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# Economics of Power Factor Correction - cscos. · PDF fileEconomics of Power Factor Correction...

Date post: 11-Feb-2018
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Economics of Power Factor Correction

• 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.

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

1000 kW

PF

PF Correction

1000 kW

lagging PF

kW =1000

kVA =1250

kvar=750

kVA =1010

kvar=150

capacitor

• Present load at 1000 kW and 80% lagging PF

• 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

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

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

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

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

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

Harmonics

• Capacitors fuse operations and failed capacitors

• Transformer heating

• Motor heating

• VFD malfunction

• Increased neutral currents

• 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

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

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