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Code No: 07A70203 R07 Set No. 2

IV B.Tech I Semester Examinations,May 2011POWER SYSTEM OPERATION AND CONTROL

Electrical And Electronics EngineeringTime: 3 hours Max Marks: 80

Answer any FIVE QuestionsAll Questions carry equal marks

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1. What is your analyzation by considering the optimization problem with and withouttransmission loss consideration. [16]

2. 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]

3. A 3 Phase overhead line has resistance and reactance per phase of 25Ω and 90Ωrespectively. The supply voltage is 145 kV while the load end voltage is maintainedat 132 kV for all loads by an automatically controlled synchronous phase modifier.If the kVAr rating of the modifier has the same value for zero loads as for a load of50 MW, find the rating of the Synchronous Phase modifier. [16]

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

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

5. A single area system has the following data:Speed regulation, R = 4 Hz / pu MWDamping co-efficient, B = 0.1 pu MW / HzPower system time constant, TP = 10 secPower system gain, KP = 75 Hz / pu MWWhen a 2% load change occurs, determine the area frequency response character-istic and static frequency error what is the value of steady state frequency error ifthe governor is blocked. [16]

6. (a) Derive equation for penalty factor.

(b) Derive equation for optimal operation of thermal power plants. [8+8]

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7. Find the expression for dynamic response of change in frequency for a step changein load for a single area control system with integral control action. Assume thatTg∼= 0, Tt

∼= 0 and damping constant. [16]

8. In a two plant operation system, the hydro plant is operation for 10 hrs, duringeach day and the steam plant is to operate all over the day. The characteristics ofthe steam and hydro plants are

CT = 0.04 PGT2 +30 PGT + 10 Rs/hr

WH =0.12 PGH2+30 PGH m3/ sec

When both plants are running, the power flow from steam plant to load is 150 MWand the total quantity of water is used for the hydro plant operation during 10 hrsis 150×106 m3. Determine the generation of hydro plant and cost of water used.Neglect the transmission losses. [16]

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1. Discuss in detail the economic dispatch control in a single area load frequencycontrol. [16]

2. A single-phase 400V, 50 Hz motor takes a supply current of 50A at power factor of0.8 lag. The motor p.f has been improved to unity by confectioning a condenser inparallel. Calculate the capacity of the condenser required. [16]

3. The fuel cost for a two unit steam power plant are given byC1 = 0.1 P1

2 + 25 P1 + 1.6 Rupees/hourC2 = 0.1 P22 + 32 P2 + 2.1 Rupees/hourWhere p’s are in megawatt. If there is an error of 1% in the representation of theinput data, find the loss in operating economy for a load of 250 MW. [16]

4. 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 ≤ 300Where P1, P2, are in MW. Neglecting line losses and including generator limits,determine the optimal generation scheduling where PD = 820MW. [16]

5. Discuss the combined hydro- electric and steam station operation. [16]

6. Two turboalternators rated for 110MW and 210MW have a governor droop char-acteristics of 5% from no load to full load. They are connected in parallel to sharethe load of 250MW. Determine the load shared by each machine assuming freegovernor action. [16]

7. A system consists of 4 identical 250 MVA generators feeding a load of 510 MWThe inertia constant H of each unit is 2.5 on the machine base. The load varies by1.4% for a 1 % change in frequency. If there is a drop in load of 10 MW, determinethe system block diagram expressing H and B on the base of 1000 MVA. Give theexpression for speed deviation, assuming there is no speed governor. [16]

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

[16]

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1. Draw the flow chart for obtaining optimal scheduling of generating units by ne-glecting the transmission losses. [16]

2. (a) Derive the transfer function of speed governing system?

(b) Explain turbine model with block diagram? [8+8]

3. A two area system connecting by a tie-line has following parameters on 1000 MVAbase;R1=4.5 % B1=0.6 H1=4.5R2=6 % B2=0.85 H2=5.0The units are running in parallel at a frequency of 50 Hz. The synchronizing powercoefficient is 1.9 pu at the initial operating angle. A load change of 150 MW occursin area 1. Determine the new steady state frequency and change in tie-line powerflow. [16]

4. Derive the co-ordination equation for the optimal scheduling of hydro-thermal In-terconnected power plants. [16]

5. Explain in detail the terms production costs, total efficiency, incremental efficiencyand incremental rates with respect to Thermal power plant. [16]

6. Show that steady state frequency error can be reduced to zero if the proportionaland integral controller is used in single area load frequency control. [16]

7. A single area consists of three generating units with the following characteristics.

Unit Rating (MVA) Speed Droop R(per unit on unit base)1 100 0.012 500 0.0153 500 0.015

The units are loaded as P1 = 80 MW; P2 = 300 MW; P3 = 400 MW.

(a) Assume B = 0; what are the new generations on each unit for a 50 MW loadincrease?

(b) If B = 1.0 p.u. (i.e. 1.0 p.u. on load base.), what are the new generations oneach unit for a 60 MW load increase? [8+8]

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8. Find the rating of synchronous compensator connected to the tertiary windingof a 132 kV star connected, 33 kV star connected, 11 kV delta connected threewinding transformer to supply a load of 66 MW at 0.8 p.f. lagging at 33 kVacross the secondary. The equivalent primary and secondary winding reactancesare 32 ohms and 0.16 ohms respectively while the secondary winding reactance isnegligible. Assume that the primary side voltage is essentially constant at 132 kVand maximum of nominal setting between transformer primary and secondary is1.1. [16]

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1. (a) What is Production cost of power generated and incremental fuel rate?

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

2. (a) What is area frequency response characteristic? Explain it in the context oftwo area system.

(b) Derive an expression for dynamic response of a controlled two area load fre-quency control problem. State the assumptions made. [8+8]

3. A power System consists of two, 125 MW units whose input cost data are repre-sented by the equations :C1 = 0.04 P1

2 + 22 P1 + 800 Rupees/hourC2 = 0.045 P2

2 + 15 P2 + 1000 Rupees/hourIf the total received power PR = 200 MW. Determine the load sharing betweenunits for most economic operation. [16]

4. (a) Explain what do you understand by control area and control area error.

(b) Two generators of rating 100 MW and 200 MW are operating with droop char-acteristic of 6% from no load to full load. Determine the load shared by eachgenerator, if a load of 270 MW is connected across the parallel combinationof those generators. [8+8]

5. A 220 kV line has tap changing transformer at both the ends. The transformer atthe sending end has a nominal ratio of 11 220 kV and that at the receiving end is220/11 kV. The line impedance is (20 + j 60) ohms and the load at the receivingend is 100 MVA, 0.8 p.f. lagging. If the product of two off nominal tap settings is1, find the tap settings to give 11 kV at load bus. [16]

6. In a two plant operation system, the hydro plant is operate for 8 hrs. During eachday and the steam plant is operate all over the day. The characteristics of thesteam and hydro plants are

CT = 0.04 PGT2 +30 PGT + 20 Rs/hr

WH =0.0012 PGH2 +7.5 PGH m3/ sec

When both plants are running, the power flow from steam plant to load is 190 MWand the total quantity of water is used for the hydro plant operation during 8 hrsis 220 ×106 m3. Determine the generation of hydro plant and cost of water used.Neglect the transmission losses. [16]

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7. An inter connector with inductive reactance of 25 ohms and negligible resistance oftwo units of generation with voltages are 33KV and 30KV at its ends. The load of6MW is to be transferred from 33KV to 30KV side of a inter connector determinethe power factor of power transmitter and other necessary conditions between twoends. [16]

8. For an isolated power system with integral control has the following data:Rating of the generator Pr=100 MWNominal operating load PD=50 MWInertia constant H=5.0 secSpeed regulation of the governor R=2.5 Hz/ pu MWIf the load would increase 1 pu for 1 % frequency increase and area is controlled byan integral controller, estimate the critical magnitude of the gain when the load isincreased by 10 MW. [16]

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