AC POWER CALCULATION Power Factor Correction SEE 1023

AC POWER CALCULATION Power Factor Correction SEE 1023 Circuit Theory Dr. Nik Rumzi Nik Idris

Power Factor Irms + Vrms = Vrms v Load Irms = Irms i As we have seen before (for sinusoidal voltage and current), p. f. = cos ( v i) P = Vrms Irms cos ( v i) The REAL power (or average power) is transformed into useful energy e. g. heat, mechanical, light, sound, etc For a given Vrms and P, loads with high power factor draw LESS current compared with loads with low power factor

Power Factor I 2, rms I 1, rms Vrms Pave p. f. = cos 1 Pave p. f. = cos 2 Vrms cos 1 > cos 2 1 < 2 1 Pave Q 2 Q 1 2 Pave For a given Vrms and P, loads with high power factor draw LESS current compared with loads with low power factor

Power Factor For a given Vrms and P, loads with high power factor draw LESS current compared with loads with low power factor Less current results in LESS losses during transmission I 2 R + Source Load Utility company (TNB) charge more to loads with LOW power factor Therefore, it is desirable to increase the power factor

Power Factor Correction Process of increasing the power factor without altering the voltage or current to the original load IL QC + + Vs QL 1 (rms) VL QT 2 PL Before C added, S = PL + j. QL After C added, S = PL + j(QL – QC) p. f. = cos 1 p. f. = cos 2 i. e. increased (voltage and current to original load retained)

Power Factor Correction How do we calculate C? Voltage across C = Vs QL 1 Impedance of C = 2 PL QC (rms) QT