SHUNT AND SERIES CAPACITOR AT MID POINT OF TRANSMISSION LINE

LT capacitors are installed on the distribution system on individual lines or consumers motors to reduce system losses system losses and improve the system voltage and capacity. In addition, they provide other advantages for the consumer, such as reduction in kVA demand, losses and stable voltage. The optimum benefit desired from the capacitors largely depends on the correct positioning of the capacitor in the system.

SERIES CAPACITOR CONNECTED AT THE MID POINT OF THE LINE

Location of Series capacitor is not very critical

K= Degree of compensation= Xc/ X

SHUNT CAPACITOR CONNECTED AT THE MID POINT OF THE LINE

Reactive current is injected into the line to maintain voltage magnitude. Transmittable active power is increased but more reactive power is to be provided. (Applicable for Facts also)

Inductive reactance X = X1 + X2 between the sending-end and the receiving-end voltages, Es and Er The line resistanceis assumed to be negligible. It is its terminal voltages,V1 and V2 at the two ports, which interact with the transmission line sections through Kirchhoffs Voltage Laws,

Es= jX1 I1+ V1 (1)

V2 = jX2I2 + Er (2)

I3=I1-I2

MID-POINT VOLTAGE SUPPORT

It is assumed that the device is located at the midpoint of the line, i.e., XI = X2 = X/2 and the device can provide 1.0 pu voltage support, i.e., I V1 I = I V2 I = 1.0 pu. q=d/2= d s- d 1= d 2- d r= d s- d r/2=90^o

Var Rating of device =P tan (d/4), Pmax= 2v²/X

COMPARISON BETWEEN SERIES AND SHUNT CAPACITOR

SERIES AND SHUNT CAPACITORS

Capacitors aid in minimizing operating expenses and allow the utilities to serve new loads and consumers with a minimum system investment. Series and shunt capacitors in a power system generate reactive power to improve power factor and voltage, thereby enhancing the system capacity and reducing the losses. In series capacitors the reactive power is proportional to the square of the load current, whereas in shunt capacitors it is proportional to the square of the voltage. There are certain unfavorable aspects of series capacitors. Generally the cost of installing series capacitors is higher than that of a corresponding installation of a shunt capacitor. This is because the protective equipment for a series capacitor is often more complicated. The factors which influence the choice between the shunt and series capacitors are summarized in Table .

Due to various limitations in the use of series capacitors, shunt capacitors are widely used in distribution systems. For the same voltage improvement, the rating of a shunt capacitor will be higher than that of a series capacitor. Thus a series capacitor stiffens the system, which is especially beneficial for starting large motors from an otherwise weak power system, for reducing light flicker caused by large fluctuating load, etc.

Reasons for the application of shunt capacitor units are because of

1. Increase voltage level at the load

2. Improves voltage regulation if the capacitor units are properly switched.

3. Reduces I2R power loss in the system because of reduction in current.

4. Reduces I2X kVAR loss in the system because of reduction in current.

5. Increases power factor of the source generator.

6. Decrease kVA loading on the source generators and circuits to relieve an overloaded condition or release capacity for additional load growth.