what is pf. how to calculate capacitor bank value to
maintain unity pf.

Answer Posted / shashikant

CALCULATIONS AND TABLES

Calculation and selection of required capacitor rating

Qc = P * {tan [acos (pf1)] - tan [ acos (pf2)]}

Qc = required capacitor output (kVAr)
pf1 = actual power factor
pf2 = target power factor
P = real power (kW)

The table below shows the values for typical power factors
in accordance with the above formula


TARGET POWER FACTOR
0.7 0.75 0.8 0.85 0.9 0.92 0.94 0.96 0.98 1
Actual Power Factor
0,40 1.27 1.41 1.54 1.67 1.81 1.87 1.93 2 2.09 2.29
0,45 0.96 1.1 1.23 1.36 1.5 1.56 1.62 1.69 1.78 1.98
0.50 0.71 0.85 0.98 1.11 1.25 1.31 1.37 1.44 1.53 1.73
0,55 0.5 0.64 0.77 0.9 1.03 1.09 1.16 1.23 1.32 1.52
0,60 0.31 0.45 0.58 0.71 0.85 0.91 0.97 1.04 1.13 1.33
0,65 0.15 0.29 0.42 0.55 0.68 0.74 0.81 0.88 0.97 1.17
0,70 0 0.14 0.27 0.4 0.54 0.59 0.66 0.73 0.82 1.02
0.75 0 0.13 0.26 0.4 0.46 0.52 0.59 0.68 0.88
0,80 0 0.13 0.27 0.32 0.39 0.46 0.55 0.75
0.85 0 0.14 0.19 0.26 0.33 0.42 0.62
0,90 0 0.06 0.12 0.19 0.28 0.48


The required capacitor output may be calculated as follows:
select the factor (matching point of actual and target
power factor) k
calculate the required capacitor rating with the formula:

Qc = k * P

Example:
actual power factor = 0.70, target power factor = 0.96,
real power = P = 500kW,

Qc = k * P = 0.73 * 500kW = 365 kVAR

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