Series & Shunt Capacitance
-
Upload
pathum-sudasinghe -
Category
Documents
-
view
226 -
download
1
Transcript of Series & Shunt Capacitance
-
7/29/2019 Series & Shunt Capacitance
1/9
Use Of Series & Shunt
Capacitances In Transmission
Line
Instructed by: Mr. Branesh Pillai Name : S.P.M Sudasinghe
Index No : 100523G
Group : G - 12
Date of Per : 2013/03/07Date of Sub : 2013/03/
Field : EE
EE 2192
Laboratory Practice IV
-
7/29/2019 Series & Shunt Capacitance
2/9
PROCEDURE
Series Capacitance
Sending end voltage Vs is kept at 100V and the receiving end voltage V r at 90V throughout the test.
Current and power at receiving end is measured for different values of series capacitance values while
keeping the Vrat 90 V by varying the load.
Shunt Capacitance
Sending end voltage Vs is kept at 100V and the receiving end voltage Vr at 90V throughout the test.
Determine the power that is received for different values of shunt capacitors.
-
7/29/2019 Series & Shunt Capacitance
3/9
OBSERVATIONS
Name : S.P.M Sudasinghe
Index No : 100523G
Group : G -12
Date : 2013/03/07
Instructed by : Mr. Branesh Pillai
Series Capacitance
C (F) Pr(W) Ir(A)
43 50 0.59
45 50 0.62
46 45 0.52
47 50 0.61
49 50 0.57
Shunt Capacitance
C (F) Pr(W) Is (A) Ir(A)
43 110 1.65 1.20
44 110 1.65 1.25
45 110 1.70 1.25
46 115 1.70 1.25
49 110 1.75 1.25
52 115 1.80 1.2555 110 1.80 1.20
-
7/29/2019 Series & Shunt Capacitance
4/9
CALCULATIONS
Series Capacitance
When series capacitance = C = 43F, L = 0.15 H and f = 50Hz
Received power = 50W , Ir= 0.59 A
Series capacitive reactance =
=
= 74.026
Inductive reactance = = = 47.124
Per unit compensation =
=
= 1.571
Series Capacitance(F)
Series CapacitiveReactance ()
Per unit compensation ofthe line Pr(W)
43 74.026 1.571 50
45 70.736 1.501 50
46 69.198 1.468 45
47 67.726 1.437 50
49 64.961 1.379 50
Shunt Capacitance
Similarly,
Shunt Capacitance
(F)
Shunt Capacitive
Reactance ()Per unit compensation Pr(W)
43 74.026 1.571 110
44 72.343 1.535 110
45 70.736 1.501 110
46 69.198 1.468 115
49 64.961 1.379 110
52 61.213 1.299 115
55 57.875 1.228 110
-
7/29/2019 Series & Shunt Capacitance
5/9
44
45
46
47
48
49
50
51
64 65 66 67 68 69 70 71 72 73 74 75
Recieved
Power(W)
Series Capacitive Reactance ()
Power Received Vs Series Capacitive Reactance
-
7/29/2019 Series & Shunt Capacitance
6/9
44
45
46
47
48
49
50
51
1.35 1.4 1.45 1.5 1.55 1.6
Recieved
Power(W)
Per unit compensation of line
Received Power Vs Per unit Compensation
-
7/29/2019 Series & Shunt Capacitance
7/9
109
110
111
112
113
114
115
116
50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80
PowerRecieved(W)
Shunt Capacitive Reactance ()
Power Received Vs Shunt Capacitive Reactance
-
7/29/2019 Series & Shunt Capacitance
8/9
DISCUSSION
1. Effect of power factor in the power system
When the power factor is 1, all the energy supplied by the source is consumed by the load. But when the power
factor is less than 1, part of the energy supplied by the source is stored and returned back to the source;
inductive loads will absorb part of the energy supplied by the source and store it in its magnetic field, and
capacitive loads will store it in its electric field. Therefore, when the power factor is less than 1, more current is
required to deliver the same amount of useful energy.
Effects of low power factor :
Low power factorcauses the kVA rating ( apparent power ) to increase. Industrial consumers have topay a demand charge depending on this kVA rating. From the point of view of supply side they have to
increase the supplied reactive power.
Poor voltage regulation The large current at low power factor causes greater voltage drops inalternators, transformers, transmission lines and distributors. This results in decreased voltage available
at the supply end, thus impairing the performance of utilization devices.
Reduced handling capacity of systemThe lagging power factor reduces the handling capacity of allthe elements of the system because the reactive component of current prevents the full utilization of
installed capacity.
The high current drawn by the system will damage the power system equipments and reduce the lifetime and also excessive heat generation can be occurred.
Large conductors would be needed to carry high currents. Low P.F. will result in a more expensive system with equipment able to absorb internal loads
and larger load requirements
2. Usefulness of Shunt Capacitors in improving power factorInductive components of a power system draw a lagging reactive power from the supply. It lags by 90 0to
the active power. The capacitive component of the power system leads by 90 0 to the active power. The
directions of the above two components oppose each other. Whenever an inductive load is connected to the
transmission line, power factor lags because of lagging load current. To compensate, a shunt capacitor is
connected which draws current leading the source voltage. The net result is improvement in power factor.
Industrial facilities tend to have a lagging power factor, where the current lags the voltage because of
having a lot of electric induction motors. This will lead to the consumption of Lagging Reactive
Power. To minimize this effect we should either consume Leading Reactive Power or Supply Lagging
Reactive Power within the system. This can be accomplished by adding Shunt Capacitors to the
system. Some industrial sites will have large banks of capacitors strictly for the purpose of correcting
the power factor back toward one to save on utility company charges.
-
7/29/2019 Series & Shunt Capacitance
9/9
3. The effects of series and shunt capacitancesSeries Connection:
This is not a very common method of connecting capacitors. In this method, the voltage regulation is high,
but it has many disadvantages. They are,
Because of the series connection, in a short circuit condition the capacitor should be able towithstand the high current.
Due to the series connection and the inductivity of the line there can be a resonance occurring at acertain capacitive value. This will lead to very low impedance and may cause very high currents to
flow through the lines.
Shunt Connection:
This is the most common method of connection. . The capacitor is connected in parallel to the unit. The
voltage rating of the capacitor is usually the same as or a little higher than the system voltage.
4. Other methods of improving power factorSynchronous Condenser
A synchronous motor takes a leading current when over excited and therefore behaves as a capacitor. An
over excited synchronous motor running on no load is known as synchronous condenser. When such a
machine is connected in parallel with the supply it takes a leading current which partly neutralizes the
lagging reactive component of the load. Thus the power factor is improved.
Filters
There are certain situations where capacitors are not connected directly to the supply lines. The reason
for this is the presence of harmonics in the waveform caused by switched mode power supplies. The
simplest way to control the harmonic current is to use a filter. It is possible to design a filter that passes
current only at line frequency (e.g. 50 or 60 Hz). This filter kills the harmonic current, which means
that the non-linear device now looks like a linear load. At this point the power factor can be brought to
near unity, using capacitors or inductors as required. This filter requires large-value high-current
inductors, however, which are bulky and expensive.
Phase Advancers
Phase advancers are used to improve the power factor of induction motors. The low power factor of an
induction motor is due to the fact that its stator winding draws exciting current which lags behind the
supply voltage by 900. If the exciting ampere turns can be provided from other AC source, then the stator
winding will be relieved of exciting current and the power factor of the motor can be improved. This job is
accomplished by the phase advancer which is simply an AC exciter. The phase advancer is mounted on the
same shaft as the main motor and is connected in the rotor circuit of the motor. It provides exciting ampere
turns to the rotor circuit at slip frequency. By providing more ampere turns than required, the induction
motor can be made to operate on leading power factor like an over-excited synchronous motor.