STUPIDSID
1 (a)
Give the merits and demerits of per unit system. Prove that the per-unit impedance of a transformer is the same regardless of the side from which it is viewed.
7 M
1 (b)
A generator is rated 1000 MVA, 33 kV. Its STAR connected winding has a reactance of 0.9 pu. Find: (a) Ohmic Value of reactance of winding if the generator is working in a circuit for which has bases are specified as 250 MVA, 22 kV. (b) The p.u. reactance of generator winding on the specified base.
7 M
2 (a)
With the simplifying assumptions explain the SC transient on a transmission line and hence prove that: \[ I_{mm}(max. possible)= 2 \left [ \sqrt{2V}/|Z| \right ]; \ i.e. \ Doubling \ Effect \]
7 M
2 (b) (i)
Classify different faults which occur in the power systems. Which of these are the most frequent?
4 M
Answer any two question from Q2 (b) or Q2 (c)
2 (b) (ii)
Explain different types of current limiting reactors.
3 M
2 (c)
For the Radial Network shown in figure 1, a 3-phase fault occurs at F. Determine the Fault Current and Line Voltage at 11 kV bus under fault conditions.
7 M
Answer any two question from Q3 (a), (b) or Q3 (c), (d)
3 (a)
Explain the ZBUS formulation techniques. Also mention all the modifications in ZBUS formation.
7 M
3 (a)
Discuss principle of symmetrical components. Derive the necessary equations to convert: (i) phase quantities into symmetrical components (ii) Symmetrical components in to phase quantities.
7 M
3 (b)
Figure 2 shows the one-line diagram of a simple Four-Bus system. Table 1 gives the line impedances identified by the buses on which these terminate. The Shunt admittance at all the buses is assumed to be negligible.
(a) Find Y BUS , assuming that the line shown dotted is not connected.
(b) What modifications need to be carried out in Y BUS if the line shown dotted is connected?
(a) Find Y BUS , assuming that the line shown dotted is not connected.
(b) What modifications need to be carried out in Y BUS if the line shown dotted is connected?
| Line, Bus-Bus | R, pu | X, pu |
| 1-2 | 0.05 | 0.15 |
| 1-3 | 0.10 | 0.30 |
| 2-3 | 0.15 | 0.45 |
| 2-4 | 0.10 | 0.30 |
| 3-4 | 0.05 | 0.15 |
7 M
3 (b)
A delta connected balanced resistive load is connected across an unbalanced three phase supply as shown in figure 3. With currents line A and B specified. Find the symmetrical components of line currents.
7 M
Answer any two question from Q4 (a), (b) or Q4 (c), (d)
4 (a)
Explain single line-to-ground fault. Write terminal conditions at fault location. Derive expression of fault current and draw the connection of sequence networks.
7 M
4 (b)
A 25 MVA, 11 kV alternator with solidly grounded neutral has a sub-transient (positive sequence) reactance of 0.2 p.u. the negative and zero sequence reactance are 0.3 and 0.1 p.u. respectively. Determine the Sub-transient current in the generator and the Line-Line voltages for the sub-transient conditions when a LG fault occurs at the generator terminals. Assume that before the occurrence of the fault, the generator is operating at no load at rated voltage. Ignore Resistance.
7 M
4 (c)
Explain line-to-line fault. Write terminal conditions at fault location. Derive expression of fault current and draw the connection of sequence networks.
7 M
4 (d) (i)
Why transient stability limit is lower than steady state stability limit?
4 M
4 (d) (ii)
Prove that the zero and negative sequence components of voltage are absent in a balanced three phase system.
3 M
Answer any two question from Q5 (a), (b) or Q5 (c), (d)
5 (a)
Describe the traditional technique and new approaches for improvement of transient stability limit of a power system.
7 M
5 (b)
Derive the power angle equation\[ P= \dfrac {E_GE_M}{X} \sin \delta \] with usual notations.
7 M
5 (c)
Explain in brief various methods of Control of voltage Profile in Power System. Explain each method in detail.
7 M
5 (d) (i)
What do you mean by infinite bus? What is meant by synchronizing of alternators?
3 M
5 (d) (ii)
Two alternators are operating in parallel. Explain the effect of increasing the excitation of one of the alternator.
4 M
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