An integrated dispatcher training simulator for use in a regional electricity distribution centre by Cs. Demjen, F? Kadar, F? Meszaros and D. Szendy KFKl Research Institute for Measurement and Computing Techniques, Hungary

At the end of 1993 the first dispatcher training simulator of the Hungarian electric power industry began operation in the regional dispatcher centre of the North Hungarian Electricity Distribution Company (EMASZ KDSZ). The simulator performs discrete, event-driven simulation of the network, the protection arrangements and the telemetry system. Its main purpose is to help the dispatchers to cope with complicated, rarely occurring disturbances in the electrical network. During a training session the trainee uses the same type of workstation as in the online system. The instructor’s man-machine interface is implemented in DECWindows using the colour graphics terminal of a VAXstation 3100.

Introduction

T performs supervisory control and data acquisition (SCADA) and energy management system (EMS) functions. The dispatcher training simulator (DTS) helps the operating personnel to use this system more efficiently. The DTS can obtain initial data from the online system but its operation is independent of that system.

disturbances occur very rarely, the DTS is primarily used t o train the dispatchers for the job in emergency situations. The dispatchers exercise the quick recognition of emergency situations and the preventive and restorative actions necessary for various power system disturbances.

In addition, the DTS is used for some long-term power system analyses, because certain types of long-term EMS functions cannot be implemented in the online SCADA- EMS system. A variety of power system states can be produced with

66

he new dual-computer process control system of EMASZ KDSZ

As serious power system

the simulated electrical network and the effects of intended modifications or development can be examined. The consequences of possible hardware or software developments within the SCADA-EMS system can also be studied in a simulated environment.

The dimensions of the electric power distribution network controlled by the EMASZ KDSZ can be characterised by the following values:

power 600 MW number of substations 53 number of measurements 2000

0 number of signals 3000

The model of the network consists of about 100 nodes and 200 edges.

According to the control hierarchy of the Hungarian power system, a regional dispatcher centre (KDSZ) is supervising and controlling primarily the operation of the 120 kV main distribution network of the region. This is done indirectly through subcentres (UIKs) belonging to the

KDSZ. The subcentres control mainly the medium voltage (35, 20, 10 kV) distribution network and execute the computer commands of the KDSZ sent to them on telecommunication lines. In addition, the personnel of the subcentre receive verbal instructions from the KDSZ by telephone. Each subcentre sends commands to and receives data from its remote terminal units (RTUs). The majority of the remote control commands are issued from the subcentres and a few remote commands coming from the KDSZ are sent unchanged to the RTUs. The subcentres send telemetered and some processed data to the KDSZ via telecommunication lines.

Configuration of SCADA-EMS and DTS systems

he configuration of the systems is shown in Fig. 1 . The front- T end system is a dual-computer

configuration, which consists of two ELTEC VME bus machines with 680x0 type processors. This front-end is connected to the telecommunication lines and sends the data in a standard format to the SCADA-EMS system operating on an onlineistandby pair of VAX 3000 host computers.

The dispatchers use PC-AT three- screen colour graphics workstations to control the operation of the SCADA-EMS system and another IBM-AT workstation is used for controlling special EMS functions. A third VAX machine is the host for the SCADA-EMS system used for training simulation. This SCADA-EMS system is basically identical to the online system, except that its host machine

COMPUTING & CONTROL ENGINEERING JOURNAL APRIL 1994

CONTROL I ::: I mimic board

ethernet

I ,__._______...___._...-....-.......------..---

1

EMS terminal and engineering workstation

2 Dispatcher's workstation

1 Dispatcher's workstatton

COMPUTER 1 L

switch ~1 simulator SCADA R long-term

TRAINING - station

instructor's printer r --[-I-- - - - -1

El ~U

EMS terminal dffipatcher for long-term training workstation EMS function

Fig. 1 SCADA-EMS and DTS systems in EMASZ KDSZ

COMPUTING & CONTROL ENGINEERING JOURNAL 67 APRIL 1994

is connected to the DTS host machine, a VAXStation 3100, instead of the front-end machines. During training sessions the dispatchers work on the same type of workstation as in the online system, while the instructor uses the VAXStation's colour graphics display, keyboard and mouse.

The computers and other devices of the online SCADA-EMS system and the training simulator are linked together by an Ethernet network. The man-machine interface devices of the DTS system [workstations, VAXStation, printer) are accommodated in a separate room, so the personnel operating the online system will not be disturbed by the training simulation courses.

Main features ince none of the equipment of the simulated power system S requires continuous simulation,

the DTS system performs a discrete simulation. Its operation is event- driven, i.e. i t responds to specified simulation events.

The progress of a training session is controlled by the instructor and by the scenario (set up earlier by the instructor). The simulation environment is very much like the real control system because the dispatcher uses the same type of equipment as in the online system.

A full-scope simulation is performed, i.e. everything the

dispatcher can experience when operating the online system is simulated, e.g. load changes, protection operations, effects of dispatcher and field personnel actions, results of subcentre processing, telemetry functions, and so on.

The DTS has a detailed topology and protection model, so the instructor can act as a field operator and is able to execute the commands received from the dispatcher by telephone. He can tell about the events that have occurred in the power system and he can read the settings of the protecting devices in the substations.

Working with the DTS training session starts with a preselected initial state of the A network, the so-called base

case. Actual network data or network data saved earlier in the online SCADA system as well as simulated network data saved in the DTS system can equally be selected as the base case for a training exercise. A simplified description of the external network is used during the simulation. There is a set of predefined external network descriptions and one of these descriptions should be selected and assigned to the base case. The instructor can modify the loaded base case and change the external network assignment before starting

'

the training exercise. Training sessions proceed

generally according to scenarios set up earlier by the instructor. A scenario contains a sequence of selected events and their relative times. Scenarios can be created and modified with the scenario editor. The instructor selects a scenario for the training session from a library of scenarios.

Loads measured at the load points of the electricity distribution system are represented by load profiles in the simulator. Load profiles can be assigned to individual load points and also to groups of load points. The profiles can be created and modified with the graphic profile editor. Load profiles are generated for every typical load situation and every profile covers a complete day [workday, weekend, holiday etc.). When preparing the training exercise, the instructor selects the load type and the time of day at which the processing of the load profiles begins. If he has selected group profile simulation, he assigns individual load points to the group load profiles. During the simulation the loads will change according to the load profiles. Training exercises are possible also with constant loads.

After finishing the preparation, the instructor starts the training simulation exercise. If the base case does not contain short circuits and

I SfhJd Fc Sontfojt6 (50 WA) , 1 4;.0 MW

25.1 t 16.4 8 I:!.; kU BORS SAJI 50.04 Hz

Z5:0 16.5 49.5 0 .0

f f +++ t A t A

11 10 9 8 A h A 7 V Fig. 2 Portion of a

substation diagram with the left circuit breaker on the secondary side of the transformer selected by the instructor

68 COMPUTING 15 CONTROL ENGINEERING JOURNAL APRIL 1994

the state estimation can be performed successfully, then the training simulation can begin. If not, the instructor has to introduce some changes in the base case in order to correct the errors indicated in the error messages sent to him by the network checking program. When the base case is free from error, it is sent to the SCADA-EMS system connected to the DTS and the simulation begins.

A reduced version of the communication protocol between the control centre and the subcentres is used between the DTS and the SCADA-EMS during a training session. The actual state of the simulated power system is determined by the commands of the dispatcher and the instructor, the scenario and the changes of the loads. The instructor can suspend the exercise, when it seems reasonable to have a pause at a given stage of the simulation. No automatic processing of the scenario and the load profiles takes place in suspended state, but the instructor and the dispatcher can issue commands.

During the exercise the actions of the dispatcher and the instructor are recorded in various logs that can be viewed and printed. The events coming from the scenario or issued by the instructor are also saved in scenario format, so they can be used as a scenario for another exercise. At the end of the exercise, the instructor can save the dynamic database of the DTS as a new base case.

The instructor prepares and controls the training simulation exercises using a menu system and graphic and semigraphic pictures implemented in DECWindows on the VAXStation machine.

The substation and network overview diagrams are displayed on the instructor’s workstation in order to observe and control the simulated system. DTS-specific data can be viewed and changed on auxiliary diagrams displayed in pop-up windows. When the instructor selects a device on a SCADA-type substation diagram a detailed diagram of the device and its environment appears in a pop-up window (Figs. 2 and 3). Switches represented by a single virtual switch in the SCADA picture are displayed in such windows, as well as protection devices and places where short circuits can be simulated. The settings and status of devices can be changed and short-circuit situations can be defined by selecting an appropriate point in the window.

The states and settings of the

NTRA 5

Fig. 3 Auxiliary diagram displaying detailed presentation of the circuit breaker shown in Fig. 2

protection devices are displayed in the same manner as they can be seen on the real devices in the substations, so the instructor can give the dispatcher the requested data.

Simulation events he DTS is driven by simulation events. During a training T simulation exercise, the system

processes events from different sources. The types of events used in the DTS system are as follows:

controlling events (e.g. start, suspend, terminate the exercise) switching events events changing the state of the model of the power or protetion system (e.g. presetting circuit breaker failure, changing protection parameters) events of the telemetry system [e.g. communication failure on a line) events on the subcentre level (e.g. short circuit in the medium- voltage network) load change events.

The events can come from the dispatcher, the instructor, the scenario and the load model. The events are processed by the models of the DTS. A control program detects the type of the actual event and starts the appropriate model.

Models in the DTS he simulation functions are performed by the models of T the DTS. The network model

produces the power, current and voltage values; the protection model

performs protecting actions: the load model simulates the loads of the real power system: and the telemetry model simulates the telemetry/telecontroI functions necessary for dispatcher training.

Network model The network model consists of

the database describing the state of the simulated power system and the topology, state estimation and load-flow calculations. The state estimation is used only at the beginning of the training exercise to create consistent initial conditions for the DTS.

The topology calculation updates the network connectivity description and the load-flow program calculates new power, current and voltage values. Topology and load-flow calculations are performed after each switching or short-circuit event, and load-flow calculation after each load change. The calculations are basically identical to those used in the SCADA-EMS system having an additional part that calculates also medium-voltage network data.

Protection model The user of the simulator has the

feeling of working with physical protection devices. A real device is represented by several virtual logical devices in the simulator. They perform all the functions of the real device. Protection errors can be simulated by disabling some or all of the functions of a selected protection device.

The basic assumption is that protection devices installed in the power system operate correctly, and they respond with definite actions to

69 COMPUTING 6( CONTROL ENGINEERING JOURNAL APRIL 1994

specified network conditions. So there is no need to calculate exactly the short-circuit values for starting protection operations. Instead of this, the simulated protection devices respond to logical short- circuits (short-circuit events). The advantage of a logical start is that there is no need for short-circuit calculation; a definite operation can be obtained even in extreme network conditions and the database requirements are also reduced.

Protection devices of the 120 kV nodes and the 120 kV lines are modelled in the DTS. Implementing models of transformer protection and protection on other voltage levels is not necessary for dispatcher training purposes.

The protection model contains the nodes of the grid (substations), the transmission lines, switching equipment, protected zones, protective relays, status of the switching devices, and the signals of protection devices.

The simulation of the protection functions requires a more detailed topological description than used by the network model: more parts of the network are identified as topology elements, e.g. busbar sections between two sectionalisen, conductors between breaker and sectionaliser, dead zones between current transformer and breaker, and so on.

protection simulation, the virtual protection device can cause breaker tripping, release, start or block the operation of another protection and produce telemetry signals. The models of all protection devices (section protections, busbar differential protections, impedance relays etc.) are built up from virtual devices.

The characteristics of a protection device can be set by switches on its front panel. By including the functions of these switches in the protection model, dynamic changes of device characteristics can be simulated. The switches are controlling functions, like overlapping, breaker failure protection starting, short-term reclosure, and so on.

Load model The load model works cyclically

and changes the load values in each working cycle according to the load profiles selected for the training exercise. The model processes individual or group load profiles. An individual profile contains load values for a single electric power consumer; a group profile contains the sum of individual load values for

The basic element of the

a group of consumers. Load simulation can work in two modes. In the first mode the profiles are fitted to the base case, in the second mode the load values coming from the profiles overwrite the load values in the base case. The instructor can also modify load values; these values will not be changed by the load model during the training exercise.

A further goal of the development project

will be the generalisation of the

DTS system for training dispatchers

of other control centres

Telemetry model

version of the communication protocol used between the dispatcher centre and subcentres. This allows that the SCADA system working together with the DTS can be basically identical with the online SCADA. In fact this SCADA is a copy of the SCADA system which runs in DTS mode. In addition to normal functions, different events influencing operation [faults of remote terminal units, telecommunication lines, subcentres) are also simulated. A logical type of simulation is implemented, so the timing and delay conditions of the real telemetry/telecontroI system are not always maintained.

The telemetry model receives actual or previously saved snapshots of the online database from the online SCADA, sends base case to the SCADA running in DTS mode, sends/receives control messages and simulates communication between the regional centre and the su bcentres.

The DTS software system he DTS programs run on a VAXStation 3100 under the T VMS operating system. The

majority of programs are written in VAX Fortran and the windows used by the instructor’s man-machine interface are defined in User Interface Language (UIL).

An offline program system generates the database of the online

The model implements a reduced

DTS system. The generation procedure receives input data from a common SCADA-DTS databank that contains all the data for the SCADA- EMS and DTS systems. The common databank is stored in a data maintenance machine and it can be generated and modified only there.

During the DTS database generating procedure the necessary databank definitions are copied into the DTS host machine and the static and dynamic DTS databases are generated and loaded into memory. A picture generation program converts the SCADA pictures and font definitions so the same substation and network overview pictures can be displayed on the colour graphics terminal of the VAXStation and on the dispatcher’s workstation. A semigraphic editor is used to create graphic presentation of DTS-specific data.

Future development ests of the DTS system are carried out in parallel with the T last phase of the development

project. Some user requirements may arise in this phase, which are expected to concern mainly the instructor’s man-machine interface, but demands for minor changes in the situation models are also possible. The man-machine interface can easily be modified on the DECWindows basis, and the modular structure of the simulation models also facilitates additional development.

A further goal of the development project will be the generalisation of the DTS system for training dispatchers of other control centres. The main task in this work will be the adaptation of the DTS databank system in order to meet the variety of requirements arising from the features of the local network.

References 1 KADAR, P.: ‘A multi-purpose substation

simulator shell’, 2nd Conference on Artificial Intelligence, Budapest, 24th- 26th,January 1991

interaction of the short-circuits and the protection operation’, 3rd Symposium on Expert System Application to Power Systems, Tokyo, 1st-5th April 1991

3 MAJOR, P., and KhDAR, P.: ‘A complex dispatcher centre’, 4th Symposium on Expert System Application to Power Systems, Melbourne, 4th-9th January 1993

2 KADAR, P.: ‘Simulation of dynamic

0 IEE: 1994

The authors are with the KFKl Research- Institute for Measurement and Computing Techniques of the Hungarian Academy of Sciences, H-1525 Budapest, PO Box 49, Hungary.

70 COMPUTING & CONTROL ENGINEERING JOURNAL APRIL 1994