Seat No.: ________ Enrolment No.

___________

GUJARAT TECHNOLOGICAL UNIVERSITY

PDDC - SEMESTER– VII (OLD) EXAMINATION – WINTER 2019
Subject Code:X70902 Date: 30/11/2019
Subject Name: Inter Connected Power System
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.

Q.1 (a) Explain cascade tripping and network islanding. 07

(b) Explain the necessity of interconnected power system. 07
Q.2 (a) Derive swing equation of synchronous machine. 07
(b) Derive Static Load Flow Equations (SLFE) from the first principle. Write it 07
in the rectangular or polar form.
OR
(b) Explain the Method of formation of Ybus using singular transformation method. 07
Q.3 (a) Write notes on load dispatch centre’s functioning. 07
(b) Compare GS method of load flow study with NR method. 07
OR
Q.3 (a) Derive transmission loss formula in terms B-coefficients. 07
(b) State the methods of Load Frequency Control and Explain bias tie line 07
Frequency Control.
Q.4 (a) What is Power system angle stability? Discuss steady state, Dynamic and 07
Transient Stability in a power system.
(b) Explain Step by Step method for stability analysis. 07
OR
Q.4 (a) In a system consisting of two generating units the incremental costs are 07
dF1/dP1 = 0.16P1 + 32 Rw/MWh, dF2/dP2 = 0.24P2 + 36 Rs/MWh
The system is operating on economic dispatch with P1 = P2 = 100 MW and
dPL/dP2 = 0.2. Find the penalty factor of plant 1
(b) With the help of neat diagram explain fly ball speed governing mechanism. 07
Q.5 (a) A certain power system network has the following data. 07
Bus code Line reactance/km Shunt susceptance/km Length(km)
1-2 j0.001 j0.0016 100
2-3 j0.001 j0.0016 200
1-3 j0.001 j0.0016 250
Compute YBUS for the network neglecting line resistance.
(b) Explain point by point method of stability. State the assumptions made. 07
OR
Q.5 (a) Explain the classification of buses. 07
(b) Explain equal area criteria of stability. 07

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1
 Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
PDDC - SEMESTER–VII - EXAMINATION – SUMMER 2018
Subject Code:X70902 Date:01/05/2018
Subject Name:Inter Connected Power System
Time:02:30 PM to 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.

Q.1 (a) Explain the function and duties of Load dispatch centre and also explain 07
Islanding.
(b) Explain the comparison between GS and NR method. 07
Q.2 (a) Explain Primitive and Bus Incidence Matrix and also classification of buses. 07
(b) Obtain Z-bus for the 4-bus sample system given in figure 1. The series 07
impedances of each line are given in table 1. Reference bus is represented by R.
No line is mutually coupled.

Line Bus-code Impedance Type of modification

No. (Z)
1 R-1 0.6 1 (New bus to reference)
2 R-2 0.5 1 ( New bus to reference)
3 2-3 0.5 2 (New bus to old bus)
4 1-3 0.25 4 (Old bus to old bus)

Table 1
1 3

R 2

Fig 1.
OR
(b) Two units of the system have the following cost curves. 07
F(Pg1) = 0.05 Pg12 + 22Pg1 + 120 Rs/h
F(Pg2) = 0.06 Pg22 + 16 Pg2 + 120 Rs/h
Where Pg is in MW. Both the unit operates at all times and the maximum and
minimum loads on each unit are 100 MW and 20 MW, respectively. Determine
the economic operating schedule of the plants for load of 80 MW, neglecting
the transmission line losses.
Q.3 (a) Explain GS method for load flow solution. 07
(b) Derive the swing equation for rotor dynamics of synchronous machines. 07
OR
Q.3 (a) Explain the different methods of frequency control. 07
(b) Explain the different method of improving transient stability. 07
Q.4 (a) Explain the unit commitment and derive the transmission loss formula ( Kron’s 07
Method)
(b) Explain the method of Y-bus matrix formation using singular transformation 07
1
 method.
OR
Q.4 (a) A 50 Hz, four pole turbogenerator rated 50 MVA, 11 kV has an inertia constant 07
of 4.0 MJ/MVA.
(a) Find the stored energy in the rotor at synchronous speed.
(b) if the mechanical input is suddenly raised to 40 MW for an electrical load of
25 MW , find rotor acceleration , neglecting mechanical and electrical losses.
(b) Explain the effect of sudden change in mechanical input with refer to equal area 07
criteria.
Q.5 (a) Explain the turbine speed governing system with schematic diagram. 07
(b) Explain the classification of power system stability studies. 07
OR
Q.5 (a) Compare the NR method with decoupled method refer to Jacobean Matrix. 07
(b) Explain the advantages of interconnection and also explain cascade tripping 07

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2
 Seat No.: ________ Enrolment No.___________

GUJARAT TECHNOLOGICAL UNIVERSITY

PDDC - SEMESTER–VII EXAMINATION – WINTER 2018
Subject Code:X70902 Date: 19/11/2018
Subject Name: Inter Connected Power System
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.

MARKS
Q.1 (a) Explain advantages and dis advantages of Interconnected Power System. 03
(b) Define: (1) Tree and Co Tree 04
(2) Planner and Non Planner Graph
(c) Obtain YBUS matrix for the system shown in figure .The Shunt admittances at all the buses are assumed 07
to be negligible. The impedances between the connected two buses are shown in figure.

Q.2 (a) Explain: Bus Incidence matrix 03

(b) Using suitable example explain Primitive admittance Matrix in load flow analysis of power system. 04
(c) Describe the methods of voltage control adopted in power system. 07
OR
(c) Explain cascade tripping and network islanding. 07
Q.3 (a) Discuss the procedure for solving the swing equation using point by point method. 07

(b) Prove that Md2 δ/dt2 = Pm-Pe, Pm is mechanical power, Pe is electromagnetic power and M is angular 07
momentum
1
 OR
Q.3 (a) Define various stability Limits. 03
(b) Explain Equal Area Criterion with suitable example 04
(c) Compare GS and NR method for load flow 07
Q.4 (a) Explain the importance of Slack bus in power system analysis. 03
(b) List the factors affects the transient Stability Limit in brief 04
(c) Explain the functions of load dispatch centre and its distribution in India in detail. 07
OR
Q.4 (a) Sate the advantages of Ybus over Zbus. 03
(b) Explain the Unit commitment. 04
(c) Derive the expression for B-coefficients. 07

Q.5 (a) Explain the various types of buses used in load flow analysis. 03
(b) Describe the concept of steady state stability in brief. 04
(c) With the help of a neat diagram explain turbine speed governing mechanism 07
OR
Q.5 (a) State the objectives of Load flow study in power system. 03
(b) Derive relation between the M and H. 04
(c) A two pole 50 Hz , 60 MVA turbo generator has a moment of inertia of 9 ×103 kg-m2 . Calculate (i) the 07
kinetic energy in MJ. (ii) Inertia constant M and H (iii)Inertia constant at 50 MVA.

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2
Seat No.: ________ Enrolment No.___________

GUJARAT TECHNOLOGICAL UNIVERSITY

PDDC SEMESTER VII– EXAMINATION – SUMMER 2017

Subject Code: X70902 Date: 01/05/2017

Subject Name: Interconnected Power Systems
Time: 02.30PM to 05.00PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Symbols have their usual meanings

Q.1
(a) Explain the process of formulation of YBUS matrix using singular transformation (7)
(b) Explain the concept of interconnection. State the advantages and disadvantages (7)
interconnections.

Q.2
(a) Derive static load flow equations (SLFE). Also state the assumptions made in (7)
in approximate load flow and explain how SLFE’s get modified due to these
assumptions.
(b) Explain in brief, how unit commitment problem can be solved using dynamic (7)
programming method
OR
(b) With the help of neat diagram explain fly ball speed governing mechanism (7)

Q.3
(a) With the help flowchart explain GS method of load flow (8)
(b) Compare NR and GS method of load flow (6)
OR
Q.3
(a) A certain power system network has the following data (7)
Bus code Line reactance/km Shunt susceptance/km Length(km)
1-2 j0.001 j0.0016 100
2-3 j0.001 j0.0016 200
1-3 j0.001 j0.0016 250
Compute YBUS for the network neglecting line resistance
(b) Derive the expression for most economical operation taking transmission losses into account (7)

Q.4
(a) Derive transmission loss formula in terms B-coefficients (8)
(b) Two generators rated 200 MW and 400 MW are operating in parallel. The droop (6)
characteristics of their governors are 4% and 5% from no-load to full load respectively from
no-load to full load. Assuming that the generators are operating at 50 Hz at no-load, how a
load of 600 MW would be shared between them, and what would be the system frequency?
 OR
Q.4
(a) Starting from the first principles, derive swing equation (8)
(b) Explain equal area criteria of stability (6)

Q.5
(a) Two turbo-alternators with ratings given below are interconnected via a short transmission (7)
line
Machine 1: 4 pole, 50 Hz, 60 MW, pf 0.80 lagging, moment of inertia 30,000 kg-m2
Machine 2: 2 pole, 50 Hz, 80 MW, pf 0.85 lagging, moment of inertia 10,000 kg-m2
Calculate the inertia constant of the single equivalent machine on a base of 200 MVA
(b) Explain the significance of synchronous coefficient of the machine in steady state stability (7)
analysis
OR
Q.5
(a) Explain numerical solution of swing equation (7)
(b) Discuss the methods employed to improve transient and steady state stability (7)

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