POWER SYSTEM MCQS SET 12

POWER SYSTEM MCQS SET 12

1․ Which of the following methods is/are used for reactive or voltage compensation
a. shunt capacitor         b. series capacitor  
c. generation excitation control              d. all of the above
Explain:
Voltage or reactive power compensation can be done in two ways. 1. Sending end method a) Generation excitation control
2. Receiving end method a) Shunt capacitor b) Series capacitor c) Shunt reactor d) synchronous phase modifier e) On load tap changing transformer f) Booster transformer

2․ Ferranti effect can be compensated by which of the following
a. shunt capacitor         b. shunt reactor      c. series capacitor
d. both 1 and 2
Explain:
Ferranti effect occurs in case of no load or light load condition of a medium and long transmission lines due to capacitance effect of the transmission line. Therefore shunt reactor is used for compensating ferranti effect. Shunt reactor will reduce the effect of capacitance. Therefore ferranti effect will reduced.

3․ Which of the following method is used for changing power factor from leading to lagging
a. shunt capacitor      b. series capacitor         c. shunt reactor
d. any of the above
Explain:
Under no load condition or light load condition, medium and long transmission lines may operate at leading power factor due to capacitance effect. This leading power factor can be changed to lagging power factor by using of a shunt reactor. By using of shunt reactor, it will compensate the effect of capacitance and changes the power factor.

4․ A transmission line has a reactance of 1 Pu is operating at Vs = Vr = 1 Pu. The generator is connected at source end which is delivering 0.5 Pu of active power. Find the load angle?
a. 35°       b.  30°        c. 45°             d. 60°
ANSWER: b
 

5․ A transmission line has a reactance of 1 Pu is operating at Vs = Vr = 1 Pu. The generator is connected at source end which is delivering 0.5 Pu of active power and the transmission line is compensated with a series capacitance of 0.5 Pu. Find the load angle with series capacitance compensation?
a. 14.5°        b. 29°          c.  35.5°          d. 10.5°
ANSWER: a

6․ Under over excitation synchronous phase modifier works as
a. shunt capacitor     b. series capacitor           c. shunt reactor
d. any of the above
Explain:
Synchronous phase modifier is basically a synchronous motor operating under no load and by adjusting the excitation it is used for controlling reactive power, so that power factor and voltage are controlled. If synchronous phase modifier is used under over excitation it works similar to a shunt capacitor delivering reactive power and absorbing leading reactive power. If synchronous phase modifier is used as under excitation it works similar to shunt reactor which absorbs lagging reactive power and delivers leading reactive power. This is used for Ferranti effect.

7․ Which of the following is/are the advantages of synchronous phase modifier over the shunt compensation?
a. single unit can be used as both capacitance and inductor by adjusting the excitation
b. smooth voltage regulation is possible by controlling excitation
c. initial cost is low
d. both 1 and 2
Explain:
Synchronous phase modifier: 1.Single unit can be used as both capacitance and inductor by adjusting the excitation
2. Smooth voltage regulation is possible by controlling excitation
3. Initial cost of synchronous phase modifier is higher
4. It consumes both active and reactive power
5. It requires more maintenance because of running equipment
6. It requires starting mechanism for bringing the synchronous motor up to synchronous speed

8․ Under excited Synchronous phase modifier works as
a. shunt capacitor      b. series capacitor      c. shunt reactor
d. any of the above
Explain:
Synchronous phase modifier is basically a synchronous motor operating under no load and by adjusting the excitation it is used for controlling reactive power, so that power factor and voltage are controlled. If synchronous phase modifier is used under over excitation it works similar to a shunt capacitor delivering reactive power and absorbing leading reactive power. If synchronous phase modifier is used as under excitation it works similar to shunt reactor which absorbs lagging reactive power and delivers leading reactive power. This is used for Ferranti effect.

9․ Advantages of shunt compensation is/are
a. single unit can be used as both capacitance and inductor by adjusting the excitation
b. smooth voltage regulation is possible by controlling excitation
c. It requires less maintanance
d. all of the above
Explain:
Shunt compensation: 1. Two separate units are required, i.e. inductor and capacitor. 2. Step by step voltage regulation is possible 3. Cost of shunt compensation is low 4. It consumes only reactive power 5. It requires less maintenance because there is no running equipment 6. It does not requires starting mechanism