Series & Shunt Capacitance

7/29/2019 Series & Shunt Capacitance

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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


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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.


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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


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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


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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


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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


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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


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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.


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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.

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Series & Shunt Capacitance