Electric Electric MotorsMotors

By: Muhammad Azhar HussainBy: Muhammad Azhar Hussain

ObjectiveObjective

• Familiarization with basic philosophy of Familiarization with basic philosophy of

electric motor operation and motor electric motor operation and motor

maintenance / protections with reference to maintenance / protections with reference to

FFC plants. FFC plants.

Electric MotorsElectric Motors

• IntroductionIntroduction

• Working PrinciplesWorking Principles

• ConstructionConstruction

• Motor ProblemsMotor Problems

• Maintenance of Electric MotorsMaintenance of Electric Motors

• Protections of MotorsProtections of Motors

IntroductionIntroduction

• Electromechanical device that converts electrical Electromechanical device that converts electrical energy to mechanical energyenergy to mechanical energy

• Mechanical energy used to e.g.Mechanical energy used to e.g.• Rotate pump impeller, fan, blowerRotate pump impeller, fan, blower• Drive compressorsDrive compressors• Lift materialsLift materials

• Motors in industry: 70% of electrical loadMotors in industry: 70% of electrical load

IntroductionIntroductionHow does Electric Motor Work?How does Electric Motor Work?

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IntroductionIntroductionTypes of Electric MotorsTypes of Electric Motors

Electric Motors

Alternating Current (AC) Motors

Direct Current (DC) Motors

Synchronous Induction

Three-PhaseSingle-Phase

Self ExcitedSeparately Excited

Series ShuntCompound

IntroductionIntroductionAC Motors – Induction motorAC Motors – Induction motor

• Most common motors in industry

• Advantages: • Simple design

• Inexpensive

• High power to weight ratio

• Easy to maintain

• Direct connection to AC power source

Construction of MotorConstruction of Motor• Frame (cast iron / aluminum)Frame (cast iron / aluminum)

• PedestalsPedestals

• End coversEnd covers

• Stator (steel lamination slots holding copper Stator (steel lamination slots holding copper winding)winding)

• Exchanger Exchanger

• Anti Rotation DeviceAnti Rotation Device

Construction of Motor Construction of Motor contd.contd.

• Rotor Shaft and bearingsRotor Shaft and bearings

• Fan for cooling (metallic / plastic)Fan for cooling (metallic / plastic)

• Terminal BoxTerminal Box

Problems of Electric MotorsProblems of Electric Motors

• GroundingGrounding

• Phase-Phase short circuitingPhase-Phase short circuiting

• Inter-turn Short CircuitingInter-turn Short Circuiting

• Abnormal SoundAbnormal Sound

• High VibrationHigh Vibration

Maintenance of Electric MotorMaintenance of Electric Motor

• Proper tools / properly installedProper tools / properly installed• Proper maintenance personnelProper maintenance personnel• Inspection / reporting / recordingInspection / reporting / recording• Four cardinal rulesFour cardinal rules

– Keep it cleanKeep it clean– Keep it dryKeep it dry– Keep it tightKeep it tight– Keep it friction freeKeep it friction free

Maintenance of Electric MotorMaintenance of Electric Motor

• Preventive Maintenance Plan Preventive Maintenance Plan – MeggeringMeggering– DismantlingDismantling– Cleaning of stator / housingCleaning of stator / housing– Varnishing of stator windingVarnishing of stator winding– Heating in OvenHeating in Oven– Replacement of bearingReplacement of bearing– Testing if requiredTesting if required

AC Motor OverhaulingAC Motor Overhauling• OverhaulOverhaul

– It is defined as thorough checking, inspection, It is defined as thorough checking, inspection, repairs and adjustments to restore good working repairs and adjustments to restore good working condition.condition.

– During overhauling, the machine is dismantled, During overhauling, the machine is dismantled, worn out parts are replaced and the machine is worn out parts are replaced and the machine is restored to good working condition. Overhaul restored to good working condition. Overhaul involves complete shutdown, dismantling, repair involves complete shutdown, dismantling, repair and reassembly.and reassembly.

Verification of Satisfactory Verification of Satisfactory Motor MaintenanceMotor Maintenance

• All new motors are provided with detailed technical All new motors are provided with detailed technical

literatures, Test Reports and list of recommended literatures, Test Reports and list of recommended

spares for future reference.spares for future reference.

Verification of Satisfactory Verification of Satisfactory Motor Maintenance Motor Maintenance (Cont’d)(Cont’d)

• In case of any further clarification the vendor or In case of any further clarification the vendor or

supplier should be contacted.supplier should be contacted.

• Only essential spares should be kept in warehouse.Only essential spares should be kept in warehouse.

Verification of Satisfactory Verification of Satisfactory Motor Maintenance Motor Maintenance (Cont’d)(Cont’d)

• History cards of all motors should be maintained, History cards of all motors should be maintained,

area wise, maintained by the respective area area wise, maintained by the respective area

engineer.engineer.

• Workshop engineer should issue job card for the Workshop engineer should issue job card for the

motor on which maintenance activity has taken motor on which maintenance activity has taken

place.place.

Verification of Satisfactory Verification of Satisfactory Motor Maintenance Motor Maintenance (Cont’d)(Cont’d)

• After rewinding / overhauling has taken place on a After rewinding / overhauling has taken place on a

motor, following tests should be carried out.motor, following tests should be carried out.

– MeggeringMeggering

– Starting currentStarting current

Verification of Satisfactory Verification of Satisfactory Motor Maintenance Motor Maintenance (Cont’d)(Cont’d)

– No-load current on all three phasesNo-load current on all three phases

– Abnormal Sound (if any)Abnormal Sound (if any)

– Vibration analysis (if required)Vibration analysis (if required)

– Bearing temperaturesBearing temperatures

– SpeedSpeed

Protections of MotorsProtections of Motors• Thermal overload (49)Thermal overload (49)

– This unit actuates the current drawing by the This unit actuates the current drawing by the motor increases beyond set value. motor increases beyond set value.

• Earth Fault (64)Earth Fault (64)

– This unit operates when the zero sequence This unit operates when the zero sequence current exceeds the set value, under normal current exceeds the set value, under normal

condition this current is nearly zero.condition this current is nearly zero.

Protections of MotorsProtections of Motors• Short Circuiting (50)Short Circuiting (50)

– This protection is activated in only those motors This protection is activated in only those motors which do not have main fuses. This actuates which do not have main fuses. This actuates when current increases 6 times the starting when current increases 6 times the starting current. current.

• Negative Sequence (46)Negative Sequence (46)– This unit operates when the value of negative This unit operates when the value of negative

sequence current increases by the set value.sequence current increases by the set value.

Protections of MotorsProtections of Motors• Locked RotorLocked Rotor (51LR)(51LR)

– This unit operates when the starting time of the This unit operates when the starting time of the motor exceeds the set value, it will protect the motor exceeds the set value, it will protect the motor against locked rotor during its normal motor against locked rotor during its normal operation. operation.

• Start-up Supervision RelayStart-up Supervision Relay (66)(66)– This unit allows the number of times the motor This unit allows the number of times the motor

can be started within a certain time. can be started within a certain time.

ThanksThanks