Power factor is simply a name given to the ratio of “actual” power (active power) being used in a circuit,
expressed in watts or more commonly kilowatts (kW), to the power which is “apparently” being drawn from the mains, expressed in
volt-ampere or more commonly kilo
volt-ampere (kVA).

All
modern industries utilize electrical energy in some form or other. Two basic
categories of load are encountered in alternate current (AC) networks.
1.

__Resistive Loads__
Devices containing only
resistance e.g. incandescent lamps, heaters, soldering irons, ovens, etc.

The current drawn from the
supply is directly converted into heat or light. Since the voltage is assumed to be constant,
the actual power (kW) being used is identical to the apparent power (kVA) being
drawn from the line. The power factor is
therefore unity or 1. In these purely
resistive circuits, the current and voltage sinewave peaks occur simultaneously
and are said to be “in phase”.

2.

__Inductive Loads__
All motors and transformers
depend on magnetism as the basis of

their operation. Magnetism is a force and in the physical
sense is not

consumed. In AC motors and transformers, magnetic
forces are only

required periodically. Consequently, a permanent magnet cannot be

used and the necessary
magnetism is produced by electrical means.

The electrical current
needed for this purpose is not fully utilised.

Having produced the magnetic
force, the current flows back to the

power station again. This current is called the reactive current
in con-

trast to the active current
which performs work and is fully utilised in

so doing. Although the reactive current is not
utilised, it imposes a

load on the electrical
distribution system and supply authorities

demand payment for this load
according to specific tariffs.

The current drawn from the
supply is made up of two separate kinds

of current “power producing
current” and “magnetising current”.

Therefore the current
flowing in an AC circuit (unless corrected) is

generally larger than is
necessary to supply the power being by the

expended point.

What does Cosϕ mean?

Reactive power and active
power flow through the motor or trans-

former. Geometrical calculation of these two powers
yield the apparent power. The ratio of
the active and apparent power is denoted by cosϕ and indicates what fraction of
apparent power flowing is actually used by the motor.The apparent power is
greater than theactive power and hence the
power factor is a value considerably lessthan unity.

__Disadvantages of Low Power Factor__

1. Increased
authorities cost since more current has to be transmitted, and this cost is
directly billed to consumers on maximum demand kVA systems.

2. Causes overloaded generators, transformers
and distribution lines within a plant, resulting in greater voltage drops and
power losses, all representing waste, inefficiency and needless wear and tear
on industrial electrical equipment

3. Reduces
load handling capability of the plants electrical system.Most electrical supply
authorities have changed to kVA demand systems from the inefficient kW demand
system. Consumers are now billed and
penalised for their inefficient systems according to the apparent power being
used. In future, consumers will be
penalised for plants with power factor below a pre-determined value.

Power Factor Improvement

The term power factor comes into picture in AC circuits only. Mathematically it
is cosine of the phase difference between source voltage and current. It refers to the fraction of total power
(apparent power) which is utilized to do the useful work called active power.

**Need for Power Factor Improvement**

• Real power is given by P = VIcosφ. To transfer a given
amount of power at certain voltage, the electrical current is inversely proportional to cosφ. Hence
higher the pf lower will be the current flowing.
A small current flow requires less cross sectional area of
conductor and thus it saves conductor and money.

• From above relation we
saw having poor power factor increases the current flowing in conductor and
thus copper loss increases. Further large voltage drop occurs in alternator,electrical
transformer and transmission & distribution lines which
gives very poor voltage regulation

How to calculate the capacitor for motor

Qc =0.9x1.73xUnI0

Un is motor voltage

I0 is no load current of induction motor

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