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INTRODUCTION

BASICS OF POWER FACTOR CORRECTION

Under normal operating conditions certain electrical loads (e.g. induction motors, welding equipment, arc furnaces and fluore-
scent lighting) draw not only active power from the supply, but also inductive reactive power (kvar). This reactive power is ne-
cessary for the equipment to operate correctly but could be interpreted as an undesirable burden on the supply. The power
factor of a load is defined as the ratio of active power to apparent power, i.e. kW : kVA and is referred to as cosφ. The closer
cosφ is to unity, the less reactive power is drawn from the supply.

A capacitive reactive power resulting from the connection of a correctly sized capacitor can compensate for the inductive reac-
tive power required by the electrical load. This ensures a reduction in the reactive power drawn from the supply and is called
Power Factor Correction.

CALCULATION OF REQUIRED CAPACITOR POWER

The reactive power which is necessary to achieve a desired power factor is calculated by the formula: Q = P·F
C
Q ... reactive power of the required power capacitor
C
P ... active power of the load to be corrected
F ... conversion factor acc. to chart 1

original conversion factor F for a target power factor
power factor cosφ 2
cosφ 1 0.70 0.75 0.80 0.85 0.90 0.92 0.94 0.96 0.98 1.00
0.20 3.879 4.017 4.149 4.279 4.415 4.473 4.536 4.607 4.696 4.899
0.25 2.853 2.991 3.123 3.253 3.389 3.447 3.510 3.581 3.670 3.873
0.30 2.160 2.298 2.430 2.560 2.695 2.754 2.817 2.888 2.977 3.180
0.35 1.656 1.795 1.926 2.057 2.192 2.250 2.313 2.385 2.473 2.676
0.40 1.271 1.409 1.541 1.672 1.807 1.865 1.928 2.000 2.088 2.291
0.45 0.964 1.103 1.235 1.365 1.500 1.559 1.622 1.693 1.781 1.985
0.50 0.712 0.85 0.982 1.112 1.248 1.306 1.369 1.440 1.529 1.732
0.55 0.498 0.637 0.768 0.899 1.034 1.092 1.156 1.227 1.315 1.518
0.60 0.313 0.451 0.583 0.714 0.849 0.907 0.97 1.042 1.130 1.333
0.65 0.149 0.287 0.419 0.549 0.685 0.743 0.806 0.877 0.966 1.169
0.70 0.138 0.27 0.4 0.536 0.594 0.657 0.729 0.817 1.020
0.75 0.132 0.262 0.398 0.456 0.519 0.59 0.679 0.882
0.80 0.13 0.266 0.324 0.387 0.458 0.547 0.75
0.85 0.135 0.194 0.257 0.328 0.417 0.62
0.90 0.058 0.121 0.193 0.281 0.484
0.95 0.037 0.126 0.329
chart 1

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