Why the capacitor are connected in Delta(Three Phase) for
power factor improvement ?

Answer Posted / jonathan r. lambert

Capacitors are paralleled with inductive (magnetic) loads
in delta, wye (aka "Star") and single phase AC power
sources to correct power factors so that motors,
transformers and other inductive loads appear to be
resistive. Power factor correction is a process that
cancels reactive current vectors leaving only a resistive
current. Inductive loads pull currents that contain both
resistive and reactive vectors. In power factor correction,
a capacitor's reactive current is used to cancel the
inductive reactive current created by magnetic coils in
inductive devices. If the capacitor is sized correctly the
current drawn by the capacitor will precisely cancel the
inductive magnetization current pulled by an inductive
load. The resulting motor current "seen" by the AC voltage
source will then be only resistive. Since power companies
charge for both reactive and resistive current, and since
only the resistive current is required to provide
horsepower and perform work, power factor correction
reduces the current drawn by inductive loads which reduces
the electrical operating expense. Hard to believe that
applying an additional parallel load, a capacitor, will
result in less total current but it works due to the
capacitive reactive current leading at +90 degrees and the
inductive reactive current lagging at -90 degrees, the two
parallel currents sum at the voltage source to equal zero
degrees and if the cap is sized correctly, zero amplitude.


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