Power Plant Operator Training » Transmission System Operations

Monitoring and Control Communications

admin — Mon, 08 Jun 2009 19:20:04 +0000

The objective of this course is to look at different modes of communication that are employed in operation of the transmission system. Communication applications are demonstrated with particular emphasis upon the SCADA system as employed for system operation. After completion of this course and associated workbook, the participant should be able to understand the following concepts and apply them in day-to-day working activities.

At the end of this course you should be able to:

The need for communication as an integral part of transmission system operation
Techniques of communication employed in transmission system operation
Typical application of the different communication techniques
The function of the SCADA system
Collection of data by RTUs
Polling of RTUs throughout the system
Transfer of data across communication links
The need for carrier signals and modems
Factors affecting the rate of data transmission
Data transfer from RTUs to the CPU memory
Frequency of CPU update
Typical master station layout
CPU and peripheral computers and devices
Fail-over stand-by computer
Applications software
The operator interface
The operator display functions
Displaying equipment attributes
Alarm annunciation
Logging operating events
Features of SCADA installations

System Voltage Control

admin — Mon, 08 Jun 2009 19:16:54 +0000

This third course in the Transmission System Operation training program develops the principles of voltage control on the transmission network. The material builds upon discussions of power flow fundamentals and transmission line characteristics from the two previous courses.

We begin by describing the systemâ€™s need for reactive power (VARs) and how VARs are generated and/or absorbed by the various components of the power system. Next it is demonstrated that the flow of VARs has a profound effect on voltage level (much more so than the flow of Watts). Transmission line MW loading and its effect on VAR requirements and voltage are also examined, as well as the effect of contingencies.

Various real-life scenarios are described in which power systems have collapsed from significant off-nominal voltage. Finally, this course discusses a wide array of equipment and methods system operators can use to effectively control transmission voltages to comply with industry standards.

At the completion of this course, you should be able to:

Name the two distinct types of power produced at the generators when load is connected
Explain the basic difference in function between Watts and VARs, and why both types of power are necessary to make electrical equipment work
Sketch and compare curves for power in a purely inductive circuit and power in a purely capacitive circuit
Recognize the difference between positive VARs and negative VARs
Name 3 power system components that create a demand for VARs
Name 3 power system components that supply VARs to the system
Describe what it means for some components to “compensate” for others
Explain how MW and MVARs are produced in an electric generator
Recognize that a change in generator voltage or MVAR supply must come from a change in the unitâ€™s DC excitation current
Discuss the function of an Automatic Voltage Regulator (AVR)
Predict the response of the AVR to an increase or decrease in MVAR demand on the system
Recognize that it takes a difference in voltage magnitude to drive MVARs through the system, and that the direction of MVAR flow is from high to low voltage
Discuss the function of a synchronous condenser and a static VAR compensator
Explain why a transmission line can be either a MVAR source or a MVAR load
Describe the effect of MVAR flow on voltage drop. Compare to the voltage drop resulting from the flow of MW
Name 3 events that can have a profound effect on MVAR flows and voltage level
Explain what happens to the MVARs required by a transmission line as MW loading is increased
State the significance of a lineâ€™s surge impedance loading (SIL)
Understand why it is important to have adequate MVAR sources located at intermediate points in the network, especially during contingencies
Sketch the voltage profile along a transmission line operating above SIL, with voltage at both ends fixed at 100%. Compare with the voltage profile below and at SIL
Explain why MVAR supply from a lineâ€™s capacitance drops off sharply at loadings above SIL
Name some typical loading levels for transmission lines in percent of SIL
Sketch a typical transfer limit curve (P vs. V) and explain the significance of the knee of the curve
Explain why line loadings must be restricted to well below the knee of the transfer limit curve
State the industry (NERC) limit for percent voltage change following any single contingency
Give examples of system conditions and events that may lead to voltage collapse.
Explain why it is important for system operators to prepare in advance for voltage emergencies
Describe how operators can adjust voltage/MVAR supply at the generating units
Understand why AVR set points must be raised/lowered in unison to effect a net change in voltage/MVAR supply
Sketch a typical generator capability curve and discuss the MW and lagging/leading MVAR limitations
Describe the function and operation of Maximum and Minimum Excitation Limiters on generating units
List some power system components that allow operators to adjust voltage/MVAR supply at locations other than generating plants
Discuss the reactive overload capability of generators, synchronous condensers, and static VAR compensators
Describe some typical applications for shunt reactor and capacitor banks on the transmission system
Explain how a series capacitor can be of assistance in voltage control
Understand the function and operation of Load Tap Changing Transformers (LTCs) in providing voltage correction on the transmission and distribution systems
Discuss the importance of operator actions in implementing voltage control: curtailing economy transfers, bringing on local generation, bringing on reactive sources ahead of the morning load rise, removing lines during light load, etc

Review of Fundamentals

admin — Mon, 08 Jun 2009 19:11:54 +0000

Review of Fundamentals The objective of this course, the first in the series on transmission system operation, is to review relevant fundamentals of electricity to provide a firm foundation on which to build an understanding of the more advanced concepts which will be presented as the program progresses.

On completion of this course, the participant should be able to understand the following concepts and apply them in day-to-day operation:

To provide unbiased control of system operation
The establishment of Independent System Operators (ISOs) or other similar entities
The tasks of the system operations group; controlling the transmission system
Frequency control of the power system through matching of power production and consumer demand plus losses
Load impedance and its effect on current flow through transmission lines
The effect of conductor resistance in a transmission line, i.e. voltage drop and energy loss due to heat dissipation
The effect of line voltage on system energy losses
The difference between power and energy, i.e. watts versus watt-hours
Typical power generator prime movers
Fundamentals of electric power generation
The sine wave and RMS values
Factors that determine frequency of generation
The effect of pure resistance in an AC circuit as shown by sine waves and vector diagrams
The effect of pure inductive reactance and capacitive reactance in an AC circuit
Power generated in resistive, inductive, and capacitive circuits
The flow of reactive power, positive and/or negative vars
The power triangle and power factor
Combined R, XL, and Xc circuits
The impedance triangle and voltage triangle
Power factor correction
The effect of transmission line inductance on voltage drop
The development of a power angle across a transmission line due to line inductance
Three phase power generation
The application of a common neutral conductor
A balanced three phase load with no neutral conductor
Voltage and current characteristics of the Wye and delta connections
The calculation of three-phase power
Current and voltage relationships between primary and secondary of a Delta/Wye connected transformer

Power Transmission

admin — Mon, 08 Jun 2009 19:08:32 +0000

The main objective of this course, the second in the series on transmission system operation, is to draw attention to the major features of transmission system equipment, and operation of transmission lines. Particular attention is paid to limitations resulting from the effects of resistance, inductance, and capacitance of the lines.

After completion of this cousre, the participant should understand the following concepts, and be able to apply them in day-to-day work activities.

Typical operating voltages for transmission lines and distribution lines
Different types of transmission towers
Conductor material and conductor layout on the towers
Insulators and the importance of conductor spacing
Features and limitations of transmission cables
The application of high voltage DC transmission
The effect of transmission line conductor resistance and inductance
Line voltage drop and power angle as shown by vectors
The effect of line loading on voltage drop and power angle
The effect of load power factor on voltage drop and power angle
The need to generate and provide megavars and megawatts to meet line losses
Charging current required due to the line shunt capacitance
Voltage rise due to line capacitance on an open-ended line, shown by vectors
Production of reactive power by line shunt capacitance
Line reactive compensation equipment, including: reactors, capacitors, synchronous condensers, and static VAR compensators
The function of transmission stations, and station equipment
Features of different bus arrangements
Types of circuit breaker
The principle of transformer operation
Transformer physical construction
Transformer cooling arrangements
Autotransformers
Instrument transformers

System Frequency and Tie-Line Control

admin — Mon, 08 Jun 2009 19:05:06 +0000

The fourth course in the Transmission System Operation training program shows how frequency and tie-line flows between control areas are controlled. We begin by developing the concepts of an AC interconnection and synchronizing forces. Frequency deviations come about when unbalances develop between generation and load and these deviations are controlled by the combined action of speed governors and Automatic Generation Control (AGC) aided by the natural change in load as frequency changes.

We describe how tie-line flows also change when generation to load imbalances occur. Finally, this course discusses Area Control Error (ACE), the fundamental input to AGC, and how it provides the intelligence required to restore generation to load unbalances.

At the completion of this course, the student should be able to:

Know what constitutes an AC interconnection
Identify the interconnection within which your facilities are located
Know at what frequency your interconnection operates
Explain why frequency is the same throughout an AC interconnection
Explain the role of transmission lines in maintaining synchronism
Know what causes frequency to deviate from nominal
Tell whether generation or load is changed to control frequency
Know what a speed governor is and what it does
Tell how the size of an interconnection affects frequency deviations
Know what limits are imposed on frequency excursions and why
Know why it is important to control tie-line flow
Know why the type of generating unit affects its speed of response to frequency changes
Explain the relationship between generation rotational speed and frequency
Understand that speed governors act as proportional controls
Describe what is meant by governor droop
Describe the units used for droop
Know that governors work to control both decreasing and increasing frequency
Understand why governor droop permits load sharing between generating units
Tell what are typical droop settings for various types of generating units
Understand why many classes of generating units do not participate in frequency control
Be able to describe the basic characteristics of the example system used
Total capacity, capacity under governor control and total load
Composite droop characteristic
Tell what happens to frequency under governor control only when an 800 MW unit trips off
Describe what is meant by the Load Effect
Describe what is meant by the Frequency Response Characteristic, Beta
Tell what happens to frequency under the influence of Beta when an 800 MW unit trips off
Be able to calculate how much generation is picked up and how much load is lost for a given drop in frequency
Understand why frequency does not drop instantly when a generation/load mismatch occurs
Be able to identify points A, B and C on a frequency chart taken while a generating unit tripped off line
Be able to compute the net tie-line flow following loss of generation within a control area
Understand how AGC assists system operators
Know how frequently AGC application software is run, typically
Be able to describe Area Control Error and how it is calculated
Know what is the Frequency Bias Coefficient, B, and how it relates to Beta
Be able to compute ACE given frequency deviation, net tie deviation and B
Know how to find the frequency stabilization point
Describe functions that AGC can perform other than responding to generation loss
Know why AGC is suspended when large frequency deviations occur

Power Dispatching

admin — Mon, 08 Jun 2009 19:01:33 +0000

The objective of this course is to present and discuss the various factors which must be taken into consideration when dispatching generation. Although most of the technical factors will remain after deregulation, it is probable that some aspects of dispatching will change to accommodate the competitive market for generation. This subject will be dealt with later in the program.

After completion of this course and associated workbook, the participant should be able to understand the following concepts, and apply them in day-to-day work activities.

The function of generation dispatch, i.e. to have sufficient generating capacity on-line at all times to meet the load demand, plus system losses, plus reserve capacity for emergencies
Make up of the power system, i.e. power pools and interconnected control areas
Major elements of a control area
Preparation of the daily generation schedule based on the load forecast
Spinning reserve requirements
Short term and long term stand-by reserve capacity
Short term and long term availability of generation units
Alternate sources of generation available to the control area
The availability of power for purchase from independent power producers or neighboring utilities
Factors affecting the order of dispatching generators, i.e. cost, location, prime mover characteristics
Characteristics of base load units
Characteristics of variable load machines
Characteristics of peaking units
Characteristics of regulating units (i.e. frequency control)
Typical limitations to be observed when bringing generators on-line
Economic dispatch based upon comparison of generation costs from different units.
Components of generation cost, i.e. start-up, shutdown, no-load running cost, and incremental cost with load
The dispatch calculation program
Marginal cost at different times of the day
The dispatch of hydropower based on marginal costing (i.e. displacement of high priced thermal power)
Hydro dispatch based upon control of water releases
Dispatch of pumped storage power
Economy interchange between neighboring utilities
Spot price for economy power
Inadvertent interchange and arrangements for compensating power flow
The effects of transmission system configuration on generation dispatch
The effect of generation location on system energy losses
The power transfer equation (power angle increases with increased power transfer)
Instability due to excessive power angle
Restrictions placed upon generation dispatch due to excessive power angle
Availability of computer programs to assist the load dispatcher

System Security

admin — Mon, 08 Jun 2009 18:57:27 +0000

System Security is the focus of this 6th course in the Transmission System Operation training program. The concept of operating security is developed as the ability of a power system to withstand or limit the adverse effects of any credible contingency, including: overload beyond emergency rating, excessive or inadequate voltage, loss of stability, or abnormal frequency deviation.

This course begins with a discussion of the nature of large synchronous interconnections, and how AC power flows within such a network. It is demonstrated that, each time a large unit trips in an interconnected system, there is an inrush of power into the affected area that could seriously overload the transmission system. The operatorâ€™s role of assuring that line loadings remain within pre-established limits is discussed, as well as the concept of transmission line loadability.

Line loadability is analyzed from the standpoint of three major limits that can restrict the flow of MW across a given transmission corridor: the thermal limit, the voltage drop limit, and the stability limit. Loading limitations of other transmission equipment is described as well, including cable and transformer loading.

This material then proceeds to give an overview of security monitoring in the control room, with the help of SCADA and EMS systems, on-line power flows and contingency analysis, and dynamic security monitoring. Finally, techniques for improving system security are presented, including the role of Security Coordinators, the exchange of security data, loading relief options, preservation of operating reserve, and emergency methods.

At the completion of this course, the student should be able to:

Explain what is meant by operating security
State and discuss two major reasons why individual companies or areas choose to interconnect their power systems
Name the four North American Interconnections
Describe what is meant by a â€˜control areaâ€™
Explain what happens to tie-line flow in the first 10 to 20 seconds following a large unit trip in an interconnection
Understand the effect of a capacity emergency on the security of the interconnection
Discuss the problems that may be associated with loop flow and parallel flow during normal operating conditions
State the three main factors that determine a transmission lineâ€™s loadability
Give examples of continuous, long-term emergency and short-term emergency thermal ratings for a transmission line
Describe the consequences of operating a transmission line above its emergency thermal rating
Explain how “on-line”, or “dynamic” thermal ratings are used to increase line loadability
Understand the effect of increased MW loading on the reactive requirements of a transmission line and, consequently, on voltage drop
State applicable industry standards for maximum permissible voltage drop following credible contingencies
Explain what is meant by the “steady-state stability limit” across a given transmission path. Give the expression for steady state stability limit in terms of voltage and reactance
Describe the consequences of loss of synchronism on the transmission network
Sketch a typical power angle curve and compare it to the curve that would result if one or more parallel circuits trip
Sketch a typical line loadability curve for transmission lines of different lengths. Explain what the overriding limit is for short lines vs. long lines
Describe the effect of compensation on line loadability
Name other transmission equipment (besides overhead lines) that may be the limiting factor in determining how much power can be transmitted across a given path
Discuss the thermal and charging limitations of high voltage (transmission-level) underground cables
Explain the thermal capability of power transformers, as well as cooling methods that are employed to increase MVA rating
State a typical transformer overload magnitude, duration, and expected loss of life, based on established loading guides for power transformers
Describe how SCADA/EMS systems help operators to continuously monitor the security of the power network
Give examples of software tools (incorporated into an EMS) that alert operators to actual and predicted security problems on the network
Explain what is meant by dynamic security assessment (DSA)
Discuss the North American Electric Reliability Council (NERC) and its mission in preserving security in the 4 North American Interconnections
Understand the role of Security Coordinators in the North American Interconnections
List several examples of operating security data that must be provided and updated by each control area every 10 minutes
Give 3 examples of loading relief methods that may be undertaken and supervised by Security Coordinators
Explain how FACTS devices can dynamically control the flow of power over specific transmission circuits
Describe the purpose and operation of a phase angle regulator (PAR)
Explain what is meant by “operating reserve”, and state what portion of this reserve must be spinning. List examples of what can be included in “non-spinning” reserve
Give examples of typical operating reserve practices
Describe 2 emergency measures for dealing with a capacity emergency

Operating Under Abnormal Conditions

admin — Mon, 08 Jun 2009 18:54:24 +0000

The previous courses in this series have mainly dealt with the elements of the power system when it is operating in its normal state. This course extends that knowledge into some of the abnormal situations that can occur on the power system and describes how different pieces of apparatus can act under those conditions. Several actual incidents are described.

At the end of this course you should be able to:

Define the boundaries of normal operation
List events that can move the system into an abnormal condition
List five conditions that describe abnormal conditions
List three characteristics of the emergency state
Draw a diagram showing the interrelation of the different states on the power system
Understand the information shown on a control center dynamic wall map
Describe the interrelation of system operators, regional operators, and plant operators
List seven probable events against which systems are tested to ensure their ability to survive contingencies
List eight events that should be simulated to investigate how the system will behave under abnormal conditions
Recognize the limitations of capacitor banks and generators to supply reactive power when the system voltage is declining
Describe the relation between energy consumption and supply in a small part of a large interconnected system
Understand how interconnections reduce the need for generation reserves.
Describe how economy interchanges are made
Recognize how heavy economic interchanges on one interface can restrict the emergency support on other interfaces
List seven strategies to prevent a system in the alert state from dropping into the emergency or blackout state
Describe the use of a phase shifting transformer
Understand the reasons for putting tie-line tripping relays on interconnections and the limitations that they can impose
Describe how a part of the system can lose synchronism with the remainder of the system
Write the equation for the maximum amount of power that can be transferred across a transmission line
Understand why a relay can think that a line is faulted when the voltage vectors across the line are 180 degrees out of phase
Recognize the main parts of a hydro-electric governor
Describe the use of a dashpot bypass on a hydro-electric governor and the problems that can arise if the dashpot is bypassed when it is in an island
Understand the difference between the temporary droop and the permanent droop on a hydro-electric governor
Recognize the limitations imposed on hydro-electric machines by the finite amount of high pressure hydraulic oil
Understand why auxiliary governors are sometimes fitted to steam turbines
Recognize how auxiliary governors destabilize islands where they control the dominant generators
Describe how turbine blade resonances limit the under frequency operation of steam turbines
Explain the difference between under frequency relaying and frequency trend relaying
Recognize the water flow disturbances that can be caused by islanded operation and the restrictions to the operation of islanded hydro-electric plants
Describe why a steam turbine may have a short burst of energy at the start of an island but then have its power output decay
Recognize the need for load-frequency control in areas prone to islanding
List typical maximum and minimum voltages
Describe the Ferranti effect on lightly loaded lines
List six voltage collapse situations
List four causes of voltage collapse
Understand why switching capacitors may not arrest a voltage collapse
List the stages of a voltage collapse
Describe how switched reactors can be used to prevent a voltage collapse
Describe the effect of a geomagnetic storm on transformers
State the return period for geomagnetic storms

System Restoration

admin — Mon, 08 Jun 2009 18:51:31 +0000

System Restoration The earlier courses in this series have mainly dealt with the elements of the power system when it is operating in its normal state. The previous course extends that knowledge into some of the abnormal situations that can occur on the power system and describes how different pieces of apparatus can act under those conditions. Several actual incidents are described. This course extends that discussion to the situation where the system or a part of it collapses and the possibilities for system restoration.

At the end of this course you should be able to:

List 3 critical parameters to be determined after a major system upset
Describe the importance of communications
List 3 items of circuit breaker status
List 3 events which can cause the breakers to open
Describe how cold weather affects breakers
Suggest alternatives possible if a control center is blacked out
List 3 reasons to sectionalize a blacked out system
List 3 things to be done before intentionally separating from a system that is descending into a blackout
Describe the procedure for reenergizing a blacked out system from a neighboring healthy system
Describe the procedures for connecting generation and load
Describe the requirement for re-establishing direct current connections
Describe how to establish a power source within a blacked out system
Describe how to pick up load and transmission from a power source within a blacked out system
Understand the black start characteristics of different types of power plants.
List the minimum requirements for standby power at a fossil steam plant
Explain why nuclear plants are not suitable for black start
Describe the characteristics of heating and lighting loads
Describe the characteristics of motor loads
Describe the characteristics of thermostatically controlled loads
Draw the curve of current vs. time for a reconnected feeder
List 4 ways that the inrush on a re-energized feeder can be reduced
Describe the precautions required when starting synchronous condensers after a blackout
Define the amount of synchronized generation which must be on line to start a synchronous condenser
Define the amount of synchronized generation which must be on line to pick up a block of load
Prioritize feeders for pick-up
List 4 things to be considered when picking up load
Draw a re-energization route map for a part of a system
Describe how lines may trip out again if oscillations occur
List 6 ways of reducing oscillations when rebuilding the system
Describe the precautions necessary when synchronizing islands
Explain how to control frequency when picking up loads
Describe how to prepare a system which will be islanded deliberately
List the limitations of fossil fired steam plants in islanded operation
Describe the operation of nuclear units in an island
Recognize the different perspective of independent power producers
List allowable normal and emergency voltage deviations
Describe how reactors and load current can be used to reduce the voltage rise on transmission lines
Describe why cables have a much greater voltage rise than overhead lines
Describe how parallel and series ferroresonance occurs
Draw typical wave forms of a system experiencing ferroresonance
Explain how a trapped charge can cause high voltage on a transmission line
List 4 communication media which could be used for system control
Estimate how long to wait before starting to pick up lines in the absence of any communications
List 2 tests which can be performed without disrupting customers
Describe how restoration simulations could be carried out
List 10 training priorities suggested by NERC
List the classes of disturbances which must be reported to the Department of Energy in the United States
Define the 3 disturbance severity levels used by CIGRE
List the 9 initiating causes used by CIGRE
Recognize the importance of gathering post disturbance information

Transmission System Protection

admin — Mon, 08 Jun 2009 18:45:59 +0000

The objective of this course is to examine the function of protection schemes from the point of view of the transmission system operator. Details of the major types of protection relays are discussed with the emphasis on function rather than mechanical construction.

After completion of this course and associated workbook, the participant should be able to understand the following concepts and apply them in day-to-day working activities.

Causes of electrical faults
Fault characteristics; changing parameters
Common types of 3-phase fault
Effect of impedance on magnitude of fault current, i.e. generator impedance, transformer impedance, line impedance, and fault impedance
Unbalanced phase conditions due to fault
Elements of the protection scheme
Protection relay input and output signal
Circuit breaker tripping circuit
CTs and VTs (PTs)
The need for back up protection
Protection zones
Power system grounding
Protection relay sensitivity, selectivity, and operating speed
Reporting and analysis of protection relay operations
The principals of differential protection, instantaneous overcurrent, inverse time overcurrent, directional overcurrent, distance relays (impedance relays), mho relays, pilot protection
Application of protection schemes to generators, transformers, feeders, transmission lines, and bus bars