AIM:
STUDY OF POWER FACTOR IMPROVEMENT.
Objective: after studying this experiment, it
will be possible to;
(1) Identify the disadvantage of low
power factor.
(2) Identify the causes of low power
factor
(3) Mechanism of power factor
correction improvement
Significance:-Machines
and devices with inductive property forms the considerable part of energy
considerable part of energy consumption system. Due to the inherent property of
inductor the current always lags behinds voltage with reference to time and
thus the total amount of electrical energy produced is divided into two
sectionsL1)
Real power : the main function desired from the device (2) Reactive Power: the
power necessary for the functioning of the device. The ratio of such division
is governed by the important parameter named as power factor and is a versatile
master key for unlocking the many of our power systems problems.
Theory:
Technically,
the power factor is defined as cosine of angle between voltage vector and
current vector of a.c. circuits. It is represented diagrammatically as shown in
figure-1. It can also be derived from other relations as shown in figure-2 and
figure-3.
Disadvantages of low power factor: As mentioned previously, majority of inductive
devices present
in the system results into low power factoe which leads to one or more of the
following disadvantages:
1.
Large KVA rating of equipment
2.
Greater conductor size in transmission,
distribution and consumer systems.
3.
Large copper loss
4.
Poor voltage regulation
5.
Reduction handling capacity of the
system.
Thus low power factor
is an objectionable feature in the supply system as well as form economical
point of view.
Causes of low power factor: Normally
the power factor of the load on the supply system is lower than 0.8 lag.
Following are the causes of low power factor.
1.
Induction motor works at a power factor
which is extremely small on light load (0.2 to 0.3) and rises to 0.8 to 0.9 at
full load.
2.
Arc lamps, electric discharge lamps and
industrial heat furnaces operate at low lagging power factor.
3.
The load on the power system is varying:
being high during morning and evening and low at other time. During low load
periods, supply voltage is increased which increases the magnetization current.
This results in the decreased power factor.
Power factor improvement: So,
to eliminate the causes and improve the power factor, we desperately require to
consider the property of the elements which is compensative in nature.
Capacitor is one of each element in which the current leads the applied voltage
and this property can be utilized to improve the power factor. The same thing
is illustrated diagrammatically in figure-4.
As shown in the figure, due to the capacitive effect the
charging current flows ahead of voltage vector and resultant current drawn from
supply is brought to II and from ф1 to ф2. Thus improving
the power factor.
Elements utilized in power factor
improvement: The following equipment can be utilized
for power factor improvement.
1.
Static capacitors
2.
Synchronous condensers
3.
Phase advancers
Calculation of power factor
correction: With the of power factor triangle, the
power factor improvement can be calculated in terms of leading KVAR supplied by
power factor correction improvement.
As shown in figure-5,
KVAR1=KVAR2=KVARc
Therefore,
KVARc = KVAR1
+ KVAR2
Where KVARc =
Leading KVAR supplied by power factor correction improvement. If we divide the
main triangle into two subordinate right angle triangles, we can have the
following relationship of KVAR from the basic rules:
1.
KVAR1/KW = tan ф1 i.e.
KVAR1 = KW tanф1
2.
KVAR2/KW = tanф2 i.e.
KVAR2 = KW tanф2
Utilizing these results
for equation (a) we get,
KVARc = KW tanф1 - KW tanф2
Therefore,
KVARc =
KW(tanф1 - tanф2 )
This is an important
relation to find out the leading KVARc supplied by power factor
correction improvement.
As power factor
improvement is intended for reducing maximum demand and also decreasing the
tariff rate on KWH, it also incurs the capital the cost of p.f. improving
equipment in terms of rate interest and depreciation. The net saving is also
affected by all such factors. Therefore,
The value to which the
power factor should be improved so as to have maximum net annual saving is
known as the MOST ECONOMICAL POWER FACTOR.
Importance of
power factor improvement:
It is desired below for
both consumers and generating stations.
(i) Consumers: A consumer has to pay less
electricity charges for his maximum demand in KVA plus the units consumed.
(ii) Generating Stations: Number of units
supplied by it depends upon the power factor. Greater the p.f. of generating
stations, higher the KWH it delivers to the system. This is according to the
formula, KW = KVAcosф
Suppose if we consider
the following parameters for power factor improvement, P- Peak load in KW taken
by consumer at p.f. cosф, rate is x Rs. Per KVA maximum demand per annum, cosф2
is improved p.f. due to p.f. improving equipment, y Rs. Is expenditure incurred
on p.f. improving equipment per KVAR per annum then,
Most economical p.f.
cosф2 = square root of (1-(y/x)2).
