POWER SYSTEMS- I

INSTRUCTIONS FOR EXPERIMENT NO. 3

1. Aim: To study and verify the Ferranti Effect of Transmission Line at no load.

2. Theory:

Under no load conditions receiving end voltage is more than that of sending end

voltage. This phenomenon is known as Ferranti effect. This effect becomes more pronounced

as the line length increases. A general explanation is as below:

The equation for the voltage at the point which is at a distance of x from the

receiving end of the transmission line is as

Where Zc is characteristic Impedance of the line and γ is called the propagation constant.

γ =α+jβ;

Substituting x=l and IR=0 (no load) in Eq. (1) , we have

The above equation shows that at l=0 , the incident (Ei0) and reflected (Er0)

voltage waves are both equal to VR/2. With reference to fig .a, as l increases, the incident

voltage wave increases exponentially in magnitude 0.5VR eαl

and turns through a positive

angle βl (represented by phasor OB); while the reflected voltage wave decreases in

magnitude exponentially 0.5VR e-αl

and turns through a negative angle βl (represented by

phasor OC). From the geometry of the figure , it is known that the sending end voltage VS is

such that |VR|>|VS|.

A simple explanation of the Ferranti effect on an approximate basis can be

advanced by lumping the inductance and capacitance parameters of the line as shown in the

fig .b. The capacitance is lumped at the receiving end of the line.

Fig .a Fig.b

Here

Since C is small compared to L ,wLl can be neglected in comparison to 1/wCl.

Thus

Electric Power Transmission Line Training Kit:

i. The transmission line training kit consists of main parts like Generating station,

transmission line, receiving station and VAR compensators.

ii. At the sending end side, there are digital voltmeter, ammeter and power analyzer

for measurement purposes. A transformer tap changer is present for adjusting the

input voltage level. Supply is given to the source through auto-transformer. A

circuit breaker is present that isolates the source from transmission line model.

iii. The electric power transmission line training kit is designed as a 3 phase medium

length transmission line of 180 km. it is divided into 6 identical pi-models, each

section being 30 km long. In each pi-model, lumped capacitor is divided in two

equal sections.

iv. At the receiving end side, there are digital voltmeter, ammeter and power analyzer

for measurement purposes. A transformer tap changer is present for adjusting the

output voltage level. A circuit breaker is present that isolates the transmission line

model from load.

v. The last section consists of VAR compensators having various arrangements of

inductive and capacitive loads for reactive power compensation of line. The block

consists of three phase shunt reactors, delta connected capacitors and series

reactors.

vi. The transmission line kit can tolerate maximum current of 2 A. Hence care should

be taken to keep the current within limits while operating the kit.

3. Procedure:

1) Set up the transmission line training kit

2) Apply 200v supply to the sending end

3) Remove the load from receiving end

4) With the help of multimeter ,measure the voltage after every 30km upto full distance

of 180km

5) Values of resistance, inductance and capacitance are predefined standard values for

this experiment

6) Note down the rise of voltage after every 30km

7) Plot the graph of Vr against line length

4. Attach the following pages-

a. Diagram of Electric Power Transmission Line Training Kit

b. Graph for VR (V) vs. Line Length (km).

5. Calculations:

a. Calculate the value of voltage at receiving end after every 30 km.

6. Observation Table:

For Vs = ____ V

Sr. No. VR Observed (V) VR Calculated (V)

VR1

VR2

VR3

VR4

VR5

VR6

7. Conclusion: Write appropriate conclusion based on the rise in voltage as per the

increase in line length.