Merged Document

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CODE No.:10BT70202

SREE VIDYANIKETHAN ENGINEERING COLLEGE (An Autonomous Institution, Affiliated to JNTUA, Anantapur)

IV B.Tech I Semester (SVEC10) Supplementary Examinations June - 2014 POWER SYSTEM OPERATION AND CONTROL

[ Electrical and Electronics Engineering ]

Time: 3 hours Max Marks: 70 Answer any FIVE questions

All questions carry equal marks

1. a) What is an incremental fuel cost? How is it used in thermal plant operation? b) Name the components of production cost and explain.

2. Give algorithm for economic allocation of generation among generators of a thermal system taking into account transmission losses. Give steps for implementing this algorithm and also derive necessary equations.

3. Explain about Hydro thermal co-ordination with necessary equations.

4. a) Explain the mathematical modeling of speed governing system with block diagram approach. b) Discuss briefly about small signal transfer function.

5. Explain the dynamic response of load frequency control of an isolated power system with a neat block diagram. Draw the plots of change in frequency with respect to time with and without making approximations in the analysis.

6. a) Explain how the tie-line power deviation can be incorporated in two-area system block diagram. b) What are the features of the dynamic response of a two-area system for step load disturbances?

7. a) Explain different methods of voltage control with neat block diagrams. b) Compare the different types of compensating equipment for transmission systems.

8. What are the various entities of deregulated power system and explain in detail about their functional operations.

CODE No.:10BT70202

SREE VIDYANIKETHAN ENGINEERING COLLEGE(An Autonomous Institution, Affiliated to JNTUA, Anantapur)

IV B.Tech I Semester (SVEC10) Regular Examinations January - 2014POWER SYSTEM OPERATION AND CONTROL

[ Electrical and Electronics Engineering ]Time: 3 hours Max Marks: 70

Answer any FIVE questionsAll questions carry equal marks

1. a) Explain the input output characteristics of thermal power plants.b) Explain different generation scheduling methods in steam plants. Explain their merits and demerits.

2. a) Assuming any relevant data and notation, derive the transmission loss formula.b) Discuss about the optimum allocation of generators without line losses.

3. Describe different methods for solving hydro thermal scheduling.

4. a) Explain the mathematical modeling of speed governing system with block diagram approach.b) Discuss briefly about small signal transfer function.

5. a) Briefly explain the control area concept and control area error.b) A power system has load of 1250 MW at 50 Hz. If 50 MW load is tripped, find the steady state frequency deviation when i) there is no speed control ii) the system has a reserve of 200 MW spread over 500 MW of generation capacity with 5 % regulation on this capacity. All the generators are operating with valves wide open. Due to dead band, only 80 % of governors respond to load change. Assume load damping constant B=1.5.

6. Two areas are connected via an inter tie line. The load at 50 Hz, is 15000 MW in area 1 and 35000 in area 2. Area 1 is importing 1500 MW from area 2. The load damping constant in each area is B=1.0 and the regulation R=6 % for all units. Area 1 has a spinning reserve of 800 MW spread over 4000 MW of generation capacity and area 2 has a spinning reserve of 1000 MW spread over 10000 MW generation. Determine the steady state frequency, generation and load of each area and tie-line power for:a) Loss of 1000 MW in area 2, with no supplementary control.b) Loss of 1000 MW in area 2, with supplementary controls provided on generators with reserve.

7. A 3Φ feeder having a resistance of 3Ω and reactance of 10Ω supplies a load of 2 MW at 0.85 p.f. lagging. The receiving end voltage is maintained at 11 kV by means of static condenser drawing 2.1 MVAR from the line. Calculate the sending end voltage and power factor. What is the regulation and efficiency of the feeder?

8. a) Define Deregulation of Power systems and explain the need for deregulation in Power systems.b) What is the role of modern technology in deregulated power market?

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POWER SYSTEM OPERATION AND CONTROL

Time: 3 hours Max Marks: 80Answer any FIVE Questions

All Questions carry equal marks? ? ? ? ?

1. (a) Discuss in detail about incremental heat rate curve and cost curve?

(b) Write the expression for hourly loss of economy resulting from error in incre-mental cost representation. [8+8]

2. What is load factor and loss factor and state the criterion for economic operationof power system? [16]

3. (a) Explain the operation of two generating stations connected by a tie line.

(b) Explain about Maximum hydro efficiency method of hydro thermal scheduling.[8+8]

4. Briefly explain swing equation with simplified diagram. [16]

5. (a) With first order approximation explain the dynamic response of an isolatedpower system for load frequency control.

(b) Two generating units rated for 250 MW and 400 MW have governor speedregulations of 6.0 and 6.4 percent, respectively, from no load full load. Theyare operating in parallel and share a load of 500 MW. Assuming the freegovernor action, determine the load shared by each unit. [8+8]

6. (a) What are the features of the dynamic response of a two area system for stepload disturbances?

(b) What are the considerations in selecting the frequency bias parameters? [8+8]

7. Explain the various criteria by which the performance of the system can judged incase of two area load frequency control with integral action. [16]

8. Explain the reasons for variations of voltages in power systems and explain any onemethod to improve the voltage profile. [16]

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R5Code No: R5410204

IV B.Tech I Semester6(R05) Supplementary Examinations, November 2011

(Electrical & Electronics Engineering)

Sonti Soft

Rectangle

Code: R5410204 R05 IV B.Tech I Semester (R05) Supplementary Examinations, May 2012

POWER SYSTEM OPERATION & CONTROL (Electrical & Electronics Engineering)

Time: 3 hours Max Marks: 80 Answer any FIVE Questions

All Questions carry equal marks *****

1. (a) Explain the following terms with reference to power plants, heat input - power output curve. Heat rate input, incremental input, generation cost and production cost.

(b) What are the methods of scheduling of generation of steam plants? Explain their merits and demerits.

2. (a) What is incremental transmission loss and derive the general transmission loss formula. (b) 150 MW, 220MW, 220MW are the ratings of three units, located in a thermal power station. Their

respective incremental cost are given by the following equations dc1/dp1 = Rs (0.11p1 + 12) dc2/dp2 = Rs (0.095P2 +14) dc3/dp3 = Rs (0.1p3 + 13) Where p1, p2 and p3 are the loads in MW. Determine the economical load allocation between the units, when the total load on the system is (i) 300MW. (ii) 450MW.

3. Explain optional load flow solution without inequality constraints.

4. Draw the block diagram, turbine and synchronous generator indicating their transfer functions. For a step disturbance of ∆P D, obtain the response of “increment in frequency” making suitable assumptions for with and without PI controllers.

5. (a) Explain how the variation of load effects the frequency of a power system. (b) Two generators rated 200MW and 400MW are operating in parallel. The droop characteristics of

their governors are 4% and 5% respectively. From no-load to full-load. Assuming that the generators are operating at 50Hz at no – load, how would a load of 600MW be shared between them? Assume free governor operation, repeat the problem if both the governors have a drop of 4%.

6. (a) Explain load frequency control problem in a multi area power system. (b) Two generating stations A & B have full load capacities of 500MW and 210 MW respectively. The

interconnector connecting the two stations has a motor generator set (plant ‘C’) near station. A of full load capacity of 50MW percentage changes of speed of A,B and C are 5,4 and 2.5 respectively. The loads on bus bars A and B are 250MW and 100MW respectively. Determine the load taken by set C and indicate the direction in which the energy is flowing.

7. A 11KV supply bus bar is connected to a 11/132 KV, 100MVA, 10% reactance, transformer. The

transformer feeds a 132 KV transmission link consisting of an overheat line of impedance (0.014 + j 0.04) p.u and a cable of impedance (0.03 + j 0.01) p.u in parallel if lagging calculate the power and reactive power carried by the cable and line. All p.u values relate to 100MVA and 132 KV bases.

8. Explain clearly what you mean by compensation of line and discuss briefly, different methods of

compensation.

*****

Code No: R5410204 1IV B.Tech I Semester(R05) Regular&Supplementary Examinations, December 2009

POWER SYSTEM OPERATION AND CONTROL(Electrical & Electronic Engineering)



1. (a) What is an incremental fuel cost? How is it used in thermal plant operation?

(b) Name the components of production cost and explain. [8+8]

2. The fuel cost functions in Rs./hr. for two thermal plants are given by

C1=420+9.2P1+0.004P12, 100 ≤ P2≤200

C2=350+8.5P2+0.0029P22, 150≤P3≤500

Where P1, P2, P3 are in MW and plant outputs are subjected to the following limits, Determine the optimalscheduling of generation if the total load is 640.82MW. Estimate value of λ = 12Rs. /MWhPL(pu) = 0.0346P1(pu)

2+0.00643 P2(pu)2. [16]

3. Derive the co-ordination equation for the optimal scheduling of hydro-thermal interconnected power plants. [16]

4. Two generators rated 100 MW and 200 MW are operating in parallel. The droop characteristics of their governorsare 3% and 5% respectively from no load to full load. Assuming that the generators are operating at 50 Hz at noload, how would a load of 300 MW be shared between them? What will be the system frequency at this load?Assume free governor operation. Repeat the problem if both the governors have a droop of 3%. [16]

5. (a) With a neat diagram explain the process of speed governing system.

(b) Two generators are rated at 120 MW and 250 MW are operating in parallel. The governor settings on themachines are such that they have 4 % and 3% droops. Determine

i. the load taken by each machine for a load of 200 MW

ii. The percentage adjustment in the no load speed to be made by the speeder motor if the machines areto share the load equally. [8+8]

6. Two areas are connected via an inter tie line. The load at 50 Hz, is 15000 MW in area 1 and 35000 in area 2.Area 1 is importing 1500 MW from area 2. The load damping constant in each area is B=1.0 and the regulationR=6 % for all units. Area 1 has a spinning reserve of 800 MW spread over 4000 MW of generation capacityand area 2 has a spinning reserve of 1000 MW spread over 10000 MW generation. Determine the steady statefrequency, generation and load of each area and tie-line power for

(a) Loss of 1000 MW in area2, with no supplementary control.

(b) Loss of 1000 MW in area2, with supplementary controls provided on generators with reserve. [8+8]

7. The single area control system has the following data:TP =10 sec, Tg = 0.3 sec, Tt=0.2 sec, KP =200 Hz/pu MW, R=6 Hz/pu MW,∆PD=0.5 pu MW, Ki=0.5.Compute the time error caused by a step disturbance of magnitude 0.5 pu (as given above). Prove, in particular,that the error is reduced by increasing the given Ki. Express the error in seconds and cycles if the systemfrequency is 50 Hz. [16]

8. A 3φ feeder having a resistance of 3Ω and reactance of 10Ω supplies a load of 2 MW at 0.85 p.f. lagging. Thereceiving end voltage is maintained at 11 kV by means of static condenser drawing 2.1 MVAr form the line.Calculate the sending end voltage and power factor. What is the regulation and efficiency of the feeder?

[16]

Code No: R5410204 1? ? ? ? ?





1. A constant load of 300 MW is supplied by two 200 MW generators 1 and 2, for which the respective incrementalfuel costs are:d C1

d PG1= 0.10 PG1 + 20.0

d C2d PG2

= 0.12 PG2 + 15.0With power PG in MW and costs C in Rs/hr. Determine:

(a) The most economical division of load between the generators.

(b) The saving in Rs./ day there by obtained compared to equal load sharing between two generators. [16]

2. (a) Explain with diagram the physical interpretation of co-ordination equation.

(b) Derive the condition for the optimum scheduling of generation of units in a steam power plant. [8+8]

3. Write the advantages of operation of hydro thermal combinations. [16]

4. Two generators rated 200 MW and 400 MW are operating in parallel. The droop characteristics of their governorsare 4% and 5% respectively from no load to full load. Assuming that the generators are operating at 50 Hz atno load, how would a load of 600 Mw be shared between them? What will be the system frequency at this load?Assume free governor operation. Repeat the problem if both the governors have a droop of 4%. [16]

5. A power system has load of 1250 MW at 50 Hz. If 50 MW load is tripped, find the steady state frequencydeviation when

(a) there is no speed control

(b) the system has a reserve of 200 MW spread over 500 MW of generation capacity with 5 % regulation onthis capacity.

All the generators are operating with valves wide open. Due to dead band only 80 % of governors respond toload change. Assume load damping constant B=1.5. [16]

6. (a) Explain how the tie-line power deviation can be incorporated in two-area system block diagram.

(b) Two areas of a power system network are interconnected by a tie-line, whose capacity is 500 MW, operatingat a power angle of 350. If each area has a capacity of 5000 MW and the equal speed regulation of 3 Hz/PuMW, determine the tie line power deviation for step change in load of 85 MW occurs in one of the areas.Assume that both areas have the same inertia constants of H = 4 sec. [8+8]

7. Obtain an expression for steady state response of a load frequency controller with integral control. How it isdifferent from with out integral control. [16]

8. (a) Write short notes on compensated and uncompensated transmission lines.

(b) Explain briefly about the shunt and series compensation of transmission systems. [8+8]

? ? ? ? ?





1. (a) Explain input - output characteristics of thermal power stations.

(b) Define in detail cost curve of thermal stations. [8+8]

2. What is load factor and loss factor and state the criterion for economic operation of power system? [16]

3. Write algorithm for Mathematical Formulation for Hydro thermal scheduling. [16]

4. A 2- pole, 50hz, 11 KV, turbo - generator has a rating of 60MW, Power factor of 0.85 lagging. Its rotor has amovement of inertia of 8800 kg - m2 . Calculate its inertia constant in MJ / MVA and its momentum in MJ - s./electrical degree.

[16]

5. Determine the primary ALFC loop parameters for a for a control area with the following data:Total generation capacity = 2500 MWNormal operating load =1500 MWInertia constant=5 kW-seconds per kVA; Load damping constant, B=1 %; frequency, f=50 Hz; and Speedregulation, R=2.5 Hz / p.u MW. [16]

6. Two areas are connected via an inter tie line. The load at 50 Hz, is 15000 MW in area 1 and 35000 in area 2.Area 1 is importing 1500 MW from area 2. The load damping constant in each area is B=1.0 and the regulationR=6 % for all units. Area 1 has a spinning reserve of 800 MW spread over 4000 MW of generation capacityand area 2 has a spinning reserve of 1000 MW spread over 10000 MW generation. Determine the steady statefrequency, generation and load of each area and tie-line power for

(a) Loss of 1000 MW in area 1, with no supplementary control.

(b) Loss of 1000 MW in area 1, with supplementary controls provided on generators with reserve. [16]

7. Draw the block diagram of a power system showing the governor, turbine and synchronous generator, indicatingtheir transfer functions. For a step disturbance of ∆PD, obtain the response of “increment in frequency”, makingsuitable assumptions.

(a) Without proportional plus integral controller and

(b) With proportional plus integral control. [16]

8. (a) A single-phase motor connected to a 230 V, 50 Hz supply takes 30 A at a p.f of 0.7 lag. A capacitor isshunted across the motor terminals to improve the p.f to 0.9 lag. Determine the capacitance of the capacitorto be shunted across the motor terminals.

(b) Explain the specifications of load compensation. [8+8]

? ? ? ? ?





1. The fuel cost functions in Rs./hr. for three thermal plants are given byC1 = 400+8.4P1+0.006P1

2, 100 ≤ P1 ≤ 600C2 = 600+8.93P2+0.006P2

2, 60≤P2 ≤ 300C3 = 650+6.78P3+0.004P3

2, 300 ≤ P3 ≤ 650Where P1, P2, P3 are in MW. Neglecting line losses and including generator limits, determine the optimalgeneration scheduling Where PD = 550MW. [16]

2. 100 MW, 150 MW and 280 MW are the ratings of three units located in a thermal power station. Their respectiveincremental costs are given by the following equations:dc1/dp1 = Rs(0.15p1 + 12);dc3/dp3 = Rs(0.21p3 + 13)dc2/dp2 = Rs(0.05p2 + 14)Where P1, P2 and P3 are the loads in MW. Determine the economical load allocation between the three units,when the total load on the station is 300 MW.

[16]

3. .Discuss optimal power flow procedures with its inequality constraints, and how to handle dependent variableswith penalty function. [16]

4. Discus in detail the following components of excitation system.

(a) Error Amplifier

(b) SCR Power Amplifier

(c) Main Exciter and

(d) Alternator. [4+4+4+4]

5. (a) Explain the concept of control area in a load control problem.

(b) Derive the expression for the frequency deviation, when a step load disturbance occurs in a single controlarea. [8+8]

6. In the actual block diagram of a two area interconnected system, the system 2 represents a system so large thatit is effectively an “infinite bus”. The inertia constant M2 is much greater than inertia constant M1 and thefrequency deviation in system 2 is zero. Draw a block diagram including tie-line between the areas 1 and 2.What is the transfer function for a load change in area 1 and the tie flow?

[16]

7. Discuss in detail the economic dispatch control in a single area load frequency control. [16]

8. Explain the reasons for variations of voltages in power systems and explain any one method to improve thevoltage profile. [16]

? ? ? ? ?

Code No: RR410204 RRIV B.Tech I Semester(RR) Supplementary Examinations, May/June 2010




1. (a) What is an incremental fuel cost? How is it used in thermal plant operation?(b) Name the components of production cost and explain. [8+8]

2. (a) Incremental fuel cost in Rupees per mega watt hour for two units comprising a plant are givenby the following equations.dc1dp1

= .012p1+21; dc2dp2

= .01p1+18;Assume that both units are operating at all times, that total load varies from 40 to 200 MW andthe maximum and minimum loads on each unit are to be 125 and 20 MW respectively. Find theincremental fuel cost & the allocation of loads between units for the minimum cost of varioustotal loads. Derive the formula used.

(b) Discuss the costs associated with hydro plants. [10+6]

3. Using steepest descent method obtain the optimal power flow solution with controlled and uncontrolledparameters. [16]

4. Making suitable assumptions, derive the T.F.of syn generator and the steam turbineset. [16]

5. A control area has a total rated capacity of 10,000MW. The regulation R for all the units in the areain 2Hz/pu MW. A 1% change in frequency causes a 1% change in load. If the system operates at halfof the rated capacity and the load increases by 2%

(a) Find the static frequency drop(b) If the speed governor loop were open, what would be the frequency drop. Derive the formula

used. [16]

6. (a) Explain tie line bias control for multi area power system.(b) Two power stations A & B each have regulation (R) of 0.1 p u (on respective capacity bases) and

stiffness K of 1.0 p. u. The capacity of system A is 1500 MW & of B 1000 MW. The two systemsare interconnected through a tie line and are initially at 60 Hz. If there is 100 MW load changein system A, calculate the change in the steady-state values of frequency and power transfer P12

without the participation of governor control. [7+9]

7. (a) Explain about the losses that occur due to VAR flow in power systems.(b) Explain how the generators act as VAR sources in a power network. [8+8]

8. Explain clearly what do you mean by compensation of line and discuss briefly different methods ofcompensation. [16]

? ? ? ? ?

Code No: RR410204 Set No. 1

IV B.Tech I Semester Regular Examinations, November 2007POWER SYSTEM OPERATION AND CONTROL

(Electrical & Electronic Engineering)Time: 3 hours Max Marks: 80

Answer any FIVE QuestionsAll Questions carry equal marks

⋆ ⋆ ⋆ ⋆ ⋆

1. (a) Explain the following terms with reference to power plants: Heat input -power output curve, Heat rate input, Incremental input, Generation cost andProduction cost.

(b) What are the methods of scheduling of generation of steam plants? Explaintheir merits and demerits? [9+7]

2. (a) Incremental fuel cost in Rupees per mega watt hour for two units comprisinga plant are given by the following equations.dc1dp1

= .012p1+21; dc2dp2

= .01p1+18;Assume that both units are operating at all times, that total load varies from40 to 200 MW and the maximum and minimum loads on each unit are to be125 and 20 MW respectively. Find the incremental fuel cost & the allocationof loads between units for the minimum cost of various total loads. Derive theformula used.

(b) Discuss the costs associated with hydro plants. [10+6]

3. Give the computational procedure for optimal power flow with out in equalityconstraints. [16]

4. Making suitable assumptions, derive the T.F.of syn generator and the steam tur-bineset. [16]

5. (a) Derive the generator load model and represent it by a block diagram.

(b) Consider the block diagram model of LFC given in figure 5b. Make the fol-lowing

approximation:

(1 + sTsg)(1 + sTt) = 1 + (Tsg + Tt)s = 1 + sTeq

Solve for ∆f(t) with parameters given below. Given ∆Pd = 0.01 pu

Teq = 0.9 s; Tps= 20 s; KsgKt= 1; Kps = 100; R = 3. [16]

1 of 2


Figure 5b

6. Give a typical block diagram for a two-area system inter connected by a tie line andexplain each block. Also deduce relations to determine the frequency of oscillationsof tie line power and static frequency drop. List out assumptions made. [16]

7. Find the rating of synchronous compensator connected to the tertiary winding of a132 kV star connected, 33 kV star connected, 11 kV delta connected three windingtransformer to supply a load of 66 MW at 0.8 power factor lagging at 33 kV acrossthe secondary. Equivalent primary and tertiary winding reactances are 32 ohm and0.16 ohm respectively while the secondary winding reactance is negligible. Assumethat the primary side voltage is essentially constant at 132 kV and maximum ofnominal setting between transformer primary and secondary is 1:1.1. [16]

8. Explain clearly what do you mean by compensation of line and discuss brieflydifferent methods of compensation. [16]

⋆ ⋆ ⋆ ⋆ ⋆

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⋆ ⋆ ⋆ ⋆ ⋆

1. (a) Explain how the incremental production cost of a thermal power station canbe determined.

(b) Explain the various factors to be considered in allocating generation to differ-ent power stations for optimum operation. [8+8]

2. Give algorithm for economic allocation of generation among generators of a thermalsystem taking into account transmission losses. Give steps for implementing thisalgorithm, and also derive necessary equations. [16]

3. Write short notes on:

(a) Equations of Load flow.

(b) Solving of Load flow equations. [16]


5. (a) Derive the generator load model and represent it by a block diagram.

(b) Consider the block diagram model of LFC given in figure 5b. Make the fol-lowing

approximation:

(1 + sTsg)(1 + sTt) = 1 + (Tsg + Tt)s = 1 + sTeq

Solve for ∆f(t) with parameters given below. Given ∆Pd = 0.01 pu

Teq = 0.9 s; Tps= 20 s; KsgKt= 1; Kps = 100; R = 3. [16]

Figure 5b

6. (a) Draw the block diagram representation of load frequency control.

1 of 2


(b) For two-area load frequency control with integral controller blocks, derive anexpression for steady values of change in frequency and tie line power forsimultaneously applied unit step load disturbance inputs in the two areas.

[7+9]

7. (a) Discuss in detail about the generation and absorption of reactive power inpower system components.

(b) A load of (15 +j10) MVA is supplied with power from the busbars of a powerplant via a three phase 110 kV line, 100 km lagging. The transmission line isrepresented by π-model and has the following parameters.R= 26.4 ohms, X = 33.9 ohms, B = 219× 10−9 mhoVoltage across the power plant bus bars V1 = 116 kV. Find the power consumedfrom the power plant bus bars. [8+8]

8. A three(S)phase transmission line has resistance and inductive reactance of 25 Ωand 90 Ω respectively. With no load at the receiving end a synchronous compensatorthere takes a current lagging by 900, the voltage at the sending end is 145 kV and132 kV at the receiving end. Calculate the value of the current taken by thecompensator. When the load at the receiving end is 50 MW, it is found that theline can operate with unchanged voltages at sending and receiving ends, providedthat the compensator takes the same current as before but now leading by 900.Calculate the reactive power of the load. [16]

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⋆ ⋆ ⋆ ⋆ ⋆

1. (a) Describe in detail, with suitable examples, the methods of optimum schedulingof generation of power from a thermal station.

(b) What is Production cost of power generated and incremental fuel rate?

(c) Write the expression for hourly loss of economy resulting from error in incre-mental cost representation. [6+5+5]

2. (a) Discuss and define the loss formula coefficients.

(b) What is the objective in economic scheduling? [8+8]

3. Discuss the optimization of power flow with suitable cost function without inequal-ity constraints. [16]

4. (a) Explain the necessity of maintaining a constant frequency in power systemoperation.

(b) Two generators rated 200 MW and 400 MW are operating in parallel. Thedroop characteristics of their governors are 4% and 5% respectively from noload to full load. Assuming that the generators are operating at 50 Hz at noload, how would a load of 600 Mw be shared between them? What will be thesystem frequency at this load? Assume free governor operation. Repeat theproblem if both the governors have a droop of 4%. [6+10]

5. Draw the block diagram of a power system showingthe governor, turbine andsyn.generator, indicating their transfer functions. For a step disturbance of ∆PD, obtain the response of “increment in frequency”, making suitable assumptions.

(a) Without proportional plus integral controller, and

(b) With proportional plus integral control. [16]

6. (a) What is load frequency control problem in a 2-area power system? Why is itessential to maintain constant frequency in an inter-connected power system?

(b) Two power stations A & B are inter connected by tie line and an increasein load of 250 MW on system B causes a power transfer of 150 MW from Ato B. When the tie line is open the frequencies of system A is 50 c/s and ofsystem B is 49.5c/s. Determine the values of KA & KB which are the powerfrequency constants of each generator. [8+8]

7. (a) Explain about the losses that occur due to VAR flow in power systems.

(b) Explain how the generators act as VAR sources in a power network. [8+8]

1 of 2



⋆ ⋆ ⋆ ⋆ ⋆

2 of 2





⋆ ⋆ ⋆ ⋆ ⋆

1. (a) Explain the following terms with reference to power plants: Heat input -power output curve, Heat rate input, Incremental input, Generation cost andProduction cost.

(b) What are the methods of scheduling of generation of steam plants? Explaintheir merits and demerits? [9+7]

2. (a) Develop the loss formula coefficients for a two plant system. State the as-sumptions made.

(b) The transmission loss coefficients in p.u. on a base of 100 MVA are given by

0.009 − 0.001 − 0.002−0.001 0.0015 − 0.003−0.002 − 0.003 0.025

The three plants, A, B and C supply powers of PA = 100MW, PB = 200MW,PC= 300MW, into the network. Calculate the transmission loss in the networkin MW and the incremental losses with respect to plants A,B,C. [7+9]

3. Explain how the load flow equations are solved using gauss-seidel method. [16]

4. (a) With a neat diagram, explain briefly different parts of a turbine speed gov-erning system.

(b) Two generators rated 200 MW and 400 MW are operating in parallel. Thedroop characteristics of their governors are 4% and 5% respectively from noload to full load. The speed changers are so set that the generators operateat 50 Hz sharing the load of 600 MW in the ratio of their ratings. If the loadreduces to 400 MW, how will it be shared among the generators and what willthe system frequency be? [8+8]

5. (a) Explain the concept of “control area” in the load frequency control of a powersystem.

(b) Show how the steady state error of frequency in a typical load frequency controlof a power system is reduced to zero. [8+8]

6. Two power stations A & B each have regulation (R) of 0.1 p u (on respectivecapacity bases) and stiffness K of 1.0 p. u. The capacity of system A is 1500 MW& of B 1000 MW. The two systems are interconnected through a tie line and areinitially at 60 Hz. If there is 100 MW load change in system A, calculate the changein the steady-state values of frequency and power transfer P12 (with and withoutthe participation of governor control). [16]

1 of 2


7. (a) Discuss in detail about the generation and absorption of reactive power inpower system components.

(b) A load of (15 +j10) MVA is supplied with power from the busbars of a powerplant via a three phase 110 kV line, 100 km lagging. The transmission line isrepresented by π-model and has the following parameters.R= 26.4 ohms, X = 33.9 ohms, B = 219 × 10−9 mhoVoltage across the power plant bus bars V1 = 116 kV. Find the power consumedfrom the power plant bus bars. [8+8]

8. What is load compensation? Discuss its objectives in power system. [16]

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2 of 2


IV B.Tech I Semester Supplimentary Examinations, November 2008POWER SYSTEM OPERATION AND CONTROL



⋆ ⋆ ⋆ ⋆ ⋆

1. Explain the problem of scheduling hydro - thermal power plants. What are theconstraints in the problem? [16]

2. (a) Derive the conditions to be satisfied for economic operation of a loss less powersystem.

(b) 150 MW, 220 MW and 220 MW are the ratings of three units located in athermal power station. Their respective incremental costs are given by thefollowing equations:dc1/dp1

= Rs(0.11p1 + 12);

dc3/dp3 = Rs(0.1p3 + 13)dc2/dp2 = Rs(0.095p2 + 14)Where P1, P2 and P3 are the loads in MW. Determine the economical loadallocation between the three units, when the total load on the station is

i. 350 MW

ii. 500 MW. [7+9]

3. Define the cost function of power flow problem with control variables and explaina method to obtain the solution. [16]


5. Define area control error “ACE” in a power system. Discuss how the “proportionalplus Integral” control system is implemented to minimize the “Integral of ACEwith time” for a step load disturbance. [16]




8. What is load compensation? Discuss its objectives in power system. [16]

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1. (a) Explain how the incremental production cost of a thermal power station canbe determined.

(b) Explain the various factors to be considered in allocating generation to differ-ent power stations for optimum operation. [8+8]

2. Give algorithm for economic allocation of generation among generators of a thermalsystem taking into account transmission losses. Give steps for implementing thisalgorithm, and also derive necessary equations. [16]




4. (a) Derive the model of a speed governing system and represent it by a blockdiagram.

(b) A 100 MVAsynchronous generator operates on full load at a frequency of 50Hz. The load is suddenly reduced to 50 MW. Due to time lag in the governorsystem, the steam valve begins to close after 0.4 secs. Determine the changein frequency that occurs in this time. H=5 KW-s/KVAof generator capacity.

[8+8]

5. The following data is available for an isolated area, capacity 4000MW, frequency50Hz, operating load 2500MW, speed regulation constant 2HZ/pu MW. Inertiaconstant = 5secs. 2% of change in load takes place for 1% change in frequency.Find

(a) Largest change in step load if steady state frequency is not to exceed by morethan 0.2Hz

(b) Change in frequency as a function of time after a step change in load. Derivethe formula used. [8+8]

6. (a) What is load frequency control problem in 2-area power system? Why is itessential to maintain constant frequency in an inter-connected power system?

(b) Explain the power frequency characteristics of an inter-connected power sys-tem? [8+8]

7. (a) Write short notes on compensated and uncompensated transmission lines

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(b) Explain briefly about the shunt and series compensation of transmission sys-tems. [8+8]

8. A three(S)phase transmission line has resistance and inductive reactance of 25 Ωand 90 Ω respectively. With no load at the receiving end a synchronous compensatorthere takes a current lagging by 900, the voltage at the sending end is 145 kV and132 kV at the receiving end. Calculate the value of the current taken by thecompensator. When the load at the receiving end is 50 MW, it is found that theline can operate with unchanged voltages at sending and receiving ends, providedthat the compensator takes the same current as before but now leading by 900.Calculate the reactive power of the load. [16]

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1. (a) State what is meant by base-load and peak-load stations. Discuss the com-bined hydro- electric and steam station operation.

(b) Discuss about the incremental fuel cost and production cost. [8+8]

2. (a) Derive the conditions to be satisfied for economic operation of a loss less powersystem.

(b) 150 MW, 220 MW and 220 MW are the ratings of three units located in athermal power station. Their respective incremental costs are given by thefollowing equations:dc1/dp1

= Rs(0.11p1 + 12);

dc3/dp3 = Rs(0.1p3 + 13)dc2/dp2 = Rs(0.095p2 + 14)Where P1, P2 and P3 are the loads in MW. Determine the economical loadallocation between the three units, when the total load on the station is

i. 350 MW

ii. 500 MW. [7+9]





5. A control area has a total rated capacity of 10,000MW. The regulation R for all theunits in the area in 2Hz/pu MW. A 1% change in frequency causes a 1% change inload. If the system operates at half of the rated capacity and the load increases by2%

(a) Find the static frequency drop

(b) If the speed governor loop were open, what would be the frequency drop.Derive the formula used. [8+8]


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7. (a) Write short notes on compensated and uncompensated transmission lines

(b) Explain briefly about the shunt and series compensation of transmission sys-tems. [8+8]


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1. Explain: long range hydro scheduling, deriving necessary expressions. [16]

2. The equations of the input costs of three power plants operating in conjunctionand supplying power to a system network are obtained as follows:C1 = 0.06 P

2

1+ 15 P1 + 150 Rupees/hour

C2 = 0.08 P2

2+ 13 P2 + 180 Rupees/hour

C3 = 0.10 P2

3+ 10 P3 + 200 Rupees/hour.

The incremental loss-rates of the network with respect to the plants 1,2 and 3are 0.06, 0.09 and 0.10 per MW of generation, respectively. Determine the mosteconomical share of a total load of 120 MW which each of the plants would takeup for minimum input cost of received power is Rupees per mMWH. [16]

3. Define the lagrangian function for optimization of power flow solution with con-trolled variables and using the gradient method obtain the solution. [16]

4. (a) Explain the necessity of maintaining a constant frequency in power systemoperation.

(b) Two generators rated 200 MW and 400 MW are operating in parallel. Thedroop characteristics of their governors are 4% and 5% respectively from noload to full load. Assuming that the generators are operating at 50 Hz at noload, how would a load of 600 Mw be shared between them? What will be thesystem frequency at this load? Assume free governor operation. Repeat theproblem if both the governors have a droop of 4%. [6+10]

5. A control area has a total rated capacity of 10,000MW. The regulation R for all theunits in the area in 2Hz/pu MW. A 1% change in frequency causes a 1% change inload. If the system operates at half of the rated capacity and the load increases by2%

(a) Find the static frequency drop

(b) If the speed governor loop were open, what would be the frequency drop.Derive the formula used. [8+8]

6. Draw the block diagram for two-area load frequency control with integral controllerblocks, and explain each block. [16]



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8. What is a static compensator? Explain with diagrams working principle of varioustypes of static compensators. [16]

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