AN ADVANCED TRANSPORTABLE OPERATOR TRAINING SIMULATOR

J.G. Waight, K. Nodehi, M. Rafian, H. Van Meeteren* A. Bose Empros Systems International Arizona State University

R. Wasley E. Stackfleth E. Dobrowolski Macro Corporation Hughes Training Systems Philadelphia Electric Company

ABSTRACT widely accepted in other contexts, was first introduced as a tool for operator training with the announcement and demonstration Since the introduction of the first Dispatcher Training of the Dispatcher Training Simulator (DTS) at PICA in 1977 [1]. Simulator (DTS) at PICA in 1977, DTS systems have evolved in This DTS had limited capabilities in terms of model size and in scope, complexity and performance. This paper outlines the the fidelity of the simulation, the User Interface, and the control design of an advanced, transportable Operator Training functions. Simulator (OTS) which was developed as part of EPRI research project 1915-2. Advanced modeling technology and instructor In the following years many vendors introduced DTS systems, capabilities are described along with training examples which mostly integrated with new energy management systems [2], demonstrate the capabilities of this OTS. [3], [4], [5]. Model sizes grew, and improvements were made in the fidelity of the training devices. Yet certain limitations persisted especially in the area of simulation of complex INTRODUCTION voltage phenomena, in instructor tools, and in capabilities for trainee evaluation. The Electric Power Research Institute During the past few decades, the complexity of the job of the undertook the development of an advanced Operator Training power system control center operator has increased Simulator (OTS) with improvements over other simulators then dramatically. Several factors have contributed to this change in on the market. Research Project 1915-1, [6] laid out the complexity. The utilities of the United States have become guidelines which could be used to develop a such a simulator. increasingly interconnected, coalescing today into three major interconnections. Later environmental and economic factors This paper reports the research and development of the advanced combined to favor the construction of new generating stations transportable simulator. at sites remote from existing load centers and with limited transmission access to these load centers. The increase in the cost of petroleum fuels and the availability of relatively cheaper REQUIREMENTS hydroelectric power from Canada has led to transmission of electric power over long distances over a strained transmission The overall requirement was to develop an Operator Training network. During the late 1980's, large unforecasted increases in Simulator suitable for simulation of normal, emergency, and peak summer demand has further aggravated the situation. The restorative conditions of an electric power system and to have a nature of operating problems has changed in many instances useful simulation tool for operations, planning and after-the­ from concern about thermal problems, to concern over fact analysis. The overall requirement was subdivided into five VoltNAR coordination and the potential for voltage collapse. specific requirements.

All of these factors have increased the complexity of the jobs of The first requirement was to develop simulation capabilities system control center operators. To meet these challenges, needed for system operator training. This led to the utilities have procured and installed computer based SCADA and development of requirements and specifications for models and EMS systems. Sophisticated tools such as state estimators, algorithms suitable for simulation based training of operators contingency analysis, and optimal power flows have been in emergency conditions including complex voltage placed in the hands of system operators as operating aids in the phenomena in real time. Fidelity requirements were stated in new environment. These new tools have brought with them the two ways. The simulator must behave as the real world does as need for more training of system operators in the use of these seen by the operator. The man machine interface and the tools, especially during emergency operating conditions. control functions used by the trainee must be the same as those used by the operator in the Energy Management System (EMS). At the same time other economic factors and the deregulation of utilities have led to the downsizing of utility operations staff. The second requirement was to develop the OTS on a practical, In many cases early retirement options may lead to the loss of realizable platform. This meant that the OTS must run on veteran operators with many years of operating experience. commercially available, all digital computer hardware. Custom These positions are then filled with junior operators with less built hardware, such as analog or hybrid simulators, was not on-the-job experience. considered as a development option.

All of these factors have accentuated the need for training The third requirement was to develop improved instructor system control center operators in all phases of system capabilities. These capabilities support the instructor in operations: normal operations, emergency operations, and in preparing the training sessions, executing the training system restoration. Simulation based training, which has been sessions, and evaluating the performance of the trainee.

The fourth requirement was to develop a simulator which is *Mr. Van Mecteren is now with Energy Control Consultants. transportable and applicable to a broad range of utilities. This objective was established to ensure that the developed OTS is of benefit to as many utilities as possible.

The fifth requirement was to demonstrate and evaluate the OTS in the operational environment of a host utility. Philadelphia Electric was selected by EPRI as the result of a formal process which included proposal solicitation, evaluation, and selection.

Reprinted from IEEE Proceedings of the PICA Conference, pp. 164-170, May 1991.

278 OTS CONFIGURATION Trainee Consoles Primary Secondary CPU CPU The OTS is comprised of three major hardware components: the (EMS) (CCM) Power System Modeling (PSM) computer, the Control Center Modeling (CCM) computer and the Instructor Position(s) (lP). Communications Processors The PSM computer is used to simulate the Power System Modeling and Educational Subsystems. The Power System Modeling subsystem consists of the models for the electrical network, generating units, prime movers, loads, relays, local Controllers controls for the system, the AGC systems of external companies, and possible power pool controllers. The Disk Educational Subsystem allows the instructor to set up events InstructorConsoles which occur during the simulation. The PSM has an instructor PSM interface that allows personnel other than the system control Tape CPU center operator to control the electrical power system. Typically, such persons include substation operators, power Line plant operators, and system control operators of neighboring Printer utilities and possible power pools. The instructor interface is provided through the Instructor Position(s). The PSM also has ~ = New EqlApmenl an interface to the CCM. This interface includes simulations of the SCADA RTU traffic and of inter-utility data links. o = Exlslng EquIpment

The CCM computer contains a model which replicates the user Figure 1. Generic Configuration of OTS utility's EMS. Functions included in the user utility's EMS are modified to communicate data to and from the PSM instead of Software Implementation the RTUs and other utility or power pool computer systems. These functions typically include: One of the requirements was to develop an OTS that is transportable and can be made available to a broad range of Alarm Processor utilities either as part of a new EMS or an an extension to an Data Acquisition existing EMS. In order to fulfill these requirements a Economic Dispatch configuration was selected whereby the CCM could be Interchange Scheduling implemented on redundant control center hardware and the PSM Load Frequency Control and IP could be implemented on additional hardware. A further Man-Machine Interface Network Analysis Applications requirement was that the PSM software could be ported from the Scheduling Applications selected hardware platform to other hardware with minimal Supervisory Control efforts. At the time of the design, software standards for portable operating systems, user interfaces, and data base The Instructor Position is based on a workstation. This management systems were not widely accepted nor available. workstation has features to support instructor activities during simulation. These features include: In the OTS design the portability requirement was satisfied by the construction of an OTS Executive which includes the Instructor MMI necessary subset of the capabilities available in proprietary Education subsystem interface EMS executives. The PSM software contains interfaces to the Logging OTS Executive which in tum is interfaced to the proprietary operating system available on the selected hardware. Figure 1 shows the generic configuration of the OTS. The PSM software is made up of a number of tasks which are In order to implement the OTS software, the Central Processing executed concurrently, both on a periodic and demand basis. Unit (CPU) used for the PSM should be a computer with the The OTS Executive was developed in ANSI Fortran to schedule following main features as a minimum: tasks and to accomplish intertask communication. Intertask communication is handled using a messaging scheme, where 10 MIPS one task can direct a message to any other task. Messages are 1 MegaFlop placed in a mailbox in a queue which is processed in FIFO order. Floating point hardware The flow of messages is unidirectional. Each task has a 64 MB directly accessible memory mailbox and can only read messages from its allocated mailbox, A minimum of 4 data channels but it may send messages to any other task's mailbox. CPU requirements for the CCM are identical to those of the EMS When porting the PSM to a hardware platform with a different primary system. These requirements may be satisfied by using operating system it is only necessary to modify the interfaces the secondary CPU of the EMS for the CCM. of the OTS Executive to the new operating system. The instructor console is based on an Apollo DN 3000 The PSM has its own data management system which is workstation or equivalent Hewlett Packard/Apollo workstation. independent from the one used on the EMS. Because of A second workstation will be required if the user utility plans on requirements for portability, the data management system is having two instructor consoles. The workstation(s) are written in ANSI Fortran 77. The data management system is connected to the PSM by means of an ethernet (TCP/IP) comprised of three main modules: a builder, a populator, and a connection. mapper. The data base builder, mapper, and populator together perform the data base generation function. The PSM handles the communication process with the CCM via data interface hardware. The communications protocol required The data base builder uses source data to size both the data base is the CCITT X.25 protocol. and program code and to create the data base directories used by the access function. The data base populator function uses Data communication between the PSM and CCM uses two source data to fill the data base areas needed by the PSM dedicated lines. Redundancy is supported. Typically, however, applications software. The source data is checked by the data both lines arc fully operational. For each line, two service management system so that errors can be found as early as classes (normal and high priority) are defined. The lines possible during data base generation. operate in full-duplex mode at a speed of 56 Kbs.

279 The data base mapping function builds maps which allow features is included in the load model and therefore does not transfer of PSM simulated RTU values to the CCM SCADA data require the network model to extend into the individual feeders base' and CCM supervisory control values to the PSM data base. [7]. These features of the load model are important for the simulation of complex voltage phenomena such as voltage The interaction between the instructor and the OTS is supported collapse. by the IPMMI software and hardware. Control of the OTS, data entry into the data base, and presentation of data on displays are Relay Models performed by the IPMMI. All data requests and updates performed by the IPMMI relate to data resident in the PSM Relays important for the simulation are modeled. Over/Under database. The IPMMI also has the ability to initiate PSM tasks voltage relays trip generators due to high voltage and drop load and to transmit program generated messages to the instructor. at buses with low voltage. Volts/Hertz relays trip generators if a volt/Hertz ratio is violated. Over/under excitation relays Displays used by the IPMMI consists of static masks and allow units to violate their MV AR capability curves for a linkages. Static masks are presented as created initially while specified duration. Inverse time overcurrent relays trip data linkages allow the presentation of dynamic data on branches if flow limits are violated for a given duration. Auto displays. Function key and poke point linkages are features of reclosure relays simulate reclosure attempts of branches due to the IPMMI which are used for task executions, display faults. Over/under frequency relays trip generators due to high selection and data entry. A windowing technique is used to view frequency, and shed load at low frequencies. The amount of load multiple displays simultaneously. shed depends on the frequency. Synchro check relays check voltage magnitude and angle difference when two sides of the controlled circuit breaker are within the same island. Voltage OTS CAPABILITIES magnitude and frequency are checked if the two sides of the The capabilities of the OTS may be described in four categories: controlled circuit breaker are in two different islands. the Power System Modeling (PSM) subsystem, the Educational subsystem, the Scenario building Subsystem, and the Control Network Model Center Modeling (CCM) subsystem. The power system Tap changing and phase shifting transformer actions are modeling subsystem consists of the models and algorithms modeled outside power flow calculations because changes which simulate the power system. The control center modeling usually occur in a longer time frame than the OTS five second subsystem is a replica of the EMS used by the trainee. The cycle time. Thus, separate modules compute the new tap educational subsystem is comprised of the tools and settings and the power flow considers those values fixed. The capabilities which allow the instructor to use the other network model of the transformer is a series impedance and subsystems. The scenario building subsystem consists of tools unequal shunt legs. A piecewise linear capability curve is which aid the instructor to construct training scenarios. available for each generator. Thus, maximum and minimum reactive power output of the units are determined from the Power System Model capability curves. The power system model consists of the static and dynamic models which represent the slow dynamic behavior of the The network model of the AC line is a series impedance and system. [7], [8]. unequal shunt legs. An HVDC multi-terminal model is also available. The rx: system power flow is solved iteratively with Power Plant Models the rest of the system. Each multi-terminal system must have one slack bus, but all of the other buses can have a power The PSM includes energy source models for fossil, hydro, control or angle control converter. The current and angle limits combustion turbines and nuclear units. Various boiler models are monitored and in case of violation, the control type is are provided in tiers of complexity. The boiler models for switched. There are also some soft angle limits which when fossil fuel come in three levels of complexity: a complex, an violated, initiate transformer tap changes. The slack bus is intermediate, and a simple model. There are only two tiers for automatically changed if limits are violated at that bus. the pressurized water reactor (PWR) and combustion turbines. Fossil fuel models represent once-through subcritical, once­ Solution Methods through supercritical, and drum boiler. Boiler control is provided in a simplified form. Coordinated control as well as The trapezoidal method of integration is used to solve the boiler following control are provided. Nuclear plant models differential equations. A one second integration step was include boiling water reactors and pressurized water reactors. A determined to be sufficiently accurate for the models represented common steam turbine model is available for fossil fuel and in the OTS. nuclear plants. A hydro turbine model as well as a combustion The topology processor determines the network connectivity turbine model is available. The PSM data base provides default and keeps track of changes to the network. It determines bus data for the power plant models if some or no data are available. optimal order using Tinney scheme 2. Load Models The power flow solution technique is the fast-decoupled power The load model calculates the network real and reactive loads flow. Generator VAR limiting and remote voltage control are from a specified load curve. done within the power flow solution. The OTS uses a special topology processor which is integrated with the OTS power The power system is divided into several zones. A separate flow. Information about network topology changes is used to zone load curve may be defined for three day types (Weekday, incrementally reorder and incrementally update the factors of Saturday, Sunday), and two seasons (Summer, and Winter). the matrices used in the power flow solution. After the OTS has Distribution factors distribute load from zone level to load run for some time the effects of topology changes accumulate. groups, and from load groups to feeders. Loads distributed to Then matrices must be rebuilt and refactored to avoid buildup of feeders are computed at nominal voltage and frequency. Feeder computational inefficiency. This is done during a cycle when load may consist of a non-conforming portion, and a there are no topology changes and the operator is not sensitized conforming portion. The non-conforming portion of load does to the response of the OTS. not follow the load curve; however, it may have a time schedule to be turned on or off. A random noise portion can be added to Educational Subsystem the loads to represent random fluctuations in load. Voltage dependency of load can be represented by a second degree The Educational subsystem consists of tools which assist the polynomial. Frequency sensitivity, load management, and instructor during pre-session, session, and post-session voltage regulation by feeder tap changer and switchable shunts activities. A brief description of each session is as follows. can be selected in various combinations. The effect of these

280 Pre-Session Activities The HSB uses expert system technology to assist the instructor in building scenarios automatically. Given the condition of the The main part of a pre-session activity is preparing base cases. system in a base case, the HSB searches for the combination of Base cases or snapshots consist of sufficient network and model equipment outages in order to achieve a pre-specified goal. The data such that when restored, the conditions at the time of save goal must be specified by the instructor and may be a line are recreated. An important source of base cases are snapshots overload, or a low voltage problem. The location of the goal of the system taken either manually, or by turning on the state may be either specified by the instructor, or it may be automatic time interval snapshot feature of the OTS. The selected by the HSB depending on the specified training instructor can prepare for a session activity by restoring a objectives. These objectives include the degree of scenario snapshot which is pertinent to goals that are intended to be difficulty and the trainee experience level. achieved during a training session. Furthermore, the instructor can modify the restored snapshot to set the starting conditions. These modifications are for instance changing the date/time of OTS IMPLEMENTATION AT PHILADELPHIA simulation, or changes in load, generation, topology, etc .. ELECTRIC COMPANY Finally, the instructor can save the modified snapshot as a base case which can serve as a starting point for the session activity. An important objective of this project was the demonstration of the developed software at a host utility. This meant that the Another part of pre-session activities includes set up of power system models and algorithms and the educational scenarios. Scenarios are either designed and pre-tested by the subsystem had to be implemented in a real-time environment instructor using the OTS Simulation capabilities to achieve which included a real-time data base and a real-time man­ certain operating conditions, or produced by scenario creating machine interface. The PSM computer had to be connected to tools such as the Heuristic Scenario Builder or a transient the secondary computer of an EMS and a CCM had to be stability program. developed starting with the host utility's EMS.

Session Activities Philadelphia Electric Company was selected as the utility to host the demonstration of the OTS and to participate Session activities are comprised of the following steps substantially in the development of the OTS. Initialization of the simulator and restoration of the PECO OTS Hardware Implementation base case prepared as part of the pre-session activities. For the implementation of the OTS at Philadelphia Electric Execution of scenarios created for the session. Company, a PSM computer was selected, the OTS data was Participation by the instructor in the training collected, checked and populated into the OTS data base, and session. displays were created at the instructor's position. The PSM Setting criteria for performance measures. computer was connected to the secondary computer of PECD's EMS (System Automatic Monitoring and Control or SAMAC) in Participation in the session activities includes execution of which a control center model (CCM) was implemented. scenarios as required, modifying events as deemed necessary, and responding to trainee requests as power plant and substation SAMAC was originally implemented by North American operators for actions not supported by supervisory control. Rockwell, TRW and PECD. SAMAC is based on Unisysl The instructor should also monitor the trainee's responses to Burroughs A10H processors and assorted peripherals and front­ the events and should set the system parameters intended to be end devices. monitored. For example, voltages at certain buses, frequency of a given island, etc. may be monitored in order to gain adequate The computer used for the PSM is a CYBER 962-11 with the information about the trainee's performance during the training following features: session. 64 MBytes memory 10 peripheral processors Post-Session Activities 12 data channels Following the completion of a training session, the instructor Operators console can evaluate the performance of the trainee through the NOSNE Operating System monitored parameters and snapshots which the instructor designated to be monitored throughout the simulation. Also the The computer used for the CCM is a Unisys/Burroughs A10H instructor can review comments he might have entered during which is also the secondary processor of the SAMAC system. the training session regarding the ability of the trainee to The AIOH is a dual processor with the CCM running in one CPU handle the emergency cases, or the efficiency of means advised and PECO accounting and system maintenance running in the by a trainee to bring the system back to normal. second cpu. The Unisys/Burroughs MCP Operating System was used. Scenario Building Subsystem Two instructor positions are supported at PECO. Each IP is This subsystem consists of the tools that aid the instructor in based on an HP/Apollo DN3000 workstation. In addition, two building training scenarios. These tools are: The EPRI ETMSP CCM consoles are available for the instructors. These Transient Stability program, and the Heuristic Scenario Builder instructor CCM consoles can be initialized to either active or (HSB). slave mode. In active mode, the instructor CCM console provides normal interactive capabilities. In slave mode, one of The Transient Stability (TS) program and its associated power its CRTs displays exactly the same information as the master flow are interfaced to the OTS such that they can be executed at CRT ofa specified trainee console. any time during simulation without any manual data preparation. However, since the TS program cannot be executed Two communications processors were utilized to connect the in real time, the OTS must be paused during the execution of this PSM computer to the CCM computer. The PSM program. communications processor consisted of the following products:

The output of the TS program can be directed to the PSM printer. CDC Distributed Interface (Communications Also, as a result of operation of the relays modeled in the TS Network Unit) program the post-transient network topology can be easily re­ created for the OTS. This is done by translating these topology CDC CDCNET Communications Software running changes into circuit breaker trip events. These events are then X.25 protocol (Telenet{fymnet certified) transferred to the OTS event library upon request by instructor.

281 The CCM communications processor consisted of the following the time the snapshot was taken. The snapshot may also be products: saved permanently in the PSM, via a base case save command, as part of the initialization sequence. The base case restore and Unisys CP2000 Communications Processor snapshot restore are activated during initialization to establish Unisys Communications Management System the starting point of a training session either from a (CMS) permanently saved base case in the PSM (base case restore) or a Unisys Network Architecture Network Services previously saved snapshot in the CCM (snapshot restore). (BNA) Telenet{fymnet CCITI X.25 Protocol The CCM provides broadcasting capability which allows the instructor to send text messages from the instructor CCM The DrS at PECD also includes two trainee consoles, a front-end consoles to the trainee consoles. system which drives the consoles, and a duplicate copy of the mimic boards used in SAMAC. PECO Testing PECO OTS Software Implementation The CCM software and the PECO software modifications were developed on a Burroughs B6925 computer located at Empros To support the implementation of the OTS at PECO, data was using remote terminals located at Macro. A CCM/PSM interface provided for the PECO power system network, for the PIM and PSM simulator were developed to facilitate CCM testing. interconnection, and for a simplified representation of the All unit testing and preliminary system integration were world external to PIM. Special models were developed to performed at PECO using an off-line Unisys AIOH computer simulate the PIM power pool operations, and the operation and with limited Man-Machine Interface (MMI). The final control of pumped storage and hydro units at Conowingo and PSM/CCM integration was performed at Empros on a CCM Muddy Run. platform configured with a Burroughs B6925 computer, a subset of MMI equipment, and a CYBER 962-11. The Factory The CCM has the same power system monitoring and control Acceptance Test (FAT)" was conducted on the same CCM capabilities as SAMAC. The CCM was built from SAMAC and platform at Empros. The Site Acceptance Test (SAT) was included customized software that allows data, normally performed at PEeD on the final CCM configuration consisting transferred between SAMAC and its RTUs and PIM, to be of the Unisys/Burroughs A I OH computer and all of the transferred between the CCM and PSM. SAMAC functionality appropriate MMI equipment. After the completion of SAT, the is retained including the same man-machine interface, steam CCM custom software and PECO software modifications were generation control, economic dispatch, hydro plant control, merged into PECO's SAMAC software using conditional system status processing and security analysis, supervisory and compilation techniques so that PECO's SAMAC and CCM combustion turbine control, limit checking, CRT trending, software will be maintained as a single source file and remain report generation, logging, and alarm/event capabilities. equally current as enhancements and changes occur to the SAMAC software and data base. SAMAC functionality is not fully supported by the PSM, however, because implementation of some SAMAC capabilities is considered non-essential and would have incurred too much OTS RE-IMPLEMENTATION AT ANOTHER SITE cost for too little training benefit. Thus, the PSM does not support: (1) on-demand reports between SAMAC and PIM other Re-implementation of the PSM at another site may require than the critical lines-out-of-service report, (2) SAMAC modification in some or all of the following aspects of the external device and communications circuit testing and (3) PSM. SAMAC scanning of pulse accumulator data (normally every hour). All other SAMAC functions are fully supported. a. Data Base

The CCM supports OTS instructional features. These features Format definitions for some data may require changes, or include initialization, simulation control, snapshot save and new data may need to be introduced. Limits for sanity restore, base case save and restore, and snapshot review. checking of some data need to be re-examined.

The initialization command originates from the Instructor The mapping function that establishes relations between Position MMI (IPMMI). Based on the parameters received with data articles in the CCM SCADA tables and particular the command, the CCM initializes its data base and sets up the equipment in the PSM network model, both internal and trainee consoles and the instructor CCM consoles accordingly external to the user utility may be of a different nature and for the training session. For PECO, either trainee console may may require modification or redesign. The SCADA be defined as a Power Director, Assistant Power Director, Shift messages exchanged over the CCM to PSM data link are Supervisor, North Load Dispatcher, Assistant North Load subject to design modification. Extended mapping points Dispatcher, South Load Dispatcher, or Assistant South Load that signify CCM points (analog and digital) which have Dispatcher position. no direct representation in the network model may vary from one user utility to another. Simulation control supported by the CCM includes start, stop, pause and resume. These commands are normally initiated from Although care has been taken to develop models for all the IPMMI. If enabled, they can also be initiated from the commonly used utility equipment, any utility may have trainee consoles. The start command will be accepted by the some special requirements, such as a particular type of CCM only after the completion of initialization to start a pumped storage, power plant, or equipment which is not training session. The stop command stops simulation and all defined or is defined differently than the ones in the present CCM activities. The pause command suspends simulation. OTS. These specials may require additional development After a pause command, the CCM is still active. It can be used to review SAMAC displays but accepts only stop, resume, and b. Power System Models snapshot save commands. The resume command continues all simulation features after pause. Most of the items for re-implementation described previously affect the modeling software directly or The snapshot save command originates from the IPMMI. It is indirectly, so the related modules should be adjusted used to take a snapshot of the CCM data during a training accordingly. session. The snapshot saved in the CCM may be reviewed after initialization and before starting a training session via the Special features may require that new models be developed snapshot restore command which allows the instructor and and new displays created. Unit control modes and the trainee to examine the state of the power system and the CCM at CCM's dispatch program may be different from one utility

282 to another which may call for modification of the related substantially in their MYAR output due to the low voltage PSM modules. profile in the system. The condition gradually deteriorated to lower values of voltage in many busses. This process lasted Power pool operations may have certain energy policies approximately one minute before some voltages dropped below and constraints that impact the modeling software. 50% of their nominal value. At this point the system voltage collapsed and all generating units were tripped. The CCM may be implemented on the reserve computer of a dual redundant EMS. Alternatively, it may be implemented on a Another observation made in this scenario was that due to the standalone computer which is a replica of the one used in the initial impact of the original disturbance the voltages in the EMS. When implemented on the secondary computer of an entire system were affected. The LTCs which are normally EMS, the failover capability of the EMS must be preserved. controlling their lower voltage sides, change taps in a direction Some type of trainee console switchover capability may be to increase the voltage at the controlled busses. This further required so that a trainee console may display simulated data and reduces the voltage at the high voltage busses. The LTC models execute programs which run on the secondary computer. of the OTS model the time delay associated with moving taps. Usually in the PECD system initial tap is moved within 90 The CCM development effort for PECD is somewhat simplified seconds with subsequent taps within 15 seconds. This by the fact that the PECO EMS is a centralized system. The contributes to the fact that the voltage in the system collapsed CCM development for another site must consider the approximately 2 minutes after the initial disturbance. implications of distributed processing and the availability of source code if it is a turnkey system. The design of the data link Islanding software may be transportable, but it is unlikely that all software will be. Basic differences between other EMS systems A generating plant in the PECO system which consists of two that will effect the data processing implementation are: 130 MW steam units, and four 20 MW combustion turbines was external data links, data acquisition data types, and floating selected for this scenario. The generation of the plant was point formats. The level of CCM development effort will adjusted to supply the 130 MW of load fed by the plant. Breaker depend on the amount of necessary customization and the ease tripping which resulted in islanding the plant was performed by with which the custom software can be integrated. the event scheduler. The instructor displays reflected the existence of two islands with two different frequencies. The new Any part of the PSM which relates to the CCM directly or island was next blacked out by tripping one of the steam units. indirectly may be affected and may need to be re-examined. The busses were cleared, and all loads were disconnected except for approximately 10 MW of load. Next, a combustion turbine was started to pickup the load. After the new island frequency EXAMPLE SCENARIOS stabilized, another combustion unit was brought on line to pick up an additional 10 MW of load. The newly formed island was The capabilities of the DTS were demonstrated to a group of next connected to the main island after the frequency had engineers, programmers, training program instructors, and stabilized close to 60 Hz. operations personnel representing twenty-three EPRI member utilities. This seminar was sponsored by EPRI in June 1990 at Blackstart/Restoration PECO. The demonstrations were arranged to show the modeling capabilities of the OTS as well as the use of the OTS as an A very large block of load was dropped in order to blackout the effective training tool. Experienced control center operators system. All units tripped and simulation continued with no from Philadelphia Electric Company were actively involved in generators on line. A section of the system was selected for the preparation and conduct of the demonstrations. The blackstart. The selection was based on PECO's system following topics were the main theme of the seminar: Voltage restoration guidelines with some simplifications to Collapse, Blackstart/Restoration, Islanding, and Scenario accommodate for the limited time allocated to this demo. Five Building. Also, an actual historical event on the PECO system hydro turbine generators were gradually brought on line to was re-created to demonstrate a specific training session. pickup small amounts of load. Two parallel paths to a load center were established, and approximately 35 MW of load and Voltage Collapse generation was restored. Philadelphia Electric Company as part of the Pennsylvania, Scenario Building New Jersey, Maryland (PJM) interconnection covers a service area of 2475 square-miles with a population of 3,500,000 This demonstration involved routine activities performed by an people. Vast amounts of power are imported from generation instructor. Actions such as changing taps, regulating voltage centers in the west of the interconnection to load centers in the by generators, and dispatching generation were performed to east across high voltage transmission lines. According to a obtain a training case. 1988 study conducted by PJM loss of a 500 KV line simultaneous with the loss of a large generator in the east could Re-Creation or a Historical Event result in a serious voltage dip in the system. On Friday, May 4, 1990 the Philadelphia Electric system This study was used to develop a voltage collapse scenario for experienced a fault at the Emilie substation. The fault occurred the OTS. The system was set up with larger than normal power when a 230 KV breaker was closed to energize a capacitor bank. imports from the west. The given contingencies were Subsequent investigations showed that the substation copper programmed in the event scheduler to occur at a certain time ground cable had been stolen. As a result, flashover in the after the start of simulation. The voltages at several key capacitor bank developed extremely high voltage surges which locations were monitored using the instructor displays. destroyed the lightening arrestors of two 230 KV lines. The Voltage at a monitored bus dropped from 515 KV, before the result was the loss of two 230 KV lines and complete loss of event, to 485 KV after the event. This condition lasted for power to the Emilie 34 KV distribution substation. Inspection approximately one minute before the voltage dropped to 476 of the contingency analysis package at the control center KY. During the one minute interval the generating units were showed that further loss of a 138 KV line would result in several trying to boost their controlling voltages by raising their lines violating their emergency ratings. MYAR output above maximum. Most of the over excitation relays modeled in the OTS have a trip time of one minute. This To re-create the system conditions on May 4th, the historical accounts for the fact that the voltages in the system were records were studied and adjustments to load and generation were prevented from declining for approximately one minute because made to make the conditions similar. All equipment that was the units were supplying the needed reactive power. The out of service on May 4th, were taken out of service in the OTS. capacitors which support and maintain the voltage, declined The new condition was saved as a base case. Using this case, the tripping of the lines and loss of load at the substation were 283 programmed as scenario events. Two experienced operators were seated at the trainee positions, and two members of the PECO training staff were seated at the instructor positions. After the events occurred, the instructors, role playing different station operators and the supervisory control center operator, informed the trainees of the events at the substation. The interaction between instructor and trainees continued during the entire training exercise.

Inspection of the contingency report showed very close similarities to the report generated at the control center on May 4th. An instructor under direct order from one of the trainees started three combustion turbines. Although this did not eliminate the contingencies, the situation was slightly improved ( this was also true on May 4th). At this point the OTS was taken one step further and the line in the contingency report was tripped (this event did not happen on May 4th). As the contingency report had predicted, two lines were loaded beyond their emergency ratings. The only option left to the trainee was dumping load at several substations (this was the plan on May 4th if ever the contingency had materialized). Soon after dumping load the overloads were relieved.

CONCLUSION An advanced, transportable OTS has been developed and implemented at Philadelphia Electric Company. The requirements for simulation capabilities which allow training in normal, emergency, and restorative conditions have been met through advanced models and algorithms. The requirements for transportability have been met through the unique configuration. Software transportability has been achieved through the use of standards available at the time of design and the selected design techniques. The requirement for improvement of instructor capabilities has been met through the development of instructor tools. The demonstration of the OTS has been described.

ACKNOWLEDGEMENT The work described in this paper has been funded by the Electric Power Research Institute as part of RP1915-2.

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