Final Internship Report 2015

Project Title: Electrical Motor Efficiency Analysis

At the TS Power Plant

Newmont Nevada Energy Investment,

Battle Mountain Nevada, 89820

Electrical Engineering Internship,

May-August 2015

By Cameron P. Iverson

Colorado State University-Pueblo

Contents

Executive Summary……………………………………………………………………………….2

I. Background………………………………………………………………………..2

II. Project Objectives…………………………………………………………………3

III. Project Description………………………………………………………………..3

IV. Theory of Electrical Motors……………………………………………………….4

V. Methodology………………………………………………………………………7

VI. Results……………………………………………………………………………..8

VII. Discussion………………………………………………………………………..11

VIII. Conclusion and Recommendations………………………………………………11

IX. Acknowledgements………………………………………………………………12

X. References………………………………………………………………………..13

Iverson P a g e | 2

Executive Summary

This report presents work that was carried out at the TS Power Plant to determine the electrical

efficiency of motors used at the plant to power equipment as an auxiliary load. The assessment

included an observation of the overall parasitic load (MW) on the plant’s output meter which

determined the in-house power consumption. The assessment included all sizes of motors

ranging from 100 hp to 4500 hp. Examples of the motors studied include the feed water pumps,

circulating water pumps, compressors and boiler fans (forced draft, induced draft, and primary

air fans).

It was observed that an increase in plant power output did not necessarily result in a significant

motor load and efficiency increase. The motors were determined to be running on lower loads

which led to decreased efficiencies. The low motor loads were determined to be inefficient and it

was advised that the mechanical motor loads be increased on the motor shafts or otherwise be

taken out of service and replaced with more load appropriate models.

Background

The TS Power Plant is capable of generating a gross electrical power output of 242 MW or 215

MW net. The facility is a coal fired power plant that uses a B&W boiler and a Toshiba steam

turbine generator. The facility has state of the art emissions control systems and is one of the

cleanest coal fired power plants in the US. The plant is owned by Newmont and supplies power

to the nearby mining operations and was commissioned in 2008. The plant uses approximately

10% of its total output as its auxiliary load. Station service is comprised of boiler fans,

circulating water pumps, service water pumps, condensate water pumps, feedwater pumps,

Iverson P a g e | 3

bottom ash conveyors, and vacuum producing compressors. If the plant was able to reduce its

own station load it would save its operating cost per megawatt hour produced. The way that this

could be done is through evaluating each individual motor and determining what their motor

efficiency is and whether or not they are the right size for the specific job they are assigned to.

Most electric motors are capable of running a good efficiency between 50% and 100% but

maximum efficiency is usually achieved around 75% load. Efficiency has a tendency to drop at

lower motor loads. Large motors can operate at high efficiency even at lower loads. Smaller

motors tend to have a much more narrow range of operating load to maintain a good efficiency.

It is important to determine whether a motor is properly loaded as it will help to decide whether

it is the right motor for the duty. Motor load and efficiency analysis tests should be treated as

preventative maintenance once the proper and safest way of gathering the required data for the

operations are found.

Project Objectives

1. To assess electrical motor energy consumption.

2. To determine motor efficiency

3. To analyze overall plant station load consumption

Project Description

TS Power Plant has been in service since 2008 and it was necessary to determine the actual

energy consumption of each electrical motor that contributes to the station load. In addition to

power consumption it was necessary to determine the efficiency of these motors after seven

years in service. Even though the overall station load is measured by the plant metering system,

Equation 2

Equation 1

Iverson P a g e | 4

it was important to relate each large electrical motor load to the in-house power consumption.

Optimizing motor energy usage would reduce the plants energy costs through saved fuel

consumption.

Theory of Electrical Motors

Just about every motor located on site at the power plant is an AC three phase electric squirrel

cage induction motor. These types of motors use electricity to power their shaft coupled to their

load. Efficiency is determined by output power over input power. If a motor is being fed more

power, then it is working with a higher load percentage. An inductive circuit has a lagging power

factor which means the circuits current is lagging behind voltage as power reaches the motors

copper windings. The amount of electricity that feeds a motor is calculated using Ohm’s law

which states that:

PI =PF × I × V ×√3 (Watts)

or

PI =PF × I ×V ×√31000 (kiloWatts)

Where:

PI = Three-phase power in kW

V = RMS voltage, mean line-to-line of three phases

I = RMS current, mean of three phases

PF = Power factor as a percentage

Load of a motor can also be determined using the slip method given below.

Equation 3

Equation 4

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Load = Slip

Ss−Sr×100 %

Where:

Load = Output power as a % of rated power

Slip = Synchronous speed minus Measured speed in rpm

Ss = Synchronous speed in rpm

Sr = Nameplate full-load speed

Efficiency is calculated by the equation below.

Efficiency=OutputInput

× 100%

Output power is determined from the load equation.

Input power is calculated from equation #2.

This power can be referred to as the apparent power leading into the stator windings. A three

phase circuit is the most efficient RLC circuit and yields the highest power factor. Reactance

opposes the electrical current flow in a circuit due to electromagnetic fields or magnetic flux.

The rotor is designed as a piece of combined metal consisting of hundreds of very thin sheets of

iron laminations that reduce surface area in order to help in reducing the effects of eddy currents

running through the core shown in Figure 1.

The core laminations are also wrapped

in a very large amount of stranded

copper wire. Throughout the process of

creating motor output power there are

several other electrical losses that occur including:

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-Heat losses I 2× R

Where:

I = RMS Current

R = Circuit resistance

-Stator copper and iron core losses

-Rotor copper core loss

-Windage and friction losses

These losses can be seen in Figure 2 below.

Figure 2

Motor output power is to be measured in horsepower by the product of full-load horsepower and

the measured motor load percentage. Motors begin to break down over time or after great strain

on different parts, when a motor is in decline it can begin to output less power compared to the

input. The efficiency depends on how close the output power is to the input power. If the

efficiency is low the motor is requiring much more power to produce rotational speed for the

pump, fan, or gearbox. A low efficiency could mean that there’s something malfunctioning

inside the motor including worn down gears or bearings, bad cables or cable connections, excess

heat due to high resistance in the copper windings or insufficient cooling of the motor, too low of

a load on the shaft, and friction due to loose particles inside the motor casing. A motor with high

Iverson P a g e | 7

heat causes the internal windings and other components where insulation to overheat and cause

the bonding materials to break down. Electrical wiring is very important to be aware of when

heat rises beyond an acceptable level, if the insulating material around the copper wire starts to

wear away then short circuits can easily become a problem. The fan size, design, and the seal of

the motor cooling system impact motor efficiency. The fan helps dissipate heat losses in an

efficient manner and keeps the machinery in an acceptable operational atmosphere. Without

proper ventilation, motors would overheat and breakdown within minutes.

Methodology

The primary measurements of the project included voltage, current, rotational speed of the

motor, and power factor. For 480V motors, voltage, current, and power factor were furnished by

the LM-10 protection relays located in the plant motor control centers. The 6.9kV motor voltages

were provided by the bus volt meter readouts and the currents were read from the SEL749 motor

protection relays. The nameplate power factor was used for the input power calculations.

Rotational speed was measured using a Csi 2130 Machinery Health Analyzer and the load was

determined by the slip method described in equation #3 and in this case the rotational speed was

an input value into the slip equation. All of the full-load motor data was recorded off of motor

nameplates, process and instrumentation diagrams, and datasheets found in the plant’s library. A

sample nameplate can be seen in Figure 2 below.

Size

Voltage

SpeedEfficiency

Power Factor

Amperage

Iverson P a g e | 8

The information recorded off of the nameplates included the horsepower (HP), motor speed,

volts, amps, power factor, and efficiency. Excel was used to process the information. Some data

was brought automatically through the plant historian (PIDatalink) onto an excel spreadsheet.

The test data was collected at these various net plant loads; 82MW, 107MW, 146MW.

Results

Plant Output Power = 82MW net Plant Auxiliary Load = 11.72MW

Motor NameNEMA Rated

Full-Load Efficiency

Nameplate HP Input (HP)(Equation 2) Output (HP)

Measured Motor Load(Equation 3)

Efficiency(Equation 4)

Bottom Ash Conveyor

91.70% 20 5.38 1.72 9.22% 25.57%

Forced Draft Fan B 950 379.15 378.13 51.04% 96.13%Primary Air Fan A 1000 447.69 328.24 53.18% 88.62%Primary Air Fan B 1000 477.61 454.44 61.00% 94.89%Seal Air Fan A 150 74.78 65.50 59.67% 90.23%Induced Draft Fan A

3950 1672.60 1760.65 49.25% 87.28%

Induced Draft Fan B

3950 1808.64 1465.98 46.95% 76.65%

Compressor 95.60% 800 461.13 321.73 55.76% 72.17%Cooling Water Tower Fan #1

200/50 35.13 9.40 27.82% 29.44%

Cooling Water Tower Fan #2

200/50 157.98 109.91 73.80% 69.75%


200/50 26.48 11.19 28.26% 39.88%


200/50 145.84 117.07 79.20% 81.42%


200/50 26.69 10.85 26.44% 36.93%


200/50 145.28 101.36 66.11% 67.93%


200/50 26.81 14.55 31.02% 43.17%

Circulating Water Pump A

25 10.21 7.11 38.59% 70.61%

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Lime Handling Pump

25 8.71 5.91 30.61% 65.80%

Make-up Water Pump A

50 24.42 21.71 56.58% 86.64%

Plant Drains Pump 90.20% 7.5 3.19 1.91 34.23% 63.49%Service Water Pump 100B

94.50% 100 43.97 31.41 41.36% 71.98%

Table 1 - Summary of Motors at a Plant Load of 39%







Condensate Booster 90B

84.9% 350 184.493 140.17806 56.56% 80.05%

Seal Air Fan A 150 93.707806 85.9392 77.07% 91.80%Condensate Booster 50B

89.9% 300 155.4972 118.4648 51.93% 74.49%

Primary Air Fan A 90.4% 1000 546.61449 438.275 64.58% 88.46%Primary Air Fan B 90.4% 1000 576.44923 520.335 67.28% 87.07%FeedWater Booster Pump A

95.8% 125 65.461999 53.587667 56.67% 80.13%

FeedWater Bootster Pump C

95.8% 125 71.224902 62.228833 67.73% 88.71%

Feedwater Pump 110C

96.2% 4500 2071.9437 809.7084 21.14% 34.11%








Condensate Booster Pump 90B

84.9% 350 174.82734 114.39 45.98% 68.66%


89.9% 300 160.13749 119.5092 53.12% 74.28%


84.9% 350 174.78992 136.09837 53.95% 80.59%


Iverson P a g e | 10

53% 65% 72%87.00%88.00%89.00%90.00%91.00%92.00%

1BG-FAN-0300A (1000HP)

Percent Full LoadFigure 4

Efficie

ncy

52% 53% 53%72.50%73.00%73.50%74.00%74.50%75.00%

1CN-P-0050B (300HP)


Efficie

ncy

51% 54% 58%91.00%92.00%93.00%94.00%95.00%96.00%97.00%

1BG-FAN-0100B (950HP)


Efficie

ncy

40% 40% 57%60.00%65.00%70.00%75.00%80.00%85.00%

1FW-P-0100A (125HP)


Efficie

ncy

46% 54% 57%60.00%65.00%70.00%75.00%80.00%85.00%

1CN-P-0090B (350HP)


Efficie

ncy


Discussion

The results of this study are presented in Tables 1 through 3, and also in Figures 3 through 8 for

a selected set of motors. The plant loads for this study were 82MW net, 107MW net, and

146MW net. From the data it can be seen that at 82MW net the small motors ranged from 25% to

86% efficiency and the large motors ranged from 70% to 90%. These results showed that larger

motors could maintain a higher efficiency even at lower loads but the smaller motors

significantly dropped in efficiency as the load decreased. Those motors which had a higher

mechanical load on them were found to be closely related to their full-load efficiency and those

motors that were recorded as low mechanical loads were usually farther off from the full-load

efficiency. Larger nameplate motors were not affected as much with fluctuating loads as the

smaller motors. The changing plant loads caused different motor loads but higher plant loads did

not always yield higher motor loads. The higher the plant was running at, the more power the

motors would need to supply resulting in more backup motors contributing to the load.

Conclusions and Recommendations

61% 67% 76%82.00%84.00%86.00%88.00%90.00%92.00%94.00%96.00%

1BG-FAN-0300B (1000HP)


Efficie

ncy


In this study plant auxiliary load was assessed and motor efficiency was determined. Overall

large motor efficiency remains good compared to the manufacturers data at all loads but for

small motors the efficiency is very low at lower loads. During this study it was observed that bus

voltage dipped below 6600 volts more than once and the plant should be vigilant about voltage

regimes that are lower than 6600 volts for the 6.9kV motors. The same applies for the 480V

motors. It is recommended that the plant continue to monitor motor efficiencies in order to

optimize station service power consumption.

Acknowledgements

For giving me an opportunity of a lifetime and a helping hand through my schooling I want to

thank North American Newmont Gold Mining Company for allowing me to have an opportunity

to work at the TS Power Plant.

I want to give thanks to everyone at the TS Power Plant for a great work experience and a home

welcoming atmosphere and for showing me what it’s like to work in a professional setting.

Lastly I want to give special thanks to Kuda Mutama the engineering manager at TS Power Plant

as he has been my guidance through many obstacles I have faced here.


References

DETERMINING ELECTRIC MOTOR LOAD AND EFFICIENCY: 16. Office of Energy Efficiency and Renewable Energy. Web. 1 June 2015. <http://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/10097517.pdf>.

Final Internship Report 2015

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