WELCOME SEMINAR ON ELECTRIC CRANE DUTY MOTOR & S.S. Ghatpande Ex Crompton Greaves, L.T. Motors Ameya Co Con nsultants,Pune 43 Phone:020-24379151
CONTENTS • • • • • • • • • • • • •
Basic terminology Raw materials Constructional details o off Induction mo motors Guide for selection of motors: Mech & Elect Special features of Crane Duty 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
CONTENTS • • • • • • • • • • • • •
Basic terminology Raw materials Constructional details o off Induction mo motors Guide for selection of motors: Mech & Elect Special features of Crane Duty 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 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 voltage e.g. Silver copper Aluminum & most of metals
Basic Materials • Copper : Winding,Busbars,Lugs etc Best conductivity, low resistivity leading high efficiency thereby small sizes Cost factor • A l u m i num , motor,Busbars in panels Ease of construction ,castable at low temp Leading to high temperature –bulky sizes Lower cost hence preferable
Basic Materials • Sta tamp mpin ings gs// Lam amiina nattio ions ns:: thin pieces of CRGO steel to reduces hystersis loss Various grades depending on B-H curve products, Energy conservation • Steel: used for shafts,body,housing,covers shafts,body,housing,covers Shafts of motors are of EN8 or EN24 • Other materials like bearings, accessories Like meters,Relays,Cables, meters,Relays,Cables,Oil, Oil,
Basic Materials • Insulation : Depending on temperature divided in various classes. Most common Class B- Max temp 120 °C Class F- Max temp 150°C Class H- Max temp 180 °C General trend use higher class but restrict temp rise to lower class -General forms solid-papers , shapes,tapes or 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) • ync ronous spee o es : o e , ng e spee 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 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
PULL OUT TORQUE
TORQUE Vs SPEED
250
STARTING TORQUE
200
E U Q R O150 T D A PULL UP TORQUE
L L 100 L U F %
STAR DELTA
ACCELERATING TORQUE
RATED TORQUE
50 LOAD CURVE 1 LOAD CURVE 2
0 0
10
PROBLEM AREA
20
30
40
50
60
% SYNCHRONOUS SPEED
70
80
90
100
TEMP. OF INSL.CLASS Insulation Class
Amb. Temp. °C
Max. Temp. °C
Allowance Max. for Hot Spot Permissible Temp. °C °C
A
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 tem & Altitude deratin 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 (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 • , 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
• calculated by following formulae : • Vr x ( Ns-N) x Mn Rc= 3 x Lr x Ns x M - Rr Where Vr= Rotor Voltage , Lr= rated current , Rr= rotor resistance Ns= 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 : • • • • 1. 2. 3. 4.
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 : A.C. Induction motor of SCR type Encapsulated brake coil housed at NDE ends held Brake liner attached to armature disc near cooling fan 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 • 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 components Special Skew on rotor Reduce interbar current in rotor
Low loss Stamping steel Low flux density More core material
Accuracy of component Smaller 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 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 Standard Motor
Eff1 Motor
Small Fan More Copper
Eff2 Motor
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)
Longer Core length
DESIGN OPTIMISED FOR HIGHEST EFFICIENCY
Special Slot Geometry
LOWER STRAY LOSS LOWER WINDAGE LOSS
Special manufacturing process for high accuracy Optimosed Fan Design& material
Motors With VFD : Selection & care Motors with VFD can be used in following applications for speed control with energy saving: • Constant torque : Speed Range 1:10 , 1:5, 1:2 Cranes,Hoists,reciprocating compressors. otors w t orce coo ng eparate an 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 . . 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 •
• 1. 2. 3. 4. 5. 6.
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: Motors with VPI treatment leading to less voids Special insulation schemes for rated V >500 Dual coated winding wires Deration in ratings by 15-20 % Insulated Bearings for frames 315 & above Overheating protection like PTC Thermisters
Motors With VFD : Recommendations 1. 2.
3. 4. 5. 6. 7.
Locate drive such that cable length between drive & motor will not exceed 10 meters. 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 Switching frequency restricted to 5 kHz Voltage THD of drive output < 5 % Use integrated drive & motor combination Earth conductor of drive & motor to be separately grounded & not loop earthed or connected in series Use PTC thermisters for temperature control in motors
Motors (IS:325) • 1. 2. 3. . 5. 6. 7. 8.
Routine Tests : ( On 100 % Motors) Measurement of winding resistance Measurement of insulation resistance before & after HV test High Voltage test o oa test at rate vo tage requency Locked rotor test at suitable reduced voltage Reduced voltage running up test at 0.733 x rated volts in both direction Measurement of open circuit rotor volts (wound rotor motors only) Polarization index test after HV test (for HT motors )
Motors (IS:325) • 1. 2. 3.
Type Tests : ( Sample basis 1 / Rating) All routine tests mentioned above Temperature rise test Measurement of Efficiency & power factor at
4. Measurement of breakaway torques & pull out torques 5. Measurement of vibration & noise level 6. Dimensional check 7. Shaft Voltage, TAN Delta, Polarization index etc for HT motors
SHEDULE OF TOLRANCES As per IS:325-1996 • Efficiency: Sum loss Motors up to 50 KW Motors above 50 Kw • Power Factor • Slip at Full Load • Starting Current • Starting Torque • Rotor Voltage in SR
• -15% of (1-η ) • -10 % of (1-η ) • -1/6 of (1- PF. ) • ±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
1. 2. 3. 4. 5.
Direct On Line (DOL) Star-delta start Resistance start Auto transformer start Soft Start /VFD start
MOTOR STARTING • DOL Start: Motor started directly on line Smaller & 3 lead motors are started by DOL If grid is strong then big motors are also started directly . This is preferred method as full starting • 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 a acce era on orque rema n a equa e • 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 • Class “B” Alarm: PTC110 Trip: PTC130 Class “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 slot Lead wires are connected to temp. controller or • 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 ex ansion is sensed b 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 brittle Color change on rotor face Causes:Execessive current drawn as compared to FL Improper Cooling /blocked ventilation Reasons: Non manufacturing 1) Overloading/Wrong selection 2) Seizing/Jamming of load 3) Voltage/Frequency variation, V- unbalance 4) Frequent start-stop 5) Long starting time Manufacturing 1) 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
•
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 blackened Change in winding resistance Defect occurrence on overhang or inside slot Sparking Observed • Cause: short circuit of winding wires within same phase • Reason: Manufacturing Damaged 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 failure Observations: Peculiar noise while running/ PEN OPEN High bearing temperature Shaft jamming during running Longer idle time without rotation V-belts or excessive tensions on belts Foreign particle entered in grease Reasons: Faulty /Noisy bearing End shield loose on bearings Wrong selection of bearings type/size
MECHANICAL FAILURES 2) Rotor Defective: Observations: Motor does not take load Low RPM on load High unbalance current in SC Current hunting on low voltage Cause: Bad workmanship of rotor making Reason: Die-casting not proper or brazing not O.K. in case of built up rotor
MECHANICAL FAILURES 3) High Vibrations Observations: Vibration value high on meter Loosening of foundation bolts Chattering of frame Causes: Unbalance in rotor/fan Alignment with load not O.K. Foundation is not rigid Soft Foot of motor Reasons: balancing of rotor not done properly
Control Panels •
• 1. 2. 3. 4. 5. 6. 7. 8.
Following information required for design of panels in system i) 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: Power Control center (PCC) :distribution to various sections Motor Control Center (MCC) : Distribution to various motors Switch Distribution Board ( SDB): Supply entry to building Light Distribution Board (LDB) :Lowest ranking, Power cum motor control center ( PMCC) common Automatic Power Factor Control Panel ( APFC) Programmable logic control ( PLC) :intelligent & special 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 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 ngrave en ca on erru es mar e o correspon ng w r ng 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 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 diagrams 4) Insulation resistance test IR> 10 Mohms 5) High Voltage test between phases, phase & earth & neutral
APENDIX
