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ABSTRACT
In the present technological revolution power is very
precious so we need to find out the cause of power
loss and improve the power system. Due to
industrialization the use of inductive load increases
and hence power system losses its efficiency. So we
need to improve the power factor with a suitable
method. Whenever we are thinking about any
programmable device then the embedded technology
comes into forefront.
The embedded is nowadays very much popular and
most of the product are developed with
microcontroller based embedded technology.
The project is designed to minimize penalty for
industrial units by using automatic power factor
correction unit. Power factor is defined as the ratio of
real power to apparent power. This definition is often
mathematically represented as kW/kVA, where the numerator is the active (real) power and the
denominator is the (active + reactive) or apparent
power. Reactive power is the non-working power
generated by the magnetic and inductive loads, to
generate magnetic flux. The increase in reactive power
increases the apparent power, so the power factor also
decreases. Having low power factor, the industry
needs more energy to meet its demand, so the
efficiency decreases.
In this proposed system the time lag between the zero
voltage pulse and zero current pulse duly generated
by suitable operational amplifier circuits in
comparator mode are fed to two interrupt pins of the
microcontroller. It displays the time lag between the
current and voltage on an LCD. The program takes
over to actuate appropriate number of relays from its
output to bring shunt capacitors into the load circuit
to get the power factor till it reaches near unity. The
microcontroller used in the project belongs to 8051
family
INTRODUCTION
POWER FACTOR THEORY:
In any AC system the current, and therefore the
power, is made up of a number of components based
on the nature of the load consuming the power. These
are resistive, inductive and capacitive components. In
the case of a purely resistive load, for example,
electrical resistance heating, incandescent lighting,
etc., the current and the voltage are in phase that is
the current follows the voltage. Whereas, in the case
of inductive loads, the current is out of phase with the
voltage and it lags behind the voltage. Except for a
few purely resistive loads and synchronous motors ,
most of the equipment and appliances in the present
day consumer installation are inductive in nature, for
example, inductive motors of all types, welding
machines, electric arc and induction furnaces, choke
coils and magnetic systems , transformers and
regulators, etc. In the case of a capacitive load the
current and voltage are again out of phase but now
the current leads the voltage. The most common
capacitive loads are the capacitors installed for the
correction of power factor of the load.
The inductive or the capacitive loads are generally
termed as the reactive loads. The significance of
these different types of loads is that the active (or
true or useful) power can only be consumed in the
resistive portion of the load, where the current and
the voltage are in phase.
(Watt less or) reactive power which is necessary for
energizing the magnetic circuit of the equipment (and
is thus not available for any useful work). Inductive
loads require two forms of power - Working/Active
power (measured in kW) to perform the actual work
of creating heat, light, motion, machine output, etc.,
and Reactive power (measured in kVAr) to sustain
the electromagnetic field. The current known as wattless
current is required to produce the magnetic field
around an electric motor. If there was no watt-less
current then an electric motor would not turn. The
problems arise due to the fact that we can sometimes
have too much watt-less current, in those cases we
need to remove some of it.
The vector combination of these two power
components (active and reactive) is termed as
Apparent Power (measured in kVA), the value of
which varies considerably for the same active power
depending upon the reactive power drawn by the
equipment. The ratio of the active power (kW) of the
load to the apparent power (kVA) of the load
is known as the power factor of the load.
It is a measure of how effectively the current is being
converted into useful work output and more
particularly is a good indicator of the effect of the
load current on the efficiency of the supply system.
A load with a power factor of 1.0 result in the most
efficient loading of the supply and a
Load with a power factor of 0.5 will result in much
higher losses in the supply system.
Low power factor leads to large copper losses, poor
voltage regulation and reduce handling capacity of
the system. The increase in the load current, increase
in power loss, and decrease in efficiency of the
overall system Net industrial load is highly inductive
causing a very poor lagging power factor. If this poor
power factor is left uncorrected, the industry will
require a high maximum demand from Electricity
Board and also will suffer a penalty for poor power
factor. Standard practice is to connect power
capacitors in the power system at appropriate places
to compensate the inductive nature of the load.
Disadvantage of low power factor can be easily
understood by an example:
Supplied Voltage = 240 Volts Single phase.
Motor input = 10 KW
Power Factor = 0.65
Current (I1) = Power (kW)/Volts (V)*P.F
= 10000/240*0.65 = 64.1 Amp.
If the power factor of the motor is increased to 0.9
the current
Drawn by the motor shall be –
Current (I2) = Power (kW)/Volts (V)*P.F
= 10000/240*0.9 = 46.3 Amp.
Thus, as the power factor decreases the current
required for the same value of active, or useful,
power increases. The result is that the sizes of the
equipment, like the switchgear, cables, transformers,
etc., will have to be increased to cater the higher
current in the circuit. All this adds to the cost.
Further, the greater current causes increased power
loss or I2R losses in the circuits. Also due to higher
current, the conductor temperature rises and hence
the life of the insulation is reduced.
So it is evident to improve the power factor by
applying certain methods and application doing so
will lead to improve the system quality and will be
cost effective A poor power factor due to an
inductive load can be improved by the addition of
power factor correction
The various conventional methods for the power
factor correction are the using static capacitors,
synchronous condensers, phase advancers, etc. doing
so will increase the power factor
The advantages of an improved power factor:
Higher power factors result in–
a) Reduced system losses, and the losses in the
cables, lines, and feeder circuits and hence lower
sizes could be opted.
b) Improved system voltages, thus enable
maintaining rated voltage to motors, pumps and other
equipment. The voltage drop in supply conductors is
a resistive loss, and wastes power heating the
conductors. A 5% drop in voltage means that 5% of
your power is wasted as heat before it even reaches
the motor. Improving the power factor, especially at
the motor terminals, can improve your efficiency by
reducing the line current and the line losses.
c) Increased system capacity, by release of kVA
capacity of transformers and cables for the same kW,
thus permitting additional loading without immediate
augmentation.
d) Reduce power cost due to reduced kVA demand
charge and so also by reduced power factor charge.
Example: Let us take an example of an industry with
initial load Condition of 5000 kVA at 60% power
factor with a consumption of 19, 20,000 units per
month, supplied at 33 KV.
Taking the Tariff as below:
1. Demand charges Rs. 144/kVA/month
2. Energy Charges Rs. 4.11 / Unit
3. PF surcharge for each 1% below 90% 1% of
(Demand charges + Energy Charges)