WELCOMESEMINAR ON ELECTRIC CRANE DUTY MOTOR &

CONTROL PANELSCONTROL PANELSS.S. Ghatpande

Ex Crompton Greaves, L.T. MotorsAmeya Consultants,Pune 43

Phone:020-24379151

CONTENTS• Basic terminology • Raw materials• Constructional details of Induction motors• Guide for selection of motors: Mech & Elect• Special features of Crane Duty Motors• Slip Ring motors & Brake motors• Slip Ring motors & Brake motors• Energy Efficient motors• Motor suitability for VFD application• Testing of Induction motors• Some common motor accessories• Construction & design aspects of panels• Inspection of control panels• Open House

BASIC TERMINALOGY

• Frequency: Cycles per seconds . Hz• DC signal : Has constant Voltage & current irrespective

of time. E.g. Battery• Alternating Current :is a fluctuating current that is

associated with a changing potential difference (AC Voltage). Sinusoidal e.g. household powerassociated with a changing potential difference (AC Voltage). Sinusoidal e.g. household power

• Insulator: A material that restricts the flow of current. Large potential differences are required to push electrical current through these materials.e.g. Wood, rubber etc

• Conductor: A material that allows for the easy establishment of a current with a minimal applied voltagee.g. Silver copper Aluminum & most of metals

Basic Materials

• Copper : Winding,Busbars,Lugs etcBest conductivity, low resistivity leading high efficiency thereby small sizesCost factor

• Aluminumtransmission lines,rotor conductor in transmission lines,rotor conductor in motor,Busbars in panels Ease of construction ,castable at low tempLeading to high temperature –bulky sizesLower cost hence preferable

Basic Materials

• Stampings/ Laminations: thin pieces of CRGO steel to reduces hystersis lossVarious grades depending on B-H curveLow loss stampings : Energy Efficient Low loss stampings : Energy Efficient products, Energy conservation

• Steel: used for shafts,body,housing,coversShafts of motors are of EN8 or EN24

• Other materials like bearings, accessories Like meters,Relays,Cables,Oil,

Basic Materials

• Insulation : Depending on temperature divided in various classes. Most commonClass B- Max temp 120 °CClass F- Max temp 150°CClass H- Max temp 180 °C Class C- Max temp 200 °CClass C- Max temp 200 °CGeneral trend use higher class but restrict temp rise to lower class -General forms solid-papers , shapes,tapesor Liquids –insulating varnishes,oils,coats

AC Induction Motors

Classification depending upon various factors• Voltage levels : Low tension ( LT ), High Tension (HT)• Phases : Single / Three• Connection : Star / Delta• Type of rotor construction : Squirrel Cage Rotor (SCR) / Slip Ring

(SR)• Synchronous speed /Poles : 2 /4/6/8 Pole , Single speed• Synchronous speed /Poles : 2 /4/6/8 Pole , Single speed

Multi speed : 2/3/4 speeds• Ventilation : External fan (TEFC), Internal Fan (SPDP), Forced

cooled without fan (TE), Air stream rated • Environment : Safe Area motors / hazardous area motors• Mounting : Horizontal , vertical ,foot, flange, foot cum flange etc• Starting Method ; DOL, Star/ Delta, Auto transformer, Soft starters

DETAIL OF SLOT

PARTICULARS REQUIRED FOR SELECTING SUITABLE INDUCTION MOTOR

• Name of the application e.g. crane,pump,compressor , machine tools etc

• Voltage/Frequency with variations• Power required in kW• Rated speed of operation• Rated speed of operation• Ambient temp./ Altitude/Mounting/IP protection• Load Gd² &Torque–speed curve of the load• Type of duty , No of starts/stops• Method of drive ( directly coupled, belt, gear,

chain drive etc. )• Refer IS:13555-1993 for more details

TORQUE Vs SPEED

150

200

250%

FU

LL L

OA

D T

OR

QU

E

STARTING TORQUE

PULL UP TORQUE

PULL OUT TORQUE

0

50

100

0 10 20 30 40 50 60 70 80 90 100

% SYNCHRONOUS SPEED

% F

ULL

LO

AD

TO

RQ

UE

PULL UP TORQUE

ACCELERATING TORQUESTAR DELTA

LOAD CURVE 2

LOAD CURVE 1

PROBLEM AREA

RATED TORQUE

TEMP. OF INSL.CLASS

InsulationClass

Amb.Temp.

°C

Max.Temp.

°C

Allowance for Hot Spot

°C

Max. Permissible Temp. °C

A 50 105 05 50A 50 105 05 50

B 50 130 10 70

F 50 155 15 90

H 50 180 15 115

Crane Duty Motors: Electrical Features

• Supply conditions: Voltage 415 +/-10 %,Frequency:50+/-5% Combined Variation +/- 10%

• Ambient Temp : Designed for 45/50 °C • Altitude For altitude up to 1000 m above mean sea level

For different ambient temp & Altitude derating factors For different ambient temp & Altitude derating factors • Insulation : Class F but temp rise restricted to class B• Winding : Winding uses polystermide enameled (Temp

class 155) copper wires & impregnated with class F varnish.Dual coated Cu wire & VPI on motors>315 frame

• Thermal protection: PTC Thermisters/Thermostat if reqd• Anti condensation : Space heaters if required•

Crane Duty Motors: Mechanical Features

• Enclosures: Stator body material is either aluminum for frames up to 132 & Cast Iron for frames above 132 . For frames 90-132 Cast iron construction may available. But for crane duty CI to be preferred

• Degree Of Protection : IP55 as standard• Cooling : All motors are totally enclosed fan cooled • Cooling : All motors are totally enclosed fan cooled

(TEFC) achieved by self driven bidirectional fan mounted on shaft . Forced cooling arrangement for VFD if reqd

• Mounting : Horizontal Foot mounting (B3) Or vertical flange mounting ( V1) is common

• Air Gap : Increased Air gap between stator & rotor• Special Rotor design : For higher staring torque LM6

diecast or High resistance , Sq. end ,D/S etc

Types Of Duties

• The various operating cycle of driven machine can be classified into 9 basic duties from S1 to S9 . S1= CMR. For crane duty motors only S2 ( Short time ) S3,S4 &S5 i.e. intermittent duties with starting & electrical braking

• S2- Recommended values for short time duty are 10 , • S2- Recommended values for short time duty are 10 , 30 & 90 minutes

• S3- Standard duration of duty cycle is 10 minutes. The recommended values for CDF are 25 % , 40 % & 60%

• While calculating for the duty , allowance should be made for inching & reverse current braking in S4 & S5

• General no of starts /Stops per hour are 90,150,300 ,600

Short Time Duties :S 2& S 3

Short Time Duties :S 4

Short Time Duties : S 5

Slip Ring Motors

• Suitable for high starting current limitations for high inertia load & frequent starts /Stops. Available in 4/6/8 poles

• Construction is similar to SCR except winding on rotor & facility for adding external rotor resistance though slip rings & brush gears. Once motor is picked to required speed SR are short circuited

• Staring & speed control archived through external resistance • Staring & speed control archived through external resistance calculated by following formulae :

• Vr x ( Ns-N) x MnRc= 3 x Lr x Ns x M - Rr

Where Vr= Rotor Voltage , Lr= rated current , Rr= rotor resistanceNs= Synchronous speed , N=required speed Mn=Rated Torque

• As cooling is reduced at lower speed ,Torque & O/P must be reduced or larger motor to be selected

• If ventilated by separate fan motor can provide FLT at low speed also

Brake Motors :

• For applications requiring almost instantaneous stopping of load• Fail safe mode i.e. brake is applied when motor supply is off• At present brake motors are available for frames up to 180 size• Construction: brake motor consist of following :1. A.C. Induction motor of SCR type2. Encapsulated brake coil housed at NDE ends held3. Brake liner attached to armature disc near cooling fan4. Rectifier unit provided in motor TB for DC supply to brake coil

ENERGY EFFICIENT MOTORS- NEED:

• Increasing cost of electrical power• Reduced selling cost due to globalization• Increased manufacturing cost due to

quality consciousnessquality consciousness• Efficiency levels now becoming mandatory

by law in India & abroad ( BEE * concept)Accordingly Eff1 , Eff2 & standard motors

• While repairing or replacing motors option available

LOSSES IN INDUCTION MOTOR

ENERGY EFFICIENT MOTOR –Managing of loss

Higher section of copper conductor in stator and rotor

Accuracies of componentsSpecial Skew on rotorReduce interbar current in rotor

Low loss Stamping steelLow flux densityMore core material

Accuracy of componentSmaller and more efficient fan

EE Motors –Some facts

1. The motor efficiency varies with load

2. The pattern of load vs efficiency is different for different size of motors

3. Efficiency of motors 3. Efficiency of motors designed for 60hz is inherently higher than those designed for 50hz .

4 Efficiency of motors at higher speed is more as compared to lower speed

THREE DIFFERENT EFFICIENCIES FOR THE SAME HORSE POWER RATING

Eff1 Motor

Standard Motor

Eff2 Motor

Small FanMore Copper

Larger

COST OF ENERGY EFFICIENT MOTOR

WHY MORE COST ?

LOWER COPPER LOSS

LOWER IRON LOSS

More Copper than standard motor

Higher Grade of Laminations

LOWER MAGNETISATION (LOW FLUX DENSITY)

DESIGN OPTIMISED FOR HIGHEST EFFICIENCY

LOWER WINDAGE LOSS

LOWER STRAY LOSS

Longer Core length

Special Slot Geometry

Special manufacturing process for high accuracy

Optimosed Fan Design& material

Motors With VFD : Selection & care

Motors with VFD can be used in followingapplications for speed control with energy saving:• Constant torque : Speed Range 1:10 , 1:5, 1:2

Cranes,Hoists,reciprocating compressors. Motors with Forced cooling ( Separate fan on Motors with Forced cooling ( Separate fan on ODE side ) or in higher frame size

• Variable Torque: Centrifugal pumps,Fans,Blowers etc

• Constant Power : Metal cutting Lathes, wire winding machines etc

Motors With VFD : Issues

• Voltage Spikes: Power transistors switches at high rates (2-15 kHz). This results in high dv/dt.Maximum repetitive voltage peaks at motor terminals can be 3.1 times RMS with rise time not less than 0.1 microsec.Hence for 415V not less than 0.1 microsec.Hence for 415V motor these will be of order of 1286.5 V. Amount of voltage will depend on 1) Pulse Rise time,2) Cable length 3) Minimum time between pulses,4) Minimum Pulse duration 5) Transition type (Single or double) & 6) use of multiple motors on single VFD

Motors With VFD : Issues

• Temperature Rise: With VFD motor temperature rise will be more . This is because harmonics are present in VFD output. It is assumed that TR is more by 20°C by VFD.

• Special Design Features for Motors:• Special Design Features for Motors:1. Motors with VPI treatment leading to less voids2. Special insulation schemes for rated V >5003. Dual coated winding wires4. Deration in ratings by 15-20 %5. Insulated Bearings for frames 315 & above6. Overheating protection like PTC Thermisters

Motors With VFD : Recommendations

1. Locate drive such that cable length between drive & motor will not exceed 10 meters.

2. Use appropriate filters at drive output when cable length more than 10 meters. Also cable length between Filter & drive should not more than 3 meters

3. Switching frequency restricted to 5 kHz3. Switching frequency restricted to 5 kHz4. Voltage THD of drive output < 5 %5. Use integrated drive & motor combination6. Earth conductor of drive & motor to be separately

grounded & not loop earthed or connected in series7. Use PTC thermisters for temperature control in motors

Motors (IS:325)

• Routine Tests : ( On 100 % Motors) 1. Measurement of winding resistance2. Measurement of insulation resistance before & after

HV test3. High Voltage test4. No load test at rated voltage & frequency4. No load test at rated voltage & frequency5. Locked rotor test at suitable reduced voltage6. Reduced voltage running up test at 0.733 x rated volts

in both direction 7. Measurement of open circuit rotor volts (wound rotor

motors only)8. Polarization index test after HV test (for HT motors )

Motors (IS:325)

• Type Tests : ( Sample basis 1 / Rating)1. All routine tests mentioned above2. Temperature rise test3. Measurement of Efficiency & power factor at

various load pointsvarious load points4. Measurement of breakaway torques & pull out

torques5. Measurement of vibration & noise level6. Dimensional check7. Shaft Voltage, TAN Delta, Polarization index

etc for HT motors

SHEDULE OF TOLRANCESAs per IS:325-1996

• Efficiency: Sum loss Motors up to 50 KWMotors above 50 Kw

• Power Factor

• -15% of (1-η )• -10 % of (1-η )• -1/6 of (1- PF. )• Power Factor

• Slip at Full Load• Starting Current• Starting Torque• Rotor Voltage in SR

• ±20% of comm. slip• +20% of comm. A• -15 to +25 % of Com• ±10 % of Comm. RV

STARTING OF MOTORS

• While starting motor draws 6-8 times FLC• This put stress on electrical system• Hence various starting methods are used to

restrict starting current & avoid heat up• Various starting methods are as follows:• Various starting methods are as follows:1. Direct On Line (DOL)2. Star-delta start3. Resistance start4. Auto transformer start5. Soft Start /VFD start

MOTOR STARTING

• DOL Start: Motor started directly on lineSmaller & 3 lead motors are started by DOLIf grid is strong then big motors are also started directly . This is preferred method as full starting torque is availabletorque is available

• Y/ D start: If starting current is to be limited due to supply restrictions this is used. Only Delta connected motors with 6 leads can be started with this starter. Starting current reduced to 1/3 as well as torque. Hence care to be taken for matching load torque-speed curve over entire range otherwise motor will not start at all.

MOTOR STARTING

• Resistance Start: Resistance connected in series with winding during starting. Resistance reduces starting current linearly & torque by square proportion

• Capacitor Start: It is DOL with shunt capacitor switched in. Reactive power demand during starting taken from capacitor. Suitable for weak supplies. While switching off motor care to be taken to switch off capacitor first, otherwise capacitor will be damaged

MOTOR STARTERS

• Auto Transformer start: Auto transformer reduces starting current & torque in direct square proportion of voltage ration of transformer . The secondary tap is so chosen that acceleration torque remain adequate that acceleration torque remain adequate

• Soft Starter: Soft starters provides smooth start & limits starting current. Employs power electronics devices. VFD now very common. Apart from staring it is very good for energy conservation. Most suitable for higher Kw motors

MOTOR STARTERS-Circuit diagrams

MOTOR STARTERS-Circuit diagrams

THERMISTERS

• Positive Temperature Coefficient (PTC) thermisters are most common temperature detector for LT/HT windings

• Resistance hardly varies with increasing temperature till threshold temp.is reached thereafter resistance increases sharply

• Two protection can be provided alarm & trip• Two protection can be provided alarm & tripClass “B” Alarm: PTC110 Trip: PTC130Class “F” Alarm: PTC130 Trip: PTC150

• Thermisters are identified by color of lead wire• PTC110-Brown, PTC130-Blue, PTC150-Black• There are Three thermisters of same type to be inserted

in motor winding for each type of protection in SEREIS• Generally used in LT & requires Thermostat controller

Typical electrical wiring diagram for dual type PTC protection

Motor

RESISTANCE TEMPERATURE DETECTORS ( RTD & BTD)

Resistance temperature detectors are used to measure winding temperature of LT/HT motors

• Embedded between two coil sides in slotLead wires are connected to temp. controller or scanner for monitoringscanner for monitoring

• Generally used RTD is of platinum with 100 ohms at 0°C & 138.5 ohms at 100°C

• RTD’s are fitted for every coil of motor • Formula for converting resistance of RTD to °C

Temp =(Measured Rest.Of RTD-100) x2.59 °C

BEARING TEMPERATURE DETECTORS (BTD)

• The temperature detector may be either platinum resistance( just like RTD) or Mercury in steel type (Dial type Thermometer DTT)

• Mercury in steel type thermometer operates on principle of volumetric expansion of mercury due to heating. The expansion is sensed by Bourdon tube & translated into movement of pointer against temperature calibrated expansion is sensed by Bourdon tube & translated into movement of pointer against temperature calibrated scale. These are generally provided with alarm and trip contacts. These are activated by use of preset ‘Alarm’ & ‘Trip’ level. Used for monitoring of local temperature as mounted on motor

• BTD generally provided on HT motors & higher frames of LT motors of 315 & above.

• Settings( Alarm/Trip) : Grease 85°C/95°c & Oil 75°C/8 5°

Electrical Failures Of Motors

1. Overloading / Overheating• Observations: Change in color

Insulation paper brittleColor change on rotor face

• Causes:Execessive current drawn as compared to FLImproper Cooling /blocked ventilation

Non manufacturing• Reasons: Non manufacturing1) Overloading/Wrong selection2) Seizing/Jamming of load3) Voltage/Frequency variation, V- unbalance4) Frequent start-stop5) Long starting time

Manufacturing1) Rotor bar defective 2) Heavy rubbing rotor 3) Wrong D

Photo of Overloaded / burnt Motor

2) Single Phasing

• Observations: -All coils on one phase (Delta connection) blackened/overheated

- 2 Phases (Star) blackened/overheated

- Change in resistance on affected phase

- severe sparking ,Carbon deposition &

copper globules present

- Melting of insulation papers- Melting of insulation papers

• Cause: No electrical supply at one terminal

• Reasons: Non Manufacturing

1) Single phasing at site

2) Loose cable connection at motor / Distribution Board

Manufacturing

Crimping of lug on insulation / breakage of lead wire

Photo of Single Phased Motor

3) Interturn Short Circuit:• Observations: Few coils of one phase

blackenedChange in winding resistanceDefect occurrence on overhang or inside slotSparking ObservedSparking Observed

• Cause: short circuit of winding wires within same phase

• Reason: ManufacturingDamaged winding wires /pin holes on wire enamel

4) Phase to phase short circuit:

• Observations:Occurance on overhang or inside slot of Double layer windings

Sparking is present

Copper deposition and copper globules

• Reasons: Failure of phase separator due to overheating of nearby coils

Touching of different phase coils to each other

Insufficient length of insulation paper

MECHANICAL FAILURES

1. Bearing failureObservations: Peculiar noise while running/ PEN OPEN

High bearing temperatureShaft jamming during running

Causes: Insufficient grease in bearings capCauses: Insufficient grease in bearings capLonger idle time without rotationV-belts or excessive tensions on beltsForeign particle entered in grease

Reasons: Faulty /Noisy bearingEnd shield loose on bearingsWrong selection of bearings type/size

MECHANICAL FAILURES

2) Rotor Defective:Observations: Motor does not take load

Low RPM on load

High unbalance current in SCHigh unbalance current in SC

Current hunting on low voltage

Cause: Bad workmanship of rotor makingReason: Die-casting not proper or brazing not O.K.

in case of built up rotor

MECHANICAL FAILURES

3) High VibrationsObservations: Vibration value high on meter

Loosening of foundation boltsChattering of frameChattering of frame

Causes: Unbalance in rotor/fanAlignment with load not O.K.Foundation is not rigid Soft Foot of motor

Reasons: balancing of rotor not done properly

Control Panels

• Following information required for design of panels in systemi) Classification of panels depending on usage ii) Forms of separation inside panel iii) Protection reqd.iv) Type test criteria

• Classification of panels based on usage of panels is as follows:1. Power Control center (PCC) :distribution to various sections2. Motor Control Center (MCC) : Distribution to various motors3. Switch Distribution Board ( SDB): Supply entry to building4. Light Distribution Board (LDB) :Lowest ranking, 5. Power cum motor control center ( PMCC) common6. Automatic Power Factor Control Panel ( APFC)7. Programmable logic control ( PLC) :intelligent & special8. Double Bus Bar panels: Emergency & Non emergency in same

Design Features of PDB

• Degree of Protection required minimum IP42 . IP55 preferred• Construction : 2 mm thick CRCA for front & 1.6 mm for other sides.

Removable hinged doors at front with handle & lock key facility• Cable entry preferably from bottom with 3 mm thick gland plates • Bus Bar size should be 25 x 6 mm of tinned copper & should be

supported by flame resistant Non hygroscopic insulating materialsupported by flame resistant Non hygroscopic insulating material• Earth Bus of tinned copper of 25 x 3 mm size with adequate

numbers with earthing bolt s size of M8• Protection cover shall be provided above all MCBs & TBs for human

safety• Main isolator shall be DPST ( Double Pole Single Tone ) type &

individual feeders shall have MCBs of DPST type• MCB shall be hand operated with overload & short circuit protection

Design Features of PDB

• All incoming & outgoing MCBs shall have mechanical ON/OFF indications & rating shall be as per load . Shall be DIN Rail mounted

• Fuses shall be HRC type or Semi conductor type• Internal Wiring shall be carried out with 1100/600 V grade PVC

insulated stranded copper conductors . Cable shall be FRLS type• Wire marking philosophy shall be direct double cross ferruling type• Engraved identification ferrules marked to corresponding wiring • Engraved identification ferrules marked to corresponding wiring

diagram shall be fitted at both ends of each wire. Ferrule shall be of yellow color with black numbers engraved.

• Terminals should be suitable for cable size 4-120 sq mm. Terminal block shall be one piece molded 500 Volt preferably stud type for higher current ratings ,such that wires can be connected by cable lugs . Minimum current rating for terminal should be 20 Amps . Terminals for voltages exceeding 125 V should be shrouded

• Each wire should be terminated on separate terminal using self insulating crimping lug.

Inspection & testing of PDBs• Fabrication Quality : 1) Thickness of sheet ( Main frame & Gland

plate 2 mm & Base plate 3 mm )2) Overall Dimensions of panel

• Painting & : 1) Paint Shade ( RAL-7032 Siemens grey )Powder Coating 2) Paint Coating Thickness > 60 microns

3) Peel test if anticorrosive paint required• Assembly 1) Gasketing arrangement• Assembly 1) Gasketing arrangement

2) Clearance between live parts to earth & between live parts

• Final Inspection 1) Visual checking, Nameplate, Tag plate etc 2) Verification of bill of materials wrt make,qty 3) Functional test e.g. operation of power &

control circuits as per wiring diagrams4) Insulation resistance test IR> 10 Mohms5) High Voltage test between phases, phase

& earth & neutral

APENDIX

Thank You