Economics of Power Factor Correction
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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.
• 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.
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2
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
Real power(kW)
𝜃
Reactive power(kvar)
Apparent power(kVA)
• Apparent Power (kVA) – total power,
vector sum of kW and kvar
Real power kW
= cos 𝜃
Apparent power kVA
Expressed in a percentage or decimal number (95% or 0.95) and also
with an added “Lag” or “Lead” term.
Power Factor is a measure of efficiency =
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4
PF Correction
kW =1000
kvar=150
kVA =1010
1000 kW
load@
@.99
.8
load
lagging
PF PF
kvar=750
kVA =1250
600 kvar
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
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5
Typical PF by Industry and by Operation
Industry
Auto parts
Brewery
Cement
Chemical
Coal mine
Clothing
Electroplating
Foundry
Forge
Hospital
Machine manufacturing
Metalworking
Office building
Oil-field pumping
Paint manufacturing
Plastic
Stamping
Steelworks
Textile
Tool, die, jig
Power Factor
75-80
76-80
80-85
65-75
65-80
35-60
65-70
75-80
70-80
75-80
60-65
65-70
80-90
40-60
55-65
75-80
60-70
65-80
65-75
60-65
Operation
Air compressor:
External motors
Hermetic motors
Metal working:
Arc welding
Arc welding with
standard capacitors
Resistance welding
Machining
Melting:
Arc furnace
Inductance furnace
60Hz
Stamping:
Standard speed
High speed
Spraying
Weaving:
Individual drive
Multiple drive
Brind
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Power Factor
75-80
50-80
35-60
40-60
40-60
40-65
75-90
100
60-70
45-60
60-65
60
70
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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8
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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9
Savings Analysis
Multiplier
kVAR charge
kVAR added
Month
Mar-12
Apr-12
May-12
Jun-12
Jul-12
Aug-12
Sep-12
Oct-12
Nov-12
Dec-12
Jan-13
Feb-13
0.39523
$2.60
2000
Max kW
Max kvar Base kvar1 Excess kvar2
Penalty3
4020
1961
1589
372 $
968
3948
3296
1560
1736 $
4,513
4011
2391
1585
806 $
2,095
4276
1869
1690
179 $
465
4426
3536
1749
1787 $
4,645
4383
3645
1732
1913 $
4,973
3632
3281
1435
1846 $
4,798
3937
3344
1556
1788 $
4,649
3883
2859
1535
1324 $
3,443
3891
2394
1538
856 $
2,226
3724
2891
1472
1419 $
3,690
3616
1446
1429
17 $
44
Total $
36,509
1
Base kvar = Max kW x Multiplier
2
Excess kvar = Max kvar - Base kvar
New kvar
-39
1296
391
-131
1536
1645
1281
1344
859
394
891
-554
3
Penalty = Excess kvar x kvar Charge
• 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.
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10
Harmonics
• Harmonic producing loads can lead to
Fundamental
• Capacitors fuse operations and failed capacitors
• Transformer heating
Distorted Waveform
• Motor heating
3rd Harmonic
0
• VFD malfunction
5th Harmonic
• 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.
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11
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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12
Total Solutions Process
Pre Installation
Installation Support
Maintenance
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Utility bill analysis
PF correction
Harmonic studies
Filter design
Acceptance testing
Installation
Verify protection
Commissioning
Training
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Capacitor testing
Switch testing
Control testing
Thermography
Service contracts
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