B.E/ B.Tech. Degree Examination, November / December 2011

Sixth Semester

Electrical and Electronics Engineering

EE 2351 – Power System Analysis

(Regulation 2008)

Time: Three hours Maximum: 100 marks

Answer all questions

Part A – (10 × 2 = 20 marks)

1 . What is single line diagram?

2. How are the loads represented in reactance or impedance diagram?

3. What are the different types of buses in power systems? What are the quantities specified in each bus?

4. How are the disadvantages of Newton-Raphson method overcome?

5. What is the need for short circuit studies?

6. List the various types of shunt and series faults.

7. Define negative sequence impedance.

8. Name the faults which do not have zero sequence currents flowing.

9. Give an expression for swing equation. Explain each term along with their units.

10. State equal area criterion.

Part B – (5 × 16 = 80 marks)

11. (a) (i) The parameters of a 4-bus system are as under: Bus Code Line impedance (p.u) Charging admittance (p.u)

1 – 2 0.2 + j0.8 j0.02

2 – 3 0.3 + j0.9 j0.03

2 – 4 0.25 + j1.0 j0.04

3 – 4 0.2 + j0.8 j0.02

1 – 3 0.1 + j0.4 j0.01

Draw the network and find bus admittance matrix. (10)

(ii) A three phase, Δ-Y transformer with rating 100 KVA, 11 KV / 400 V has its primary and

secondary leakage reactance as 12 Ω / phase and 0.05 Ω / phase respectively. Calculate the

p.u. reactance of transformer. (6)

(OR)

(b) Determine Zbus for system whose reactance diagram is shown in given figure, where the

impedance is given in p.u. Preserve all the nodes.

12 (a) The one line diagram of three bus power system is shown in given figure,

Bus 1: Slack bus, Especified =

Bus 2: PV bus, , PG = 3 p.u

Bus 3: PQ bus, PL = 4 p.u, QL = 2 p.u.

Carry out one iteration of load flow solution by Gauss-Seidel method. Take Q limits of

generator 2 as 0 ≤ Q ≤ 4. Take α = 1.

(OR)

(b) (i) Draw the flow chart of fast decoupled load flow method. (10)

(ii) Briefly explain the importance of power flow analysis. (6)

13 (a) The given figure shows a generating station feeding a 132 KV system. Determine the total

fault current, fault level and fault current supplied by each alternator for a 3-phase fault at the

receiving end bus. The line is 200 Km long.

(OR)

(b) (i) What are the basic assumptions made in fault calculations? (6)

(ii) Explain how the fault current can be determined using Zbus with neat flow chart. (10)

14 (a) (i) The given figure shows a power system network. Draw the positive sequence network,

negative sequence network and zero sequence network. The system data is given

below. (8)

Equipment MVA rating Voltage rating X1 (p.u) X2 (p.u) X0 (p.u)

Generator G1 100 11 KV 0.25 0.25 0.05

Generator G2 100 11 KV 0.2 0.2 0.05

Transformer T1 100 11 / 230 KV 0.06 0.06 0.06

Transformer T2 100 11 / 220 KV 0.07 0.07 0.07

Line 1 100 220 KV 0.1 0.1 0.3

Line 2 100 220 KV 0.1 0.1 0.3

(ii) Derive an expression for fault current for a Line-Line fault. (8)

(OR)

(b) A 30 MVA 11 KV generator has Z1 = Z2 = j0.2 p.u, Z0 = j0.05 p.u. A line to ground fault

occurs on the generator terminals. Find the fault current and line to line voltages during limit

conditions. Assume that the generator neutral is grounded and that the generator is operating

at no load ad at rated voltage at the occurrence of fault.

15 (a) (i) A generator is operating at 50 Hz delivers 1.0 p.u power to an infinite bus through a

transmission circuit in which resistance is ignored. A fault takes place reducing the maximum

power transferable to 0.5 p.u whereas before the fault, this power was 2.0 p.u and after the

clearance of the fault, it is 1.5 p.u. By the use of equal area criterion, determine the critical

clearing angle. (10)

(ii) Discuss the methods by which the transient stability can be improved. (6)

(OR)

(b) Derive the swing equation of a single machine connected to an infinite bus system and

explain the steps of solution by Runge-Kutta method.

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