ecmeasuresmgmorshad

8/3/2019 ECmeasuresMGMorshad

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Energy Conservation Measures In Industrial Drives Through

Selection, Operation and Maintenance.

M.G.Morshad, Deputy Chief Engineer / Electrical maintenance / Thermal station II

Neyveli Lignite Corporation Ltd

INTRODUCTION-

The need for energy conservation dose not requires any explanation. The simple logic is

- energy saved is equivalent to energy generated. But the question is - how much energy can be

saved? Right answer - the energy, which is being wasted, can only be saved.

Energy waste is always associated with improper selection, operation and maintenance

of equipments. But financial constraint and reliability - are the two factors, which industry is

always concerned about, get top priority neglecting energy account intentionally or

unintentionally. Energy conservation is an effort to consider the factor of selection, operation

and maintenance seriously and arrest energy waste as much as possible without disturbing

reliability and increasing financial burden.

Electrical motor (industrial, commercial, domestic and agriculture) alone consumes about

70% of country's total generated power (83000MW). If, by effective energy conservation it is

possible to improve the efficiency of drive system by 0.5%, electrical power amounted to 83000

x 0.7 X 0.005 = 290 MW can be saved or alternately generated every day. This huge potential

for power generation through energy conservation is much more economical, viable andpractical than obtaining similar amount of power from renewable source like solar, wind, tidal

etc.

Therefore, considering the present energy situation energy conservation is not merely an

option but compulsion, which have to be adopted without any compromise for prolonging the life

of our modern civilization beyond the estimated limit.

Energy losses in electrical motor-

Mainly three phase induction motors are used for industrial application and the typical

percentage of losses and their root causes are found as shown in the table

TYPE OF LOSSESTYPICAL %

OF LOSSES

ROOT CAUSE OF THE

LOSSES

FACTOR AFFECTING

THESE LOSSES

Stator Copper (I2R)

loss35 to 40%

I2R losses minimum at no

load. It increases with the

increase of motor load and

additionally with temperature

Stator conductor size,

material and

temperature rise

Rotor Loss 15 to 20%

I2R losses in bar and end

rings virtually zero at no load.

Increases as the square of

the load and additionally as

the temperature increases.

Rotor core losses due to mainflux are virtually zero.

Rotor conductor size,

material and

temperature rise


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Core loss

a) Hysteresis

b) Eddy current

15 to 20%

a) Energy expended by

reversal of magnetic flux

b) I2R losses in core steel

cause by circulating currentinduced by the flux reversal.

a) Type and quality of

magnetic material

b) Quality of lamination

used for core

Stray load loss 10 to 15%

Addition load losses in stator

and rotor mainly caused by

leakage flux and high

frequency pulsation.

Manufacturing and

design methods

a) Friction losses

b) Windage losses 5 to 10%

a) Viscous flow of the

lubrication in bearings

b) Air resistance and

turbulence in cooling fans

Selection / design of

fan and bearings

Rated efficiency of motor is decided during design stage and cannot be improved further,

whereas operating efficiency, which mainly depends on operating condition is possible to

improved by proper selection, operation and maintenance.

SELECTION

1) Proper sizing of motor

Convinced by the general perception that higher size is more reliable, there is always a

tendency to prefer oversize motor. Such practice not only increases the investment cost but also

causes tangible amount of energy loss.

For successful acceleration of load, motor capacity must always be higher than load capacity. In

centrifugal pump type load (low starting torque) it is normally kept 25% higher - considering

other aspect like temporary overload due to higher frequency, over discharge, and future

expansion of load. Based on this calculation - a pump of capacity 13.8 KW at 1465-rpm

requires 13.8 + 13.8 x 0.25 = 17.25KW motor. Since motors are available with standard capacity

and frame, only two capacities i.e. 18.5 KW and 22 KW are available in this frame and the

appropriate size of motor for driving the pump should be considered 18.5 KW. Instead of that, if

22 KW is selected - it becomes oversize for the pump and the financial burden for selecting

oversized motor can be calculated as shown in the table.

REQUIRED MOTOR OVERSIZED MOTOR

Motor capacity 18.5 KW 22 KW

Motor frame 180M 180L

Motor loading % (13.8/18.5) x100 = 75% (13.8 / 22) x100 = 62%

Motor efficiency 92% 90%

Motor input 13.8 / 0.92 = 15 KW 13.8 / 0.90 = 15.33 KW

Motor loss 15 - 13.8 = 1.2 KW 15.33 -13.8 = 1.53 KW

Power loss in oversized motor ********** 1.53 -1.2 = 0.33 KWEnergy loss / day *********** 0.33 x 24 = 7.92 Unit


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REQUIRED MOTOR OVERSIZED MOTOR

Energy loss / year *********** 7.92 x 300 = 2376 Units

Energy cost @ Rs 2.50 / year ************ 2376 x 2.50 = Rs 5940/-

Energy cost in five years Rs 29700/-

Motor cost (Rs 2500/KW) Rs 46250 /- Rs 55000/-Difference in motor cost ************ Rs 8750/-

Interest - for 5 Years Rs 6550 /-

Cumulative financial loss in 5 years ************* 8750 +6550 + 29700 = 45000

2) Energy efficient motor

There are some drives like conveyor belt, where high starting torque is required for successful

acceleration of load. In such case motor capacity must be at least 30% higher than load

capacity and designer normally prefer 35% higher - considering other aspects like temporary

overload and future expansion of load. Based on this calculation - for driving a conveyor belt of

capacity 3.5 KW, motor capacity 5.5KW is preferred. Such unavoidable over sizing [(3.5/5.5)

x100= 63% loading] always causes energy loss due to partial loading of motor.

There are two basic advantages in energy efficient motors - a) Motor full load efficiency is 1 to

2% higher than standard motor and b) This efficiency remains more and less unchanged till 50%

of loading. The effective energy saving for replacing standard 5.5 KW motor with similar

capacity energy efficient motor can be found as shown in the table

Type of motor Standard motor Energy efficient motor

Motor Capacity 5.5 KW 5.5KW

Motor Loading % (3.5/5.5) x100 = 63% (3.5/5.5) x100 = 63%

Operating efficiency 82% 83%

Motor loss (3.5/0.82) - 3.5 = 0.76 KW (3.5/0.83) - 3.5 = 0.71 KW

Power saving *************** 0.76 - 0.71 = 0.05 KW

Energy saving / day **************** 0.05 x24 = 1.2 Units

Energy saving / year **************** 1.2 x 300 = 360 Units

Cost saving (Rs 2.50) / year **************** 360 x 2.50 = Rs 900/-

Motor cost (Rs 2500/ KW) Rs 13750/- Rs 16500/-

Difference in cost Rs 2750 /- **************

Pay back period ************** Three years

3) Variable Speed Drive (VSD)

Conventionally, throttling / re-circulation in pump and damper control in fan / blower are used for

controlling out let flow. Such methods always increase the system resistance and consume

about 12.5% more power at 50% of flow. The energy waste due to throttling or damper control

can be avoided by selecting following methods for flow control -

a) For higher head pump - Recirculation through NRV (instead of valve less recirculation)

b) For lower head pump - Variable Speed motor (instead of throttling)

c) For fan and blower - Variable speed motor (instead of damper control)


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4) Soft starter

To avoid over sizing and harmful starting, motor for high inertia load like heavy conveyor belt is

provided with fluid coupling. Transmission loss due to slip is a permanent feature in this type of

coupling. The slip is normally found 3% at full load and increases with the decreases of load.

Such load dependent slip in coupling always causes energy loss - particularly in conveyor belttype load where uniformity in loading can never be maintained and average loading level is

normally found less than 50%.

Soft starter limits the starting current by controlling terminal voltage and helps to achieve starting

alike fluid coupling with direct coupling. Therefore, by starting motor through soft starter, fluid

coupling can be replaced with direct coupling and some amount of energy can be saved. The

typical energy saving for replacing fluid coupling with direct coupling can be calculated as shown

in the table

Fluid coupling Direct coupling

Motor capacity 45 KW 45 KW

At Ave. 60% motor loading 27 KW 27KW

Approximate slip in coupling 7% 0

Transmission efficiency 93% 100%

Motor out put 29 KW 27KW

Motor efficiency 89% 89%

Motor input 32.58 30.33 KW

Motor loss 5.58 KW 3.33 KW

Energy saving ********* 2.25KW

Energy saving / day ********** 54 Units

Energy saving / year ********* 16200 Units

Cost of the energy / year ********* RS 40500 /-

Soft starter also can find out optimum operating voltage required for a particular loadingcondition. Utilizing this feature, soft starter applies the minimum terminal voltage during idle

running and saves considerable amount of energy.

5) High slip motor for pump & blower operation

Since the power input in centrifugal type pump, fan and blowers is proportional to (Speed) 3,

power consumption in motor gets increased with the increase of operating speed. Full load

speed of motor for a particular specification varies from manufacture to manufacturer. Selecting

lower speed motor (high slip) for such application some amount of energy can be saved. The

energy saving potential of high slip motor for pump application can be calculated as shown in

the table

Selected motor capacity 67 KW 67KW

Rated speed of the motor 1490 RPM 1485 RPM

Slip of the motor 0.66% 1%

Pump input power (PN3) 49.00 KW 48.51 KW


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Discharge (Q N) 109.26 m3/h 108.9 m3/h

Outlet pressure (H N2) 15.78 Ksc 15.68 Ksc

Motor input power ( 87%) 56.32 KW 55.75KW

Motor current 50.84 A 50.33 A

Energy saving ****** 56.32-55.75=0.57KWEnergy saving / year ******* 0.57X24x300 = 4104 Units

Cost saving / year ******** 4104 X 2.50 = Rs 10260 / -

6) Rewinded motor

After rewinding, efficiency of all types of motors gets reduced by 2 to 3 %. Energy loss due to

lower efficiency can only be avoided if rewinded motors are discarded completely. But

considering financial constraints involves with such practices, it is never recommended and

rewinded motors are allowed to run with extra energy losses. The financial loss for rewinded

motor can be calculated as shown in the table

New motor Rewinded motor

Capacity 110 KW 110KW

Motor out put at 75% loading 82.5KW 82.5KW

Operating efficiency 92% 89%

Motor loss 7.71 KW 10.19 KW

Extra energy loss / day ********* 59.6 units

Extra energy loss / year ********* 17880 units

Cost of energy / year ********** Rs 44700

Motor cost Rs 2,75000 Rs 40000 (Rewinding cost)

Cost saving for rewinding *********** Rs 2,35000 / -

Extra energy cost in 5 years ********* Rs 2,23500 /-

Energy waste in rewinded motor can be avoided by proper planning such as - a) Using only for

less running hours drive. b) Keeping as emergency reserve for temporary use. c) Discarding as

and when operating cost of rewinded motor becomes equal to the cost of new motor.

4) Unidirectional motor cooling fan

Normally bi directional fan is used for cooling motor. The efficiency of this type of fan is very

poor (30%) and therefore needs more fins area for delivering required quantity of air. The airresistance encountered by more fins area virtually increases the windage loss in motor.

Bi-directional Fan Unidirectional Fan


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Alternatively, efficiency of unidirectional fan is very high (80%). It needs minimum fins area for

delivering same quantity of air and reduces the windage loss in motor. Energy saving potential

of unidirectional fan can be calculated as shown in the table

Bi-directional Fan Unidirectional Fan

Motor capacity 160KW 160 KWSpeed 1485 rpm 1485 rpm

Rated efficiency of the motor 95.3 % 95.3 %

Rated loss 7.89 KW 7.89 KW

Rated windage loss (8%) 6.31 KW 6.31 KW

Efficiency of the fan 30% 80%

Power consumption by fan 4.41 KW 1.26 KW

Power saving ****** 3.14 KW

Energy saving / day ****** 75.36 Units

Energy saving / year ****** 22608 Units

Cost of energy / year ****** Rs 56520 /-

Therefore by knowing the Direction Of Rotation of machine, unidirectional cooling fan may be

preferred for saving unwanted windage loss in motor.

4) Higher size cable

Since the DC resistance in cable decreases with the increases of size, energy loss in higher

size cable is always found less. Therefore, by providing higher size cable some amount of

energy can be saved as shown in the table

Standard size Higher size Highest size

Motor capacity 15KW 15KW 15KW

Full load current of 28 Amps 28 Amps 28 Amps

Operating current of motor 22 Amps 22 Amps 22 Amps

Cable size 3C AL 10 mm2 3C Al 16mm2 3C Al 25mm2

Length of the cable 0.3Km 0.3Km 0.3Km

DC resistance in cable 0.92 Ohms 0.57 Ohms 0.36 Ohms

I2R loss 445.3 W 275.8 W 174.2 W

Energy saving ******* 0.17 KW 0.27 KW

Energy saving / day ******* 4.08 Units 6.48 UnitsEnergy saving / year (300 days) ******** 1224 Units 1944 Units

Cost saving / year ********* Rs 3060/- Rs 4860/-

Cost of the cable Rs 12000/- Rs 15000/- Rs 18000/-

Difference in cost ********** Rs 3000/- Rs 6000/-

Pay back period ********** 0.98 years 1.2 years


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8) Proper bearing selection-

In small motor mainly shield or sealed bearings are used. Improper selection of theses bearings

may result in increase of bearing friction and causes energy loss. Shielded bearing for high

speed motor (2 and 4 pole) and sealed bearing for low speed motor may be preferred to avoid

such energy loss.

9) High grade lubricants-

Friction in bearing mainly depends on viscosity of the lubricants. There is some high-grade

grease available in market, which offers less friction. The application of such grease in a 2 pole

45 KW motor is found to have saved 200-watt of power.

OPERATION1) Power quality-

Rated Voltage - It should be maintained within +/- 5% of operating voltage. Voltage above 5%

increases core loss by 2%. Similarly voltage below 5% increases copper loss by 10%.

Voltage imbalance - It should be within a tolerance of 1%. Voltage imbalance of 3.5%

increases motor temperature rise by 14%, which interns increases the motor loss.

High Power Factor- Motor operating PF should always be maintained as high as possible to

avoid distribution loss.

Rated frequency - Motor should be operated as close as to the rated frequency (50Hz.).

Higher frequency of 1% increases the pump input by 3%.

Low harmonic content - Harmonic content increases the core loss in motor. Therefore it

should be maintained as low as possible.

2) Over current -

Mechanical overload, high friction in bearings / gearbox or high core loss are some primary

reasons that may increase the motor operating current more than normal. Such over current

proportionally increases the copper loss in motor.

3) Hot running

Motor temperature may increase due to over current, improper cooling or high ambient

temperature. High temperature always increases the motor winding resistance in cyclic manner

and increases copper loss.

MAINTENANCE

1) Periodical maintenance

Blocked ventilation, high friction in bearing due to defect or low grease, looseness in bearing

retainer, end shields etc are some flaws motor generally develop in course of long service and

causes increase in energy loss. Such losses can be avoided by periodical greasing, cleaning

and overhauling of motor.


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2) Condition monitoring

Any abnormality like high current, hot running, vibration, sound or noise always involves with

energy loss and therefore condition monitoring can be initiated for detecting and analyzing such

abnormalities at initial stage for avoiding energy loss as well as unforeseen break down.

3) Quality overhauling and erection

Poor overhauling and erection (alignment) also causes energy loss due to friction. It can be

detected by seeing no load current, noise and vibration level. Therefore after each overhauling

and erection those parameters need to be corrected for avoiding any energy loss.

CONCLUSIONS

Energy waste in motor is always found lower than total waste in system. Therefore, for effectiveenergy conservation - energy waste in other components of system like gearbox & coupling,

pump& pipeline etc. are also to be considered along with motor. Such thing can be achieved

only through teamwork and industry determined to conserve energy must follow the road map

decided by the team.

Convention -

1) One year = 300 days (82% PLF).

2) Energy cost =Rs 2.50 per unit

********************************************************************************************************

ADDRESS -

Office - M.G.MORSHAD/ Deputy Chief Engineer (Electrical Maintenance)

Thermal Station II / Neyveli Lignite Corporation Ltd.

Neyveli / Tamil Nadu / Pin - 60780

Residence - M.G.MORSHAD

Qr No 139/D Type II Block 7NLC township

Neyveli / Tamil Nadu / Pin - 60780

Ph No - 04142- 269753

E-mail - [email protected]

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