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Answer all parts of the following (2 marks each)
1. The function of speed changer is
(a) Change the speed of governor
(b) Limit the speed of governor
(c) Steady state power output of turbine*
(d) All of the above
Explanation: This part of the system is used to provide a constant power setting to the turbine in order to get a constant output under steady state condition.
2. 250 MW machine with an operating load of 125 MW. Let the change in load be 1% for 1% change in frequency (scheduled frequency = 50 Hz) then B is equal to
(a) 0.05 pu MW/Hz
(b) 0.01 pu MW/Hz*
(c) 0.1 pu MW/Hz
(d) None of the above
Explanation: (∂PD/∂f) = 1.25 / 0.5 = 2.5 MW/Hz
B = (∂PD/∂f)/Pr = 2.5/250 = 0.01 Pu MW/Hz
3. The change in real power P produces little effect on receiving end voltage because
(a) The voltage drop associated with this change is in phase with reference voltage
(b) The voltage drop associated with this change is in quadrature with reference voltage*
(c) The voltage drop associated with this change has on relation with reference voltage
(d) The voltage drop associated with this change is 180 degree with reference voltage
4. Mostly the high voltage transmission is provided by overhead lines due to
(a) Low cost*
(b) Low losses
(c) Easy installation
(d) All of the above
5. The power transmission capability of bipolar lines is approximately
(a) Same as that of 3-ph single circuit line*
(b) Same as that of 3-ph double circuit line
(c) Twice to that of 3-ph single circuit line
(d) Half as that of 3-ph single circuit line
6. Single line diagram of which of the following power system is possible?
(a) Power system with LG fault
(b) Balanced power system*
(c) Power system with LL fault
(d) Power system with LLG fault
Explanation: Only balanced power system can be represented by a single line diagram. Single line diagram is drawn on per phase basis. A power system with LLG, LG and LL faults becomes unbalanced and can not be represented in per phase basis.
7. A 200 bus power system has 160 PQ bus. For achieving a load flow solution by N-R in polar coordinates, the minimum number of simultaneous equation be solved is
(a) 359*
(b) 334
(c) 357
(d) 345
Explanation: Total buses = 200
PQ buses = 160
PV buses = 200 - 160 = 40
Slack bus = 1
Total number of equation = (40 - 1) x 1 + (160 x 2) = 359
8. A protection system engineer is planning to provide the complete protection, he can achieve this by ____.
(a) a two phase fault relays and three earth fault relays
(b) a two phase fault relays and two earth fault relays
(c) two phase fault relays and three earth fault relays
(d) three phase fault relays and two earth fault relays*
Explanation: For the complete protection of the power system, one can use 3 phase fault relays and two earth fault relays so that to cover the entire zone of operation.
9. If all the sequence voltages at the fault point in a power system are equal, then fault is ____.
(a) LLG fault*
(b) Line to Line fault
(c) Three phase to ground fault
(d) LG fault
Explanation: In double line to ground fault, all the sequence networks are connected in parallel. Therefore, all the sequence voltages at the fault point are equal. VR0 = VR1 = VR2 Where, VR0, VR1 and VR2 are sequence voltages.
10. Which of the following is not neglected during formation of reactance diagram from impedance diagram?
(a) Shunt component of Transformers
(b) Static loads
(c) Resistance of various power system components
(d) Reactance of alternators*
Explanation: Reactance diagram is drawn by the help of symmetrical network of various power system components by neglecting resistance of various components, static loads like induction motors and shunt component of Transformers.
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