Page 104 - E24 Electrical Notebook

100 - Power Factor Correction - How to Select

How to Select Power Factor Correction Determining PFC Requirements

Power factor correction technology has been around for many years but • Conducting a site study • From specification
more recently is seen as an increasingly important element of an electrical • Carrying out a site survey • From electricity billing information
installation due to: • By calculation • From electricity metering

• Significantly increasing energy costs year on year The power factor is shown as the cosine of the angle of lagging power
• Reduction of the production of greenhouse gases through increased factor in an inductive circuit or leading power factor in a capacitive circuit.

efficiency of the electrical installation Power Factor Cosφ = kW (Useful power)
Recent changes to Part L of the Building Regulations recognise the kVA (Total / apparent power)
importance of power factor correction in reducing the carbon footprint of
an organisation. Useful power (kW)

Most loads on an electrical distribution system fall into one of three categories: Wattless Apparent power (kVA)
component of
• Resistive – such as heating elements
Power factor = 1 (also referred to as ‘unity’) load (kVAr)

• Inductive – such as transformers, fluorescent lighting & AC induction Power Factor Improvement by Adding Leading kVAr
motors. Power factor <1 (lagging)
Note: it is possible to over-compensate and too much capacitance can
• Capacitive - such as rotary phase advancers, synchronous motors lead to over-correction through the creation of a leading power factor.
& capacitors. Power factor <1 (leading)
Leading kVAr Reduced
A power factor of less than 0.85 is considered to be poor. Correction added apparent power
should typically achieve 0.95 to 0.98. Any piece of electrical plant that after correction
draws inductive current such as motors, will reduce the power factor and (Capacitor)
increase the kVA Power Demand and obviously increase the kVAr units. Useful power (kW)

Advantages of Power Factor Correction: Resultant Apbpeaforreentcoporrwecetrio(nkVA)
effective
Reduction of heating losses in transformers and distribution equipment
= improved efficiency: kVAr

• Longer plant life
• Stabilised voltage levels
• Increased capacity existing system & equipment
• Improved profitability
• Every kVAr of capacitors installed reduces the amount of CO2

generation by 160kg

Calculation of kVAr Requirements Example

Consumption of active energy EW = 300000kWh Consumption of reactive energy EB = 400000kVArh

Number of working hours: ..........t = 600 H

Resulting average active factor: P=300000kWh = 500kW
6000h

Calculation of the original power factor COSφ1 1 = 1 2 = 0.6

2 400000kVAr h

E +1
B
300000kWh
EW +1

Origal PF Conversion Factor for a Target Power Factor

COSφ1 COSφ2

0.2 0.7 0.75 0.8 0.85 0.9 0.92 0.94 0.96 0.98 1
0.25 3.879 4.017 4.149 4.607 4.696 4.899
0.3 2.853 2.991 3.123 4.279 4.415 4.473 4.536 3.581 3.670 3.873
0.35 2.160 2.298 2.430 2.888 2.977 3.180
0.4 1.656 1.795 1.926 3.253 3.389 3.447 3.510 2.385 2.473 2.676
0.45 1.271 1.409 1.541 2.000 2.088 2.291
0.5 0.964 1.103 1.235 0.560 2.695 2.754 2.817 1.693 1.781 1.985
0.55 0.712 0.850 0.982 1.440 1.529 1.732
0.6 0.498 0.637 0.768 2.057 2.192 2.25 2.313 1.227 1.315 1.518
0.65 0.313 0.451 0.583 1.042 1.130 1.333
0.7 0.149 0.287 0.419 1.672 1.807 1.865 1.928 0.877 0.966 1.169
0.75 0.138 0.270 0.729 0.817 1.020
0.8 0.132 1.365 1.500 1.559 1.622 0.590 0.679 0.882
0.85 0.458 0.547 0.750
0.9 1.112 1.248 1.306 1.369 0.328 0.417 0.620
0.95 0.193 0.281 0.484
0.899 1.034 1.092 1.156 0.037 0.126 0.329

0.714 0.849 0.907 0.970

0.549 0.685 0.743 0.806

0.400 0.536 0.594 0.657

0.292 0.398 0.456 0.519

0.130 0.266 0.324 0.387

0.135 0.194 0.257

0.058 0.121

For the improvement of the power factor form 0.6 to 0.94, read the factor 0.970 from the chart above.
The required capacitor power is 500kW x 0.970=48kVAr

Building Information Modelling

Eaton Corporation is proud to offer Building Information Modelling (BIM) friendly models for a wide range of electrical distribution products. Architects,
design-build contractor and surveyors, consulting engineers and others are able to integrate Eaton equipment into their drawings with ease, and without
cost. BIM-friendly models from Eaton bring seamless integration to your building plan.

Eaton Electric Ltd Customer Support Centre
Grimshaw Lane Tel : 08700 545 333
Middleton Fax : 08700 540 333
Manchester
M24 1GQ Email : ukcommorders@eaton.com
Website : www.eaton.uk.com/electrical