# Power Systems Questions and Answers – Ferranti Effect & Methods of Voltage Control

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This set of Power Systems Multiple Choice Questions & Answers (MCQs) focuses on “Ferranti Effect & Methods of Voltage Control”.

1. Ferranti effect is not a problem for ________
a) Long Transmission lines
b) Medium Transmission lines
c) Short Transmission lines
d) Transmission line having high capacitance

Explanation: Ferranti effect is happens when line to earth capacitance becomes more than the inductance parameter. This effect is more predominant in medium and long transmission lines but is not a problem for short transmission lines. This is because line to earth capacitance for short transmission line is negligible.

2. What happens during the Ferranti effect?
a) Reciving end current becomes more than sending end current
b) Reciving end voltage becomes more than sending end voltage
c) Reciving end power becomes more than sending end power
d) Reciving end frequency becomes more than sending end frequency

Explanation: In a medium or long transmission line when open circuited or lightly loaded the receiving end voltage is found more than the standing in voltage. This phenomenon of rise in voltage at receiving end of open circuited or lightly loaded line is called Ferranti effect.

3. During Ferranti effect the voltage drop across line resistance ___________
a) In phase with reciving end voltage
b) lags behind reciving end voltage
c) lead the reciving end voltage
d) lags behind sending end voltage

Explanation: During Ferranti effect the leading charging current is more than lagging component of current. Net line current leads the sending end and reciving end voltage. Hence the iR drop leads these voltages.
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4. A transmission line of 200 Km is supplying at 50Hz frequency. What is the percentage rise in voltage at reciving end?
a) 20%
b) 1.2%
c) 2.19%
d) 20.8%

Explanation: Percentage rise in voltage = (ω2 l2 10-8 )/18
Solving this % Vrise = {(2 × Ω × 50) × 2002 × 10-8}/18
= 2.19%.

5. Which of the following equipment or element can reduce Ferranti effect?
a) Relay
b) Circuit Breaker
c) Resistors
d) Current limiting reactors

Explanation: For high voltage and extra high voltage lines shunt reactors are provided to absorb part of charging current. As leading charging current is reduced. Ferranti effect is also reduced.

6. Under no load condition inductance of line predominant the line to earth capacitances.
a) True
b) False

Explanation: Under no load condition capacitance between line and earth predominant the inductance of long and medium transmission lines.

7. What is the limit within which the consumer’s end terminal voltage should be maintained?
a) ± 9 %
b) ± 10 %
c) ± 5 %
d) ± 6 %

Explanation: The voltage fluctuations at consumers end may cause malfunction or event damage of consumer’s equipments. So, the voltage at the consumers end must be maintained within prescribed limit upto ± 6% of declared supply voltage so that the consumers apparatus may operate satisfactorily.

8. What is the main reason for maintaining consumer end voltage within prescribed limit?
a) Because it is declared by the supplier
b) For satisfactory operation of electrical equipments
c) For easy calculation of units supplied
d) To reduce the line losses

Explanation: All electrical equipments are designed to work at a certain voltage mentioned as voltage rating of that equipment. Change of supply voltage beyond a certain limit may cause malfunction or even damage to the equipment. So, the consumer end voltage must be maintained to a prescribed limit for satisfactory operation of consumer’s equipments.

9. Which of the following equipment is not used for voltage control?
a) Tap changing transformer
b) Induction generators
c) Series compensators
d) Synchronous phase modifiers

Explanation: Induction generators are not used for voltage control. Tap changing transformer is used to control distribution end voltage for upto limited voltage variations. Series compensators and Synchronous phase modifiers controls line voltage by supplying required leading or lagging VAR.

10. What is the full form of AVR? This term is related to voltage control?
a) Automatic Voltage Rectifier
b) Actuated Voltage Rectifier
c) Automatic Voltage Rectifier
d) Automatic Voltage Regulator

Explanation: AVR stands for Automatic Voltage Regulator. It operates on the principle of detection of error and is used to control the line voltage.

11. On which side of the transformer tap changer is provided?
a) On High Voltage side
b) On low voltage side
c) On high voltage and low voltage side
d) In core

Explanation: In tap changing transformer there is always a typing on the high voltage winding which when connected to the rated voltage gives rated voltage on the low voltage side. This tapping is called principal typing.

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