Power Large quantity of induction motors are used

Power factor improvement in a weak
distribution grid is a challenging problem, particularly when it may not be an
economical to simply upgrade the network. Therefore to cope with an outdated
and overstressed distribution power network of Pakistan, the electricity
consumers have mostly employed voltage regulators or capacitor banks to
regulate the voltage on AC power distribution lines. The consumers need to
correct the power factor for the following reasons:

•        
Large
quantity of induction motors are used to drive their pumps, conveyors, and
other machinery in the plant causes power factor to be inherently. For lower
power factor, usually below 0.80 or 0.85, electric utility companies place
power factor penalty on the industry.

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•        
Many
electric utility companies charge for maximum metered demand based on either
the highest registered demand in kilowatts (KW meter), or a percentage of the
highest registered demand in KVA (KVA meter), whichever is greater. If the
power factor is low, the percentage of the measured KVA will be significantly
greater than the KW demand.

•        
Loads
drawing reactive power also demand reactive current causing excessive loss in
distribution system

•        
A lower
power factor causes a higher current flow for a given load. As the line current
increases, the voltage drop in the conductor increases, which may result in a
lower voltage at the equipment due to which they do not operate effectively

•        
Uncorrected
power factor causes excessive loss in distribution system

•        
Excessive
voltage drops causes overheating and premature failure of other equipment

•        
Energy
saving is achieved

The voltage regulators tries to maintain
constant output voltage for loads (air conditioners, refrigerators, induction
motors etc.). The voltage stabilizers are equipped with VARIAC
(autotransformer) where a servomechanism is used to select an appropriate tap
on multiple taps autotransformer. If the output voltage is not in acceptable
range, the servomechanism switches the tap, changing the turn’s ratio of the
transformer in order to move the secondary voltage close to acceptable level.
The controls also provide a dead band preventing it from constantly adjusting
the voltage as it varies by an acceptably small amount.

In summers, the air conditioning and
refrigerating heavily loads the distributions grid. As these loads demand high
reactive power and if not provided with an adequate supply results in low
voltage. The voltage stabilizers, if installed, help in maintaining the voltage
close to its nominal level. However, each tap changing operation will also
result in an increase in the line current and thus the reactive losses. If the
weak distribution grid is predominantly equipped with voltage stabilizers, then
the cumulative voltage stabilizing actions will result in high currents and
thus high losses, and may result in short term voltage stability. On the other
hand, switched capacitors relieve the power grid by providing the reactive
power support; however, the control is manual and only helpful in constant low
voltage. The voltage level varies on weak grid as the load demand changes and
therefore requires a control device that can automatically regulate reactive
power.

1.1      
State of
the Art

In Pakistan, the substantial part of
electrical power distribution system is outdated and overstressed 1 2. This weak grid
infrastructure is hampering the provision of available electricity in its
proper form, i.e. the electricity is provided to the end consumer in poor power
quality, that not only increases the rate of losses but also reduces the power
system efficiency 3.Also the loads
connected to the poor power quality electrical network are less efficient and
have a reduced lifetime 4. The main
contributor to the poor power factor is an inadequate supply of reactive power
where low voltages loads up the supply system unnecessary.

It has been identified that majority of the
industrial load and certain domestic loads are highly inductive in nature such
as induction motors, air conditioners, AC/DC drives, welding machines, arc
furnaces, fluorescent Lightings, electronic controls and computers 5.The heavy inductive
loads results in very poor lagging power factor and if left uncorrected, the
consumers will heavily load the grid. The weak distribution grid generally
unable to compensate the reactive power demand and therefore results in reduced
electrical network efficiency.

In order to cope, the consumers have
installed either voltage regulators or switched capacitors 5 however the former
heavily loads the grid and reduces power factor while later is unable to
compensate frequent load variations resulting in high voltages that might
damage the consumer’s equipment. A possible solution to these problems is
Static Synchronous Compensator (STATCOM). The basic idea behind STATCOM is to
detect the load current and calculate the reactive current demand of load and
inject the required reactive current to compensate for the poor power factor.
The most important factor to be considered in designing STATCOM is how to
obtain the compensating current. The compensating current can be obtained by
means of Instantaneous Power Theory or Filtration methods. Traditionally
reactive power in single-phase or three- phase circuits for steady state is calculated
using average value concept for sinusoidal voltage and current waveforms. 6 Proposes a novel
instantaneous reactive power compensator which requires practically no energy
storage components. The instantaneous reactive power in three-phase circuits
including transients is calculated on the basis of the instantaneous value
concept for arbitrary voltage and current. However  .VSC based system can control active and
reactive power independently. It could also lower down harmonic contents of AC
current and improves power factor of the connected AC system. 7 Proposes a dynamic
model of VSC and method for respective power control has been derived according
to the switching function model and predictive current control theory, such a
control system give a good response than the one designed on steady state model
with no overshoot in the power adjustments. __This research project will
investigate the latest technology of voltage regulation that will provide
real-time control of reactive power employing the power electronic devices and
the pulse width modulated (PWM) switching technique, i.e. Flexible Alternating
Current Transmission Systems (FACTS). The project will develop a power quality
improvement device for small industrial consumer that will be able to maintain
voltage at its nominal level and thus improves efficiency of distribution grid
and electrical loads. The device will be more robust and will work well under
different system conditions.

1.2      
Research
objective

This research aims to develop power factor
correction device that can provide real time control of reactive power with
solid state devices (power electronic) and eliminating the electromechanical
relays.  The desired device will have a potential
to provide both steady state and transient reactive power compensation under
different loading conditions for the domestic and small industrial loads
connected to the weak distribution grid. The purpose of this project is to
improve consumers load efficiency and relieves the distribution grid from
overloading.