12
© 2013 Eaton. All rights reserved. Economics of Power Factor Correction
© 2013 Eaton. All rights reserved.
Economics of Power Factor Correction
2© 2013 Eaton. All rights reserved.
• Kilowatt demand – Based on maximum recorded kW demand interval
for the month and represents how much a utility has to provide in terms
of transformers, wire and generation capability. Typically a unit charge
times max kW demand interval for the month.
• Power factor penalties – Charged by some utilities. Usually based on
falling below a minimum PF level. Penalties vary widely among utilities.
Understanding Utility Bills
• Kilowatt hours (kWH) – kWH consumption is
measure of electrical energy that has been used
during the billing period. Consist of a unit rate
times accumulated kWH reading from the meter.
• Fuel charge adjustment – Monthly charge
based on the cost of fuel used to produce power
each month. Typically a unit charge times kWH.
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What is Power Factor?
Inductive loads (motors) require two kinds of
power
• Real Power (kW) – that actually performs
the work
• Reactive Power (kvar) – that maintains the
electromagnetic field
• Apparent Power (kVA) – total power,
vector sum of kW and kvar
𝜃
Real power(kW)
Apparent power(kVA)
Reactive power(kvar)
Power Factor is a measure of efficiency =Real power kW
Apparent power kVA= cos 𝜃
Expressed in a percentage or decimal number (95% or 0.95) and also
with an added “Lag” or “Lead” term.
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1000 kW
load @ .99
PF
PF Correction
1000 kW
load @ .8
lagging PF
kW =1000
kVA =1250
kvar=750
kVA =1010
kvar=150
Add 600 kvar
capacitor
• Present load at 1000 kW and 80% lagging PF
• Adding capacitors improves PF by providing leading kvar.
• Capacitors cancel the effects of the lagging kvar required by
inductive loads. PF improved to 99%.
• Use capacitors to correct PF to desired value based on utility
penalties
600 kvar
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Typical PF by Industry and by Operation
Industry Power Factor
Auto parts 75-80
Brewery 76-80
Cement 80-85
Chemical 65-75
Coal mine 65-80
Clothing 35-60
Electroplating 65-70
Foundry 75-80
Forge 70-80
Hospital 75-80
Machine manufacturing 60-65
Metalworking 65-70
Office building 80-90
Oil-field pumping 40-60
Paint manufacturing 55-65
Plastic 75-80
Stamping 60-70
Steelworks 65-80
Textile 65-75
Tool, die, jig 60-65
Operation Power Factor
Air compressor:
External motors 75-80
Hermetic motors 50-80
Metal working:
Arc welding 35-60
Arc welding with
standard capacitors
40-60
Resistance welding 40-60
Machining 40-65
Melting:
Arc furnace 75-90
Inductance furnace
60Hz
100
Stamping:
Standard speed 60-70
High speed 45-60
Spraying 60-65
Weaving:
Individual drive 60
Multiple drive 70
Brind 70-75
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HV and LV Recommendations
Low Voltage capacitors
• Applicable for secondary (LV) or primary (HV) metering
• located closest to inductive load for optimum loss reduction and
voltage boost
• Can be switched with the load
• Solutions for harmonic issues can be more complex
Medium Voltage capacitors
• Applicable for primary metering on HV side of the transformer
• Less expensive installed cost per kvar
• Simplifies solutions for harmonic issues
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Medium Voltage Solution Options
• Pole Mounted Rack
• Group fuse protection
• Fixed or switched, single or multi step
• Lowest cost solution
• Open Rack Design
• Individual fuse protection
• Unbalance protection scheme required
• Fixed or switched, single or multi step
• Fenced area required
• Moderate cost solution
• Metal Enclosed
• Current limiting fuses or fusesless designs
• Fixed or switched, single or multi step
• Reduced space requirements, indoor or outdoor
• Fully assembled and tested
• Most costly solution
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Savings Analysis
• Power factor penalty = $2.60/kvar for all excess kvar
• Excess kvar = Max kvar - (Max kW for the Billing Period x .39523)
• Annual savings = $36,000
• Possible solution - 2000 kvar metal enclosed bank. Could range from
$30-90K depending on steps. Payback 1-3 years.
Multiplier 0.39523
kVAR charge $2.60
kVAR added 2000
Month Max kW Max kvar Base kvar1 Excess kvar2 Penalty3 New kvar
Mar-12 4020 1961 1589 372 968$ -39
Apr-12 3948 3296 1560 1736 4,513$ 1296
May-12 4011 2391 1585 806 2,095$ 391
Jun-12 4276 1869 1690 179 465$ -131
Jul-12 4426 3536 1749 1787 4,645$ 1536
Aug-12 4383 3645 1732 1913 4,973$ 1645
Sep-12 3632 3281 1435 1846 4,798$ 1281
Oct-12 3937 3344 1556 1788 4,649$ 1344
Nov-12 3883 2859 1535 1324 3,443$ 859
Dec-12 3891 2394 1538 856 2,226$ 394
Jan-13 3724 2891 1472 1419 3,690$ 891
Feb-13 3616 1446 1429 17 44$ -554
Total 36,509$ 1 Base kvar = Max kW x Multiplier2 Excess kvar = Max kvar - Base kvar3Penalty = Excess kvar x kvar Charge
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Harmonics
• Harmonic producing loads can lead to
• Capacitors fuse operations and failed capacitors
• Transformer heating
• Motor heating
• VFD malfunction
• Increased neutral currents
• Common harmonic producing loads
• Power electronic equipment (drives, rectifiers, inverters, computers, etc.)
• Rotating machines (generators, motors)
• Iron saturating devices (transformers)
• Arcing devices (welders, arc furnaces, florescent lights, etc.)
• Harmonic Study should always be performed in conjunction with
power factor correction capacitors when there are significant sources
of harmonics in the system.
0
Fundamental
3rd Harmonic
5th Harmonic
Distorted Waveform
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Engineering Service’s Harmonic Analysis
• Do field measurements
• This is a recommended but optional step to
benchmark system
• Develop system model
• Transformers, lines, loads, harmonic sources,
switches
• Power Flow analysis to determine
• Reactive power needs
• Location of capacitors
• Capacitor bank ratings (steps)
• Harmonic analysis:
• Impact of capacitors on harmonic performance
• Analyze alternatives to comply with harmonic
distortion requirements
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Total Solutions Process
Pre Installation
• Utility bill analysis
• PF correction
• Harmonic studies
• Filter design
Installation Support
• Acceptance testing
• Installation
• Verify protection
• Commissioning
• Training
Maintenance
• Capacitor testing
• Switch testing
• Control testing
• Thermography
• Service contracts
14© 2013 Eaton. All rights reserved.
