The document contains questions and answers related to power system operation and control. It discusses topics like the objectives of power system operation and control, definitions of terms like average demand and spinning reserve, types of load forecasting and frequency regulation needs in a power system, economic dispatch control and functions of an excitation system. It also covers concepts like area frequency response characteristic, coherent group of generators, static and dynamic response of ALFC loops, and unit commitment constraints.

1. Power system operation and control, Question
and answers
Answers by GPT-4, Claude 2
L
A
TEXformat by GPT4-turbo, Claude instant
Complied by Adhithya (200901002@rajalakshmi.edu.in)
Question collected from Anna university previous year paper.
1. List the objectives of power system operation and control.
The objectives of power system operation and control are to ensure the
reliability and security of the power system, to maintain the balance
between the generated power and the load demand, to maintain the
system frequency and voltage within permissible limits, and to mini-
mize the cost of generation.
2. Define average demand.
Average demand is the total energy consumed during a specified period
divided by the length of that period. It is usually measured in kilowatts
(kW) or megawatts (MW).
3. List out the various needs for frequency regulation in a power
system.
Frequency regulation in a power system is needed to maintain system
stability, to prevent damage to equipment due to frequency deviations,
to ensure the quality of power supply, and to facilitate the integration
of renewable energy sources.
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2. 4. Define spinning reserve.
Spinning reserve is the extra generating capacity that is available by
increasing the power output of generators that are already connected
to the power system. It is used to respond to sudden changes in load.
5. Mention the types of load forecasting.
The types of load forecasting include short-term load forecasting, medium-
term load forecasting, and long-term load forecasting.
6. State Area frequency response characteristic.
Area frequency response characteristic (AFRC) is a measure of how
the frequency of a power system changes in response to a change in
power imbalance in the system. It is usually expressed as a percentage
change in frequency per unit change in power imbalance.
7. What do you understand by coherent group of generators?
A coherent group of generators is a group of generators that respond
in a similar manner to system disturbances. They can be considered
as a single equivalent generator in stability studies.
8. Differentiate between static and dynamic response of an ALFC
loop.
Static response of an ALFC loop refers to the steady-state response,
while dynamic response refers to the transient response following a
disturbance. Static response does not consider the time factor, while
dynamic response considers the time factor.
9. Write about the economic dispatch control.
Economic dispatch control is a method used in power systems to min-
imize the total operating cost of generation while meeting the load
demand. It involves determining the optimal combination of power
outputs of all generators in the system.
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3. 10. What are the various functions of an excitation system?
The functions of an excitation system include controlling the generator
voltage, providing reactive power control, enhancing system stability,
and protecting the generator from damaging conditions.
11. State whether changes in AVR loop will be reflected in ALFC
loop.
Yes, changes in the Automatic Voltage Regulator (AVR) loop can af-
fect the Automatic Load Frequency Control (ALFC) loop, as both are
interconnected systems in power system control.
12. List the advantages of SVC FACTS devices.
The advantages of Static Var Compensator (SVC) Flexible AC Trans-
mission System (FACTS) devices include improved power system sta-
bility, increased power transfer capability, improved voltage regulation,
and reduced transmission losses.
13. Compare between shunt and series capacitor.
Shunt capacitors are connected in parallel with the load and are used
to improve power factor and voltage regulation. Series capacitors are
connected in series with the transmission line and are used to increase
power transfer capability by reducing line reactance.
14. Spinning Reserve
Spinning reserve is the extra generating capacity that is available by
increasing the power output of generators that are already connected
to the power system. It is a backup energy source that is always on
standby and can be used when there is a sudden increase in demand
or a sudden loss of a generator.
15. Load Forecasting
Load forecasting is essential for efficient and reliable operation of power
systems. It helps in planning and operation of power systems, schedul-
ing of power plants, maintenance scheduling, fuel reserve management,
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4. and demand side management. Accurate load forecasting can lead to
significant cost savings in these areas.
16. Speed Changer
The purpose of a speed changer is to control the speed of a machine.
In power systems, it is used to control the speed of generators. By
controlling the speed, we can control the frequency of the generated
electricity, which is crucial for maintaining the stability of the power
system.
17. Per Unit Droop
Per unit droop is a measure of how much the output frequency of
a generator changes for a given change in load. It is defined as the
percentage change in frequency for a 100% change in load. It is a key
parameter in load frequency control of power systems.
18. Stability Compensation in AVR Loop
Stability compensation in AVR (Automatic Voltage Regulator) loop is
important to prevent oscillations and ensure stable operation of the
power system. It helps in damping out oscillations that can occur due
to sudden changes in load or generation. Without stability compensa-
tion, these oscillations can lead to instability and even system collapse.
19. Power Flow Equations
The relation between voltage, power and reactive power at a node can
be given by the power flow equations. The real power P and reactive
power Q at a node are given by:
P = V
X
k
VkGik cos(θi − θk) + VkBik sin(θi − θk)
Q = V
X
k
VkGik sin(θi − θk) − VkBik cos(θi − θk)
where V is the voltage at the node, G and B are the conductance and
susceptance of the line connecting the nodes, and θ is the phase angle
of the voltage.
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5. 20. Unit Commitment Problem Constraints
The constraints that are accounted in unit commitment problem in-
clude minimum and maximum generation limits of each unit, ramp rate
limits, minimum up and down time constraints, start-up and shut-down
costs, and reserve requirements.
21. Load Frequency Controller and Economic Dispatch Controller
Load frequency controller and economic dispatch controller are two key
components of power system control. While both aim to balance supply
and demand, they have different objectives. Load frequency controller
aims to maintain system frequency at the desired level by adjusting the
output of generators. On the other hand, economic dispatch controller
aims to minimize the total generation cost while meeting the demand
and maintaining system constraints.
22. State Estimation
State estimation is a process used in power system operation to es-
timate the state of the system (e.g., voltages, power flows) based on
measurements and system models. It is used to obtain the most ac-
curate and reliable estimate of the system state, which is crucial for
real-time monitoring, control, and decision-making.
23. Control Centre Information
The control centre can receive and transmit various types of infor-
mation, including real-time measurements of voltages, currents, power
flows, and frequencies; status of circuit breakers and other equipment;
alarms and events; load forecasts; and control commands to generators,
substations, and other equipment.
24. Define the term Load curve and Load duration curve.
Load curve: It shows the variation of system load over a period of time
such as daily, weekly or yearly. Load duration curve: It is a cumulative
curve that shows the load variation on a percentage basis over a period
of time.
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6. 25. What is load forecasting in power system?
Load forecasting refers to the process of estimating future load demand
over a specified period of time.
26. What is the need for load forecasting in power systems?
The need for load forecasting:
- To estimate future generation capacity
- Plan transmission and distribution facilities
- Determine operating strategies
- Scheduling of maintenance
- Planning of fuel purchases
- Financial evaluation of future projects
27. State the factors affecting the load forecasting.
Factors affecting load forecasting:
- Weather conditions
- Random disturbances
- Economy and industrial growth trends
- Population growth
- Usage pattern of consumers
- Prices of electricity
28. Define Daily Load Curve and Monthly Load Curve.
Daily load curve shows the variation of load demand over a day. Monthly
load curve shows the variation of load demand over a month.
29. What is Diversity factor?
Diversity factor is defined as the ratio of the sum of the individual
maximum demands to the maximum demand of the entire system.
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7. 30. Write the implications of high diversity factor and list any
two methods employed to increase the diversity factor.
Implications of high diversity factor:
- Reduces spare capacity needed
- Saves capital investment
Methods to increase diversity factor:
- Load management techniques
- Energy storage systems
31. State the need for Load Forecasting in Power Systems.
The need for Load Forecasting in Power Systems:
- Adequate generation and transmission capacity planning
- Scheduling of fuel purchases and maintenance
- Load flow and stability analysis
- Estimating peak load demand
- Determining best operating conditions
32. List any two conditions for proper Synchronizing of Alterna-
tors.
Two conditions for proper synchronizing of alternators:
- Voltage difference should be within permissible limit
- Frequency difference should be zero or very small
33. Give the two conditions for proper synchronizing of alterna-
tors.
Same as above
34. Define the concept of Tie-Line Bias Control.
Tie-line bias control: It modifies the net interchange of power over tie-
lines between control areas to maintain scheduled system frequency.
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8. 35. What is the objective of tie-line bias control?
Objective of tie-line bias control: To maintain zero steady state fre-
quency deviation in a control area following a disturbance by control-
ling the net interchange over tie-lines.
36. Define area control error.
Area control error: It is the instantaneous difference between actual
and scheduled power interchange over control area tie-lines, taking into
account the effect of frequency deviation.
37. Sketch the V — I characteristics of SVC.
38. What is SVC?
SVC: Static VAR Compensator. It provides fast acting dynamic reac-
tive power support.
39. Mention the different types of Excitation System used in Power
Systems.
Types of excitation system:
- DC excitation system
- AC excitation system
- Static excitation system
40. What are the various functions of an excitation system?
Functions of excitation system:
- To provide necessary field current to maintain the terminal voltage
- To ensure good recovery of voltage following disturbances
- To suppress oscillations by damping
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9. 41. What is exciter ceiling voltage?
Exciter ceiling voltage: It is the maximum exciter voltage available to
excite the generator field winding.
42. What are the Constraints in Unit commitment?
Constraints in unit commitment:
- Power balance constraints
- Generator operation constraints
- Fuel constraints
- Crew constraints
- Emission constraints
43. What are the techniques available for the solution of unit
commitment problem?
Techniques for solution of unit commitment:
- Priority list methods
- Dynamic programming
- Lagrangian relaxation
- Evolutionary algorithms
44. Define crew constraints?
Crew constraints: The minimum uptime and downtime to be provided
to generating units based on labour contracts and thermal stress con-
siderations.
45. What are the constraints in unit commitment?
Same as question 18
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10. 46. State the assumptions made in Economic Dispatch Problem.
Assumptions in economic dispatch:
- Load is known and fixed
- Transmission losses are neglected
- Generator operating limits are ignored
47. Write about the term incremental operating cost of a power
system.
Incremental operating cost refers to the fuel cost for producing one
additional MW of power from a generator.
48. Define incremental cost in power dispatch.
Incremental cost refers to the cost of producing one additional MW of
power from a generator.
49. Write the condition for the optimal power dispatch in a loss-
less system.
For a lossless system, incremental cost is same for all committed gen-
erators at optimal dispatch.
50. Write the coordination equation taking the effect of transmis-
sion losses.
The coordination equation considering transmission losses equates the
incremental cost and incremental transmission losses at optimal dis-
patch.
51. Relate the necessary condition for the existence of minimum
cost-operating for the thermal power system.
At optimal dispatch, the incremental fuel cost and incremental reduc-
tion in system transmission losses should be equal for all dispatched
generators.
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11. 52. List out the Functions of SCADA.
Functions of SCADA:
- Data acquisition
- Network control
- Data display
- Alarm processing
- Historical data collection
53. What is SCADA?
SCADA: Supervisory Control and Data Acquisition. It refers to an
automated system that monitors and controls industrial/infrastructure
facilities.
54. What are the functions of SCADA?
Same as question 28
55. Define Energy Control Centre.
Energy Control Centre: It monitors the performance of generators
and the transmission network. Determines economic dispatch and unit
commitment.
56. What are the major functions that are carried out in an op-
erational control centre?
Major functions of operational control centre:
- Economic dispatch
- Unit commitment
- Load forecasting
- State estimation
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12. 57. Define state estimation.
State estimation: It is the process of assigning a state vector to the
power system through statistical analysis of telemetered measurements.
58. Define state estimation.
Same as above
59. Define state estimation.
Same as above
60. What is the need for load forecasting?
The need for load forecasting:
- Planning of future generation and transmission requirements
- Scheduling generator maintenance
- Determining fuel requirements
- Financial analysis of new projects
61. What is spinning reserve?
Spinning reserve: Unloaded synchronized generating capacity that is
ready to take additional load immediately.
62. What is the use of Secondary loop?
Secondary loop: It is used to damp out oscillations resulting from
sudden load changes.
63. Define control area.
Control area: It consists of an electric system or systems, bounded by
interconnection metering and telemetry. It controls its generation and
interchange schedules to maintain its interchange schedule with other
control areas.
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13. 64. What do you understand by control area?
Same as above
65. Define control area.
Same as above
66. State the advantage of switched capacitors in voltage control.
Advantages of switched capacitors:
- Smooth voltage control
- Low operating cost
- Long life
67. Comment on the use of series capacitors in transmission lines.
Series capacitors reduce effective line reactance, thereby increasing
transmittable power and improving stability.
68. What are the different types of Static VAR Compensator?
Types of SVC:
- Thyristor controlled reactor (TCR)
- Thyristor switched capacitor (TSC)
- Mechanically switched capacitor (MSC)
- Thyristor switched reactor (TSR)
69. Distinguish between Economic dispatch and Unit commit-
ment.
Economic dispatch minimizes operation cost for supplying the load de-
mand. Unit commitment determines the committed status and output
level of available generators over a time period.
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14. 70. What are the priorities for operation of modern power sys-
tem?
Priorities for operation of modern power system:
- Safety
- Reliability
- Economy
- Ecology
71. Define the term Load curve and Load duration curve.
Same as question 1
72. What are the types of ALFC for interconnected power sys-
tem?
Types of ALFC:
- Flat frequency control
- Flat tie-line control
- Tie-line bias control
73. State the different types of ALFC for interconnected power
system.
Same as above
74. What is the function of load frequency control?
Function of load frequency control: To maintain zero steady state fre-
quency deviation and good dynamic response following a system dis-
turbance.
75. What are the advantages and disadvantages of synchronous
compensators?
Advantages: Flexible control, black start capability Disadvantages:
Higher cost, higher losses
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15. 76. What is meant by FLAPC?
FLAPC:Full load average production cost.
77. Specify the use of static and dynamic response of the ALFC.
Static response: Proportional feedback control Dynamic response: Uses
integral control action
78. Mention the purposes of series compensation.
Purposes of series compensation:
- To increase transmittable power
- To enhance system stability
79. What is the need for frequency regulation in power system?
Need for frequency regulation:
- To maintain constant speed of motors
- To prevent damage to synchronous machines
- To minimize fluctuations in power transfer
80. Define load duration-curve.
Same as question 1
81. Classify the system load.
System loads can be classified as residential, commercial, industrial and
agricultural loads.
82. What are the sources of reactive power? How it is controlled?
Sources of reactive power: Synchronous generators, capacitors, reac-
tors, SVCs, STATCOMs. It is controlled by excitation control, switched
capacitors/reactors, tap changing transformers.
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16. 83. What is the use of off-load tap changer and TCUL?
Off-load tap changers: To adjust transformer turns ratio during light
load conditions. TCUL: To prevent transformer overloading during
emergencies by online tap changing.
84. What is blackout in power grid?
Blackout refers to the total loss of electric supply over a large area for
a significant period of time.
85. What are brownouts?
Brownouts refer to drops in voltage in an electrical power supply sys-
tem.
86. What is the need for integral controller in ALFC?
Integral controller: To eliminate steady state errors and ensure zero
frequency deviation under normal operating conditions.
87. List out the conditions for normal operation of a power sys-
tem.
Conditions for normal operation:
- Frequency within limits
- Voltages within limits
- Loading within thermal limits
- All equipment in service
88. Outline the role of synchronous generators adopted for gen-
eration and absorption of reactive power.
Synchronous generators can operate at leading/lagging power factors
to generate/absorb reactive power thereby controlling bus voltages.
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17. 89. Compare unit commitment and economic dispatch problems.
Economic dispatch minimizes operating cost for a given load demand
while unit commitment determines the committed status and output
levels of generators over a time period.
90. State the Weighted Least Square Criterion.
Weighted Least Square Criterion: It minimizes the weighted sum of
squared residuals between estimated and measured state variable val-
ues.
91. List the basic functions of EMS.
Basic functions of EMS:
- Data acquisition
- State estimation
- Security analysis
- Load forecasting
- Economic dispatch
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