Improved Power System Performance through Wide Area Monitoring

Improved Power System Performance through Wide Area Monitoring, Protection and Control

Computed by PSGuarderation

2 ABB

The typical application areas of PSGuard systems

Transmission networks Regional, national and cross-national transmission networks

Power supply rings Power supply rings for heavy load centers

Interconnections Transmission corridors, grid interconnections

Industrial areas Transmission network for industrial areas

Power generation Power systems including power generation

A big step forward to improve power system observability and performanceContinued load growth without a corresponding increase in transmission resources has resulted in reduced operational margins for many power systems worldwide and has led to operation of power systems closer to their stability limits and to power exchange in new patterns. These issues, as well as the on-going worldwide trend towards deregulation of the entire industry on the one hand and the increased need for accurate and better network monitoring on the other hand, force power utilities exposed to this pressure to demand new solutions for wide area monitoring, protection and control.

In this regard, the PSGuard Wide Area Moni-toring, Protection and Control system provides state-of-the-art solutions for counteracting sys-tem instabilities and preventing power outages.

PSGuard Wide Area Monitoring, Protection and Control

Examples:

■ SECURITY — Installation of a PSGuard system into a transmission network

for continuous stability monitoring and protection

■ OPTIMIZATION — Installation of PSGuard into a transmission corridor connecting

two areas for power flow optimization in cooperation with FACTS, online calculation

of available transmission capacity and automatic control

■ MONITORING — Installation of PSGuard into a transmission grid for monitoring

of network parameters — U, I, frequency — Average line temperature —

Voltage phase angle and difference between locations — Active and reactive power

and direction

PSGuard is designed to detect incipient ab-normal system conditions and to take counter-actions to preserve system integrity and ascer-tain acceptable power system performance.

Natural loading computed by PSGuard

Point of maximal loadability

2 ABB

Highlights

■ Lowered risks of power system instabilities

■ Minimized outages to secure income

■ Increased transmission capacity to generate more revenue

■ Optimized power flow to improve congestion management

■ Improved power system reliability

■ Assured power system investment planning

Early warning

Emergency alarm

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To avoid large area disturbancesWide area disturbances usually have excessive consequences as observed from voltage collap-ses and cascading effects, which have happened all over the world. Numerous analyses of the causes of these problems have revealed, that they are mainly caused by multi-contingencies, which can appear solely or combined everywhere in power systems and at any time. While it is not possible to predict or prevent all contingencies that may lead to power system collapse, a wide area monitoring, protection and control system supports the operator with important online information, provides a set of coordinated measurements. The result is themi-tigation or prevention of the spreading of large area disturbances. This increases the reliability of power systems and minimizes outages.

To improve exploitation of existing power transfer capacityWide area monitoring systems maximize the uti-lization of the existing power system by online assessment of the safety margin towards system instabilities. Today, power transfer limits are

based on simulations that are conducted during the system operation planning phase, and are based on worst-case scenarios (n-k). Online assessment of the system stability makes it possible to increase exploitation of the transfer limits. Both thermal and stabi-lity limits are calculated. By transferring ma-ximum possible power through the existing transmission corridors, future extension of line installations may be considerably deferred.

To ascertain power system integrityIn contrast to conventional protection devices, which provide local protection of individual equipment (transformer, generator, line, etc.), the wide area protection system provides comprehensive protection covering the whole power system. When compared to SCADA/EMS systems, that are responsible for network control and management, the PSGuard system is focused on maintaining power system inte-grity. The idea is that a wide area monitoring, protection and control system shall complement rather than substitute any of the existing control and protection systems.

Driving forces for the implementation of Wide Area Monitoring solutions

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PSGuard, the solution to prevent wide area disturbancesPSGuard is the ABB solution for wide area moni toring, protection and control in corpo-rating the approved new technologies applied to identify insta bilities in power systems and to evaluate the most effective measures against large area distur bances. The PSGuard system utilizes phasors, which are measured by GPS time synchronized phasor measurement units (PMU) resulting in an accuracy of < 1 µs.

Effective measures

to maintain power system

integrity.

PSGuard allows an incomplex integration in existing utility communication environments to link the PMUs data stream from different substations to the PSGuard system in the control center.

Data exchange can be established between PSGuard and other control and protection systems to allow for optimal data sharing and control actions.

■ PSGuard is a system for wide area monitoring,

protection and control

■ PMU, Phasor measurement units

for GPS time synchronized phasor measurement

and local protection

■ Communication system linking PMUs

to the PSGuard system

6 ABB 7ABB

The PSGuard system is designed to cope with the needs for network-related wide area monitoring and protection applications. The PSGuard is of distributed architecture and can easily be extended if new applications or new stations have to be implemented.

PSGuard workstations are equipped with a state-of-the-art HMI allowing optimal monitoring, operation and system engineering.

Communication SystemA suitable communication system is required that is able to cope with the information exchange load between PSGuard and the PMUs. It must provide the necessary reliability and transmission capacity for the on-line data transmission in distributed control and protection systems.

The following transmission capacity has to be provided as a minimum:– Dedicated channels > 64 kB/s per PMU– TCP/IP networks

If a communication system already exists, it is recommended to perform a communication system assessment at the beginning of the PSGuard project to evaluate the actual status and its adequacy for use in such projects.

The PSGuard system

PSGuard is designed to detect incipient abnormal system conditions, to recommend or and to take predetermined counteractions to preserve system integrity and ascertain power system performance.

Main benefits:

■ Improved power system operationThe operators are additionally provided with online information on the power system status at the right time.

■ Better use of existing equipmentThe online information on the current power system status (e.g. remaining transmission capacity) allows transmission lines to be operated closer to the safety limits. Therefore, more power can be transmitted over existing transmission lines and the construction of new lines can be deferred.

■ Increased power transmission capacityInstability limits that are calculated online permit an in-crease in transmission capacity for power transmission lines while maintaining the same level of security. The additional transmission capacity increases profitability.

■ Optimized power flowThe continuous monitoring of the power system stability margins provides valuable information that can be used for the optimization of the power flow in transmission corridors in coo-peration with other control equipment (FACTS, SVC, etc.).

■ Lowered risks of power system instablitiesEarly recognition of incipient power system instabilities allows counter measures to be initiated early, so that the spreading of large area disturbances can be prevented. This helps to significantly reduce the costs caused by outages.

■ Reduced impact of disturbancesPSGuard can evaluate suitable countermeasures due to improved knowledge of the power system conditions and corrective actions. Therefore, excessive or unnessesary load shedding can be avoided.

■ Improved power system planningEnhanced knowledge about the dynamic power system behaviour enables countermeasures to be prepared more precisely, and provides improved data for the planning of system extensions.

6 ABB 7ABB

to 20 ms and a high time and angle accuracy (< 1 µs, < 0.1°) over wide areas.

The time synchronization provided by GPS signals assures that the measurements across the entire power system are taken precisely at the same instant. In addition, phasor measure-ments are obtained directly from CTs and VTs to avoid any other errors that may be caused by transducers. These two aspects ensure that the state calculation of the power system is an accurate image of the actual power network conditions.

Instability can occur anywhere in the network, depending on the actual load distribution, sub-station equipment outages, and available power generation. In order to cope with the various situations, it is recommended to install PMUs at selected locations the power network where sta-bility problems are expected to occur. Detailed studies, which are offered by ABB, supports to identify the most suitable locations.

Phasor measurement: High-precision data acquisition Each monitoring and control system computes an image of the process based on the actual process data and on other information available in the system. This process image reflects the dynamic behaviour of the process and is used to initiate necessary actions to optimize the power system operation. Accurate and informative data can be provided by the system, which enables the real status of the process and the precision of its responses to incipient problems to be assessed.

In contrast to conventional control systems, where RTUs are used for the acquisition of RMS values of currents and voltages, the PSGuard system takes GPS synchronized current and voltage phasor measurement from critical locations of the power system. It is the first commercially operative system which continuously records the dynamics of power networks with a time resolution down

Phasor measurement units

(PMU) providing precise

information about the

dynymic behaviour of the

power system.

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Scalable to meet individual requirementsThe architecture of the PSGuard system pro-vides a scalable solution, which is suitable for customer requirements ranking from small installations for phasor measurement and visualization up to comprehensive power system protection for determination of critical network stability and initiation of automatic counteractions.

The scalability of the PSGuard system enables utilities to start with a small installation and expand to a full scope wide area monitoring, protection and control system meeting actual and future requirements of power utilities.

Positioning and architecture

Positioning in control and protection schemesNowadays a control and protection scheme in power systems mainly comprises two types of systems:

Network control systems SCADA/EMS systems for network operation and energy management. They act based on a static or quasi-dynamic view of the power system created from RTU data and may cooperate with other control systems.

Object protection Devices for protection of individual objects (transformer, line, generator, etc.) in power systems. They act dynamically but mainly without any coordination with other control systems.

PSGuard acts based on a dynamic view of power systems created from synchronized phasor measurement in cooperation with other control and protection systems. It therefore bridges the security gap between existing control and protection systems, and it enables the power system operation and protection to be optimized.

The PSGuard system is designed to provide protection for the entire power system. It is focused on power system security. Network control and object protection remains with SCADA/EMS respectively with SA systems.

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Open for extension and upgradingModular system architecture allows to extend and upgrade PSGuard system easily:

■ Extension of the power system

New stations can be equipped with PMUs and

connected to the PSGuard system. The most

suitable location of PMUs in the power system

will be analyzed by means of network modelling

and study.

■ System adjustment

to new network topology

If substations have to be removed or modified,

new lines have to be built, etc., then it is also

necessary to investigate and to re-evaluate the

impact of the modified new network topology.

These new network data should be entered into

PSGuard, and the system has to be adapted to

new network topology.

■ Adding further applications

to PSGuard

The PSGuard system provides a comprehensive

platform for implementing several types

of monitoring and protection applications.

New applications can be added in order to

meet the future requirements of a certain

power utility.

PSGuard is bridging the gap between

control and protection systems.

The scalability of the PSGuard system meets the individual customer requirements.

10 ABB 11ABB

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System structure

The structure of PSGuard system is designed to cope with the requirements for performing wide area monitoring, protection and control functions.

Commercially available components are used throughout the system to keep the costs low for acquisition, maintenance and stocks of the spare part.

The PSGuard system enables full scope wide area monitoring, protection and control solutions to be created comprising PSGuard itself, a communication system and PMUs installed in substations as shown in the graph below.

10 ABB 11ABB

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PSGuard system structure

overview

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Phase angle monitoringPhase angle monitoring based on snapshots

of phasors.

The following functions are provided:

■ Phase angle difference between selected

locations

■ Display of the phase angle curve between two

selected locations

■ Real and reactive power at selected locations

■ Display of the maximum acceptable phase

angle between two selected locations

■ Online warning and emergency alerting

■ Configuration of the above mentioned functions

■ Self-monitoring

Line thermal monitoring Online average temperature calculation based on

phasors measured on both ends of transmission lines

with assessment of line loadability taking thermal

limits into consideration.


■ Line average temperature calculation as well as

display of temperature changes

■ Assessment of thermal limits based on measured

and design parameter of the line

■ Assessment of transmission line loadability

■ Present line resistance and line loss

■ Self-monitoring

Voltage stability monitoringVoltage stability monitoring for transmission corridors

as well as for meshed networks.


■ Contingency detection

■ Prediction of power system status after each

contingency, enabling to recognize collapses at

early stage and initiating countermeasures

■ Continuous calculation of power margin toward

voltage instability limit

■ Online calculation of available transmission

capacity

The voltage stability assessment for meshed

networks requires basic monitoring package.

ConnectivityThe connectivity package is based on OPC Server and

can be equipped with data viewer for displaying phasor

data.


■ Phasor data acquisition from PMUs in IEEE

1344-1995 data format

■ Checking the validity of acquired data

■ Monitoring of the communication links to PMUs

Basic monitoringProvides state-of-the-art WAM platform enabling

integration of PSGuard software packages.


■ Aspect Integrator Platform (AIP)

■ GUI enabling process-oriented navigation

■ Historical data and trending facility

■ Integrated engineering tool

Data storage and exportThis is an advanced historical data package, which

is provided as option if the historical data in the

Basic System package would not meet customer

requirements.


■ Data processing and storage

■ Navigation through historical data

■ Trending facility

Advanced monitoringThis package supervises network topology

and calculates values of substations, which are not

equipped with PMUs for providing full observation of

monitored area.


■ Topology detection

■ Islanding recognition

■ Dynamic network parameter calculation

■ Modal analyses

PSGuard system portfolio

Application modules

The PSGuard system provides a portfolio of software modules, which can be bundled to packages to form solutions suitable to customers requirements (see system structure overview on page 10–11).

12 ABB 13ABB

Power oscillation monitoring Power oscillation monitoring in power systems.


■ Identification and size/variation of the most

important oscillation frequency

■ Amplitude of the most important kind of

oscillating

■ Absorption of the most important kind of

oscillating

■ Estimated current average of the analyzed signal

■ Estimated oscillating amplitude of the analyzed

signal

■ Trend indication to oscillating and the

appropriate absorption

■ Online warning and emergency alerting, release

and basic value for load shedding intended

remedial action schemes with a data repetition

rate of 1 second

Frequency stability monitoringFrequency stability monitoring based on snapshots

of phasors.


■ Contingency detection

■ Identification and size/variation of the most

important frequency

■ Amplitude of the most important kind of

frequency change

■ Absorption of the most important kind of

frequency change

■ Gradient of the frequency change

■ Estimated current average of the analyzed signal

■ Estimated oscillating amplitude of the analyzed

signal

■ Trend indication to oscillating and the

appropriate absorption

■ Online warning and emergency alerting, release

and basic value for load shedding of intended

remedial action schemes with an datarepeat

guess/advice from 1 second

Prediction of power system status after each

contingency, enabling collapses to recognize at

early stage and counter measures to be initiated.

State calculatorOnline state calculator based on snapshots

of phasors.


■ Network topology

■ Voltage magnitudes and angles

■ Branch current magnitudes and angles

■ Selected loads and generators current magnitudes

and angles

■ Statuses (ON or OFF) of the branches in the

supervised areas

Online state calculator provides improved

power stability.

Control action suggestionOperator guidance by suggesting control actions to

bring power system into a safe state.

Advanced controlEvaluation and performing most suitable actions

based on information from stability assessment

applications.

Remedial action schemes optimizes performance of

load and generator shedding in response to system

disturbances and/or topology changes.


■ Automatic actions for system protection

■ Automatic actions for transmission corridor

optimization

■ Dynamic set point determination

for FACTS/Wide area control

■ Online warning and emergency alarming, trigger

and base value for load and generation shedding

for the designated remedial action schemes

■ Controlled generator tripping or equivalent

reduction of energy input to the system

■ Tripping of interruptible load, DC line ramping,

insertion of braking resistors, insertion of

series capacitors and controlled opening of

interconnection and/or other lines including

system islanding

14 ABB 15ABB

Wide Area Measurement PSG 830The PSG 830 provides wide area measurement and phasor data viewing. The PSG830 allows you to integrate existing or newly installed PMUs to a wide area measurement system providing phasor data at a central location. It is the basic platform for wide area solution enabling power utilities to familiarize them-selves with WAMS technology with minimal investment.

The PSG 830 provides additionally process- oriented navigation using single- line diagram, GUI, etc. It is based on an WAM platform allowing implementation of software packages to form wide area measurement, monitoring, protection and control solutions. The PSG 830 acquires phasor data from PMUs and provides dynamic information of power systems, which helps operators to initiate correct actions in due time.

The package includes

■ Connectivity

■ Basic monitoring

■ Data storage and export

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PSGuard system portfolio

Application packages

The scalability of the system enables to start with a small installation that grows up to the system con figuration meeting the full customer requirements and needs.

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Wide Area Monitoring PSG 850Various monitoring applications are provided in PSG850 for monitoring different instabilities in power systems. Depending on the type of in-stability occuring in power systems, the related applications can be selected and implemented. Based on phasor data acquired from PMUs the PSG850 creates a picture showing the stability status of the nodes in the monitored area and suggests actions to prevent large area distur-bances. Countermeasures can then be initiated by the power system operator. Automatic ac-tions are not included in PSG 850.


■ Connectivity



Optional the following modules are available

■ Advanced monitoring

■ Event driven data archiving

■ Phase angle monitoring

■ Line thermal monitoring

■ Voltage stability monitoring

■ Power oscillation monitoring

■ Frequency stability monitoring

■ State calculator

Wide Area Protection and Control PSG 870The PSG870 is designed to be used fortransmission corridors for optimizing powerflow in cooperation with local control devices(FACTS, SVC, etc.). Based on phasormeasurement from both sides of transmissioncorridors the PSG870 monitors actual power flow, available transmission capacity, average temperature, thermal limits, etc., and initiates commands to local control equipment for optimizing power flow and minimizing conges-tion. PSG870 detects incipient instabilities and abnormal conditions, evaluates most suitable countermeasures and initiates automatic actions to protect power systems from large area distur-bances. Automatic commands can be initiated to existing control systems (SCADA/EMS, SA, etc.) if those systems are able to perform them in due time. Otherwise the commands are sent directly to PMUs or other control equipment in the stations.


■ Connectivity



■ Advanced monitoring

Optional the following modules are available

■ Event driven data archiving

■ Phase angle monitoring

■ Line thermal monitoring

■ Voltage stability monitoring

■ Power oscillation monitoring

■ Frequency stability monitoring

■ State calculator

■ Control action recommendation

■ Advanced control

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PSGuard software module functionalities

Stability monitoringAt present, power systems are usually operated based on static or quasi-dynamic information derived from RMS measurements. Phasor measurements at nodes help system operators to have a dynamic view of the power system and initiate the necessary measures in proper time. This can be supported significantly by stability assessment algorithms, which are designed to take advantage of the phasor measu-rement information. This increases the efficiency of power system operation and maintains security at the desired level.

Monitoring of transmission corridors – congestion managementThe interconnections (transmission corridors) between the power systems are mostly used for energy trading activities and physical energy

Voltage stability monitoring with early warning

and emergency alarm

delivery, contributing a significant proportion of the cost of energy in liberalized markets. The transmission capacity of such corridors is often constrained by the stability concerns having their origin in the uncertainty about the sys-tem state. The traditional way to reinforce the transmission paths is building new lines. This solution offers very high availability, but, on the other hand, the associated cost is very high. The alternative solution can be significantly improved monitoring by using a Wide Area Monitoring approach resulting in the reduction of uncertainties and thus the operational risk. In contrast to the traditional investment into the assets (i.e. transmission lines), the trans-mission increase is significant under certain conditions. This can be e.g. an increase due to lower ambient temperatures. However, the so-lution can be far more cost-effective due to the much lower investment needed for acquisition of a WAM System. Therefore, the WAM system can be seen as a tool playing an important role in congestion management.

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Voltage stability monitoring

on power transmission lines

Control action recommendation Operator guidance

PSGuard has a user-friendly HMI, where power system information is clearly displayed. Furthermore an operator guidance facility is pro-vided with following actions:

■ Continuous display of relevant information

■ Configurable warning and alarm

■ Notifications of emergency or warning to the

operator as well as in an event list

■ The suggestion of the most suitable operation to

overcome existing emergencies

This supports the operator’s work and prevents operational mistakes, especially in an emergency.

■ Two transmission lines are lost, as shown on the

single-line diagram, and displayed in the fault-related

event list

■ Two generators are producing 100% reactive power

to support the system

■ Three phasor measurement units (DACU 1, 2 and 4)

show significant voltage decline

■ The indicators for network stability (NSI) and

reactive power (RPI) are in yellow and indicate very

little safety margin left to power system collapse

■ The PSGuard suggests that the under load tap

changer control (ULTC) should be blocked

At a glance, the operator is in the position to see all information he needs to take counter measures in order to avoid power system col-lapse and he is guided in taking the right actions in manual operation mode.

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Phase angle monitoringThe application for monitoring the phase angles is a function that monitors the demands on the network that are caused by heavily loaded lines. It provides the operators with online informa-tion on the differences between the voltage phase-angles—a decisive factor in the successful reclosing of lines.

The main function of phase angle monitoring is to provide the operator with sufficient informa-tion so that he can assess the current difference in the phase angles between two locations. When PSGuard detects an abnormal state, the operator is informed with an early warning, or in critical cases with an alarm.

The current version has monitoring functions, the results of which should be a reliable aid for decisions taken by the operators. The measures that the operator can initiate to improve the sta-bility of the network range from rescheduling the energy generation or the compensation of the reactive power, blocking the tap-changers in the load area, or in extreme cases load shedding.

Line thermal monitoringLoading of the lines is in many cases constrai-ned more by thermal limits than by voltage insta bility concerns. The thermal limit of a line is usually set according to conservative and stable criteria, i.e. high ambient tempera-ture and no wind. This results in an assump-tion of very limited cooling possibilities and thus low loading. However, often the ambient conditions are much better in terms of possible cooling. This would allow higher loading of a line with a minimal risk. This is possible if an online working tool for line temperature assessment is available. One of the algorithms serves precisely this purpose.

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Time-synchronized

phasor snapshots at

various locations.

PSGuard software module functionalities

18 ABB 19ABB

Voltage stability monitoringof the transmission corridorsThe voltage stability assessment functionality provides a basis for effective monitoring of trans-mission corridors. It is based on and extends the basic functionality of Wide Area Measurement Systems with functions related to the monitoring of voltage stability for a transmission line and/or corridor. It’s main function is to provide the ope-rator of the power system with sufficient infor-mation for the evaluation of the present power margin with respect to voltage stability. That is the amount of additional active power that can be transported on a transmission corridor wit-hout jeopardizing the voltage stability. Voltage in a power system may become instable because of a shortage of reactive power. However, this ap-plication provides online monitoring functions, the results of which are available to the operator as the main support for decisions. Actions that the operator may take to improve voltage sta-bility may range from generation rescheduling or reactive load compensation, blocking of tap changers in the load area up to incremental or complete load shedding in extreme cases.

Power oscillation monitoringPower oscillation monitoring is the algorithm used for the detection of power swings in a po-wer system. The algorithm is fed with the selec-ted voltage and current phasors. The algorithm processes the input phasors and detects the various swing (power oscillation) modes. The algorithm quickly identifies the frequency and the damping of the least damped swing modes, that can e.g. lead to angular instability causing major power system disturbances (blackout). The algorithm employs adaptive Kalman filtering techniques.

Frequency stability monitoringFrequency stability monitoring is based on data from Basic Monitoring. The difference between the consumed and generated power is detec-ted early. The frequency stability monitoring algorithm estimates the impact of such a power unbalance on the frequency by modeling the response of the load and the inertia of the genera-tors. If the estimated frequency is not acceptable, the proposed actions to reach the desired fre-quency are computed and proposed.

Control and stabilizing measuresControl and stabilizing measures are operational actions issued by PSGuard to protect power systems from instabilities and collapses. Each measure could consist of one or a combination of several control actions, which will be advised by PSGuard and initiated by the operator or by PSGuard directly.

The feasibility criteria for specific control actions would have to be identified in the course of analytical system studies, which take into account envisaged network conditions, operation policies and switching procedures, actual load levels and generation capacity.

In case of power system conditions detected that require corrective actions, PSGuard identifies suitable locations and the extent of counter measures. The selection of control actions is based on power system conditions and identified contingencies. Coordination of wide area pro-tection with legacy control and protection is vital to the reliability of the transmission network.

20 ABB 21ABB

Measures against voltage instabilityVoltage instability occurs when heavy system loading causes large reactive power demands that result in an excessive voltage decline at load centres.

Increase reactive power supply

■ Increase Static Var Compensator (SVC) output

■ Increase reactive power output from synchronous

machines

■ Switch on capacitors and switch off inductors

■ Provide adaptive protection devices to prevent

tripping on overload or overcurrent

Under Load Tap Changers (ULTCs),in combination with Automatic Voltage Regulators (AVR), progressively adapt tap changer position to compensate for primary side voltage decline. To prevent this from happening during contingencies, the following approaches are possible, but this must be applied to ULTCs at all levels, from transmission down to distribution transformers.

■ Modify the AVR voltage setting

■ Disable tap changer position to reduce load

voltage and power

PSGuard software module functions

Load sheddingThe last measure against voltage collapse is load shedding. This action directly tackles the pro-blem of excessive load demand at the specific location in the power system. This measure, however, should be carefully pre-planned by selecting various load-shedding steps with priorities assigned that take the sensitivity of the consumers concerned and the impact of outages into account.

Many utilities rely on the operator’s experience to shed load when system voltages are too low. However, in case of rapid voltage decline the o ator may not be in a position to react fast enough to avoid voltage collapse and un-controlled loss of load. Some utilities apply un-der-voltage load-shedding relays as an attempt to automatically respond to voltage decline. However, taking the RMS voltage value as the only criteria is not a very reliable indicator for an incipient voltage collapse. Apart from this, the setting of these relays is delicate to assure reliable operation.

The PSGuard approach provides intelligent algorithms for reliable detection of incipient instabilities. PSGuard assesses the optimal load that is needed to be shed at the most suitable locations. The operator can rely on PSGuard recommendations for load-shedding, and he can be sure that the power supply is endangered and shedding of customer load is justifiable.

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Measures against frequency/angular instabilityFrequency/angular instability occurs after the tripping of generators or heavily loaded trans-mission lines. In the event of imbalance of generation and load, the optimal actions have to be determined to restore equilibrium taking the actual network topology into account.

To prevent the spreading of frequency instabi-lity, which leads to large area disturbances, it is necessary to have information available on the power system conditions at several locations in terms of voltage and current phasors. In addi-tion to this, a defence plan has to be established to determine which circuit breakers are to be blocked or to be tripped for under-frequency initiated load-shedding or, as last defence measure, islanding of subsystems. It might also be necessary to adapt the setting of the protec-tion relays concerned.

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Voltage instability prediction

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Implementation steps:

Initial

Basic network assessment

Definition of system configuration

Installation of basic platform PSG 830

Verification of initial installation

Detailed network assessment

Main implementation

Implementation of Wide Area Monitoring application modules (PSG 850)

System verification

Implementation of wide area protection and control application modules (PSG870)

Implementation

A PSGuard implementation project will be planned and executed in cooperation with the utility so as to assure compliance with financial, functional and operational objectives of the project. The main aim of the project would be to implement the most suitable system solu-tion meeting actual and future requirements.

A scalable implementation is recommended in view of the size of the project. Each implemen-tation step will be tested thoroughly, reviewed, verified, and fine-tuned by ABB in close coo-peration with the utility before commencing the next steps. This procedure will stepwise improve the utilization of the power system up to peak performance.

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ABB as system and service supplierABB provides entire solutions including all de-liveries required to satisfy utility’s needs in wide area monitoring, protection and control from one supplier. This avoids interface problems and facilitates a smooth execution of the project.

Main deliverables:

Analysis phase

■ Post-mortem problem analysis

■ Network assessments

■ Protection and control system study

■ Communication system study

■ System concept elaboration

Implementation phase

■ Control and protection systems

■ Communication systems

■ Bay level equipment

After-sales services

■ Operation and maintenance

■ Spare part services

■ Planning support

■ Upgrades and migrations

■ System extensions

■ Maintenance control

■ 24 x 24 x 365 service

■ Remote system upgrade

ConclusionWide Area Monitoring System helps to signifi-cantly improve grid utilization during phases of peak transmission demand while enabling the detection of critical factors influencing network stability. Online monitoring applications will significantly reduce investment costs for utilities while safeguarding high levels of dynamic grid loading and availability. In this context, Wide Area Monitoring extends the capability and security of existing local monitoring, protection and control equipment to further levels of asset utilization.

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ABB Switzerland LtdUtility Automation SystemsBrown Boveri Strasse 6 CH-5400 Baden/SwitzerlandPhone +41-58-585 77 44Fax +41-58-585 55 77e.Mail [email protected]

www.abb.com/poweroutage

Documents

Improved Power System Performance through Wide Area Monitoring