque characteristics and must be deter-mined for each application. Although startingtimes of 2 to 20 seconds are common, highinertia loads may take several minutes to bringto full speed. Starting time is increased if busvoltage is less than nominal.

SHORT START TIMESWhen the margin between the maximum starttime and the hot stall time is at least 2 to 5seconds, locked rotor protection can easily beachieved with a definite time overcurrent (50TP)as shown in Fig. 5. By setting this relay close tothe Full Load Current, good protection againstfailure to accelerate is obtained. To prevent the50TP relay from operating under temporaryoverloads once the motor is running, it issupervised by the 62 timer. The time delay onthe 50TP should be set at the maximum starttime plus 25% of the thermal limit margin time.The delay on the 62 timer should be set slightlyhigher than the 50TP time delay to allow a oneor two second window for the locked rotorprotection to operate. This protection is easy toimplement in the Basler 851 and MPS multifunc-tion relays.

FIGURE 5. Locked rotor protection – Short starting times.

Another approach often used with single-function relays is shown in Fig. 6. The 50S or 12(speed switch) device is used to supervise the51S relay which is set for locked rotor protec-tion. The speed switch is set at 10%-50% of fullspeed and the 50S is set about 85% of LockedRotor Current (at minimum allowable voltage).

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The 51S should be set between the hot stalltime and the start time. The 51P relay is asecond 51 relay set for running thermal over-load. If no transient overloads are expected, the51P and 50S relays may not be required. The51S will then provide starting and runningprotection.

FIGURE 6. Locked rotor protection short start times –Single function relays.

LONG START TIMESThe starting current of a motor falls between thelocked rotor value when the rotor begins to turn.Therefore, the stator heating is reduced whenthe motor accelerates. For some large inductionmotors with low starting voltages or with highinertia loads and long starting times, the startingtime may exceed the allowable locked-rotortime without excessively heating the rotor.

When the start times approach or exceed themaximum safe stall time, protection againstlocked rotor requires a 51S relay that must beprevented from tripping soon after the motorhas successfully started as shown in Fig. 7.(The 51S contact is likely to close due to theintensity of the starting current following thelocked rotor current.) A speed switch set at10%-50% of nominal speed or a 50S relay set atabout 85% of Locked Rotor Current (at mini-

mum voltage) are commonly used to supervisethe 51S relay. The 51S curve must be set tooperate below the hot stall time. When themotor starts successfully, the 12 or 50S devicedrops out and prevents the 51S from trippingthe breaker.

If the motor starts but does not accelerate tonominal speed, this protection may not tripsince the 51S relay is cut out early in the startsequence. The failure to accelerate would haveto be detected by the thermal overload 51P, setfor running conditions (shown in Fig. 6). How-ever, the 51S may be used to alarm for subse-quent overloads, including failure to accelerateonce the motor has started.

FIGURE 7. Locked rotor protection – Long start times.

3.2.2 Thermal Overload Protection

STATIC REPRESENTATIONThe life of the motor is reduced if the windingtemperatures are allowed to exceed theirinsulation class levels for a significant time. It isusually assumed that for every 10 degrees Cabove the design temperature limit the life of themotor is reduced by a factor of 2.

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When normal cooling and ambient tempera-tures are present the temperature of the statorwinding is directly related to the stator current,and the running thermal overload limit can bestated on a time-current plot as recommendedin IEEE STD 620. Running thermal overload canthus be provided by an overcurrent relay whichhas a time-current characteristic similar to thethermal overload limit. The Minimum Pick Up ofthis relay is the continuous overload specifica-tion of the motor, i.e. the (Full Load Current)x(Service Factor). The characteristic is usually anI2t curve. The time dial is chosen to coordinateagainst the thermal limit and allow short dura-tion overloads predictable from the processanalysis.

Fig. 8 shows two IEEE device numbers (51 or49). These devices may have nearly identicalstatic characteristics, but will differ in theirdynamic response and, therefore, in their ability

to track the motor temperature over time.

FIGURE 8. Thermal overload – Running.

DYNAMIC CONSIDERATIONSIn order to force the static characteristic to passthrough point P in Fig.8, the user adjusts thetime dial in a 51 relay or the time constant in a49 relay. These terms imply that the dynamicresponse of a 51 element is linear, whereas the49 element has an exponential response. Whenthe 49 element, found in dedicated motor relays(as opposed to general purpose overcurrentrelays) takes the load level into account, itbecomes a realistic thermal model of the motor.In this case, the 49 element does not reset tozero when the current is below the overloadlimit (as does the 51 relay) but settles at percentof pickup value corresponding to the usedthermal capacity at the given load level.

Fig. 9 compares the 51 and 49 response fornearly identical static settings. The 51 relay is amore conservative choice since it tends to tripfaster than the 49 relay. The 51 is an acceptablechoice for any process where temporaryoverloads are abnormal. The 49 is preferredwhen the process requires the tolerance oftemporary overloads.

FIGURE 9. Compare 51 and 49 dynamic response.

TEMPERATURE SENSINGMotors are typically cooled by means of a rotor-mounted fan blade that forces air through themotor frame while the motor is running. Thermallimits and temperature rise are based on thiscooling functioning as designed with a knownlevel of ambient air temperature. If normal

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cooling is blocked, overheating at normal loadcurrent is possible. The only protection will betemperature-measuring devices located in themotor such as RTD’s or thermocouples. BaslerMPS100 and 200 series relays provide thisprotection with inputs from RTD’s or thermo-couples imbedded in one or more of the wind-ing slots.

The MPS relays monitor the RTD resistance andaccept two setting levels for each monitoredpoint: a low setting for alarm and a high settingfor shutdown. The specific settings are derivedfrom the winding insulation class, defined inNEMA MG-1, and judgment based on the plantoperating conditions. The recommended settingfor alarm temperature level is the sum of themaximum ambient, plus 10 degrees hotspotallowance, plus the full load temperature rise.This value should be below the insulation classrating. The trip level can be up to 50 degrees Cabove the class rating if the process is critical,since the loss of life from occasional shortoverload periods is insignificant. Setting the triptemperature at the insulation class limit is aconservative setting.

3.2.3 Repetitive Starts and JoggingProtection

In repeated starting and intermittent operationvery little heat is carried away by the cooling airproduced by a turning rotor. Repeated startscan build up temperatures to dangerously highvalues in either stator or rotor windings unlessenough time is provided to allow the heat to bedissipated.

The NEMA MG1-1993 (Motor Guide) sections12.50, 20.43 and 21.43 provide guidelines fortypical installations. These standards allow twostarts in succession, coasting to reset betweenstarts with the motor initially at ambient tem-perature, and for one start when the motor is ata temperature not exceeding its rated loadoperating temperature. This assumes that theapplied voltage, load torque during accelera-tion, method of starting, and load inertia are allwithin values for which the motor was designed.The application and protection of motors havingabnormal starting conditions must be coordi-nated with the manufacturer.

The Basler MPS relays have protection for toomany starts. The user selects a setting fornumber of starts and time period to matchmanufacturer recommendations. Exact determi-nation of starting frequency is a very complexcalculation that is affected by many factorsincluding motor size, enclosure, voltage,ambient temperature, inertia, load-speed-torquecharacteristic, and running time. Motor restartswill typically depend more on the stator thermalcapacity than on rotor thermal capacity and stalltime. The best rule, by far, is to minimize thenumber of starts since each start reduces thelife of the motor.

Motors protected by Basler MPS relays includea protective element for thermal overloadprotection. Unlike their inverse time electrome-chanical counterparts, these relays can remem-ber the stored value of the “accumulatedthermal capacity”. Motor starting alone may useup 50%-65% of the available thermal capacity.These multifunction devices also recognize astopped motor will cool slower than a runningmotor because there is no cooling air producedby the rotor. Therefore, it is possible thatattempting to start a motor twice in rapidsuccession may cause a protective trip onthermal overload. However, we should stilladhere to the manufacturer’s recommendationfor frequent starts.

3.2.4 Unbalance Protection

CAUSE AND EFFECTSUnbalance in the feeder phase voltages ormotor winding impedance will cause unbal-anced currents to flow to the motor. The nega-tive sequence current from the unbalance willcause rotor heating and additional copperlosses in the stator windings due to an increaseline current. Due to the low negative sequencemotor impedance the % negative sequencecurrent is typically about five times larger thanthe % negative sequence voltage. Unbalancedconditions must be detected to avoid thermaldamage to the running motor.

DETECTIONAlthough the current unbalance is the param-eter directly responsible for the temperatureincrease in the motor, two detection methodsare available: voltage and current unbalance.

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Voltage Sensing (47)This method has the advantage of detecting theunbalance voltage for a complete bus to whichseveral motor loads may be connected, but hasthe disadvantage of requiring that all motors betripped when an unbalance exceeds the setting.The bus voltage unbalance may be tolerated bya motor if its load is lighter at the time of theunbalance.

Two common measuring techniques have beenimplemented: the NEMA defined unbalance andnegative sequence voltage measurement. TheNEMA definition, found in MG1 is:%Unbalance=(Max Deviation from Avg.)/Avg.The negative sequence voltage is usuallydefined in % of nominal voltage.

Current Sensing (46)Current unbalance is measured in the motorfeeder itself and has the advantage of beingadapted to each motor. It is easy to implementin multifunction and dedicated motor protectionrelays. Measuring algorithms include the truenegative sequence measurement and thedifference between the maximum and minimumphase currents.

SETTINGS

Voltage RelayNEMA recommends in MG1 that continuousvoltage unbalance should never exceed 5%. Forsmall to moderate unbalance, the NEMA andnegative sequence formulae yield approxi-mately the same result. A voltage unbalancerelay can, therefore, be set at an MPU of 5%. Toset the time delay to trip, consider the thermaldamage by the corresponding negative se-quence current. To this voltage unbalance of5% corresponds an I

2 of about 25%, provided

the voltage is measured at the motor terminals.Assuming the motor can tolerate I2t=K, themaximum time delay for a 5% voltage unbal-ance and K=40 would be 640 seconds. Al-though no standard exists for motors, a value ofK=40 is often used.

Unfortunately the 47N relay does not offer anextremely inverse characteristic that couldemulate the I2t characteristic. It is suggested tobase the time delay on the worst case expectedunbalance, i.e. open phase in the motor feedercable. The positive and negative sequencecurrents are then equal (1pu at full load). The

trip time for this unbalance condition would thusbe equal to K (I

2 =1pu). For K=40, the maxi-

mum delay for an open phase should be 40seconds. If the relay uses a definite time, thiswill have to be the setting, and result in overpro-tection if the unbalance is less severe. If thetiming curve is inverse, the time dial should beselected to cause tripping when the voltageunbalance, at the motor terminals, correspond-ing to the 1 pu I

2 is equal to 20%.

In most applications the voltage seen by the47N will not come from the motor terminal, butfrom the bus. Depending on the size and natureof other loads (static Vs motor) connected to thebus, the 47N may not sense the open phase inthe motor feeder. Therefore, 47N applicationrequires careful analysis.

Current relayIn order to relate the current unbalance MPUsetting to the 5% NEMA voltage unbalance limit,it is necessary to establish the correlationbetween the current unbalance algorithm andthe unbalanced voltage. For a negative se-quence type element, the I

2 % MPU setting is

approximately 5 times the % voltage unbalancefor the worst case nominal load condition. Forother algorithms, the Instruction Manual mustbe consulted.

The current unbalance measuring elementshave an I2t=K like characteristic which makesthe time delay settings easier to apply than withthe voltage relay. If no other information isavailable choose K=40. The worst case unbal-ance occurs for an open phase at full load. Thenegative sequence current is then equal to thepositive sequence current, i.e. 1 pu. The timedial should be set to cause tripping in 40seconds in this case where K=40.

3.3 Abnormal Supply

According to the NEMA MG1-1993 section20.45, motors are generally expected to operatesuccessfully under running conditions at ratedload with a variation of plus or minus 10% ofrated voltage, plus or minus 5% of rated fre-quency, or a combination of the two, providedthe sum of the absolute values of the deviationsdoes not exceed 10% and the frequencyvariation does not exceed plus or minus 5%. Forsynchronous motors, rated excitation currentmust be maintained.

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Fig. 10 shows the effects of voltage and fre-quency variations on induction motor character-istics.

Given these limits, there is no one protectivedevice that can make a direct determination ofthese quantities simultaneously. However,variation in voltage or frequency will usuallyresult in an increase in stator winding tempera-ture over a long period of time. Direct tempera-ture measuring devices, such as RTDs, willdetect the change and provide adequatewarning or tripping, provided the abnormalcondition is not extreme.

A large induction motor rotating at rated speedor a large synchronous motor with fixed excita-tion may be approximated at steady-stateconditions as a constant kilovoltampere devicefor a given shaft load, and, therefore, currentvariations follow voltage variations inversely. Anundervoltage condition will result in an overcur-rent condition. Single phase over- orundervoltage is likely to be detected by unbal-anced voltage or current protection if soequipped. Three-phase undervoltage will beprotected by thermal overload protection sincethe current will be higher than normal for agiven load. Voltage relays, per se, are generallynot always sensitive enough to provide reliableprotection, especially on busses where severalmotors are connected, since the spinningmotors will support the voltage on the low ormissing phase. However, an inverse time ordefinite time undervoltage relay is recom-mended to trip when a prolonged undervoltagecondition exists and as a backup. Pickupsettings of 0.8-0.85 per unit will provide ad-equate protection. The time delay should be setslightly longer than the maximum starting timewith minimum allowable voltage to ensureundervoltage will not trip for a start.

A separate concern of undervoltage is its impacton starting a motor. Unlike a running motor, lowvoltage on starting of a motor produces lowerstarting current and, hence, lowers torque. If thetorque is too low to overcome the torquerequirements of the load, the motor will notsuccessfully start. The MPS210, equipped withcontrol functions, checks the supply voltagebefore starting; if the voltage is too low, therelay prevents starting.

3.3.1 Voltage Drop During Starting

Another concern during motor starting is thevoltage drop caused by the locked rotor currentflowing through the supply transformer. A weaksystem or undersized supply transformer willonly aggravate the situation. When the supplyvoltage decreases during start, then so does thecurrent and starting torque. If there are otherrunning motors on the bus, the reduced voltagewill cause higher currents and further increasethe voltage drop. Should the voltage drop lowenough, it is possible for the motor torque to below enough to prevent a successful start of themotor.

Whether motor starting or system weakness isthe problem, reduced voltage may causetrouble at times other than during acceleration.Reduced voltage running will cause overheatingwith time. Short term voltage dips may alsocause an already running motor to stall. Theuser should also consider the effect of trying tostart more than one motor at the same time,which will only aggravate the undervoltagecondition. Many motors use motor contactorspowered by the ac line voltage. Reducedvoltage could drop out the motor contactor andcause an already running motor to be droppedoff line when the motor contactor drops out.

Voltage drop calculations should be performedto determine what the motor voltage conditionswill be during starting. The calculation shouldbe checked at maximum and minimum ex-pected bus voltage before start. In a properlydesigned power system, with a good matchbetween bus and motor design voltages,starting voltage dips of 15%-20% are notuncommon. Designers frequently assume thatan accelerating motor draws its full voltageinrush current and calculate the upstreamvoltage drops on that basis. Clearly, any voltagedrop in the supply system means that fullvoltage and corresponding inrush currentcannot be present.

3.3.2 Reduced Voltage Starting

When voltage drops are excessive duringstarting, reduced voltage starting techniquesmay be employed. These add to the motorcontrols but may be less expensive than chang-ing transformers and cables. All of these tech-

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niques use some method to apply partialvoltage to the motor during the initial startingsequence, then when the motor is at partialspeed, full voltage is applied to finish the startsequence. The Basler MPS210 supports re-duced voltage starting.

Wye-Delta starting applies a reduced voltage atthe beginning of the start sequence with a wyeconnection of the motor and then changes tothe delta connection of the motor to completethe start sequence. This arrangement reducesstarting torque and voltage drop on the motorbus.

Another method of reduced voltage starting isautotransformer start. The autotransformer isconnected in wye with the supply voltage and,during starting, the tapped partial voltage isapplied to the motor. When the startingcontactor makes its transition, the partialvoltage source is opened, and full supply

voltage is applied. Detailed descriptions ofthese schemes may be found in the InstructionManual for the Basler MPS210 relay.

3.3.3 Frequency Protection

Frequency in excess of rated frequency but notin excess of 5% over the rated frequencywithout a corresponding voltage increase is notconsidered to be a hazardous condition forsynchronous or induction motors provided thedriven equipment does not overload the motorsat the higher frequency.

At decreased frequency without a correspond-ing voltage drop, the flux requirements of amotor are increased, thus increasing thehysterisis and eddy current losses and heating.Sustained operation at 5% below nominalfrequency and rated or overvoltage is notpermissible per NEMA MG1-1993 section 20.45.Protection against this type of operation is

FIGURE 10. The effects of voltage and frequency variation on induction-motor characteristics.

Characteristic Voltage Frequency110% 90% 105% 95%

Torques*Starting andMax Running

Increase 21% Decrease 19% Decrease 10% Increase 11 %

Speed†SynchronousFull-loadPercent Slip

No Change

Increase 1%

Decrease 17%

No Change

Decrease 1.5%

Increase 23%

Increase 5%

Increase 5%

Little Change

Decrease 5%

Decrease 5%

Little Change

EfficiencyFull-load

3/4-load1/2-load

Increase 0.5 to1 point

Little Change

1 to 2 points

Decrease 2points

Little Change

Increase 1 to 2points

Slight Increase

Slight Increase

Slight Increase

Slight Decrease

Slight Decrease

Slight Decrease

Power FactorFull-load

3/4-load

1/2-load

Decrease 3points

Decrease 4points

Decrease 5 to6 points

Increase 1point

Increase 2 to 3points

Increase 4 to 5points

Slight increase

Slight Increase

Slight Increase

Slight Decrease

Slight Decrease

Slight Decrease

CurrentStarting

Full-load

Increase 10 to12%

Decrease 7%

Decrease 10 to12%

Increase 11%

Decrease 5 to6%

Slight Decrease

Increase 5 to6%

Slight Increase

TemperatureRise

Decrease 3° to4°C

Increase 6° to7°C

Slight Decrease Slight Increase

Max Over-LoadCapacity

Increase 12% Decrease 19% Slight Decrease Slight Increase

Magnetic Noise SlightIncrease

Slight Decrease Slight Decrease Slight Increase

* Torques of an induction motor will vary as the square of the voltage.† The speed of an induction motor will vary directly with the frequency.

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typically thermal overload or RTD temperaturemeasurement. However, more refined protec-tion can be obtained with the Basler 81O/Uover/under frequency relay. Time delay settingsof 20-30 seconds will allow it to ride thoughtransient conditions without nuisance tripping.

Many utility substations are equipped withunderfrequency load shedding relays to reducethe system load during a loss of generation andsubsequent decay in system frequency. Largemotor loads connected to the distributionsubstation may interfere with the normal opera-tion of the underfrequency relay by allowing it tosee a decline in frequency without a completeloss of voltage. This can happen when thedistribution bus is disconnected from the supplytransformer and the underfrequency relay isconnected to the distribution bus. The relay willthen see the residual voltage from the motorload and may operate incorrectly. Relocatingthe underfrequency voltage transformer to thehigh side of the supply transformer or addingadditional time delay to the underfrequency timedelay may solve the problem.

3.4 Mechanical or Process Protection

3.4.1 Undercurrent

We generally think of protective relays asdevices that protect electrical equipment. In thecase of motor protection, there may be timeswhen they are used to protect the process. Forexample, the water pumping station that isintended to operate continuously at 90% of fullload current. If the pump were to be damaged,lose its prime, or the shaft break, the load onthe motor would be drastically reduced. TheBasler MPS relay monitors for undercurrent orunder power conditions. These elements are notin service until the motor is running and can beset to detect these loss-of-load conditions toalarm or trip.

3.4.2 Bearing Protection

To minimize damage caused by bearing failure,protective devices should be used to sound analarm or de-energize the motor. Bearing protec-tive devices responsive to one or more of thefollowing conditions may be included:

(1) Low oil level in reservoir: (device 71) levelswitch

(2) Low oil pressure: (device 63) pressureswitch

(3) Reduced oil flow: (device 80) flow switch

(4) High temperature: (device 38) thermo-couples or resistance temperature detector

(5) Rate of temperature rise

(6) Vibration (used on motors with anti-frictionbearings in place of thermal devices)

Large motor bearings are usually monitored bya resistance temperature detector (RTD) whichcan be used as one of the inputs to the BaslerMPS200 or 210 relay. The dual-setpoint of theRTD function of the MPS allows for alarm andtrip settings at two different temperatures.

4. BUS TRANSFER AND RECLOSING

Many motor busses are critical to process orplant operation and, therefore, must be main-tained if at all possible. For static loads, highspeed reclosing or transfer to an alternatesource is appropriate. Motor loads requirespecial considerations. When the motor isdisconnected from the voltage supply, thevoltage at the motor terminals does not go tozero. The machine generates a voltage at itsopen-circuited terminals that decays with time.A fast reclose applies the full bus supply voltagein series with the residual motor voltage, pro-ducing a total winding voltage that can bedangerously high. Capacitors in the circuit onlymake the situation worse.

A second complication is the decay in motorspeed with respect to the supply system. Thefrequency of the residual voltage in the motorwill be a decaying value of frequency as themotor begins to slow down. The worst casecould be nearly 2.0 per unit voltage and 180degrees out of phase with the supply voltage.The possibility of damage exists for localreclosing of the motor, high side reclosing fromthe utility, transferring to an alternate source, orreduced voltage motor starting; they all meanthe motor will be re-energized after some deadtime and the same principles apply.

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4.1 Parallel Transfer

Parallel transfer is a method of transferringprocess loads from one source to an alternatesource. In this method, the bus tie breaker isclosed before the normal source breaker isopened. This method has gained wide accep-tance because the transient on the motor bus iseliminated, assuming the two sources are inphase. However, the bus system designed forthis transfer method may violate the interruptrating for the circuit breakers and the short-termwithstand ratings of the normal and alternatesource power transformers. A fault in a motor orits leads occurring during the time the sourcesare paralleled may produce fault current levelsin excess of the circuit breaker ratings. Theprobability of this happening may be viewed assmall; however, the consequences of such afault should be thoroughly understood beforethe parallel transfer system is used.

Parallel transfer requires a high-speed sync-check relay such as the Basler BE1-25 asshown in Fig. 11 to ensure that the phasedifference across the bus tie breaker is withinacceptable limits prior to transfer. Without thispermissive relay, a large phase angle wouldcause a power surge through the bus systemthat could cause damage to the bus systemcomponents. An angle setting of 15-25 degreeswith no time delay may be used.

FIGURE 11. High-speed sync-check relay.

4.2 Fast Transfer

Fast transfer involves opening the normalsource breaker prior to closing the tie breaker,thus avoiding the problems associated withparallel transfer. This method is intended tominimize the transfer time between sources.However, the bus must always be completelydisconnected from both sources for a shortperiod of time.

One technique involves issuing simultaneoustrip and close commands to the normal sourceand bus tie breaker. If the tripping breaker isabnormally slow, the sources can be brieflyparalleled, introducing the problems of paralleltransfer. Another method involves using a “b”contact from the normal source breaker to closethe bus tie breaker.

Especially during abnormal transient conditions,supervision of the fast transfer requires a high-speed sync-check relay such as the Basler BE1-25 to ensure that the phase angle between themotor bus voltage and the alternate source

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voltage is within acceptable limits prior toclosing the bus tie breaker. An angle setting of15-25 degrees with no time delay may be used.

4.3 Delayed Transfer on Residual Voltage

Residual voltage transfer involves waiting untilthe bus voltage drops below a predeterminedpoint before closing the alternate sourcebreaker. This technique is the slowest of themethods in that the open-circuit time of the busis the greatest. By waiting until the voltage is33% of rated voltage, the resultant voltageacross the alternate source breaker is reducedto a maximum of 1.33 p.u. This supervision canbe achieved with a 27 relay set at .33 per unitwith no time delay or by adding a fixed timedelay to the closure of the alternate source.

Typical residual voltage decay is shown in Fig.12. The length of time required for the voltageto decay depends on how quickly the storedelectromechanical energy dissipates. Themotor’s open circuit time constant may bedefined as follows:

where:f = frequencyXm = per unit magnetizing reactance of the

motorX2r = per unit rotor reactance at running speedR2r = per unit rotor resistance at running speed

At a value of one time constant, the voltage willhave decayed to 36.8% of its initial value. Eachsuccessive time constant will drop the voltageand additional 36.8% until no voltage remains.A safe value of residual voltage is considered .33per unit per ANSI and IEEE. Meeting that re-quirement requires a delay in circuit reclosure ofat least one to one and one-half time constants.

When auto-reclose of the motor feeder or auto-reclose of the utility source takes place, theresidual voltage considerations should be used.Either the motor should be disconnected prior toreclose by using an 81O/U relay, or the recloseshould be delayed until the voltage has decayedto .33 per unit.

FIGURE 12. Decay of open circuit voltage and phase angle.

When the user does not wish to reclose ortransfer the motor load but wants to protect itfrom being re-energized out of phase or withhigh residual voltage, a Basler BE1-81O/U set at97 to 98% of rated frequency with a time delayof 10-20 cycles will protect the motor by detect-ing and underfrequency condition as the motoris decelerating and tripping the supply breaker.The time delay will have to be shortened if highspeed reclosing is being used. The same relaycan be used for automatic load shedding of themotor at abnormally low frequencies. In bothcases potential transformers must be locatedbetween the motor supply breaker and themotor leads.

For synchronous motors, reclosing must not bepermitted until proper resynchronization can beperformed. This means tripping the supplybreaker with an undervoltage or underfrequencyrelay.

5. SYNCHRONOUS MOTORS

Protection of the synchronous motor is similarto that of the induction machine with additionalrequirement for field, loss of excitation and outof step conditions. The field may have its ownprotection for loss of field or field undervoltage.

Out of step protection is applied to synchronousmotors and synchronous condensers to detectpullout resulting from excessive shaft load ortoo-low supply voltage. Small synchronousmachines with brush-type exciters are oftenprotected against out of step operation (or lossof excitation) by ac voltage devices connectedin the field. No ac voltage is present when themotor is operating synchronously.

Synchronous motors can be protected againstloss of excitation by a low-set undercurrent relayconnected to the field. This relay should have atime delay drop out. On large synchronousmotors an impedance relay is frequently appliedthat operates on excessive var flow into themachine, indicating abnormally low field excita-tion. If an undervoltage unit is part of the relay,its function should be shorted out because lossof motor field may produce little or no voltagedrop.

Operation of synchronous motors drawingreactive power from the system can result inoverheating in parts of the rotor that do notnormally carry current. Some loss-of-field relays(device 40) can detect this phenomenon.

The Power Factor Relay (device 55) can also beused to detect an out of step or loss of excita-tion condition in a synchronous motor. Whenthe motor loses synchronism or loss of field itwill produce watt flow out of the motor and varflow into it. A short time delay is typical, and therelay is generally not in service until the motor isrunning at synchronous speed.

6. TYPICAL PROTECTION FOR MOTORS

CASE 1 - Small Motor (100-600HP)This example suggests the relay selection andtypical settings for motors in the 100-600HPrange. This range is somewhat arbitrary. Costand process considerations will ultimatelydetermine the choice of protection level.The proposed scheme shown in Fig. 13 appliesto situations where the load has low inertia, the

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starting times are short and a significant timemargin exists between the maximum start timeand the hot stall time. The load is assumed toremain within the motor rating during normalprocess conditions, allowing the use of one 51element for locked rotor and running thermaloverload protection.

FIGURE 13. Typical small motor protection (100-600HP)

CASE 2 Medium Size Motor (600-1500HP)Single Function RelaysThis example suggests the relay selection andtypical settings for motors in the 600-1500HPrange. This range is somewhat arbitrary. Costand process considerations will ultimatelydetermine the choice of protection level.

The proposed scheme shown in Fig. 14 appliesto situations where the load has high inertia, thestarting times are long and a small time marginexists between the maximum start time and thehot stall time. The load is assumed to periodi-cally exceed the motor rating during normalprocess conditions, requiring the use of twoseparate 51 elements for locked rotor and

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running thermal overload protection. For the 51Slocked rotor protection, an Extremely Inversecharacteristic will best match the hot stall timecurve. If the time dial range is insufficient, thetrip time can be adjusted by raising the tapsetting to decrease the effective multiple of tap.

The 51P, running thermal overload relay musthave a MPU equal to the continuous overloadlimit. A time-current coordination should beperformed if the protection is to be optimized.

FIGURE 14. Typical medium size motor protection – Single function relays (600-1500HP), High inertia-discrete relays.

CASE 2A Medium Size Motor (600-1500HP)Multifunction Relay

This example suggests the relay selection andtypical settings for motors in the 600-1500HPrange. This range is somewhat arbitrary. Costand process considerations will ultimatelydetermine the choice of the protection level.The functions are similar to Case 2, except thatthey are integrated into the BE1-851 multifunc-tion overcurrent relay shown in Fig. 15. The 851offers one time overcurrent and two instanta-

neous overcurrent for phase, ground andnegative sequence. We will also take advantageof multiple setting groups, independent timers,and programmable time overcurrent curves.Programmable alarms, metering, and oscillogra-phy will help monitor the motor performance.

The 851 uses programmable BESTLogic tocustomize the relay operation for each applica-tion. Two basic schemes are presented here,one for normal loads and one for high inertialoads. Full details of the 851 programming andsetting for each scheme can be found in the 851instruction manual.

For low inertia loads, Locked Rotor protection iscovered with a “maximum start time” logic. Asshown in the Fig. 15 logic diagram when themotor starts, the 62 starts timing and the 50P isabove pickup and timing. The definite time delayof the 50P is set at the motor maximum starttime with the 62 set a second or two longer. Ifthe motor starts successfully, the 50P will dropout before its definite timer elapses. Once themotor is running, the 62 timer times out andblocks the logic AND gate from nuisance trippingthe motor on temporary overloads if the 50Pshould pick up again. If the motor does not startsuccessfully, the 50P will stay picked up until ittimes out and will trip for locked rotor conditions.

Thermal overload protection is provided by the51P element of the 851. The user programmabletime overcurrent curve is used to simulate the I2theating. The constants shown in Case 2Asettings table will give an approximate range of2.5 to 25 seconds at 6 times tap for time dials 1and 10, respectively. If a different range isrequired, change the value of constant A.

The stator short circuit element (150TP) is oftenapplied with a short time delay to overcomeasymmetrical current during fault conditions.This is not necessary in the 851 since it onlymeasures the symmetrical current.

FIGURE 15. Typical medium size motor protection –Multifunction relays (600-1500HP), High or lowinertia-multifunction overcurrent.

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Current unbalance (46N) detection providesrotor thermal protection. The negative sequence(51Q) MPU setting in Amperes is approximately5 x (max Continuous Voltage unbalance, pu) x(Full Load Current, secondary). The time dial isset to cause tripping in K (the assumed I

22t

value) seconds for I2=Full Load Current.

The programmable alarm feature of the 851 canbe used to provide pre-trip alarms for thermaloverload and current unbalance.

For high inertia loads the 851 switches settinggroups for locked rotor protection since “maxi-mum start time“ is not feasible. When the motorbreaker is open, the 851 is using setting group 0which has the 51 set with a lower time dial tomatch the locked rotor thermal limit. This isshown as the 51S curve. As shown in the Fig.15 logic diagram when the motor starts thebreaker is closed and the 50P is picked upwhich keeps the relay in group 0 settings. Whenthe motor starts successfully, the 50P will dropout and the 851 will change to setting group 1.Setting group 1 raises the time dial on the timeovercurrent to match the running overloadcharacteristics of the motor. This is shown asthe 51P curve. When the motor breaker isopened, the 851 returns to group 0 settings.

CASE 3 Comprehensive protection for mediumand large motors (>600HP)

This protection uses dedicated microprocessorMPS200 or MPS210 relays which, in addition tothe essential 50P, 50G, 49, 46,47, 27 functions,offers undercurrent (27), underpower (32U), lowPF (55), overvoltage (59), jam protection, and 10RTDs. There are dual setting levels for trip andalarm for most functions. These relays track themotor temperature accurately (thermal model-ling) and offer calculated, statistical and faultdata to help the operators and maintenancepersonnel. See Fig. 16.

Model variations allow the users to chooseamong integrated protection, control and meter-ing.

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FIGURE 16. Comprehensive protection for medium and large motors (greater than 600HP)

CASE 3A Multifunction Protection for MediumMotors (600-1500HP)

This protection option is similar to Case 3, usingthe MPS100 relay. Protective functions are thesame as the MPS200 except without voltage orpower functions and with only one RTD. Phasesequence is checked upon energization and isdetected in less than 500ms. The motor tem-perature is tracked through the thermal model,assuring correct dynamic performance.See Fig. 17.

COMMUNICATIONSCommunications ports are standard in theMPS100, MPS200 and MPS210. Each relay hasone RS-485 with MODBUS® protocol standard.The BE1-851 relay comes standard with oneRS-485 and a front and rear RS-232. ASCIIprotocol is standard in the 851, MODBUS®

protocol is optional.

FIGURE 17. Multifunction protection for medium motors.

7. BIBLIOGRAPHY

1) Guide for AC Motor Protection, ANSI/IEEEStandard C37.96-1988.

2) Blackburn, J.L., Protective Relaying Prin-ciples and Applications, Marcel Dekker,1987.

3) Hornak, D. L. And Zipse, D. W., AutomatedBus Transfer Control for Critical IndustrialProcesses, IEEE Transactions on IndustryApplications, Sept/Oct 1991.

4) Motor Guide, NEMA Standard MG1-1993.

5) Nailen, R. L., Motors, Electric Power Re-search Institute, 1989.

6) Dymond, J. H., Stall Time, AccelerationTime, Frequency of Starting: The Myths andthe Facts, IEEE Transactions on IndustryApplications, Jan/Feb 1993.

7) IEEE Guide for the Presentation of ThermalLimit Curves for Squirrel Cage InductionMachines, IEEE Standard 620-1996.

8) Boothman, D. R., Thermal Tracking – ARational Approach to Motor Protection,IEEE Power System Relay Committee, Jan1974.

ANSI QTY Basler Model/ Description Basler TypicalNo Function Style Number Settings

50P 3 BE1-50/51 Detects stator BE1-50/51B-207 1.6x�LR

Instantaneous short circuits 51: H2E-Z3P-A1C0FOr BE1-51

51P 3 BE1-50/51 Locked Rotor and BE1-50/51B-207 MPU=1.2xFLCInverse time thermal overload 51: H2E-Z3P-A1C0F Curve: EOr BE1-51 TD: fit below max. safe

stall time with 2-5smargin above startcurrent

51N 1 BE1-50/51 Stator ground faults BE1-50/51B-207 MPU=0.5AInverse time 51: H2E-Z3P-A1C0F Curve: EOr BE1-51 TD: 0.1s @ 4xFLC

Must coordinateagainst upstream 51Nrelay

50N 1 BE1-50/51 Stator ground faults BE1-50/51B-207 MPU=4xFLCInstantaneous (Residual connection)Or BE1-51

50G 1 BE1-50/51 Stator ground faults BE1-50/51B-207 MPU=0.5AInstantaneous (Alternate to 50/51N) Consider 3�

0 from

Or BE1-50 (Toroidal CT) cable capacitancebefore setting to max.sensitivity

27 1 BE1-27 System undervoltage BE1-27: MPU=0.8xVnom.H3E-E1J-B0H0F Delay: 1-10s

Consider slow clearingsystem faults.

NOTE: Quantities correspond to single-function relays. Functions may be combined, as in 50/51 relay.

CASE 1

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ANSI QTY Basler Model/ Description Basler TypicalNo Function Style Number Settings

150P 3 BE1-50/51 Detects stator BE1-50/51B-207 1.6x�LR

Instantaneous short circuits 51: H2E-Z3P-A1C0F1 Or BE1-51

50P 1 BE1-50/51 Cuts out 51R when BE1-50/51B-207 0.85x�LR

(at lowestInstantaneous the motor reaches voltage)

about 50% speed

51S 1 BE1-50/51 Locked rotor BE1-50/51B-207 MPU>=1.2xFLCInverse time Curve: E

TD: fit below max.safe stall time andabove start current

51P 3 BE1-50/51 Running thermal BE1-50/51B-207 MPU=1.2xFLCInverse time overload 51: H2E-Z3P-A1C0F Curve: E or �

1 Or BE1-51 protection TD: below motor limit,allow for temporaryprocess overloads.Relay must haveintegrating reset.

51N 1 BE1-50/51 Stator ground BE1-50/51B-207 MPU=0.5AInverse time faults 51: H2E-Z3P-A1C0F Curve: EOr BE1-51 TD: 0.1s @ 4xFLC

Must coordinateagainst upstream 51Nrelay

50N 1 BE1-50/51 Stator ground faults BE1-50/51B-207 MPU=4xFLCInstantaneous (Residual 51: H2E-Z3P-A1C0FOr BE1-51 connection)

50G 1 BE1-50/51 Stator ground faults BE1-50/51B-207 MPU=0.5A ConsiderInstantaneous (Alternate to 51: H2E-Z3P-A1C0F 3�

0 from cable capaci-

Or BE1-51 50/51G) tance before setting(Toroidal CT) to max. sensitivity

27 1 BE1-47N System BE1-47N: MPU=0.8xVnom.undervoltage E3F-D1P-D3N0F Delay:1s-10s

Consider slow clearing

47 1 BE1-47N Phase rotation, BE1-47N: Trip MPU=5% whenvoltage unbalance E3F-D1P-D3N0F connected to motor

terminals; otherwise,check system config-uration. Time delay:depends on systemconfiguration andtiming curve selected.

CASE 2

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NOTE: Quantities correspond to single-function relays. Functions may be combined, as in 50/51 relay.

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ANSI QTY Basler Model/ Description Basler Typical settingsNo Function Style No

150P 3* BE1-851 Detects stator BE1-851 1.6x�LR

Instantaneous short circuits H5N2S10150TP

50P 3* BE1-851 Detects starting BE1-851 1.3x�FL

Instantaneous condition for Max. H5N2S1050TP Start Time

51P 3* BE1-851 Running thermal BE1-851 MPU=1.2xFLCInverse time overload protection H5N2S10 Curve: PR51P N=2, C=1, K=.028,

B=0, R=30, A=90TD: below motor limit,allow for temporaryprocess overloads.Product AD > Motorthermal time constant

51N 1* BE1-851 Stator ground faults BE1-851 MPU=0.5AInverse time (Residual Connection) H5N2S10 Curve: E51N TD: 0.1s @ 4xFLC

Must coordinateagainst upstream 51Nrelay

50N 1* BE1-851 Stator ground faults BE1-851 MPU=4xFLCInstantaneous (Residual connection) H3N2S10150TN

50G (1)* BE1-851 Stator ground faults BE1-851 MPU=0.2550TN (Alternate to 50/51N) H3N2S10 (use 1A input CT for

(Toroidal CT) neutral)

46N 1* BE1-851 Current Unbalance BE1-851 �2 MPU=1.25A for 5%51Q, 50Q, 150Q H5N2S10 voltage unbalance

Reset factor:30

27 1 BE1-47N System undervoltage BE1-47N MPU=0.8xVnom.E3F-E1P- Delay: 1s-10sD3N0F Consider slow clearing

system faults.

47 1 BE1-47N Phase rotation, open BE1-47N MPU=10% 3-5 sec.phase E3F-E1P Check load

D3N0F configuration

NOTE: *All functions contained in one 851 relay.

CASE 2A LOW INERTIA

ANSI QTY Basler Model/ Description Basler Typical settingsNo Function Style No

150P 3* BE1-851 Detects stator BE1-851 1.6x�LR

Instantaneous short circuits H5N2S10150TP

50P 3* BE1-851 Cuts out the 51S when BE1-851 0.85x�LR (at lowestInstantaneous the motor reaches about H5N2S10 voltage)50TP 50% speed

51S 3* BE1-851 Locked rotor BE1-851 MPU>=1.2xFLCInverse time H5N2S10 Curve: E51P TD: fit below max.

safe stall time andabove start current

51P 3* BE1-851 Running thermal BE1-851 MPU=1.2xFLCInverse time overload protection H5N2S10 Curve: PR51P N=2, C=1, K=.028,

B=0, R=30, A=90TD: below motor limit,allow for temporaryprocess overloads.Product AD< MotorThermal TimeConstant. Thisfunction is disabledduring start (groupswitching).

51N 1* BE1-851 Stator ground faults BE1-851 MPU=0.5AInverse time (Residual Connection) H5N2S10 Curve: E51N TD: 0.1s @ 4xFLC

Must coordinateagainst upstream 51Nrelay

50N 1* BE1-851 Stator ground faults BE1-851 MPU=4xFLCInstantaneous (Residual connection) H5N2S10150TN

50G (1)* BE1-851 Stator ground faults BE1-851 MPU=0.2550TN (Alternate to 50/51N) H3N2S10 (use 1A input CT for

(Toroidal CT) neutral)

46N 1* BE1-851 Current Unbalance BE1-851 �2 MPU=1.25A for 5%51Q, 50Q, 150Q H5N2S10 voltage unbalance

Reset factor=30

27 1 BE1-47N System undervoltage BE1-47N MPU=0.8xVnom.E3F-E1P- Delay: 1s-10sD3N0F Consider slow clearing

system faults.

47 1 BE1-47N Phase rotation, open BE1-47N MPU=10% 3-5 sec.phase E3F-E1P- Check load

D3N0F configuration

NOTE: *All functions contained in one 851 relay.

CASE 2A HIGH INERTIA

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ANSI QTY Basler Model/ Description Basler Typical settingsNo Function Style No

150T 1 MPS100 Stator short circuits MPS100-51V1 Consult Instruction50T Jam condition Manual and GUI for49 Thermal overload default settings and46 Current unbalance available template50TN Ground fault files.37 Undercurrent

ANSI QTY Basler Model/ Description Basler TypicalNo Function Style Number Settings

150T 1 MPS200/210 Stator short circuits MPS210-C2V1 Consult Instruction50T Jam condition manual and GUI for49 Thermal overload default settings and46 Current unbalance available template50TN Ground fault files.37 Undercurrent32U Underpower27 Undervoltage59 Overvoltage47 Phase Loss/Reversal

87 1 BE1-87G Percentage Restraint BE1-87G: Tap=.4ADifferential G1E-A1J-A0C0F Set higher when using

low quantity CTs

87 3 BE1-50/51 Self balancing BE1-50/51B-207 .5AInstantaneous differential

12 1 Customer Speed switch For high inertial LRsupplied protection

25-50% speed

81 1 BE1-81O/U Underfrequency BE1-81O/U: 97% of ratedLoss of Supply T3E-E1J-A6S0F frequency 10-20 cycles

CASE 3

CASE 3A

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23

NOTES

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NOTES

First printing 4/98

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Basler Electric InternationalP.A.E. Les Pins, 67319Wasselonne Cedex FRANCEPhone (33-3-88) 87-1010Fax (33-3-88) 87-0808

If you have any questions or needadditional information, please contact

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