International Journal for Research in Applied Science & Engineering Technology (IJRASET)

ISSN: 2321-9653; IC Value: 45.98; SJ Impact Factor: 6.887

Volume 6 Issue III, March 2018- Available at www.ijraset.com

Depiction and Compensation of Ferranti Effect in

Transmission Line
A. Divya Swarna Sri1, K. Tejaswini Devi2, K. Dhana Raju3, B. Tanya4
1, 2, 3, 4,
Department of Electrical & Electronics Engineering, PVP Siddhartha Institute of Technology, Vijayawada, India

Abstract: A Flexible AC transmission System refers to the system consisting of various devices to enhance the stability and
transfer capability of the transmission system. This method can be used during charging of the transmission line, when there is
no load or low load condition at the receiving end & Due to, this low current flows through the transmission line also shunt
capacitance in the transmission line will become dominant. This causes voltage amplification (Ferranti Effect) due to which
receiving end voltage will become greater than the sending end voltage (effect will be high in long transmission line). To
compensate the Ferranti effect, shunt inductors are connected across the transmission line. In this work Ferranti effect is
reduced by designing an Inductive circuit. Proposed circuit has simulated using MATALB/Simulink& practically verified in
hardware system.
Keywords: Ferranti effect, Shunt inductor, Compensation, Open circuited line

I. INTRODUCTION
There are many factors affecting temporary over voltages that may be considered in insulation.The Ferranti effect is a phenomenon
where the steady voltage at the open end of an uncompensated transmission line is always higher than the voltage at the sending end.
It occurs as a result of the capacitive charging current flowing through the line and resulting over voltage increases according to the
increase in line length [1-3].Traditionally the most accurate transmission line models have been based on a constanttransformation
matrix with frequency dependent modes [4]. This type of model may give satisfactory results for situations involving high frequency
transients, but the accuracy often deteriorates in the low frequency area due to frequency dependency of the transformation matrix
[5].In long transmission lines, the most important factors which affect the power frequency voltages on the line during normal
operation and the increase in voltages during a fault are the length of the line and the degree of shunt compensation [6]. Both
parameters have a major indirect influence on the transient phenomena as well as with normal switching operations [7-10]. In this
paper Ferranti effect has been reduced considerably & proposed design has been solved by both simulink modelling & experimental
setup.

II. FERRANTI EFFECT

The effect in which the voltage at the receiving end of the transmission line is more than the sending voltage is known as the
Ferranti effect. Such type of effect mainly occurs because of light load or open circuit at the receiving end. It is due to the charging
current of the line. When an alternating voltage is applied, the current that flows into the capacitor is called charging current. A
charging current is also known as capacitive current. The charging current increases in the line when the receiving end voltage of the
line is larger than the sending end.

A. Modelling of transmission Line

Ferranti effect has been explained by considering (Fig 1) a nominal pi (π) model.

Fig 1 Block diagram of the system

©IJRASET (UGC Approved Journal): All Rights are Reserved 1522
 International Journal for Research in Applied Science & Engineering Technology (IJRASET)
ISSN: 2321-9653; IC Value: 45.98; SJ Impact Factor: 6.887
Volume 6 Issue III, March 2018- Available at www.ijraset.com

In general for a 300 Km line operating at a frequency of 50 Hz, the no load receiving end voltage has been found to be 5% higher
than the sending end voltage. Now for analysis of Ferranti effect let us consider the phasor diagrams shown above. Here, Vr is
considered to be the reference phasor, represented by OA.
= (1 + 0) (1)
Capacitive current Ic= jωCVr
Sending end voltage Vs= Vr + resistive drop + reactive drop
= + + (3)
(2)
= + ( + ) (4)
)
= + ( +
Since =

Now − = +

This is represented by the phasor OC in Fig 2.

Fig 2:Phasor Diagram representing Ferranti effect

Neglecting resistance i.e. R=0

Thus capacitive reactance Xc= (1/ωLCo)
Average current flowing through capacitor Ic= (Vr/2XC)= (1/2)VrωlCo (where l indicates length of the transmission
line) Inductive reactance of the line = ωLol
Thus raise in voltage is given by Voltage raise = (1/2)Vrω2l2CoLo
From the above equation it is absolutely evident, that the rise in voltage at the receiving end is directly proportional to the square of
the line length, and hence in case of a long transmission line it keeps increasing with length and even goes beyond the applied
sending end voltage at times, leading to the phenomena called Ferranti effect in power system.

III. PROPOSED DESIGN

The Ferranti effect is a phenomenon where the steady voltage at the open end of an uncompensated transmission line is always
higher than the voltage at the sending end. It occurs as a result of the capacitive charging current flowing through the line and
resulting over voltage increases according to the increase in line length. This causes voltage amplification (Ferranti Effect) due to
which receiving end voltage will become greater than the sending end voltage (effect will be high in long transmission line). To
compensate the Ferranti effect, shunt inductors are connected across the transmission line. In this work Ferranti effect is reduced by
designing an Inductive circuit. Proposed circuit has simulated using MATALB/Simulink & practically verified in hardware system.

A. MATALB/Simulink model
Simulink model & output of the model has been given in Fig 3 & Fig 4. And output in Fig 4 clearly shows that Ferranti effect has
been considerably reduced.

©IJRASET (UGC Approved Journal): All Rights are Reserved 1523

 International Journal for Research in Applied Science & Engineering Technology (IJRASET)
ISSN: 2321-9653; IC Value: 45.98; SJ Impact Factor: 6.887
Volume 6 Issue III, March 2018- Available at www.ijraset.com

Fig 3:Simulation model

Fig 4: Simulation output after Ferranti effect compensation

B. Hardware Design
The system design is based on block diagram shown in Fig 5 & circuit diagram in Fig 6. Here a long transmission of certain length
is considered, voltage at the sending end and receiving end is measured. Sending end voltage is compared with receiving end
voltage under no-load condition. The analog data is given to Arduino Uno and it’s programmed such a way that it triggers OPTO-
coupler which in turn switches end to end TRIAC in such a way that inductor is shunted into the network at receiving end.

Fig 5: Block diagram of the proposed system

©IJRASET (UGC Approved Journal): All Rights are Reserved 1524
 International Journal for Research in Applied Science & Engineering Technology (IJRASET)
ISSN: 2321-9653; IC Value: 45.98; SJ Impact Factor: 6.887
Volume 6 Issue III, March 2018- Available at www.ijraset.com

Fig 6: Circuit diagram for hardware model

IV. SIMULATION STUDY

The simulation was conducted in MATLAB/SIMULINK for various values of voltage in the sending end & output values
mentioned in Table 1.
Sending end voltage Receiving end voltage (without Receiving end voltage (with
compensation) compensation)

230V 355.28V 231.62V

3300V 5097.38V 3323.20V

6600V 10195.05V 6646.40V

12000V 18536.46V 12084.36V

220000V 339835.16V 221546.66V

Table 1 Simulation output

A. Experimental Output
220V, 50Hz supply is given to the kit & the output was observed under no-load condition shown in Table 2. Shunt inductor used to
compensate the voltage raise due to Ferranti effect.

Sending end voltage Receiving end voltage Receiving end voltage

(Without compensation) (With compensation)

213V 217V 214V

215V 219V 216V

Table 2 N of the Experimental study

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 International Journal for Research in Applied Science & Engineering Technology (IJRASET)
ISSN: 2321-9653; IC Value: 45.98; SJ Impact Factor: 6.887
Volume 6 Issue III, March 2018- Available at www.ijraset.com

V. CONCLUSION
In this paper Ferranti Effect has been successfully reduced by the proposed Inductive circuit through designed practical model. Also
proposed system has been tested in Matlab/simulink. Normally in long transmission line (For example, 400 kilometres) Ferranti
effect is more, where the receiving end voltage greater than the sending end voltage. As the length of line increases, effect also
increases and by this work the effect has been considerably reduced by suitable design.

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