syllabus ee6603 power system operation and control … fileee6603 power system operation and control...

REGULATION:2013 ACADEMIC YEAR:2018-2019

JIT-JEPPIAAR /EEE/Mrs.S.SARUMATHI/ IIIrdYr /SEM 06/EE6603/Power system Operation & Control/UNIT1-5/QB+ KEYS /VER 1.0

4.1

SYLLABUS

EE6603 POWER SYSTEM OPERATION AND CONTROL

L T P C

3 0 0 3

OBJECTIVES:

• To have an overview of power system operation and control. • To model power-frequency dynamics and to design power-frequency controller.

• To model reactive power-voltage interaction and the control actions to be

implemented for maintaining the voltage profile against varying system load.

• To study the economic operation of power system.

• To teach about SCADA and its application for real time operation and control of power

systems. UNIT I INTRODUCTION 9 An overview of power system operation and control - system load variation - load

characteristics - load curves and load-duration curve - load factor - diversity factor -

Importance of load forecasting and quadratic and exponential curve fitting techniques of

forecasting – plant level and system level controls . UNIT II REAL POWER - FREQUENCY CONTROL 9 Basics of speed governing mechanism and modeling - speed-load characteristics – load

sharing between two synchronous machines in parallel - control area concept - LFC control

of a single-area system - static and dynamic analysis of uncontrolled and controlled cases -

two-area system – modeling - static analysis of uncontrolled case - tie line with frequency

bias control - state variable model - integration of economic dispatch control with LFC. UNIT III REACTIVE POWER–VOLTAGE CONTROL 9 Generation and absorption of reactive power - basics of reactive power control - excitation

systems – modeling - static and dynamic analysis - stability compensation - methods of

voltage control: tap-changing transformer, SVC (TCR + TSC) and STATCOM – secondary

voltage control. UNIT IV UNIT COMMITMENT AND ECONOMIC DISPATCH 9 Formulation of economic dispatch problem – I/O cost characterization – incremental cost

curve - co-ordination equations without and with loss (No derivation of loss coefficients) -

solution by direct method and λ-iteration method - statement of unit commitment problem –

priority-list method - forward dynamic programming. UNIT V COMPUTER CONTROL OF POWER SYSTEMS 9 Need for computer control of power systems - concept of energy control centre - functions -

system monitoring - data acquisition and control - system hardware configuration – SCADA

and EMS functions - network topology - state estimation – WLSE - Contingency Analysis -

state transition diagram showing various state transitions and control strategies. TOTAL : 45 PERIODS

OUTCOMES:

Ability to understand and analyze power system operation, stability, control and protection.

TEXT BOOKS: 1. Olle.I.Elgerd, ‘Electric Energy Systems theory - An introduction’, Tata McGraw Hill

Education Pvt. Ltd., New Delhi, 34th reprint, 2010.



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2. Allen. J. Wood and Bruce F. Wollenberg, ‘Power Generation, Operation and Control’, John Wiley & Sons, Inc., 2003.

3. Abhijit Chakrabarti, Sunita Halder, ‘Power System Analysis Operation and Control’, PHI learning Pvt. Ltd., New Delhi, Third Edition, 2010.

REFERENCES:

1. 1. Nagrath I.J. and Kothari D.P., ‘Modern Power System Analysis’, Tata McGraw-Hill,

Fourth Edition, 2011. 2. Kundur P., ‘Power System Stability and Control, Tata McGraw Hill Education Pvt. Ltd.,

New Delhi, 10th reprint, 2010. 3. Hadi Saadat, ‘Power System Analysis’, Tata McGraw Hill Education Pvt. Ltd., New

Delhi, 21st reprint, 2010. 4. N.V.Ramana, “Power System Operation and Control,” Pearson, 2011. 5. C.A.Gross, “Power System Analysis,” Wiley India, 2011.



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Subject Code: EE6603 Year/Sem: III/06

Subject Name: Power System operation and control Subject Handler: Ms. S.Sarumathi

UNIT I – INTRODUCTION

An overview of power system operation and control - system load variation - load characteristics -

load curves and load-duration curve - load factor - diversity factor - Importance of load

forecasting and quadratic and exponential curve fitting techniques of forecasting – plant level and

system level controls .

PART *A

Q.No. Questions

1.

State the objective of power system control. BTL2

To maintain a continuous balance between electrical generation and varying load demand while

system frequency and voltage levels are maintained constant.

2.

State the effect of variable load in power system.(Nov/Dec 2012) BTL1

Due to variation in load there will be some effects on the power station. Some important effects

are

Need of additional equipment

Increase in production cost

3.

What is a load curve? (Nov 11,12)

The curve drawn between the variations of load on the power station with respect to time is

known as load curve.

4.

Define the term base load.

Base load is the load that has been drawn constantly throughout the time.

5.

Define load factor. (May 2012) BTL1

The ratio of average load to the maximum demand during a given period is known as load

factor.

=

6.

Differentiate load curve and load duration curve. (Nov 2014) BTL4

Load curve Load duration curve

Load curve is curve plotted between load and

time

When the load elements of the load curve are

arranged in the order of descending

magnitude.

This curve shows the variation of load on the

power station with respect to time

The curve obtained is a load duration curve.

7.

Classify different types of loads. BTL4

Lightning and heat loads

Induction motors

Electronic devices



4.4

8.

Define diversity factor. (Nov 11,13,14) BTL1

The ratio of sum of individual maximum demand on the power station is known as diversity

factor.

=

9. What is spinning reserve? (Nov/Dec 2018)BTL1

The units that can be started within a short duration of time to meet the change in load when a

particular unit fails in the power system is called spinning reserve.

10.

Define the term average load or average demand. BTL1

The average of load occurring on the power station in a given period (day or month or year) is

known as average demand.

=

11.

What is the need for load forecasting? (Nov/Dec 2015,2018) BTL2

To meet out the future demand

Long term forecasting is required for preparing maintenance schedule of the generating

units, planning future expansion of the system

For day to day operation, short term load forecasting demand and for maintaining the

required spinning reserve.

Very short term load forecasting is used for generation and distribution That is economic

generation scheduling and load dispatching

Medium term load forecasting is needed for predicted monsoon acting and hydro

availability scheduling.

12. Define connected load. (Nov 2011) BTL1

The sum of continuous rating of all the equipment connected to supply system is known as

connected load.

13.

Define capacity factor. (Nov 2013) BTL1

=

Plant capacity factor is defined as the ratio of actual energy produced to the maximum possible

energy that could have been produced during a given period.

14.

Define plant use factor. (Nov 11,13)(May 14) BTL1

The ratio of units generated to the product of plant capacity and the number of hours for which

the plant was in operation.

15.

Define system level control. BTL1

System level control consists of

Secondary automatic load frequency control

Economic dispatch control

Unit commitment

Transmission system voltage control

System security control



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16. Define maximum demand. (Nov 2012) (May 2014) BTL1

It is the greatest demand of load on the power station during a given period is known as

maximum demand.

17.

Define demand factor. (Nov 2015) BTL1

Demand factor is defined as the ratio of maximum demand to connected load.

=

18.

What is the effect of load factor on the cost of generation? (May 2013) BTL4

Load factor is always less than 1 because average load is smaller than the maximum demand.

The load factor plays a vital role in determining the overall cost per unit generated. Higher the

load factor of the power station, lesser will be the cost per unit generated

It is because higher load factor means lesser maximum demand.

19.

State the plant level controls. BTL1

Prime mover control

Excitation control

20.

Define utilization factor. BTL1

It is the measure of the utility of the power plant capacity and is the ratio of maximum demand

to the rated capacity of the power plant. It is less than unity

=

21.

What are the advantages of computer control in power system? What are the types of

comcomputer control?

Optimal operation and control

Low maintenance and operating cost

High speed of operation

Fast network monitoring

Types of computer control

Supervisory control

Direct control

22.

What are brownouts? (May 2017) BTL1

A brownout is an intentional or unintentional drop in voltage in an electric power supply

system. International brownouts are used for load reduction in an emergency. The reduction

lasts for minutes or hours, as opposed to short term voltage sag or dip.

PART * B

1.

Explain the overview of power system operation and control and the role of computer in

the implementation with the help of block diagram. (Nov 2012,2014,2018) (13M) BTL4

Answer: Page 1.33- M.Jeraldin Ahila

Definition: (2M)

Function of an electric power system to convert energy from one of naturally-available form –

electric form-transport point of consumption.

Power system operation: (3M)

Power system have the responsibility to ensure supply of good quality power when

customer demands.

Power system should able to supply ever changing load demand.

Power System Control: (3M)

Problems of dynamic and transient stability, steady state stability, voltage and frequency



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regulation, power optimization need to properly analyze.

Block diagram: (3M)

Role of computer: (2M)

Digital control by computers-enables-processing of large number of different data and

constraints involved in power system operation.

2.

Describe briefly about plant level and system level controls. (May 2013) (13M) BTL4


Diagram: (4M)

Factors: (2M)

Quality of power determined by system frequency-magnitudes of bus voltages

Plant level control: (4M)

Governor control-prime mover control-speed regulation –control of energy supply system –

boiler pressure –temperature

Automatic voltage regulator-regulate generator voltage and relative power output-terminal

voltage varies-excitation control-maintains the terminal voltage.

System level control: (3M)

Load frequency control

Economic dispatch control

System voltage control

3.

Compare various stochastical methods of load forecasting. (May 2015) (13M) BTL4

Answer: Page 14-Notes

Time series approach: (4M)

Auto-Regressive model

Auto-Regressive Moving Average

Kalman Filtering approach: (4M)

Short term load forecasting using periodic load model

Innovation model approach: (5M)

Estimating model order

Estimating gain vector

4.

Consider an inductive load of type Z =R+jX. By how much percentage the real load drop,

if the voltage is reduced by 5%.How would 2% drop in frequency affect the real load, if

the load power factor is 0.8. Derive the relations used.(May 2016) (13M) BTL4


Real load drop: (7M)

Admittance Y =

S = P+jQ

P =

Q=

Drop in frequency: (6M)

2% frequency drop results in 1.44% load increase



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5.

A power station has to meet the following demand:

Group A: 200 KW between 8 A.M and 6 P.M

Group B: 100 KW between 6 A.M and 10 A.M.

Group C: 50 KW between 6 A.M and 10 A.M

Group D:100 KW between 10 A.M and 6 P.M and then between 6 P.M and 6 A.M. plot the

daily load curve and determine

i. Diversity factor

ii. Units generated per day

iii. Load factor (Nov 2014)(13M) BTL3


Load curve: (3M)

Maximum demand = 350 KW (2M)

Diversity factor: (2M)

=

=

Units generated: (3M)

Units generated per day = 4600 Kwhr

Load factor: (3M)

Load factor = 54.76%

6.

(i)Briefly describe the importance of load forecasting and explain the method of least

square fit forecasting the base load. (May 2012) (8M) BTL4

Answer: Page 14-Notes

Importance: (3M)

Deregulated economy

Generation

Load switching

Contract evaluation

Infrastructure development

Least Square fit: (5M)

(ii) Explain the information obtained from load curves and load duration curves.

(May 2012) (5M) BTL4


Load curves: (2M)

Variation of load on power station

Maximum and minimum values of daily load.

Annual maximum and minimum value of load

Average annual load on the station

Load duration curve: (3M)

Maximum demand and minimum demand can be observed.

Units generated on that period can be obtained.



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7.

Explain the important objectives of power system and various control strategies during its

operation. (Nov 2012) (13M) BTL2

Answer: Page 1.2 and 1.33- M.Jeraldin Ahila

Objective of power system: (4M)

To maintain continuous balance between electrical generation and varying load demand.

System frequency and voltage levels are maintained constant.

Control strategies: (5M)

Plant level control-Governor control and automatic voltage regulator control.

System level control-Load frequency control-Economic dispatch control-System voltage control

Diagram: (4M)

8.

(i)What is meant by chronological load curve? Give the information obtained from load

curves. (May 2013) (8M) BTL4 Answer: Page 1.16- M.Jeraldin Ahila

Chronological load curve: (4M)

The curve drawn between the variations of load on the power station with respect to time is

known as load curve.

Information from Load curves: (4M)

Variation of load on power station

Maximum and minimum values of daily load.

Annual maximum and minimum value of load

Average annual load on the station (ii) A power plant supplies the following loads with maximum demand as below:

Type of load Individual maximum demand

Industries 100

Domestic 15

Commercial 12

Agriculture 20

The maximum demand on the power station is 110 MW. The total units generated in the

year is 332*106 KWh. Determine the load factor and Diversity factor. (May 2018) (5M)

BTL3


Load Factor: (3M)

Diversity factor: (2M)

=

=

9. Explain the following terms. (13M) (May 2014)(Nov 2013) BTL1


i) Connected load (2M)



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The sum of continuous rating of all the equipment connected to supply system is known as

connected load.

ii) Load factor (2M)

The ratio of average load to the maximum demand during a given period is known as load

factor.

=

iii) Diversity factor (3M)

=

iv) Average demand (2M)

=

v) Hot reserve (2M)

Hot reserve-reserve generating capacity which not in operation-but not in service.

vi) Cold reserve (2M)

Cold reserve –reserve generating capacity-available for service-but not in operation

10.

A power supply is having the following loads:

Type of load Maximum demand

(KW)

Diversity factor Demand factor

Domestic 10,000 1.2 0.8

Commercial 30,000 1.3 0.9

Industrial 50,000 1.35 0.95

If overall system diversity factor is 1.5, determine

Maximum demand and Connected load of each type (May 2014) (13M) BTL3


Total Maximum Demand: (3M)

Total maximum demand of load = 10000+30000+50000 = 90000 Kw

Maximum demand: (3M)

=

Connected load of each type: (7M)

PART*C

1.

A generating station has a maximum demand of 50,000 KW. Calculate the cost per unit

generated from the following data. (Nov 2011) (15M) BTL3

Capital cost = Rs 95*106

Annual load factor = 40%

Annual cost of fuel and oil = Rs 9*106



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Taxes wages and salaries etc., = Rs 7.5*106

Interest and depreciation = 12 %

Answer: Page S.53- M.Jeraldin Ahila

Cost per unit generated: (4M)

Total annual running charges = (9*106)+(7.5*106) = 16.5*106

Fixed charge: (3M)

Annual fixed charges = 12% of capital cost = Rs 11.4*106

Units generated per annum: (4M)

Maximum demand*Annual load factor*Hours in a year

50,000*0.4*8760 = 17.52*107 Kwh

Cost per unit generated: (4M)

Cost per unit generated =

2.

A generating station has a maximum demand of 20 MW, a load factor of 60%, plant

capacity factor of 48% and a plant use factor of 80%

Find the

(i)Daily energy produced

(ii)Reserve capacity of the plant

(iii)Maximum energy that could be produced daily if the plant were running all the time

(iv)Maximum energy that could be produced if the plant when running (according to

operating schedule) were fully loaded. (Nov 2011) (15M) BTL3


Load factor: (3M)

Plant capacity factor =

Average load: (4M)

Average load = 15 KW

Installed capacity: (3M)

Installed capacity =

Reserve capacity: (5M)

Energy produced per day = 15*24 = 360 Kw/day

Reserve capacity = plant capacity-maximum demand=5 Kw

3.

A generating station has the following daily load cycle.

Time (hrs) 0-6 6-10 10-12 12-16 16-20 20-24

Load (MW) 20 25 30 25 35 20

Draw the load curves and calculate,

Maximum demand

Units generated per day

Average load



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Load factor. (Nov 2013) (Nov 2015,2018) (15M) BTL3


Load curve: (4M)

Maximum demand: (3M)

Maximum demand = 35 MW

Units generated per day: (3M)

Units generated per day = Area under the load curve in Kwhr

Area under the load curve in Kwhr = (6*20+4*25+2*30+4*25+4*35+4*20) = 600*103 kwhr

Average load: (2M)

Load factor: (3M)


JIT-JEPPIAAR /EEE/Mrs.S.SARUMATHI/ IIIrdYr /SEM 06/EE6603/Power System Operation & Control/UNIT1-5/QB+ KEYS /VER 1.0 4.12

UNIT II – REAL POWER - FREQUENCY CONTROL

Basics of speed governing mechanism and modeling - speed-load characteristics – load sharing

between two synchronous machines in parallel - control area concept - LFC control of a single-

area system - static and dynamic analysis of uncontrolled and controlled cases - two-area system –

modeling - static analysis of uncontrolled case - tie line with frequency bias control - state variable

model - integration of economic dispatch control with LFC.

PART *A

Q.No. Questions

1.

State the function of load frequency control. (May 2013) (Nov 2013) BTL1

The function of load frequency control is to change the control valve or gate opening of the

prime movers as a function of load variation in order to hold system frequency constant.

2.

How is the real power in power system controlled? (May 2012) BTL4

The real power in a power system is controlled by controlling the driving torques of individual

turbine of the system.

3.

What is meant by load frequency control? (Nov/Dec 2007) (May 2012) BTL1

In inter connected system with two or more independently controlled areas, in addition to

control of frequency, generation within each area has to be controlled to maintain scheduled

power interchange.

4.

State any two necessities to put alternators in parallel. (May 2014) BTL2

Alternators may be put in parallel become of the following reason

Local or regional power use may exceeds the power of a single available generation

Parallel alternators allow one or more units to be shut down for scheduled or emergency

maintenance while the load is being supplied with power.

5.

Give two conditions for proper synchronizing of alternators. (Nov 2011) BTL1

The condition for proper synchronization are

The terminal voltage of the incoming machine must be exactly equal to that of the others

or the bus bars connecting them.

The speed of the incoming machine must be such that its frequency equals to the bus bar

frequency.

6.

Differentiate static &dynamic response of an ALFC loop. (Nov 2016) BTL4

Static response of an ALFC loop will inform response of ALFC loop will inform about

frequency accuracy. Whereas the dynamic response of ALFC loop will inform about the stability

of the loop.

7.

What is meant by control area? (Nov 14,15,16,18) BTL1

It is possible to divide an extended power system (say, national grid) into sub areas in which the

generators are tightly coupled together so as to form a coherent group, all the generators respond

in union to changes in load or speed changer settings. Such a coherent area is called a control

area in which the frequency is assumed to be the same throughout in static as well as dynamic

conditions.



8.

State the assumptions made in dynamic response of uncontrolled case. (May 2014) BTL1

Neglect the turbine dynamics

The speed changer action is instantaneous.

9.

State the principle of tie line bias control. (April/June 2016) BTL1

The control strategy is termed as tie line bias control and is biased upon the principle that all

operating pool members must contribute their share to the frequency control in addition to

taking care of their own net incharge.

10.

Define area control error. (May/June 2016) BTL1

Area control error is the change in frequency which when used in integral control loop forced

the steady state frequency error to zero.

=

=

b = area frequency bias

= change in tie line power

= change in frequency

11.

Compare the function of Speed Governor and Speed changer in a speed governing system

of a turbine-generator set. (April/May 08) BTL4

Speed Governor Speed changer

Purely mechanical speed sensitive device

coupled directly to the hydraulic amplifier the

control valve operating via the linkage

mechanism.

The speed changer makes it possible to

restore the frequency to the initial value after

operation of the speed governors having the

steady state characteristics

12.

Define inertia constant. BTL1

Inertia constant H is defined as the ratio of kinetic energy stored in the rotor to the MVA rating

of the generator

13.

State the purpose of a speed changer. BTL4

The speed changer makes it possible to restore the frequency to the initial value after operation

of the speed governors having steady state characteristics.

14.

State the purpose of fly ball speed governor. BTL4

Fly ball speed governor is purely mechanical speed sensitive device coupled directly to the

hydraulic amplifier which adjusts the control valve opening via the linkage mechanism.

15.

How can the flow of high pressure steam controlled? BTL2

By controlled the position of the control valve or gate control can be exerted over the flow of

high pressure steam through the turbine.

16.

Write the tie line power deviation equation in terms of frequency. BTL4

= 2π [s



17.

Define AFRC. BTL1

The system performance in terms of how the change in power effects the change in frequency is

evaluated through AFRC.

18. State the basic role of ALFC. BTL2

The basic role of ALFC is to maintain desired megawatt output of the generator unit and assist

in controlling the frequency of the larger inter-connection.

19.

State the need for integral controller in ALFC. (April/May 2017) BTL4

Speed changer setting can be adjusted automatically by monitoring the dynamic

frequency changes with changes in load and the synchronous clock run on time, but not

without error during transient period.

For this purpose a signal from is fed through an integrator to the speed changer

The integral controller actuates the load reference point until the frequency deviation

becomes zero.

20.

Define stiffness of the interconnected system. BTL1

= synchronizing power coefficient or electric stiffness

Synchronizing power coefficient or electric stiffness is defined as the differential power

increase obtained per differential power angle increase.

21.

Define per unit droop. BTL1

The per unit droop or speed regulation R of the generating unit is defined as the magnitude of

change in steady state speed, expressed in p.u of rated speed, when the output of unit gradullay

reduced from 1.0 p.u rated power to zero.

= p.u.

= Frequency at no load,Hz.

Frequency at rated megawatt output,

22.

State the control objective of two area load frequency control. (Nov 2014) BTL2

During normal operating condition, each control area should have the capacity to meet its own

load demand with its spinning generator.

During emergency condition, the energy can be drawn from the spinning reserve of the

neighboring area immediately due to the outage of generating unit.

To regulate the frequency of each area and to simultaneously regulate the tie line power as per

the inter area power contracts.

23. Brief the application of secondary ALFC loop in power system networks. (May 2015)

(Nov 2018)BTL2

A frequency sensor senses bus bar frequency and compares with the tie line power frequency.



The speed changer gives the response speed to the governor and to maintain the rated speed.

The integral controller is used to reduce the steady state frequency error.

24.

Find the open loop gain of an automatic voltage regulator loop if the static error does not

exceed 2%. (May 2015) BTL4

K>((100/

K>((100/

K>49

Thus the open loop gain of the AVR loop is greater than 49, then the static error will be within

2%.

25.

What is the advantage of AVR loop over ALFC? (Nov 2015) BTL2

AVR loop is much faster than ALFC loop and therefore there is a tendency, for the VR

dynamics to settle down before they can make themselves felt in the slower load frequency

control channel.

26.

Distinguish between primary and secondary feedback loops in load frequency control.

(May 2018) BTL2

Primary ALFC Secondary ALFC

The circuit primarily controls the steam valve

leading to the turbine.

The circuit involves a frequency sensor that

senses the frequency of the bus bar and

compares it with tie line power frequencies in

the signal mixer

The speed signal is compared with reference

speed, governor whose main activity is to

control the speed of the steam by closing and

opening of the control valve.

The output is an Area control Error which

sent to speed changer through integrator.

The speed changer gives the reference speed

to the governor.

PART*B

1.

Draw the block diagram of uncontrolled two area load frequency control system and

explain the salient features under static conditions. (Nov 2011)(May 2013) (13M) BTL4


Block diagram: (6M)

Static analysis: (7M)

, stat =

, stat =

2.

How is speed governor mechanism modeled? Explain its operation with the speed-load

characteristics. (Nov 2011) (13M) BTL4

What are the components of speed governor system of an alternator? Derive the

mathematical model of speed governor system with the aid of block diagram.

(May 2012) (Nov 2013)



Derive the modeling of fundamental speed governing system.(Nov 2015)

With the block diagram of speed governing system, explain the Automatic load

frequency control. Also derive necessary equations. (May 2015)


Diagram: (4M)

Explanation: (5M)

Flyball speed governor

Speed changer

Hydraulic amplifier

Linkage mechanism

Speed load characteristics: (4M)

Per unit droop or speed regulation of the generating unit defined as the magnitude of change

in steady state speed expressed in p.u of rated speed when the output of the unit is gradually


3.

Explain the dynamic response of single area load frequency control. Also discuss the effect

of P-I controller on single area load frequency control. (May 2012) (13M) BTL4


Definition: (2M)

Dynamic response of loop will inform about tracking ability and stability of the loop

Diagram: (4M)

Load frequency: (4M)

Integral value: (3M)

=

=

4.

With a neat block diagram, explain the single area load frequency control system.

(Nov 2012,2014) (13M) BTL4


Block diagram: (4M)

Frequency function: (4M)

Final value theorem: (2M)

Steady state response: (3M)



=

β= area frequency response coefficient

5.

(i)Discuss the integration of economic dispatch control with automatic generation control.

(Nov 2012) (8M) BTL4


Cost function: (2M)

Set of real generation variables must be selected that minimize the cost function.

Equality constraints: (2M)

H( ,

Inequality constraints: (4M)

(ii) List the advantages of Multiarea operation. (5M) BTL1


Under normal operating condition each control area should have the capacity to meet its

own lead from its own spinning generator.

Under emergency condition, the energy can drawn from the spinning reserves of all

neighboring areas immediately due to sudden loss of generating unit.

6.

(i)Derive an expression for load sharing between two alternators. What are the effects of

fuel supply and change of excitation? (Nov 2012) (8M) BTL4


Speed load characteristics: (2M)

Per unit droop or speed regulation of the generating unit defined as the magnitude of change in

steady state speed expressed in p.u of rated speed when the output of the unit is gradually


= p.u.

Slope: (2M)

Regulation (slope) =

Change in output: (2M)

Parallel operation: (2M)

(ii) The two system connected by a tie line describe the following characteristics



Area 1 Area 2

R = 0.01 pu R = 0.02 pu

D =0.8 pu D =1.0 pu

Base MVA =500 Base MVA = 500

A load change of 100 MW (0.2 pu) occurs in area 1. What is the new steady state frequency

what is the change in tie flow? Assume both area were at nominal frequency?

(April/May 2018)(5M) BTL3


Static frequency: (2M)

Change in tie flow: (3M)

7.

(i)Develop a schematic of speed governing system and explain its operation.

(May 2013,2018) (8M) BTL6


Schematic diagram: (2M)

Explanation: (2M)

Flyball speed governor

Speed changer

Hydraulic amplifier

Linkage mechanism

Operation: (4M)

As load increases the speed of the turbine decreases.

Speed changer gives raise command and flyball moves outwards and point B moves

downwards.

D moves upwards and high pressure oil enters to the pilot valve and press the main piston

downwards and maintains constant frequency.

(ii)Analyze the governor-Speed drop characteristics, the basics of load sharing between

two synchronous machines in parallel. (May 2018) (5M) BTL3


Power output-Speed characteristics: (2M)

Per unit droop: (1M)

Per unit droop or speed regulation defined as magnitude of change in steady state speed when

output of unit gradually reduced from 1.0 p.u rated power to zero.

Change in output: (2M)

8.

Develop the state variable model of a two area system and state the advantages of the

model. (May 2014) (13M) BTL4


Definition: (2M)

Optimum Linear Regulator design results in a controller that minimizes both transient variable

oscillations and control effects.



Block Diagram: (3M)

State variable: (3M)

X = =

Static variable form: (2M)

= + G + P

Linear state model: (1M)

Advantages: (2M)

9.

Two generators rated 200 MW and 400 MW are operating in parallel. The droop

characteristics of their governors are 4% and 5% respectively from no load to full load.

Assume that the generators are operating at 50 Hz at no 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. Also find the load sharing if both governors have a droop of 4%.

(May 2013)(Nov 2013) (Nov 2014,2018) (13M) BTL3


Load triangle: (2M)

Speed regulation: (2M)

Alternator 1: (2M)

Alternator 2: (2M)

System frequency: (2M)

f = 48.43 Hz

Load shared: (3M)

Alternator 1: 429.88 MW

Alternator 2: 570.12 MW

10. An isolated power system has the following parameters:

Turbine rated output = 300 MW, Nominal frequency = 50 Hz

Governor speed regulation = 0.05 p.u, Inertia constant =5,

Turbine time constant = 05 sec, Governor time constant =0.2 sec. Load change= 60 MW.



The load varies by 0.8% for a 1% change in frequency. Determine the steady state

frequency deviation in Hz. (May 2014) (13M) BTL3


Change in power demand: (3M)

Change in frequency: (3M)

(-

Block diagram: (3M)

Step Response: (1M)

Steady state frequency deviation: (3M)

PART*C

1.

A sub grid has total rated capacity 2500 MW. It encounters a load increase of 50 MW if

the normal operating load is 1000 MW. Assume inertia constant (H) to be 5 sec and

regulation of generator in the system as 2 Hz/p.u MW. Find

ALFC loop parameters

Static frequency drop

Transient response of ALFC loop

Assume load frequency to be linear. (May 2015) (15M) BTL3


ALFC loop parameters : (5M)

d =

= = 50 Hz/ p.u MW

= = 10 sec

Static frequency drop: (5M)



=

Transient response: (5M)

= -α [1-ϵ Hz

= -0.03846 (1-

2.

A two area power system has two identical areas with parameters and operating conditions

Rated capacity of the area =1500 MW

Nominal operating load = 750 MW

Nominal frequency = 50 HZ

Inertia constant of the area = 5s

Speed regulation = 3%

Damping coefficient = 1%

Governor time constant = 0.06s

Turbine time constant = 0.25s

A load increase M1 = 30 MW occurs in area 1.

Determine change in frequency and compare the change in frequency obtained in single

area and comment on the support. (Nov 2015) (15M) BTL3


Change in frequency: (5M)

R = 1.5 Hz/p.u MW

β Value: (5M)

B+

β=0.6766 p.u Mw/Hz

: (5M)

3.

Draw the transfer function block diagram for a single area system provided with static

analysis of uncontrolled and controlled case. (Nov 2018) (15M) BTL3


Block Diagram: (5M)

Static Analysis: (5M)



Step change

Final value theorem

Static Analysis (Controlled Case): (5M)

Step change

Final value theorem



UNIT III – REACTIVE POWER–VOLTAGE CONTROL

Generation and absorption of reactive power - basics of reactive power control - excitation systems

– modeling - static and dynamic analysis - stability compensation - methods of voltage control: tap-

changing transformer, SVC (TCR + TSC) and STATCOM – secondary voltage control.

PART *A

Q.No. Questions

1.

State the function of AVR. (May 2013) BTL1

The function of AVR (Automatic Voltage Regulator is to regulate the output of generator

voltage and thereby regulate the reactive power flow.

2.

List the various functions of excitation systems. (Nov 2013) BTL2

The various functions of excitation systems are

The DC excitation system utilizes DC generator as a source of excitation power and provides

current to the rotor of the alternator through slip rings.

The main function of excitation system is to provide dc current to the field of the field of the

generator. The AC signal is rectified using the controlled or uncontrolled rectifier and supplied

to the field of generator

3.

State the difference between P-F and Q-V control. (May 2012) BTL4

Static changes in reactive power affects essentially only the magnitude of bus voltage, leaving

the phase of bus voltage unaffected. Therefore reactive power is directly proportional to bus

voltage V (Q α V)

Static change in real power will affect only the phase angle of the bus voltage leaving the

magnitude of the bus voltage unaffected. Therefore real power is proportional to the phase angle

of bus voltage. (P α δ )

4.

State the relation between voltage, power and reactive power at a node. (Nov 2014) BTL3

The system Voltage V at a node is a function of real and reactive power.

V = f(P,Q)

(E-2V)/R

(E-2V)/X

5.

List the functional elements of excitation system. BTL1

Exciter

Regulator

Terminal voltage transducer

Load compensator

Power system stabilizer

Limiters and protective circuits

6.

Define exciter. BTL1

Exciter is a device or combination of devices which supplies the magnetizing current to generate

the working flux.

The purpose of exciter is to supply the excitation DC voltages to the fixed poles of generator.



Rotary exciter is an additional small generator mounted on the shaft.

7.

Define stability compensation. (Nov 2015 ) BTL1

In order to get static accuracy, high loop gain is needed. But this high loop gain causes

undesirable dynamic response, possibly instability. The stability compensation improves the

dynamic characteristics without offering the static loop gain. The stability compensation will

damp out the oscillations in the system.

8.

State the advantages of switching capacitors in voltage control. (Nov 2014,2018) BTL2

Transient free switching is ensured

Damping of energizing transients

Harmonics reduction

The system voltage can be maintained with the desired range.

9.

Distinguish between rotor angle stability and voltage stability. (May 2015) BTL2

Rotor angle stability voltage stability

Steady increase in generator rotor angle

creates lack of synchronizing torque in turn

rotor angle instability.

The system enters into state of voltage

instability when an increased demand in load

or a change in the system condition causes

progressive decrease in voltage.

10.

List the merits of synchronous compensator. BTL4

The system can operate at all load conditions

Smooth variation of reactive as compared to step by step variation in static

compensators.

Production of reactive power is not affected by system voltage

11.

State the different types of reactive power compensation. (Nov 2012) BTL4

Different types of reactive power compensation are

Variable Impedance-Inductor and capacitor

Switching converters-SVC,STATCOM and TCSC

12.

Define Booster transformer. (Nov 2012) BTL1

Booster transformer is a compensation device which is installed to increase the voltage in the

electric circuit. The booster transformer can be brought into the electric circuit by means of relay

operation.

13.

Comment on the use of series capacitors in transmission lines. (April/May 2017) BTL4

It is connected in series to compensate the inductive reactance of the line.

This reduces the transfer reactance between the buses to which the line is connected.

It increases the maximum power that can be transmitted and reduces reactive power loss.

The reactive power produced by the series capacitor increases with increase in power

transfer.

14.

Define exciter ceiling voltage. (April/May 2017) BTL1

Exciter ceiling voltage is the maximum voltage that may be attained by an exciter under specific

conditions.

15.

What is SVC? (May/June 2016) BTL1

Static VAR compensators are located in receiving substations and distribution system for

smooth and stepless variation of compensation of reactive power injected into line by shunt

capacitor and shunt reactors.

16.

How are voltage and reactive power interrelated? (May/June 2016) BTL4

=



R-Resistance of line is neglected

=

The flow of reactive power is determined by the difference between sending end and receiving

end voltage.

17.

List the various components in AVR loop. BTL1

Exciter

Comparator

Amplifier

Rectifier

Synchronous generator

18.

State whether changes in AVR loop will be reflected in ALFC loop. BTL4

Control actions in the AVR loop affect the magnitude of the generator emf E

As the internal emf determines the magnitude of the real power, changes in the AVR

loop must be felt in the ALFC loop.

19.

State the main objective of Reactive power and voltage control in power systems.

(May 2018) BTL1

The terminal voltage of all equipment in the power system are within acceptable limits,

both utility equipment and customer equipment are designed to operate at certain voltage

rating

The system reactive power flow is maintained so as to reduce losses to minimum in

practice.

20.

State the effects of AVR loop. BTL3

AVR must regulate the terminal voltage V within required static accuracy limit.

It must have sufficient speed response.

It must be stable.

21.

Outline the role of synchronous generators adopted for generation and absorption of

reactive power. (May 2018)BTL4

The tendency of synchronous generators can generate or absorb reactive power depending on the

excitation. When over excited the generators they supply reactive power and when under excited

they absorb reactive power.

22.

What are the different types of static VAR compensator? (Nov 2018) BTL1

Saturated reactors

Thyristor controlled reactors

Thyristor switched capacitors

Thyristor switched reactors

Thyristor controlled transformers

Fixedd capacitor and thyristor controlled reactors

PART*B

1.

Develop the block diagram of AVR and obtain its transfer function and explain its static

and dynamic response. (May 2017) (Nov 2018) (13M) BTL4

Explain with neat block diagram the excitation system and its modeling with relevant

transfer functions. (May 2018)




Potential transformer and rectifier: (2M)

Terminal voltage of the generator stepped down to value required for control signal.

Comparator: (2M)

Compares the measured signal against the reference DC signal.

Block diagram: (4M)

Amplifier: (2M)

Amplifies the input error signal depending on the amplification factor.

Exciter: (2M)

Purpose of exciter to supply field current to the rotor field of the synchronous generator.

Synchronous generator: (1M)

Generates 3 phase power (A.c) at its terminals.

2.

Describe in detail various reactive power compensation technique used in system level

voltage control. (May 2017) (13M) BTL4


Static shunt capacitors: (3M)

Shunt capacitor banks –supply reactive power at both transmission and distribution

levels.

Capacitors supply reactive power-line have lagging power factor

Series capacitors: (4M)

Series capacitor connected in lines with series to compensate the inductive reactance

of the line.

Reduces the transfer reactance the buses to which line is connected.

Shunt reactors: (3M)

Shunt reactor used to reduce or limit voltage rise due to open circuit or light load

Absorbs reactive power are usually used for EHV lines.

Synchronous condenser: (3M)

Synchronous machine running without a prime mover or a mechanical load.

By controlling field excitation it can be made to generate or absorb reactive power.

3. Explain different types of static Var compensators with a phasor diagram. (Nov 2015)

(13M) BTL4


Diagram: (3M)



The term static var compensator is applied to a number of static var compensation devices for

use in shunt reactive control.

These devices consist of shunt connected, static reactive element (linear or non linear reactors

and capacitors) configured into a var compensating system.

Explanation: (10M)

Saturated reactor

Thyristor Controlled Reactors

Thyristor Switched Capacitors

Thyristor Controlled Transformers

Fixed Capacitor and Thyristor controlled reactors

4.

Explain the different methods of voltage control. (Nov 2014) (16M) BTL4

Describe the various methods of voltage control and explain any three in detail. (Nov 2013)

(13M) BTL4


Tap changing transformers: (2M)

On load tap changing

Off load tap changing

Static shunt capacitors: (3M)

Shunt capacitor banks –supply reactive power at both transmission and distribution

levels.

Capacitors supply reactive power-line have lagging power factor

Series capacitors: (3M)


of the line.


Shunt reactors: (3M)



Synchronous condenser: (2M)

Synchronous machine running without a prime mover or a mechanical load.

By controlling field excitation it can be made to generate or absorb reactive power.

5. (i)Discuss the relation between voltage and reactive power at a node. (Nov 2012) (9M)

BTL5


Definition: (2M)



Phase voltage at a node is function of real and reactive power at node.

Diagram: (2M)

Real Power: (2M)

(E-V)V = PR+QX

Reactive power: (3M)

(E-V)V = PR+QX

Q =

(ii) Explain the tap changing transformer method of voltage control. (May 2013) (4M)

BTL4


On load tap changing: (2M)

Voltage maximum value and current are divided equally and flow in opposition through

coils

Resultant flux zero

Minimum impedance

Off load tap changing: (2M)

Offloading tap changing transformer requires the disconnection of transformer-tap setting to

changed

6.

Derive the relation between voltage and real & reactive power in a transmission line.

Explain the voltage profile variation along the line as reactive power varies. (May 2014)

(13M) BTL3


Definition: (1M)

Phase voltage at a node is function of real and reactive power at node.

Diagram: (3M)

Real Power: (3M) (E-V)V = PR+QX

Reactive power: (3M)

(E-V)V = PR+QX



Q =

Voltage: (3M)

7.

What are static Var systems? State the advantages of SVC. (May 2013) (13M) BTL4


static Var systems: (6M)

The term static var compensator is applied to a number of static var compensation

devices for use in shunt reactive control.

These devices consist of shunt connected, static reactive element (linear or nonlinear

reactors and capacitors) configured into a var compensating system.

Even though the capacitors and reactors in are shown in figure connected to the low

voltage side of a down transformer, the capacitor banks may be distributed between high

and low voltage buses.

The capacitor bank often includes, in part, harmonic filters which prevent the harmonic

currents from flowing in the transformer and the high voltage system.

Filters for the 5th and 7th harmonics are generally provided.

The thyristor controlled reactor (TCR) is operated on the low voltage value.

Advantages of SVC: (7M)

Bus voltages can be controlled

Improves system stability, voltage stability

Reduces power oscillations

Minimize transmission loss

8. Explain the steady state and dynamic response of AVR loop.(13M) BTL4 Answer: Page 3.9- M.Jeraldin Ahila Block diagram: (2M)



Steady state response AVR loop: (2M)

Position error constant: (1M)

Steady state response AVR closed loop: (4M)

Dynamic response AVR loop: (4M)

G(s) =

9.

(i) Name the generators and consumers of reactive power in a power system.

(May 2013)(8M) BTL2


Synchronous generators: (3M)

Generate or absorb reactive power

Short circuit ratio: (2M)

Reactive power supplied by synchronous generator depending upon SCR.

Explanation: (3M)

Overexcited synchronous machine operating on no load condition-synchronous

condenser-generates reactive power.

Underexcited synchronous machine absorbs reactive power.

(ii) Explain briefly the reactive power requirement for control of voltage in radial lines.

(Nov 2012)(5M) BTL4


Explanation: (5M)

All machines and equipment are designed to operate at certain voltage

Operation above or below voltage could damage the system components

System stability is increased to maximize utilization of the transmission system.

Reactive power minimized-to reduce- and -losses

10.

Explain the following methods of voltage control. (May 2013) (13M) BTL4

i. Shunt reactors


Explanation: (3M)





ii. Synchronous phase modifiers


Explanation: (3M)

Located in receiving substation and distribution system

Smooth and stepless variation of compensation.

Reactive power injected into line. iii. Shunt capacitors


Explanation: (3M) Shunt capacitor banks –supply reactive power at both transmission and distribution

levels.

Capacitors supply reactive power-line have lagging power factor. iv. Series capacitors


Explanation: (3M)


of the line.


PART*C

1.

The load at receiving end of a 3 phase overhead transmission line is 25 MW, 0.8 p.f lags at

the line voltage of 33 KV. A synchronous compensator is situated at receiving end and

voltage at both ends of the line is maintained at 3 KV. Calculate the MVAR of the

compensator. The line has resistance and reactance of 5 ohm/phase and 20 ohm/phase.

(May 2014) (15M) BTL3


P2 and Q2: (4M)

Phase Voltage: (3M)

= 19.05 V

Change in voltage: (3M)

: (3M)

Total reactive power: (2M)

Total reactive power = 3*11.024 = 33.072 MVAR



2.

Explain the injection of reactive power by switched capacitors to maintain the acceptable

voltage profile and to minimize the transmission loss in a power system. (May 2014) (15M)

BTL4


Diagram: (3M)

static Var systems: (4M)

The term static var compensator is applied to a number of static var compensation

devices for use in shunt reactive control.

These devices consist of shunt connected, static reactive element (linear or nonlinear

reactors and capacitors) configured into a var compensating system.

Even though the capacitors and reactors in are shown in figure connected to the low

voltage side of a down transformer, the capacitor banks may be distributed between high

and low voltage buses.

The capacitor bank often includes, in part, harmonic filters which prevent the harmonic

currents from flowing in the transformer and the high voltage system.

Filters for the 5th and 7th harmonics are generally provided.

The thyristor controlled reactor (TCR) is operated on the low voltage value.

Advantages of SVC: (3M)

Bus voltages can be controlled

Improves system stability, voltage stability

Reduces power oscillations

Explanation: (5M)

Saturated Reactors

Thyristor controlled reactors

Thyristor switched capacitors

Thyristor controlled transformers

3.

Find the rating of synchronous compensator connected to the tertiary winding of 60 KV

star connected, 33 KV star connected, 11 KV delta connected three winding transformer to

supply a load 60 MW at 0.8 p.f lagging at 33 KV across the secondary. Equivalent primary

and tertiary winding reactance are 18 ohm and 0.12 ohm respectively. While the secondary

winding reactance is negligible. Assume that V1 is 66 KV and maximum off nominal



setting between transformer primary and secondary is 1:1.1. (Nov 2018) (15M) BTL4


Voltage value: (5M)

t=1.1

P and Q Value: (5M)

: (5M)

11 MVAR/ph

Total reactive power required for synchronous compensation 3 = 3*11=33 MVAR

4.

Explain with neat diagrams and V-I characteristics, the basic operation of TCR and TSC.

(April/May 2018) (15M)


Explanation: (3M)

Discrete leading VARs from the capacitors and continuous lagging VAR from thyristor

controlled reactors.

Diagram: (6M)

V-I Characteristics: (6M)



UNIT IV-UNIT COMMITMENT AND ECONOMIC DISPATCH

Formulation of economic dispatch problem – I/O cost characterization – incremental cost curve -

co-ordination equations without and with loss (No derivation of loss coefficients) - solution by

direct method and λ-iteration method - statement of unit commitment problem – priority-list

method - forward dynamic programming.

PART *A

Q.No. Questions

1.

What is meant by priority list method? (May/June 2016) BTL1

Priority list method is the simplest unit commitment solution method which consists of creating

a priority list of units

The priority list can be obtained by nothing the full load average production cost of each unit.

2.

Compare unit commitment and economic load dispatch problems. (May 2018)

(Nov 2018)BTL4

Unit Commitment Economic dispatch

Optimum allocation of number of units to be

operated (to determine the units of a plant

that should operate for a given load is the

problem of unit commitment)

Optimum allocation of generation to each

station. (At each generating station at various

station load levels)

There are number of subsets of the complete

set of n units that would satisfy the expected

demand.

The problem assumes that there are n units

already connected to the system.

3.

State the need for unit commitment. BTL4

Enough units will be committed to supply the system load

To reduce the loss or fuel cost

By running the most economic unit, the load can be supplied by that unit operating closer

to its efficiency

4.

Define spinning reserve constraint in unit commitment problem. (Nov 2012) BTL1

Spinning reserve is one of the most important constraint in unit commitment problem. It is

defined as the total amount of generation available from all units which is synchronized on the

system subtracted with the present load and losses being supplied.

5.

What is the significance of unit commitment? (May 2012) BTL2

It minimizes the loss and the fuel cost

It commits the enough units to supply the system load.

It chooses the most economic unit for running to meet out the load so that the unit will

operate closer to its best efficiency.

6.

What is incremental cost criterion? (Nov 2012) BTL1

For the unit commitment table, fuel cost curve of the plant can be determined in the form of least

square fit. If transmission losses are neglected, the total system load can be optimally divided

among the various generating plants using the incremental cost criteria

= λ



7.

Write the equality and inequality constraints considered in the economic dispatch

problem. (Nov 2011) BTL1

Equality constraints are the basic load flow equation is given by

Inequality constraints:

Generator constraints

Voltage constraints

Transformer tap setting

Transmission line constraints

8.

What is meant by FLAPC? (Nov/Dec 2017) BTL1

FLAPC-Full load average production cost.

FLAPC = {Net heat rate at full load}*Fuel cost

= = K.

9.

Write the condition for optimal power dispatch in a lossless system. (Nov/Dec 2017) BTL4

The necessary condition for the existence of a minimum cost operating condition is that the

incremental cost rates of all the units to be equal to some undetermined value of Lagrangian

multiplier (λ).

=

10.

What are the constraints in unit commitment? (April/May 2017) BTL2

Spinning reserve

Thermal constraints

Minimum uptime

Minimum down time

Crew constraint

Other constraints

Hydro constraint

Must run constraint

Fuel constraint

11.

Define incremental cost in power dispatch. (April/May 2017) BTL1

The incremental fuel cost of all the generating units must be the same. The common value of

incremental fuel cost (λ) is called the system incremental cost.

C = cost function

Power generation

12. State the unit commitment problem. BTL1

To select the generating units that will supply the forecasted (estimated load in advance) load of



the system over a required period of time at minimum cost as well as provide a specified margin

of the operating reserve, known as the spinning reserve. This procedure is known as unit

commitment.

13.

Define merit order scheduling. BTL1

Merit order scheduling ensures that the incremental cost of all the generators is constant over the

full range (or) over successive discrete portions within the range. This method of scheduling is

known as merit order scheduling.

14.

Name the methods of finding economic dispatch. BTL1

The two methods to find economic dispatch are

Load scheduling

Unit commitment

15.

Write about the term incremental operating cost of the power system.

(Nov/Dec 2016)BTL4

The incremental fuel cost of all the generating units must be the same. The common value of

incremental fuel cost λ is called the system incremental cost.

16.

What is exact coordination equation? BTL1

= λ

IC = Incremental cost

ITL = Incremental transmission loss

17.

Define the term penalty factor. BTL1

= =

=

is called penalty factor

18.

State the difference between load frequency controller and economic dispatch controller.

BTL4

The load frequency controller is a fast acting controller and the economic dispatch controller in a

slow acting control.LFC adjusts the speed changes setting every minute in accordance with a

command signal generated by the central economic dispatch controller.

19.

Define Lagrangian multiplier. BTL1

The necessary condition for the existence of a minimum cost operating condition is that the

incremental cost rates of all the units be equal to some undetermined value (λ) called lagrangian

multiplier.

=

20.

State the advantages of using participation factor. BTL4

Computed implementation of economic dispatch is straight forward

Execution time for economic dispatch is short.

It will always give consistent answers when unit reach limits.

It gives linear incremental cost functions or have non convex cost curves.



21.

What are all the point to be noted for an economic load dispatch including transmission

losses? BTL4

The incremental cost of production of a plant is always positive, the incremental

transmission losses can be both positive and negative.

The individual generators will operate at different incremental cost of production

The generation with highest positive incremental transmission loss will operate at lowest

incremental cost of production.

22.

Relate the necessary condition for the existence of minimum cost operating for the thermal

power system. (May 2018) BTL4

The minimum condition is that the incremental cost rates of all units be equal to understand (λ).

In addition to this condition, adding the constraint equation that the sum of power outputs must

be equal to the power demanded by the load.

= N equation

2N equation

23. Define crew constraints. (Nov 2018) BTL1

If a plant consists of two or more units, they cannot both be turned on at the same time. Since

there are not enough crew members to attend both units while starting up.

PART*B

1.

Explain various constraints in UC and indicate the steps involved in solving unit

commitment by Dynamic programming method. (May 2012) (13M) BTL4


Unit commitment problem: (2M)

The expected system demand levels for -24 hrs of tomorrow and the operating cost, startup cost

and shut down cost of the available N units.

If N generating units, (2N -1) number of combination obtained.

Constraints: (2M)

Spinning reserve

Thermal constraints-Minimum up time and down time-crew constraint

Other constraints-Hydro constraint-Must run constraint-Fuel constraints

Forward dynamic programming: (4M)

Unit commitment table is arrived for the complete load cycle.

Algorithm-run forward from initial hour to final hour.

Previous history of unit computed at each stage.

Initial conditions are easily specified.

Flowchart: (5M)

2.

Formulate the co-ordination equations with losses neglected and also explain the

algorithmic steps of iterative method to find the solution of coordination equations. (May 2012) (13M) BTL4

Draw the flowchart for obtaining the optimum dispatch strategy of N bus system

neglecting the system transmission loss. (Nov 2015) (13M) BTL4


Cost function: (3M)

Minimize C =

C = operating cost

Lagrangian multiplier: (2M)



Minimum objective function: (2M)

Calculate λ : (1M)

Flowchart: (5M)

3.

Explain the λ-iteration method for finding the solution of economic dispatch including

transmission losses with a flowchart. (Nov 2012) (13M) BTL5


Compute λ : (3M)

Transmission loss: (4M)

Flowchart: (6M)

4.

(i)With the help of flowchart explain economic dispatch by λ-iteration method without

loss. (May 2013) (8M) BTL4


Calculate λ : (2M)

Compute : (2M)

Power balance equation: (2M)

Optimum solution: (2M)

(ii) Define the following. (Nov 2012) (5M) BTL2




Minimum up time: (1M)

Once the unit-running-should not turned off immediately.

Minimum down time: (2M)

Once the unit-decommited-minimum time-before recommitted.

Spinning reserve: (2M)

Spinning reserve is one of the most important constraint in unit commitment problem.

It is defined as the total amount of generation available from all units which is

synchronized on the system subtracted with the present load and losses being supplied.

5.

Derive the coordination equation for economic dispatch with and without loss. (Nov 2014)

(13M) BTL3


Economic dispatch with loss: (6M)

Minimize C =

C = operating cost

=

= =

=

is called penalty factor

Economic dispatch without loss: (7M)

6.

Explain the priority list method for unit commitment problem with an example.

(Nov 2012) (13M) BTL4


Priority list method: (3M)

Creates priority list of unit.

FLAPC-Full load average production cost.

FLAPC = {Net heat rate at full load}*Fuel cost

= = K.

Assumption: (3M)

No load costs are zero.

Startup cost are fixed amount.

Ignore minimum up and down time.

Unit commitment example: (7M)

FLAPC

= = 9.79



= = 9.4

= = 11.188

Priority order

Unit FLAPC Min (MW) Max (MW)

2 9.4 100 400

1 9.79 150 600

3 11.188 50 200

Unit commitment

Combination Minimum MW from

combination

Maximum MW

from combination

2+1+3 300 1200

2+1 250 1000

2 100 400

7.

State the unit commitment problem. With the help of a flowchart, explain forward

dynamic programming solution method of unit commitment problem.

(Nov 2013,2014,2018) (13M) BTL5


Unit commitment problem: (3M)

The expected system demand levels for -24 hrs of tomorrow and the operating cost, startup cost

and shut down cost of the available N units.

If N generating units, (2N -1) number of combination obtained.

Forward dynamic programming: (4M)

Unit commitment table is arrived for the complete load cycle.

Algorithm-run forward from initial hour to final hour.

Previous history of unit computed at each stage.

Initial conditions are easily specified.

Flowchart: (6M)

8.

(i)What is the significance of equality and inequality constraints in the formulation of

optimal dispatch problem? (May 2013) (4M) BTL2


Significance: (4M)

Total generation = Total demand

Particular generator reaches the limit, its loading from now on is held fixed at this value

Balanced load shared between the remaining generators on equal incremental cost basis.

(ii) The fuel cost function for the three thermal plants in Rs/h are given by



0.004

0.006

0.009

Where P1 ,P2, P3 are in MW. The total load is 925 MW. Find the optimal dispatch and the

total cost in Rs/h. (May 2017) (Nov 2018) (9M) BTL3

100 MW

100 MW

100 MW

Compute λ: (1M)

= 8.9737

Compute : (3M)

Incremental cost rule: (1M)

Optimum schedule: (4M)

390.524 MW

350MW

184.476MW

9.

(i) The fuel cost of two units are given by

0.1

1.9+ 0.1

If the total demand on the generator is 200 MW. Find the economic load scheduling of the

two units. (May 2013) (4M) BTL3

Answer: Page 6.20- M.Jeraldin Ahila Economic dispatch: (1M)

Condition: (1M)

=



Generation value: (1M)

= 150 MW

= 50 MW

(ii) Create a unit commitment using the priority list method for the following three units.

The fuel cost equation are as follows: PD = 800 MW. (May 2018) (9M) BTL3

; 150

; 100

; 50

Answer: Page 5.6- M.Jeraldin Ahila FLAPC: (3M)

= = 9.79

= = 9.4

= = 11.188

Priority order: (3M)


2 9.4 100 400

1 9.79 150 600

3 11.188 50 200

Unit commitment: (3M)


combination

Maximum MW

from combination

2+1+3 300 1200

2+1 250 1000

2 100 400

10.

Obtain the priority list of unit commitment using full load average production cost for the

given data:

0.00142

310+ 0.00194



78+ 0.00483

Unit Min (MW) Max (MW) Fuel cost (k)

1 150 600 1.1

2 100 400 1.0

3 50 200 1.2

PD = 500 MW. (May 2013) (10M) BTL3


FLAPC: (4M)

= = 9.79

= = 9.4

= = 11.188



2 9.4 100 400

1 9.79 150 600

3 11.188 50 200



combination

Maximum MW

from combination

2+1+3 300 1200

2+1 250 1000

2 100 400

11.

The incremental cost of three units in a plant are

Where are power output in MW. Determine the optimum load allocation

when the total is 242.5 MW. Using participating factors, determine the optimum

scheduling when the load increased to 250 MW. (May 2018) (13M) BTL3


Incremental cost rule: (3M)



= =λ

λ = 210 Rs/Mwh

Optimum load allocation: (3M)

Change in Generation: (4M)

Optimum Schedule: (3M)

= 65.4655 MW

PART*C

1.

The fuel inputs per hour of plants 1 and 2 are given as

0.2

0.25

Determine the economic operating schedule and the corresponding cost of generation if the

maximum and minimum loading on each unit is 100 MW and 25 MW.Assume the

transmission losses are ignored and the total demand is 180 MW. Also determine the

saving obtained if the load is equally shared by both the units. (Nov 2011,13) (15M) BTL3

Answer: Page S.55- M.Jeraldin Ahila

Compute λ : (3M)

= 0.4

= 0.5

= 75.56

and (4M)



Check for limit: (1M)

Cost of generation: (5M)

5256.64 Rs/hr

4957.80 Rs/hr

Total Cost = 10214.44 Rs/hr

Net Saving: (2M)

Net Saving = 0.56 Rs/hr

2.

Determine the priority list using full load average production cost for the data given below.

Loading units Fuel cost parameter

Unit no Minimum Maximum ai bi ci Fuel cost

1 100 400 0.006 7 600 1.1

2 50 300 0.01 8 400 1.2

3 150 500 0.008 6 500 1.0

Also obtain unit commitment solution for the power demand of 800 MW. (May 2014)

(15M) BTL3


0.006

400+ 0.01

500+ 0.008

FLAPC: (5M)

= = 11.99

= = 14.8

= = 11



3 11 150 500

1 11.99 100 400



2 14.8 50 300



combination

Maximum MW

from combination

3+1+2 300 1200

2+1 250 900

2 150 500

3.

A heat rate of 100 MW fuel fired generator is

10 MKcal\MWhr at 25% rating



Find fuel cost at 25,40,100%loading Incremental cost and Fuel input rate using quadratic

approximation to deliver 101 MW. (May 2014) (15M) BTL3


Heat rate: (4M)

+

+ *25 =10

+ *40 =9

+ *100 =8

Fuel cost: (4M)

)* = 66.66+ 7.33

Fuel input rate: (4M)

At 25% rating:

F(25) = 66.66+7.33*25 = 250MK cal/hr

C(25) = K*F(25) = 2*250 = 500 Rs/hr

At 40% rating:

F(40) = 66.66+7.33*40 = 360MK cal/hr

C(40) = K*F(40) = 2*360 = 720 Rs/hr

At 100% rating:

F(100) = 66.66+7.33*100 = 800MK cal/hr

C(100) = K*F(100) = 2*360 = 1600 Rs/hr

Quadratic approximation: (3M)

C(101) = 2*66.66+2*7.33*101 = 1614 Rs/hr



UNIT V-COMPUTER CONTROL OF POWER SYSTEMS

Need for computer control of power systems - concept of energy control centre - functions - system

monitoring - data acquisition and control - system hardware configuration – SCADA and EMS

functions - network topology - state estimation – WLSE - Contingency Analysis - state transition

diagram showing various state transitions and control strategies.

PART *A

Q.No. Questions

1.

Define Energy control centre. BTL1

The operation and interaction become more complex in power system, when its size increases.

So its necessary to monitor the information for every second for the total system is called energy

control centre.

2.

What are the major functions that are carried out in an operations of control centre?

(Nov 2016) BTL4

System monitoring

Contingency analysis

Security constrained optimal power flow

Unit commitment

Maintenance scheduling

State estimation


3.

What is SCADA? (May 2012) (Nov 2012) BTL1

SCADA is Supervisory Control and Data Acquisition system that allows operators to monitor

the generation and HV transmission system.

4.

What are the functions of SCADA? (May 2013) (Nov 13,16) BTL1

Monitoring

Data acquisition

Alarm

Data logging

ON/OFF control

Control and indication of AGC

5.

Define EMS system. (Nov 2011) BTL1 Energy management system is the process of monitoring, coordinating and controlling the

generation, transmission and distribution of electrical energy. It is performed at centre called

system control centres by a computer system called Energy Management system.

6.

What are the objectives of Automatic Generation Control? (May 2014) BTL4

To maintain each unit generation at the most economic value.

To hold frequency at very close to a specified nominal value.

To maintain the correct value of interchange power between control areas.



7.

Define state estimation. (May 2013) (Nov 2013) BTL1

State estimation is the process of assigning a value to an unknown system states variable based

on measurements from that system according to minimizing the sum of the squares of the

differences between estimated and true value of the function.

8.

Define restorative state. (May 2014) BTL1

In restorative state, the control action is being taken to reconnect all the facilities and to restore

the system load to the normal state.

9.

What is the function of load dispatch centre? (Nov 2011, May 2012) BTL1

Loading of generating stations.

Control of system voltage and reactive power flow.

Loading of units within the generating station.

10.

How is load forecasting classified? BTL2

Long term forecasting

Medium term forecasting

Short term forecasting

Very short forecasting

11.

What are the states of power system? (Nov/Dec 2015) BTL1

Normal state

Alert state

Emergency state

In-Extremis state

Restorative state

12.

What are the functions of control center? (Nov/Dec 2015) BTL4

System monitoring

Contingency analysis

Security constrained optimal power flow

Unit commitment

Maintenance scheduling

State estimation


13.

What are responsibilities of regional load dispatch centres? (April/May 2015) BTL2

Regional load dispatch centre decides generation allocation to various generating station within

the region on basic of equal incremental cost, line losses and frequency control.

14.

List the applications of SCADA. (Nov/Dec 2014) BTL1

Used to manage a physical process in many industries.

Used to make sure that productivity targets are met and all systems run smoothly in

manufacturing

Used in food production industries

Used to control the movement of power and gas throughout the distribution chain.

15.

State the weight least square criterion. (April/May 2018) BTL2

The weighted least square criterion, where the objective is to minimize the sum of the square of

the weighted deviations of the estimated measurements from actual measurements.



16.

List out the condition for normal operation of a power system. (April/May 2017) BTL1

A system is said to be in normal state if both load and operating constraints are satisfied. It is

one in which the total demand on the system is met by satisfying all the operating constraints.

(equality and inequality constraints)

17.

Define Network Topology in a power system. BTL1

In order to run the state estimation, we must know how the transmission lines are connected to

the load and generation buses. This information is called network topology

18.

What is contingency analysis program? BTL1

The problems occur on a power system and cause serious trouble and the time –period to rectify

it is insufficient and hence causes cascading failures. Due to this, the modern operation

computers are equipped with contingency analysis programme.

19.

State the typical sensors used in power system applications. BTL2

Signal conditioners

Multiplexers

A/D converters

20.

Distinguish between reliability and security of a power system.

Reliability is a probabilistic index defined as the long term average number of days on

which daily peak loads exceeds the available generating capacity.

Security depends upon the reserve capacity available in a given situation and the

contingency probability of distribution.

21. State the weight least square criterion. (May 2018) (Nov 2018) BTL1


the weighted derivations of the estimated measurements from the actual measurements.

22.

What are the priorities for operation of modern power system? (Nov 2018) BTL2

Normal state

Alert state

Emergency state

Extremis state

Restorative state

are the priorities for operation of modern power system.

PART*B

1.

Briefly explain various functions of SCADA with a neat diagram. (Nov 2011,2012)

(May 2012) (13M) BTL4

Explain the hardware configuration and function of SCADA. (Nov 2015,2018) (13M) BTL4


Diagram: (4M)



SCADA: (3M)

There are two parts to the term SCADA Supervisory control indicates that the operator,

residing in the energy control center (ECC), has the ability to control remote equipment.

Data acquisition indicates that information is gathered characterizing the state of the

remote equipment and sent to the ECC for monitoring purposes.

The monitoring equipment is normally located in the substations and is consolidated is

known as the RTU

Function: (4M)

Data acquisition

Information display.

Supervisory Control

Information storage and result display.

Sequence of events acquisition

Control Function: (2M)

Dynamic Bus bar coloring according to their actual operational status.

Automatic switching sequences.

2. Explain various state transition and controls strategies using state transition diagram.

(Nov 2011) (13M) BTL4


Diagram: (6M)



Explanation: (7M)

Normal state

Alert state

Emergency

Extremis

Restorative

3.

Discuss the various functions, system monitoring and control of load dispatch center.

(May 2012) (13M) BTL4


Functions: (4M)

Coordinate the response of the system in both normal and emergency condition.

Digital computer-process the income stream data to detect abnormalities.

System monitoring: (4M)

Loss of many generators or excess power demand by neighboring utility on tie lines

Many Alarm could be detected

System could enter an emergency state.

Control: (5M)

4.

Enumerate the operating states and the control strategies of a power system. (Nov 2012)

(13M) BTL5

Explain the different operating states in the security perspective with an example.

(Nov 2015) (13M) BTL5

Explain the various operating stages of power system. Also discuss the state transition

and control strategies. (Nov 2014) (13M) BTL5

What is normal operating state of a power system? Describe in detail the various state

that a power system takes, with their operating conditions.(May 2015) (13M) BTL5


Diagram: (6M)



Normal state: (1M)

A system is said to be in normal if both load and operating constraints are satisfied .It is one in

which the total demand on the system is met by satisfying all the operating constraints.

Alert state: (2M)

A normal state of the system said to be in alert state if one or more of the postulated contingency

states, consists of the constraint limits violated.

When the system security level falls below a certain level or the probability of disturbance

increases, the system may be in alert state.

Emergency state: (2M)

The system is said to be in emergency state if one or more operating constraints are violated, but

the load constraint is satisfied.

In this state, the equality constraints are unchanged.

Extremis state: (1M) When the system is in emergency, if no proper corrective action is taken in time, then it goes to

either emergency state or extremis state.

In this regard neither the load or nor the operating constraint is satisfied, this result is islanding.

Restorative state: (1M) From this state, the system may be brought back either to alert state or secure state .The latter is

a slow process.

Hence, in certain cases, first the system is brought back to alert state and then to the secure state

This is done using restorative control action.

5. (i)Explain the major functions of security control. (May 2013) (10M) BTL5


Security monitoring system: (5M)



Security control function: (5M) Network Topology processor-mode of the N/W

State estimator.

Power flow-V, δ,P,Q.

Optimal power flow.

Contingency analysis.

Optimal power flow.

(ii) What is EMS? What are its major functions in power system operation and control?

(May 2013) (3M) BTL5


Definition: (1M)

The EMS is a software system. Most utility companies purchase their EMS from one or

more EMS vendors.

These EMS vendors are companies specializing in design, development, installation, and

maintenance of EMS within ECCs.

Functionality Power EMS: (2M)

System Load Forecasting-Hourly energy, 1 to 7 days.

Unit commitment-1 to 7days.

Economic dispatch

Hydro-thermal scheduling- up to 7 days.

MW interchange evaluation- with neighboring system

Transmission loss minimization

6.

Draw a block diagram to show the hardware configuration of SCADA system for a power

system and explain the applications of SCADA in monitoring and control of power system.

(Nov2013) (13M) BTL4


Diagram: (4M)



SCADA: (3M)

There are two parts to the term SCADA Supervisory control indicates that the operator,

residing in the energy control center (ECC), has the ability to control remote equipment.

Data acquisition indicates that information is gathered characterizing the state of the

remote equipment and sent to the ECC for monitoring purposes.

The monitoring equipment is normally located in the substations and is consolidated is

known as the RTU

Function: (4M)

Data acquisition

Information display.

Supervisory Control

Information storage and result display.

Sequence of events acquisition

Control Function: (2M)

Dynamic Bus bar coloring according to their actual operational status.

Automatic switching sequences.

PART*C

1.

Explain the concept of energy control centre or load dispatch centre. Also discuss its

functions. (Nov 2014,2018) (15M) BTL4


Energy control centre: (5M)

Energy Control Center (ECC) is designed and built for system operation. In order to have an

efficient power system operation and control, various control centers have to be operated in the

hierarchical level. The following Table shows the level decomposition of control centers in

the power system.

Classification: (5M)

i) Local Control Centre

ii) Area Load Dispatch Centre

iii) State Load Dispatch Centre



iv) Regional Control Centre

Explanation: (5M)

Level System Monitoring and control

First Generating stations,

substations

Local control centre

Second Sub transmission and

transmission network

Area load dispatch centre

Third Transmission system State load dispatch centre

Fourth Interconnected power system Regional control centre

2.

What is state estimation with respect to power system? Explain briefly the method of

maximum likelihood weighted least squares estimation. (15M) (May 2015)BTL4


Definition: (2M)

State estimation Uses real-time status and analog measurements to determine the best estimate

of the state of the power system. It uses a redundant set of measurements; calculates voltages,

phase angles, and power flows for all components in the system; and reports overload

conditions.

Diagram: (5M)

Weighted least: (3M)



Criterion: (5M)

Objective to minimize [J] the sum of the squares of the weighted deviations of the estimated

measurements.



3.

Write short notes on state estimation? Explain the help of flow chart the weighted least

squares estimation. (15M) (May 2015) (Nov 2018)BTL4


Definition: (2M)

State estimation Uses real-time status and analog measurements to determine the best estimate

of the state of the power system. It uses a redundant set of measurements; calculates voltages,

phase angles, and power flows for all components in the system; and reports overload

conditions.

Flowchart: (5M)

Weighted least: (3M)



Criterion: (5M)

Objective to minimize [J] the sum of the squares of the weighted deviations of the estimated

measurements.

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