Motors - allindustrialtraining.com

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© Confederation of Indian Industry

Motors


Motors

�Motor

� Converts Electrical Energy into Mechanical

Energy

� Drives a mechanical load

� Types of mechanical loads

� Constant torque, variable speed loads

� Variable torque, variable speed loads

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Types of Loads

� Constant torque, Variable speed loads

� Torque is constant irrespective of speed

� Power is proportional to speed

� Screw compressor, conveyors & feeders


Types of Loads

� Variable torque, Variable speed loads

� Torque αααα (speed)2

� Power αααα (speed)3

� Centrifugal pumps and fans

� Found in all process

industries

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TYPES OF MOTORS

�AC MOTORS

� Very common in

Industries

� DC Motors

� Generally installed for

variable speed applications

� Replaced by AC drives

� Still found for kiln drive


TYPES OF MOTORS

� Slip ring induction

motors

� Used in high starting

torque applications

� Found in cranes, Mills,

large fans, etc

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TYPES OF MOTORS

� Squirrel cage

induction motors

� Used in all general

applications

� 85% of the

industrial motors

are of squirrel cage

induction motors


Capacity of Motor - Horse Power ?

1 HP = 76 Kg-m per second

76 Kg

1 HP = 0.75 kW

Work - Force applied over a distancePower – Rate of doing work

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AC INDUCTION MOTOR

Primary winding connected to

“POWER SOURCE”

STATOR

Secondary winding carries

“INDUCED CURRENT”

ROTOR


Effectiveness with which a motor

converts Electrical energy to

Mechanical energy

Motor Efficiency

Out put Power

Efficiency =Input Power

X 100

Input

Output

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Motor Losses

� Copper Loss – I2R loss

� Current dependent losses

� Stator Cu loss

� Rotor Cu loss

� Iron loss – Voltage dependent

� Hysteresis or magnetization loss

� Eddy current loss


Motor Losses

� Friction and windage losses –

mechanical losses

� Friction at bearings

� Friction offered by wind to rotor

movement

� Stray load losses

� Unaccountable losses

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Induction Motors

Motor energy balance flow diagram

Input power

Psup

Stator Copper loss3I2Rst

Rotor Copper loss3I2Rrot

Stator Iron loss3V2/Rc

out

Air gap

powerPag

Developed powerPdv = 3 Irot

2Rrot(1-s)/s

Air gap

Output power

P

Ventilation & Friction losses


Motor Power Loss Model

Typical range

Hp horsepower 5 - 200 HP

Pi input power 119 - 106 % of poPwf windage/friction losses 2.6 - 0.3 %Pcl core losses (magnetization) 5 - 2.5 %Psl stray load losses 2.2 - 0.5 %Pcu I2R losses (copper losses) 9 - 3 %Pkl total losses 18.8 - 6.3 %Po output power 100 %N motor efficiency (po/pi) 84 % - 94%

Motor Load

PCL

PWF

POPI

PSLPCU

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Range ( H.P ) % of Loss At FL

Efficiency %

1 - 10 14 - 35 65 - 86

10 - 50 09 - 15 85 - 91

50 - 200 06 - 12 88 - 94

200 - 1500 04 - 07 93 - 96

1500 & above 4 95 - 96

Range Of Losses In AC Induction Motor


Types of Losses

�Unavoidable losses

� Avoidaable losses

� Focus on avoidable losses

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Power = √√√√3 V I Cos φφφφ

Cos φφφφ is power factor

Capacity αααα Torque

αααα Voltage 2

Basic Formulas


Torque αααα s E2R___R2 +(sX0)

2

Where, s – Slip

R – Rotor resistance / Phase

Xo – Rotor Reactance / Phase

Basic Formulas

• Torque speed characteristic

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Motor Efficiency at Different Loads

Efficiency Vs Load

0 5 10 50 75 100% Load

ηηηη

94%

70%


Performance of Motor at Partial Load

� Motor ηηηη and power factor varies with % loading

� For lightly loaded motors

� Voltage related losses - high

� Power factor is very low

� More copper losses

� Motor operates in less efficiency range

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Voltage Optimisation

Impact on motor operating parameters

• Reduction in voltage dependent losses - Drop in Magnetization current

• Capacity reduces

• PF improves

• Load current drops

• Load factor improves

• Efficiency Improves

Capacity αααα Voltage 2


Motor Magnetization Losses Vs Motor Voltage2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

.1 .2 .3 .4 .5 .6 .7 .8 .9 1.0

Per unit line voltage

Per unit magnetization losses

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Voltage Optimization

What are the effects of voltage optimization?

(Voltage 415 V --> 400 V)

� 100 HP Motor - 100 % Loading

� 100 HP Motor - 80% Loading

� 100 HP Motor - 50% Loading

� Increase in Load Current

� Decrease in Load Current – Optimum Level

� Decrease in load current – Still Potential


Effect of Voltage on Motor Losses

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Optimization Of Lightly Loaded Motors

� Options � Delta connection to permanent star

connection -Steady load application

� Automatic star-delta-star converters- for

variable loads

� Soft starter cum energy savers - High

Starting torque applications

� Down sizing

� Overall voltage optimization



Options based on

� Nature of load

� Load factor

� Economic option

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Analysis of Load Pattern

� Measure kW input to motor using Portable

Power Meter / Load Manager

� Loading of motor = Actual kW / Rated kW

� Analyse Load pattern at different process

conditions

� Record the minimum & maximum Loading


Delta & Star Motor Connection

Delta connection Star connection

L1

L2

L3

VVL = VP

L1

L2

L3

VL

IL = √√√√3 Ip VL√√√√3

VP =

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Delta & Star Motor Connection

� Reduction in Voltage by √√√√3 Times

� Reduction in Current by √√√√3 Times

� Reduction in Torque by 3 Times


Convert Delta To Star Connection At Lightly Loaded Motors

�Motors normally operated in delta mode

� Permanently Lightly loaded motors can be operated in star mode

� Effect on motor performance operating in starmode

� Reduction in voltage related Iron losses

� Reduction in copper losses

� Operates with improved P.F

� Motor operating efficiency improves

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CASE STUDY

Convert Delta To Star Connection At Root Blower Motor

Rated kW - 30 kW

Actual load

Delta mode = 11 kWStar mode = 9 kW% Load = 36 %Savings in kW = 2 kW

Annual Saving = Rs 0.6 Lakhs

Caution – Reset the OLR


Automatic Star-delta-star

� Application - motors with variable loads

� Automatic star-delta-star converter has load

sensor & Timer

� Capacity ∝∝∝∝ V2

� Principle of Voltage optimization

Energy Saving Protection

% LStar Mode < 38% > 38% ∆∆∆∆ Mode

Load Sensor

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CASE STUDYAutomatic Star Delta Star Starters for Belt

Conveyors

� Most of the time lightly loaded

� Subject to heavy load� Rated KW = 90.0 KW (3 nos)� Actual load = 35.0 KW� In star mode consumes= 32.0 KW� Savings in KW = 9.0 KW

Annual savings - Rs 2.8 LakhsInvestment - Rs 1.2 LakhsPayback period - 5 months


Case Study

In a plant, if the loading of all the motors are less than 80%,

What is the method of Energy Conservation ?

Loading of Motors – Varying

Best method – Optimising the overall

Voltage of the plant.

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Optimise The Plant Operating Voltage-Overall

� Plant operating voltage plays a critical role

in energy conservation

� On line voltage optimising devices to

regulate the operating voltage

� Magnetization losses vary exponentially

with the voltage


Motor Magnetization Losses Vs Motor Voltage2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

.1 .2 .3 .4 .5 .6 .7 .8 .9 1.0

Per unit line voltage

Per unit magnetization losses

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Optimise The Plant Operating Voltage-Overall

� Voltage optimisation Potential will vary with

over all Loading pattern of all motors

� To be implemented after analysing the

loading pattern of all motors

� Reduce Voltage from rated value – In steps

� Monitor Energy Consumption

� Arrive at Optimum Voltage


Case Study

Voltage Optimisation-Overall

� Distribution Transformer : 2000 kVA, 11kV/433 V

� Operating voltage : 428 – 430 V

� LT Motors Loading : 20 – 80%

� Average Load : 850 – 900 kW

� Transformer tap position reduced from 3 (normal

tap) to 2

� Optimized voltage : 417 – 419 V

Annual Savings : Rs 1.32 Lakhs

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Role Of Frequency In Process Plant

� Fans, compressors & pumps are major loads

� 50 - 60 % power consumption

� Majority of loads are centrifugal in nature

� Power cons. ∝∝∝∝ Rpm3

� 10 - 20% over design is common

� Excess head & capacity control

� Controlled using dampers/valves

� Energy inefficient methods of control & hence VFDs

are ideal choice


Role of Frequency in Process Plant

� Variable frequency drives are ideal choice

� Power plant (without grid synchronisation) –

Reduce the frequency and optimise

�Majority of case low frequency is helpful -

reduce energy consumption

� Reduction in Frequency – depends on capacity

utilisation of Fans, pumps, Mills and other drives

Applicable for power plants operating without grid synchronisation

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Optimise operating frequency A Case study from a Cement Plant

� Has captive power plant – 45 MW

�Operated in island mode

�Operating frequency : 50 Hz

� Studied all major equipment

�Capacity utilisation : 60 – 80%

�Major fans controlled with GRR


Optimise operating frequency

� Reduced the overall frequency to 49 Hz

in steps of 0.2 Hz

�Observed the operating parameters

�No effect on production

�Found reduction in energy consumption

Annual Saving - Rs 37.0 Lakhs

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Idle Operation of Equipments in Packing Plant

� Packers 1,2 & 3

� Hardwired control

� Packers 4, 5, 6 & 7

� PLC based control

� Idle operation of equipments observed

� Bag filter fan, Bucket elevator, screens, screw conveyor, etc


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�Measured kW during idle run

� ~30 kW

� Calculated idle running 22%

� 1700 hours

� Installed interlock with timer logic for the idle running equipments



� Annual Saving - Rs 7.5 Lakhs

� Investment - Rs 1.0 Lakh

� Payback - 2 months

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Optimise the Operation of Crusher

� Lime stone crusher rated for

� 850 TPH

� 900 kW

� Crusher output

� 400 – 650 TPH

� Average output is < 500 TPH

� Power consumption

� 200 – 400 kW



� Crusher power consumption

� One week trend

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� One day trend – hourly basis



� Apron conveyor speed varied manually

� 500 rpm - Constant speed for longer duration

� Operating load on crusher is low

� Operates in idle running some times

� Action taken

� Interlocking apron conveyor speed with crusher loading

� Increased the crusher output

� Reduction in SEC


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Case StudyCooling Fans in Twin Drive Motor



� Back ground

� Mill has a Twin Main Drive with 2 Nos Cooling fans

each in parallel

� Winding temperature of both the Main drives with

both the cooling fans was 65 - 70 0C

� Trial taken by switching off one cooling fan

� Found Winding temp within the acceptable limits (80-82 0C)

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� Improvement done: � PLC Program modification done to start/stop one cooling fan each of both Main Drives.

� The cooling fan will start with winding temp 92 0C

� Stop at 82 0C

� Only one cooling fan each of both main drives operates continuously

Annual Savings - Rs 2.0 LakhsInvestment - NIL


Case StudyOptimise the Operation of GRR Cooling

fans� Cooling fans for GRR

� To dissipate the heat produced in the resistance

� 10 cooling fans for Raw Mill ESP fan GRR

� Each 2.2 kW

� Cooling fans are designed for max heat dissipation

� Raw Mill ESP fan

� Operating at full step during normal operation

� Operates at rated speed

� No external resistance in the circuit

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Optimise the Operation of GRR Cooling fans

� Cooling fans not required during normal operation

� Cooling fans were running continuously

� Programmed to operate as per no of GRR steps



Energy Efficient Motor

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� 20% more copper

�Reduce the stator losses

� Rotor losses reduced

�Increasing the mass of rotor conductors / conductivity

� Precision air gaps to reduce current requirements

� Improved winding and lamination designs to minimise energy consumption



� Lesser slip

� Improved fan design

� Cooler operation & Increases motor insulation life

� 1.15 service factor

� Greater flexibility in handling voltage variations and imbalances

� High power factor

� Eliminate need for PF correction

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Comparison of efficiencies of Standard & Energy Efficient Motors

92.2%90.0%87.0%18.5kW

85.0%78.5%76.0%1.5 kW

93.6%92.0%88.5%37 kW

95.8%95.0%Not specified160 kW



91.0%88.4%85.5%11 kW

88.3%84.0%83.0%3.7 kW

82.5%73.0%71.0%0.75 kW

Eff 1 as per IS

12615

Eff 2 as per IS

12615

IS 8789Output

4 Pole

Efficiency values are subject to tolerance as per IS325



Energy Efficient Motor – Part load Operation

5 10 50 100% Loading

94

90

80

76

ηηηη

Standard motor

Energy efficient motor

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Loading vs Efficiency

�Motors are generally loaded between

50 – 80%

� Due to Higher starting Torque

� Varying process requirements

� Efficiency of Energy Efficient Motors is

higher than conventional motors and

flat between 50 – 100% loading


Advantages of Energy Efficient Motor

�Optimum efficiency

� Longer life

� Lower operating cost

� Ability to operate at higher ambient

temperature

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When to Install EE Motors?

� New Projects

� EE Motors ideally suited

� Rewinding of Old motors

� In case of Normal Failure

� Fit case for Replacement after rewound 5 times


Rewound Motors

� Motor Burning

� Quality of insulation between stampings

detoriates

� Eddy current losses increases

� Magnetic property detoriates

� Magnetic losses increases

� Causes drop in efficiency

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Rewound Motors

� Bearing failure

� Rotor scratches stator

� Air gap becomes uneven

� Torque induced not uniform

� Net torque developed is low

� Causes drop in efficiency

� Motors replacement should be

analysed case to case basis

� Maximum 5 times motor can

undergo rewinding – normal failure


Where Not to Install EE Motors?

� Applications where EE motors cannot be

installed ?

EE Motors are not to be Installed for Intermittent duty applications like crane, Hoist etc

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Case StudyReplace old motors with Energy Efficient

Motors� Implemented in one of the cement plants

� Old motors

� More than 20 years old

� Rewound for many times

� Reduction in efficiency

� Replaced 9 numbers of motors


Investment - Rs 25.0 Lakhs

Payback period - 22 Months


Sum-up

�Causes of energy loss in motors

�Oversized /under loaded motors

�Overloaded /under sized motors

�Improper supply voltage

�Voltage fluctuations

�Poor power factor

�Idle running

�Use of less efficient motors

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Sum-up

� Sizing of the motor is critical and

important

� Over sizing will result in

� More losses

� Lower efficiency

� Undersizing will result in

� Overloading

� Overheating & failures

� Optimal sizing will result in

� Minimum losses

� Maximum efficiency


Sum-up

� History Card

� Regular Updation

� Joint Ownership with the process team

� Energy Efficient Motor

� New installations

� Replacement – Rewound Motors

Motors - allindustrialtraining.com

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Transcript of Motors - allindustrialtraining.com