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An overall distribution automation structure
Electric Power Systems Research, I0 (1986) 7 - 19
7
An Overall Distribution Automation Structure
WHEI-MIN LIN and MO-SHING CHEN
The Energy Systems Research Center, The University of Texas at Arlington, Box 19048, Arlington, TX 76019 (U.S.A.) (Received June 21, 1985)
SUMMARY
An effective distribution automation system must involve both hardware and software. The desired system has not yet been attained, but the key pieces have been developed and are ready to be assembled. A complete data base is necessary to sophisticated software, and that software is the key to distribution automation. VAX/Intergraph facilities are considered in particular since the concept derived in this paper originated from the VAX/Intergraph system. Recent development of a three-phase unbalanced load flow program and its interface with the Intergraph provide the means of attaining an effective distribution automation system.
INTRODUCTION
Distribution automation has different meanings to different people. Some people think of remote switching, some of telemetering or street lighting control. But these functions are only part of distribution automation and do n o t interpret its spirit. A more general c o n c e p t of distribution automation is essential. The conventional way of defining distribution automation puts the emphasis on hardware, e.g. remote circuit-breaker reclosure, telemetering, and so on. A modern realistic definition should involve both the hardware and the software. An effective system can be accomplished through the introduction of a complete distribution data base system and the means to use it. The basic requirement is a static data base system to store all important data. A graphical data base is useful to store physical configurations. It is also helpful 0378-7796/86/$3.50
to have a real-time data base to store dynamic data. Based on this data base system, sophisticated software can be developed, either to check the system status or to assist in the decision-making process. From the hardware (supervisory control and data acquisition (SCADA), telemetering, etc.) the system data are gathered and stored in the data base system. Processing the data via some software, a system profile (voltage, p o w e r flow, etc.) is produced. Through another data analysis process, a decision will be generated whenever necessary. The decision may come from an operator or by option software or both. Through hardware again, the decision (control signal) can be fed back to the power system. Figure 1 shows the structure described above. These procedures comprise a complete automation cycle. This a u t o m a t e d cycle is controlled in real time for decision by software, or, in relatively quick time, for decision by operator. The meaning of real time is not minute-by-minute-oriented operation in the distribution system -- two or three times a day may be good enough. The data base system and the software are the essence of this process. From this cycle the robustness of the automation system can also
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be evaluated. For example, the remote switching capability based only upon an operator's experience is not recognized as a robust distribution automation operation. However, if the operator's experience is assisted by welldesigned computer analysis, it may be a sound automation system. In Fig. 1, the introduction of the data base and the software will make the operation process more realistic. Furthermore, with the help of a state estimator, system uncertainties can be alleviated. By analyzing the data provided by a real-time data base or SCADA, the state estimator can provide better information for the software to generate more faithful results, especially for on-line operation.
Intergraph system The facilities provided by the Intergraph system [1] were found to be particularly appropriate to our research. This system provides both the mapping features and the data base management system. In addition, a linkage between the two can support some interactive features in applications. Based on this system, we have formulated an overview of distribution automation. The data base system contains a huge a m o u n t of data from the distribution area. Since only distribution personnel know how to handle their own data or to make decisions to fit their own needs, a distribution automation system should be operated by distribution people. The distribution operation should be separated from transmission. Transmission-oriented distribution automation can never be made efficient since it is a distribution-level decision whether to make economic/emergency load transfers, to balance loads, or to switch capacitor banks. To build a good distribution data base involves a great deal of work. A utility must carefully evaluate its ability to allocate its resources. However, t o d a y ' s laziness may become tomorrow's nightmare. Waiting for the best m e t h o d will a m o u n t to perpetual indecision. Faced with rapidly changing technology, we ought to pursue a state-of-the-art solution. Because the Intergraph system is popular, we used a VAX/Intergraph system to provide the complete data base. For a given distribution system, this data base structure will contain all the information about
all the power apparatus of each phase, from substation level down to each pole.
Three-phase load flow program The three-phase unbalanced load flow program [2] has proved to be a more sophisticated tool with which to compute a system profile than a conventional load flow program. This unbalanced load flow program was designed particularly for a radial system, using an unbalanced three-phase structure directly rather than a balanced one. The conventional symmetrical component-based single-line diagram approach is not considered here. It is totally unacceptable to use a symmetric sequence network for an asymmetric system. By reading in the data for each phase individually, the three-phase unbalanced load flow program can generate the unbalanced voltage profile and the power flow for each phase. This o u t p u t will describe the radial distribution system more faithfully than a balanced result. More applications can be explored with this tool. Every load flow program mentioned hereafter refers to this three-phase unbalanced load flow program. The normal unbalanced three-phase data base built via Intergraph's facilities happens to fit the needs of this load flow program.
DISTRIBUTION AUTOMATION HIERARCHY AND MAJOR FUNCTIONS
Distribution hierarchy It is a c o m m o n practice to divide the distribution a u t o m a t i o n system into three levels: substation, feeder and service [3, 4]. The structure is shown in Fig. 2. A central computer is located no lower than the level of the distribution dispatch center (DDC). With the aid of a communication system, the DDC can collect data from or activate automation functions (control, monitoring) to the substation, the feeder, or the service level. It is this typical structure between the DDC and the distribution system that should be developed in state-of-the-art distribution automation. At each level of the hierarchy, some functions of control and monitoring can be identified. Most of the major functions considered so far in distribution automation are outlined in the following sections [3, 5, 6].
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- Voltage and VAR control capacitor bank and regulator control t ransform er tap-changer control - Feeder load m anagem ent load-change/motor-starting analysis control load unbalance check e c o n o m i c / e m e r g e n c y load transfer sectionalizing switch reclosure Fault identification and p r o t e c t i o n
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Monitoring Capacitor bank and regulator step Switch positions Sectionalizer and fuse status - V o l t a g e , current, pow er and pow er factor at m et ered points - Zero-sequence current {selected points) -
Substation automation Th e substation is the most delicate part of a distribution system, involving much expensive equipment: main transformers, capacitor banks, circuit breakers, etc. Since all pieces o f e q u i p m e n t are aggregated, it is comparatively easy to cont r ol and monitor. Con trol - Capacitor bank cont r ol Main tr an s f o r m er tap-changer cont r ol A u t o m a t i c bus sectionalizing - A u t o m a t i c circuit-breaker reclosure - A u t o m a t i c switch cont r ol -
-
Monitoring - V o l t a g e , current, power, and pow er f act or on totalizers and feeder circuit breakers - Switch positions Circuit-breaker status Main tr an s f or m er t em pe r at ur e s (top oil and winding) - Synchronism check - Substation zero-sequence current -
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Feeder automation The feeder level includes the part of the p o wer system f r om substation to distribution transformers, which covers a large region. L en g th y conductors, capacitors, regulators,
-
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Service automation F r o m distribution transformers downward, this is the lowest level of the hierarchy. Transformers, w at t m et ers (M in Fig. 2), and customers are major elements here. The unique task of this level is to satisfy the needs of the customers. A good quality, reliable automatic electrical service is always appreciated; sometimes even street lights may be controlled by the system. Control Customer load m a n a g e m e n t r e m o t e service c o n n e c t i o n / d i s c o n n e c t i o n emergency load shedding A u t o m a t i c m et er reading A u t o m a t i c billing - Trouble-shooting/recovery - Street lighting -
-
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Monitoring Unbalance tracking - Customer loads - Feeder terminal voltage -
10
Other functions The distribution dispatch center should collect all the important data. Data collection can be used for both on-line control and research purposes. A remote supervisory control and data acquisition (SCADA) system is required to manage all the functions stated in the previous sections. An alarm annunciation system can be installed wherever necessary. Dispersed storage and generation elements can be controlled according to their sizes [7]. In addition, the following data are important; they should also be collected by the distribution dispatch center: - fault records - sequence-of-event records weather data records -
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D A T A BASE S T R U C T U R E
Interactive computer graphics developed by the Intergraph Corporation are widely used because of m a n y good features, although a lot of storage m e m o r y is required. A graphic station is designed to link with and to use the CPU of a Digital Equipment Corporation (DEC) system. The DEC-VAX/Intergraph Corporation system provides several facilities, some of them related to the data base and graphics used. The data base and graphic files can be built and maintained via these facilities. The term 'graphic data base' can be used if more than one file exists. However, graphic data base may indicate only one 'graphic file' in the following discussion. It is of no interest here to denote any difference. The above two data bases are generally built via Standard Interchange Form (SIF). They are maintained by a Data Management and Retrieval System (DMRS) and an Interactive Graphic Design System (IGDS). These are all facilities provided within the Intergraph system. An artificial feeder and its corresponding data bases are used for demonstration in this paper. A real feeder is also used to show the real-world application.
D M R S data base A hierarchical data base is used since a distribution system is itself hierarchical in structure. A conceptual view of the illustration data base built is shown in Fig. 3. This relationship provides an efficient structure for the
searching algorithm in the load flow study. The level traversal along this data base tree can guarantee accuracy when a record is being located. Twelve bytes are reserved for each storage record to preserve the record header and parent/child relationship.
IGDS data base The physical configuration (feeder map) of the distribution system is stored by the use of 'Graphic Elements'. A Graphic Element is an Intergraph term; it is composed of a series of 'words' storing both the global and local information of this element. Graphically, those elements are lines, circles, triangles, etc. Symbolically, they stand for line segments, poles, transformers, etc., of a power system. Grouped elements can be defined as a 'cell'. A cell library can be built for convenience of the user. These graphical elements are stored in 64 logic levels. Each level is like a sheet of transparency which can be turned on or off freely by the user. For a large system this lengthy sequential file is sometimes awkward; it is more convenient for power utilities to have an indexed sequential file structure according to the 64 levels. Data base linkage A link between a Graphic Element and a DMRS record can be created. The link ties the map features to the data base attributes. Multi-linkage is allowable, each link occupy-
11 ing four words. In lieu of this linkage the DMRS data base can be manipulated through IGDS mode via a non-procedural process. In fact, this is the linkage by which all interactive applications can take place. OVERALL SCOPE OF A DISTRIBUTION AUTOMATION SYSTEM Data and control flow o f the S C A D A To develop an overall distribution automation concept, we should first observe the data and control flow of a physical power system. From Fig. 2, it is not difficult to see that the data and control flow of most existing utilities can be interpreted as shown in Fig. 4. The distribution data {information} are collected by the SCADA system. In the DDC, some decisions are made after a data analyzing process. Those decisions will be fed back to the distribution system through the SCADA again. A good communication system is necessary. This configuration is the physical structure of most power systems. Based on this Figure, the concept of distribution automation should be investigated. The DDC has a central computer, and it is responsible for the following tasks: - issuing all the control commands data collection data base management It has to be noted here that the existing DDCs of most utilities do not have all these abilities yet. -
-
Conven tional distrib u tion au toma tion ideal For a distribution system, generally speaking, there is a huge a m o u n t of information
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flowing into the DDC, if the DDC does have a data base. There are some alarm systems, and some instrumentation designs, where the designer has forgotten that humans are in volved; for example, those which subject the operator to mental and physiological stress. Regardless of stress, the operator has to be able to find the data he needs, analyze the data, and make the right decision. In the DDC, only operators are there to do the above operation. The tremendous a m o u n t of data coming in and out are rarely utilized. The data analyzing process is based only on operators' experience. This is the conventional distribution automation methodology. Sometimes a graphic terminal is available, and a keyboard or a light pen will be used [8]. Light pens were developed in the early age of interactive computer graphics. The pen is criticized to be tiring to the user, who must pick it up, point it, and set it down for each use. The power system in Fig. 4 may represent any level of the substation, the feeder or the service. The a u t o m a t i o n functions should represent any of those major functions discussed in §2. To make the conventional distribution a u t o m a t i o n more effective and more reliable, operators' experience should be assisted by the use of structural data bases and some proper software for the data analyzing process in the DDC. Operators, data base and software should all be involved in the operation of the DDC. The concept of a modern distribution automation can be then formed. Graphic assisted overall distribution automation structure Whenever h u m a n intervention exists, it is well recognized that graphics can provide the best m a n - m a c h i n e environment. For example, until a complex non-driver automobile has been developed, direct observation of road conditions through human eyes is the best guidance to driving. A fully automated distribution system with graphic station is shown diagrammatically in Fig. 5. The SCADA system will collect all necessary data and store/update them in the data bases. A status program will search for the required data, calculate the system status according to the preset algorithm, and show the results selectively on the graphic screen, e.g., voltage profile along with the feeder map. A logic test
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will determine whether to stop (exit) or to react through another decision-making program (DMP) to issue a control command. Each block inside the DDC is explained below.
Status program This is a three-phase unbalanced load flow program; it can be coupled with the state estimator, however, for real-time application. Decision making program (DMP) This block is the heart of the system operation. Any automation function outlined before can be executed. The DMP installed should be foolproof. Synchronizer This maintains the synchronism between the power system and the map features. Data base Both the system data base and the real-time data base are combined here. The system data base (DMRS in this paper) is hierarchically structured. All important system configuration data are stored within it. The real-time data base stores information from SCADA. It is updated periodically. This data base is important in performing real-time applications including state estimation. A study data base with case studies can also be included. A second real-time data base could be included, which would have, at least, the following benefits: the system data base would be accessed only under system configuration changes; frequent access to the data base system would be avoided;
the search technique in the real-time data base should be simpler, which implies less CPU time. All the functions operate automatically according to the preset time interval. An operator is needed only to maintain the system integrity. This overall structure is designed from the point of view of operation. All the pieces have to be assembled to make it become a reality. However, for the system planning mode, this design would work well already.
Man-machine interface Instead of a fully automated system, an intermediate m a n - m a c h i n e interface is proposed. It is practical and can be implemented today. For the system shown in Fig. 5, we observe that the points (3), (4) and (5) involve hardware-software interfaces which have to be resolved although the technology is already available. The 'data base system (DBS)-Status-Graphics' procedure involves software interfaces. It will not hinder us from adopting this structure if the software interface problem can be solved. A m a n - m a c h i n e interface data analysis concept may then be formed right away. The idea is that between the DDC and the communication system, i.e., at all points (3), (4) and (5) in Fig. 5, there exists human intervention. Inside the DDC, all the functions in Fig. 5 are automated. Operator (2) receives the information from the graphic station (the broken line) from an automatic DBS-Status-Graphics computation, then determines whether to exit or to react. Operator (4) actually issues the control c o m m a n d through either remote control or manually operated switches.
13
Operators (3) and (5) will maintain the synchronism between the power system and the data bases. Operators (2), (3), (4), and (5) are n o t necessarily different persons. The system would be a perfect decision support system if the DBS-Status-Graphics could be accomplished by a single keystroke.
DATA BASE I N T E R F A C E
Single-keystroke load flow Traditionally, data preparation is a tedious and complex task. In other terms, data prep-
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aration is the most expensive procedure in running the load flow program. Today, a new era has already arrived -- no data preparation is required at all. With 'single-keystroke load flow', the data needed to run the load flow program will be searched for automatically, then the voltage profile and the power flow will be shown on the map. A criticism is that to construct a structured data base requires the same a m o u n t of work. It has to be pointed out here that the data base we describe in this paper is not a special-purpose data base. It is a general-purpose data base designed for technical as well as administrative depart-
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14 ments. In fact, single-keystroke oper a t i on has already been d e m o n s t r a t e d successfully with a real feeder and its data base.
Interface and search Figure 6 shows the data base interface and search. To run the three-phase load flow program, the system data base has to be searched to get the necessary data, then an input file for the load flow program will be built. First the feeder is located, and all the line segment data are converted. T h e regulator attribute will be checked to see w he t he r there is any regulator attachment. If the answer is 'Yes', a level traversal along the data base tree will be made to locate the regulator and the regulator data translated accordingly. A similar process will be p e r f o r m e d for the capacitor banks. After all the data are collected and converted, a numbering scheme will set up a p r o p e r input file f or the threephase load flow program, i.e. bus data, branch data, and load window selection. A n o t h e r 'geography file' will also be created to store all the geographic locations of buses. This file is used to c o m p u t e the location for t e x t placement in a graphic file (map). The accuracy, speed, and m e m o r y size are all i m p o r t a n t factors for consideration. An o u t p u t file is built by the load flow program. The voltage profile and power flow are stored in this file. Some information in this o u t p u t file has to be displayed on the map. It may involve some study in determining what is a 'pr ope r display' in this m a n machine relationship. Th e t e x t size, color, and line thickness all need to be considered to generate the proper display. A symbology scheme will set them up. The t e x t consists of different sets of data. Every set o f data has a reference a t t a c h m e n t point. The data sets have to be moved to avoid overlapping if more than one set of data are displayed on the same line. Overlapping will make the data sets unreadable if mo r e than one set of data on the same line are r o tated together. A r o t a t i o n scheme must be designed to det er m i ne a suitable r ot at i on if the line segment addressed is n o t horizontal.
Example The data base search and the map can be joined with the load flow program to accom-
plish the engineering application. In Fig. 6, the broken line linking the real-time data base has not been accomplished yet. It will be discussed in the following section. The data base-load f l o w - m a p features are integrated together, and all the process can be completed by a single keystroke. This single-keystroke interrogation scheme is very meaningful to the operator. Figure 7 shows the load flow results on a real feeder map. All values are in per units. T he base values are 1 MVA for the system and 13.8 kV for the voltage. This display is obtained using all the processes discussed in the above sections.
ON-LINE LOAD FLOW For real-time control, accurate system inf o r m a t i o n (voltage, power, current) is essential. It is i m p o r t a n t to have some real-time tool, simulating as closely as possible the actual system profile. On-line load flow is considered the potential tool. As it is a fact t hat the system configuration (physical) is m ore static than the load, it is possible to consider it so while building up the system profile. With the three-phase load flow program m e n t i o n e d above, one possibility is t hat we can use static data for line constants and dynamic data for loads. That is, the load flow will fetch data from both the system data base (line constants) and the real-time data base (load levels). The real-time data base is assumed to store the SCADA measurements. The short-term load forecasting is based on this SCADA information. The broken line in Fig. 6 indicates such an application. This combined data base idea should yield more meaningful results than conventional load flow. If enough measurements are provided, state estimation can be used to generate the system profile. The more measurements available, the m ore accurate are the results one can get. The idea of using state estimation has been investigated for a long time at the transmission level. The application of state estimation to a distribution system has, to our knowledge, never been studied. If there are not sufficient measurements the load flow technique has to be coupled with the state estimator to do the estimation. This may
15
We have to remember here that the socalled 'load forecasting' indicates estimation of 'bus load' used by the load flow program for a radial system. To c o m p u t e bus load, two basic approaches have been proposed [9, 10]: (1) the load is assigned according to historical data; (2) the load is measured directly at each bus. The first method makes use of the daily load curve and the billing data to assign a load level to each bus. The load level can also be assigned according to a historical occupant factor from the substation total consumption measurement. Since dynamic information from the feeder is rare, the terminology of 'real time' will be degraded. The second method needs extra equipment and is obviously uneconomic, at least for the present. (We agree, however, that this m e t h o d would
be what we are going to see in the future. For most utilities, however, we have only the measurements at the substation.
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16 provide the best data). A compromise between the two may be acceptable. Another topic concerns the way to select optimum metering points. This is another reason to couple state estimation with the load flow technique. Use of load windows at some buses may be another option with both methods. The above on-line load flow program is an idea obtained from the overall distribution automation structure; it has n o t been studied in detail yet. The load data used in this research are from the m o n t h l y billing data. Although the whole distribution automation system is designed from the point of view of operation, the installation of a real-time system still depends upon whether the real-time data are available or not. Nevertheless, it is a very powerful tool for off-line study and system planning.
APPLICATION OF THE DISTRIBUTION AUTOMATION CONCEPT ON THE FEEDER
Load change and m o t o r starting A m e t h o d similar to voltage and VAR control can be applied. Load unbalance check The status program is the on-line threephase load flow, and the DMP is now an unbalance check program. Interphase switching ability is necessary. The o u t p u t of DMP is a series of line-switching actions. Operators (3) and (4) may be the same person. Load transfer The status program is again the on-line three-phase load flow, but the DMP is now an optimal switching program with its output a series of line-switching actions. The ability to show the multi-feeder on a display screen is required. Operator (3) may change the data base structure interactively according to the DMP decision. He may also bypass the data base by resetting the input data of the three-phase load flow program internally instead. This is a trade-off between accuracy and complexity.
Feeder automation is, in fact, the most fertile area for developing the software. Several interesting examples are considered below at this level. With the scheme designed in Fig. 5, most features can be accomplished interactively.
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~] Voltage and V A R control This involves capacitor bank control, regulator control, and transformer tap control. Data base records for the status of these devices can be changed interactively by the operator (3). All the functions above can be accomplished easily if the status program is a load flow and has the ability to take care of capacitor banks, regulators, and transformer taps in reading input data. A decision-making program may or may not be necessary here. It has to be noted that this is the linkage between the map features and the data base attributes, so the data-manipulating technique can be greatly simplified. It is the linkage that makes the interactive mode possible. Feeder load management Setting the DMP of Fig. 5 differently, three interesting examples are shown below.
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system. This bypassed part is what we are expecting to see in the future. It can be imagined that a similar application can be developed by a system planning group. For example, by drawing a new branch in graphic mode and inserting the related data, a new system profile can be obtained through the interactive feature of the Intergraph/VAX system.
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Figure 8 shows the flow chart of this interactive application. The VAX operation system is used in Virtual Memory System (VMS) mode. In this mode the logic of Fig. 6 is completed in one keystroke. Turning to graphic mode, we can check the status and make decisions. The control signal can be issued to the power system, and the data base can be updated through an interactive non-procedural process. We can go back to VMS mode again to obtain a new system profile. The map of the whole feeder is shown in Fig. 9. Figure 10 is a capacitor bank o n / o f f demonstration example, and Fig. 11 is a regulator-step adj u s t m e n t simulation. Table 1 shows the data sets used in each Figure. These results are obtained through the process shown in Fig. 8 except for the broken line linking the power
Skyrocketing expense and political obstacles have discouraged many utilities from investing in either generation or transmission. More and more effort can be expected to be put into the area of distribution for the next few decades. With the aid of a powerful computer system, all utilities are able to do something in this area. Some are trying to build up a data base system for statistical bulk data management. Some are trying to build up a computer mapping system. More or less every company has gathered some knowledge about data to make another step forward, but the direction ahead is not yet clear. With the existing high technology of the computer industry, what we can do is much more than build a data base or do some mapping. Application to power engineering is in fact a most valuable subject, making use of both data base and mapping systems. With the knowledge accumulated by the power industry today, it is the right time and a good opportunity for utilities to make progress in this direction. This paper sets up an overall distribution automation concept, to point out a direction which can be realized in the immediate future, and to open the door for valuable engineering applications. In addition, the hidden difficulties in interfacing both the data base and computer graphics have been surmounted by the use of the popular VAX/ Intergraph system. This makes the success of the concept within reach. Different graphics ideas have been proposed before [ 1 1 - 1 3 ] ; they are considered to be part of the distribution automation concept. Finally, the conclusions are summarized below: (1) A reasonably good data base is essential. A static system data base is the basic requirement.
19 (2) S C A D A relies o n a g o o d c o m m u n i c a t i o n s y s t e m . A c h e a p a n d reliable c o m m u n i c a t i o n s y s t e m is a l w a y s a p p r e c i a t e d , b u t overeconomizing may create a bottleneck to further automation. (3) M o r e e f f o r t is n e e d e d t o d e v e l o p g o o d d e c i s i o n - m a k i n g p r o g r a m s f o r d i f f e r e n t purposes. (4) T h e d e v e l o p m e n t o f s t a n d a r d i z e d interfaces f o r h a r d w a r e a n d s o f t w a r e will b e n e f i t the automation functions. (5) As we w o r k t o w a r d the final goal o f d i s t r i b u t i o n a u t o m a t i o n t h e r e will a l w a y s be something with a new descriptive name. (6) A bigger ( b e t t e r r e s o l u t i o n ) display screen (or p r o j e c t i o n - s t y l e screen) t h a t is c o m p u t e r o r i e n t e d is desirable. (7) A n i n d e x e d sequential structured graphical d a t a base is helpful. (8) P o t e n t i a l a p p l i c a t i o n s can be e x p l o r e d b y s y s t e m p l a n n i n g engineers t h r o u g h t h e interactive feature. (9) A static d a t a base c a n at least b e n e f i t b o t h s t u d y a n d s y s t e m p l a n n i n g p u r p o s e s , so it is w o r t h while. (10) A similar a u t o m a t i o n c o n c e p t c a n be a p p l i e d o n t h e v a r i o u s p a r t s o f a p o w e r system.
ACKNOWLEDGEMENT Sincere a p p r e c i a t i o n is e x p r e s s e d t o Bill P i p p i n e a n d Travis Besier o f T e x a s Electric Service C o m p a n y , w h o s p e n t t h e i r p r e c i o u s t i m e in p r o v i d i n g t h e a u t h o r s w i t h every c o n v e n i e n c e while t h e y b e c a m e f a m i l i a r w i t h the Intergraph system.
REFERENCES 1 G. E. Montgomery, AEC Automation Newsletter, (Jan.) (1985) 13. 2 D. I. Sun, S. Abe, R. R. Shoults, M. S. Chen, P. Eichenberger and D. Farris, Calculation of energy losses in a distribution system, IEEE Trans., PAS99 (1980) 1347 - 1356. 3 R. A. Fernandes, F. A. Rushden, J. B. Bunch, H. Chestnut, J. H. Easley and H. J. Fielder, Evaluation of a conceptual distribution automation system, IEEE Trans., PAS-101 (1982) 20243031. 4 J. Carr, Considerations in the adoption of a full scale distribution automation system, IEEE Trans., PAS-IO0 (1981) 1167 - 1172. 5 L. V. McCall, A distribution automation demonstration project, IEEE Trans., PAS-IO0 (1981) 1744- 1751. 6 H. W. Beaty, Automated distribution improves system operation and reliability, Electr. World, (Jul. 15) (1977) 39- 50. 7 A. C. M. Chen, Automated power distribution, Spectrum, {Apr.) (1982) 55 - 60. 8 Computerized SCADA brings savings and improved reliability, Transmission and Distribution, (Dec.) (1981) 56 - 57. 9 A. Keyhani and S. M. Miri, On-line weathersensitive and industrial group bus load forecasting for microprocessor-based applications, IEEE PICA Conf., IEEE, New York, 1983. 10 S. Vemuri, W. L. Huang and D. J. Nelson, On-line algorithms for forecasting hourly loads of an electric utility, IEEE Trans., PAS-IO0 (1981) 3775 3784. 11 IEEE Committee Report, The distribution system of the year 2000, IEEE Trans., PAS-101 (1982) 2485 - 2490. 12 M. Launay, Use of computer graphics in data management systems for distribution network planning in 'Electricit~ de France' (E.D.F.), IEEE Trans., PAS-101 (1982) 276 - 283. 13 J. J. Henry III, Automated graphics applicationsdrafting, IEEE Trans., PAS-101 (1982) 2521 2525.
7
An Overall Distribution Automation Structure
WHEI-MIN LIN and MO-SHING CHEN
The Energy Systems Research Center, The University of Texas at Arlington, Box 19048, Arlington, TX 76019 (U.S.A.) (Received June 21, 1985)
SUMMARY
An effective distribution automation system must involve both hardware and software. The desired system has not yet been attained, but the key pieces have been developed and are ready to be assembled. A complete data base is necessary to sophisticated software, and that software is the key to distribution automation. VAX/Intergraph facilities are considered in particular since the concept derived in this paper originated from the VAX/Intergraph system. Recent development of a three-phase unbalanced load flow program and its interface with the Intergraph provide the means of attaining an effective distribution automation system.
INTRODUCTION
Distribution automation has different meanings to different people. Some people think of remote switching, some of telemetering or street lighting control. But these functions are only part of distribution automation and do n o t interpret its spirit. A more general c o n c e p t of distribution automation is essential. The conventional way of defining distribution automation puts the emphasis on hardware, e.g. remote circuit-breaker reclosure, telemetering, and so on. A modern realistic definition should involve both the hardware and the software. An effective system can be accomplished through the introduction of a complete distribution data base system and the means to use it. The basic requirement is a static data base system to store all important data. A graphical data base is useful to store physical configurations. It is also helpful 0378-7796/86/$3.50
to have a real-time data base to store dynamic data. Based on this data base system, sophisticated software can be developed, either to check the system status or to assist in the decision-making process. From the hardware (supervisory control and data acquisition (SCADA), telemetering, etc.) the system data are gathered and stored in the data base system. Processing the data via some software, a system profile (voltage, p o w e r flow, etc.) is produced. Through another data analysis process, a decision will be generated whenever necessary. The decision may come from an operator or by option software or both. Through hardware again, the decision (control signal) can be fed back to the power system. Figure 1 shows the structure described above. These procedures comprise a complete automation cycle. This a u t o m a t e d cycle is controlled in real time for decision by software, or, in relatively quick time, for decision by operator. The meaning of real time is not minute-by-minute-oriented operation in the distribution system -- two or three times a day may be good enough. The data base system and the software are the essence of this process. From this cycle the robustness of the automation system can also
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be evaluated. For example, the remote switching capability based only upon an operator's experience is not recognized as a robust distribution automation operation. However, if the operator's experience is assisted by welldesigned computer analysis, it may be a sound automation system. In Fig. 1, the introduction of the data base and the software will make the operation process more realistic. Furthermore, with the help of a state estimator, system uncertainties can be alleviated. By analyzing the data provided by a real-time data base or SCADA, the state estimator can provide better information for the software to generate more faithful results, especially for on-line operation.
Intergraph system The facilities provided by the Intergraph system [1] were found to be particularly appropriate to our research. This system provides both the mapping features and the data base management system. In addition, a linkage between the two can support some interactive features in applications. Based on this system, we have formulated an overview of distribution automation. The data base system contains a huge a m o u n t of data from the distribution area. Since only distribution personnel know how to handle their own data or to make decisions to fit their own needs, a distribution automation system should be operated by distribution people. The distribution operation should be separated from transmission. Transmission-oriented distribution automation can never be made efficient since it is a distribution-level decision whether to make economic/emergency load transfers, to balance loads, or to switch capacitor banks. To build a good distribution data base involves a great deal of work. A utility must carefully evaluate its ability to allocate its resources. However, t o d a y ' s laziness may become tomorrow's nightmare. Waiting for the best m e t h o d will a m o u n t to perpetual indecision. Faced with rapidly changing technology, we ought to pursue a state-of-the-art solution. Because the Intergraph system is popular, we used a VAX/Intergraph system to provide the complete data base. For a given distribution system, this data base structure will contain all the information about
all the power apparatus of each phase, from substation level down to each pole.
Three-phase load flow program The three-phase unbalanced load flow program [2] has proved to be a more sophisticated tool with which to compute a system profile than a conventional load flow program. This unbalanced load flow program was designed particularly for a radial system, using an unbalanced three-phase structure directly rather than a balanced one. The conventional symmetrical component-based single-line diagram approach is not considered here. It is totally unacceptable to use a symmetric sequence network for an asymmetric system. By reading in the data for each phase individually, the three-phase unbalanced load flow program can generate the unbalanced voltage profile and the power flow for each phase. This o u t p u t will describe the radial distribution system more faithfully than a balanced result. More applications can be explored with this tool. Every load flow program mentioned hereafter refers to this three-phase unbalanced load flow program. The normal unbalanced three-phase data base built via Intergraph's facilities happens to fit the needs of this load flow program.
DISTRIBUTION AUTOMATION HIERARCHY AND MAJOR FUNCTIONS
Distribution hierarchy It is a c o m m o n practice to divide the distribution a u t o m a t i o n system into three levels: substation, feeder and service [3, 4]. The structure is shown in Fig. 2. A central computer is located no lower than the level of the distribution dispatch center (DDC). With the aid of a communication system, the DDC can collect data from or activate automation functions (control, monitoring) to the substation, the feeder, or the service level. It is this typical structure between the DDC and the distribution system that should be developed in state-of-the-art distribution automation. At each level of the hierarchy, some functions of control and monitoring can be identified. Most of the major functions considered so far in distribution automation are outlined in the following sections [3, 5, 6].
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Substation automation Th e substation is the most delicate part of a distribution system, involving much expensive equipment: main transformers, capacitor banks, circuit breakers, etc. Since all pieces o f e q u i p m e n t are aggregated, it is comparatively easy to cont r ol and monitor. Con trol - Capacitor bank cont r ol Main tr an s f o r m er tap-changer cont r ol A u t o m a t i c bus sectionalizing - A u t o m a t i c circuit-breaker reclosure - A u t o m a t i c switch cont r ol -
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Feeder automation The feeder level includes the part of the p o wer system f r om substation to distribution transformers, which covers a large region. L en g th y conductors, capacitors, regulators,
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10
Other functions The distribution dispatch center should collect all the important data. Data collection can be used for both on-line control and research purposes. A remote supervisory control and data acquisition (SCADA) system is required to manage all the functions stated in the previous sections. An alarm annunciation system can be installed wherever necessary. Dispersed storage and generation elements can be controlled according to their sizes [7]. In addition, the following data are important; they should also be collected by the distribution dispatch center: - fault records - sequence-of-event records weather data records -
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D A T A BASE S T R U C T U R E
Interactive computer graphics developed by the Intergraph Corporation are widely used because of m a n y good features, although a lot of storage m e m o r y is required. A graphic station is designed to link with and to use the CPU of a Digital Equipment Corporation (DEC) system. The DEC-VAX/Intergraph Corporation system provides several facilities, some of them related to the data base and graphics used. The data base and graphic files can be built and maintained via these facilities. The term 'graphic data base' can be used if more than one file exists. However, graphic data base may indicate only one 'graphic file' in the following discussion. It is of no interest here to denote any difference. The above two data bases are generally built via Standard Interchange Form (SIF). They are maintained by a Data Management and Retrieval System (DMRS) and an Interactive Graphic Design System (IGDS). These are all facilities provided within the Intergraph system. An artificial feeder and its corresponding data bases are used for demonstration in this paper. A real feeder is also used to show the real-world application.
D M R S data base A hierarchical data base is used since a distribution system is itself hierarchical in structure. A conceptual view of the illustration data base built is shown in Fig. 3. This relationship provides an efficient structure for the
searching algorithm in the load flow study. The level traversal along this data base tree can guarantee accuracy when a record is being located. Twelve bytes are reserved for each storage record to preserve the record header and parent/child relationship.
IGDS data base The physical configuration (feeder map) of the distribution system is stored by the use of 'Graphic Elements'. A Graphic Element is an Intergraph term; it is composed of a series of 'words' storing both the global and local information of this element. Graphically, those elements are lines, circles, triangles, etc. Symbolically, they stand for line segments, poles, transformers, etc., of a power system. Grouped elements can be defined as a 'cell'. A cell library can be built for convenience of the user. These graphical elements are stored in 64 logic levels. Each level is like a sheet of transparency which can be turned on or off freely by the user. For a large system this lengthy sequential file is sometimes awkward; it is more convenient for power utilities to have an indexed sequential file structure according to the 64 levels. Data base linkage A link between a Graphic Element and a DMRS record can be created. The link ties the map features to the data base attributes. Multi-linkage is allowable, each link occupy-
11 ing four words. In lieu of this linkage the DMRS data base can be manipulated through IGDS mode via a non-procedural process. In fact, this is the linkage by which all interactive applications can take place. OVERALL SCOPE OF A DISTRIBUTION AUTOMATION SYSTEM Data and control flow o f the S C A D A To develop an overall distribution automation concept, we should first observe the data and control flow of a physical power system. From Fig. 2, it is not difficult to see that the data and control flow of most existing utilities can be interpreted as shown in Fig. 4. The distribution data {information} are collected by the SCADA system. In the DDC, some decisions are made after a data analyzing process. Those decisions will be fed back to the distribution system through the SCADA again. A good communication system is necessary. This configuration is the physical structure of most power systems. Based on this Figure, the concept of distribution automation should be investigated. The DDC has a central computer, and it is responsible for the following tasks: - issuing all the control commands data collection data base management It has to be noted here that the existing DDCs of most utilities do not have all these abilities yet. -
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Conven tional distrib u tion au toma tion ideal For a distribution system, generally speaking, there is a huge a m o u n t of information
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flowing into the DDC, if the DDC does have a data base. There are some alarm systems, and some instrumentation designs, where the designer has forgotten that humans are in volved; for example, those which subject the operator to mental and physiological stress. Regardless of stress, the operator has to be able to find the data he needs, analyze the data, and make the right decision. In the DDC, only operators are there to do the above operation. The tremendous a m o u n t of data coming in and out are rarely utilized. The data analyzing process is based only on operators' experience. This is the conventional distribution automation methodology. Sometimes a graphic terminal is available, and a keyboard or a light pen will be used [8]. Light pens were developed in the early age of interactive computer graphics. The pen is criticized to be tiring to the user, who must pick it up, point it, and set it down for each use. The power system in Fig. 4 may represent any level of the substation, the feeder or the service. The a u t o m a t i o n functions should represent any of those major functions discussed in §2. To make the conventional distribution a u t o m a t i o n more effective and more reliable, operators' experience should be assisted by the use of structural data bases and some proper software for the data analyzing process in the DDC. Operators, data base and software should all be involved in the operation of the DDC. The concept of a modern distribution automation can be then formed. Graphic assisted overall distribution automation structure Whenever h u m a n intervention exists, it is well recognized that graphics can provide the best m a n - m a c h i n e environment. For example, until a complex non-driver automobile has been developed, direct observation of road conditions through human eyes is the best guidance to driving. A fully automated distribution system with graphic station is shown diagrammatically in Fig. 5. The SCADA system will collect all necessary data and store/update them in the data bases. A status program will search for the required data, calculate the system status according to the preset algorithm, and show the results selectively on the graphic screen, e.g., voltage profile along with the feeder map. A logic test
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will determine whether to stop (exit) or to react through another decision-making program (DMP) to issue a control command. Each block inside the DDC is explained below.
Status program This is a three-phase unbalanced load flow program; it can be coupled with the state estimator, however, for real-time application. Decision making program (DMP) This block is the heart of the system operation. Any automation function outlined before can be executed. The DMP installed should be foolproof. Synchronizer This maintains the synchronism between the power system and the map features. Data base Both the system data base and the real-time data base are combined here. The system data base (DMRS in this paper) is hierarchically structured. All important system configuration data are stored within it. The real-time data base stores information from SCADA. It is updated periodically. This data base is important in performing real-time applications including state estimation. A study data base with case studies can also be included. A second real-time data base could be included, which would have, at least, the following benefits: the system data base would be accessed only under system configuration changes; frequent access to the data base system would be avoided;
the search technique in the real-time data base should be simpler, which implies less CPU time. All the functions operate automatically according to the preset time interval. An operator is needed only to maintain the system integrity. This overall structure is designed from the point of view of operation. All the pieces have to be assembled to make it become a reality. However, for the system planning mode, this design would work well already.
Man-machine interface Instead of a fully automated system, an intermediate m a n - m a c h i n e interface is proposed. It is practical and can be implemented today. For the system shown in Fig. 5, we observe that the points (3), (4) and (5) involve hardware-software interfaces which have to be resolved although the technology is already available. The 'data base system (DBS)-Status-Graphics' procedure involves software interfaces. It will not hinder us from adopting this structure if the software interface problem can be solved. A m a n - m a c h i n e interface data analysis concept may then be formed right away. The idea is that between the DDC and the communication system, i.e., at all points (3), (4) and (5) in Fig. 5, there exists human intervention. Inside the DDC, all the functions in Fig. 5 are automated. Operator (2) receives the information from the graphic station (the broken line) from an automatic DBS-Status-Graphics computation, then determines whether to exit or to react. Operator (4) actually issues the control c o m m a n d through either remote control or manually operated switches.
13
Operators (3) and (5) will maintain the synchronism between the power system and the data bases. Operators (2), (3), (4), and (5) are n o t necessarily different persons. The system would be a perfect decision support system if the DBS-Status-Graphics could be accomplished by a single keystroke.
DATA BASE I N T E R F A C E
Single-keystroke load flow Traditionally, data preparation is a tedious and complex task. In other terms, data prep-
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14 ments. In fact, single-keystroke oper a t i on has already been d e m o n s t r a t e d successfully with a real feeder and its data base.
Interface and search Figure 6 shows the data base interface and search. To run the three-phase load flow program, the system data base has to be searched to get the necessary data, then an input file for the load flow program will be built. First the feeder is located, and all the line segment data are converted. T h e regulator attribute will be checked to see w he t he r there is any regulator attachment. If the answer is 'Yes', a level traversal along the data base tree will be made to locate the regulator and the regulator data translated accordingly. A similar process will be p e r f o r m e d for the capacitor banks. After all the data are collected and converted, a numbering scheme will set up a p r o p e r input file f or the threephase load flow program, i.e. bus data, branch data, and load window selection. A n o t h e r 'geography file' will also be created to store all the geographic locations of buses. This file is used to c o m p u t e the location for t e x t placement in a graphic file (map). The accuracy, speed, and m e m o r y size are all i m p o r t a n t factors for consideration. An o u t p u t file is built by the load flow program. The voltage profile and power flow are stored in this file. Some information in this o u t p u t file has to be displayed on the map. It may involve some study in determining what is a 'pr ope r display' in this m a n machine relationship. Th e t e x t size, color, and line thickness all need to be considered to generate the proper display. A symbology scheme will set them up. The t e x t consists of different sets of data. Every set o f data has a reference a t t a c h m e n t point. The data sets have to be moved to avoid overlapping if more than one set of data are displayed on the same line. Overlapping will make the data sets unreadable if mo r e than one set of data on the same line are r o tated together. A r o t a t i o n scheme must be designed to det er m i ne a suitable r ot at i on if the line segment addressed is n o t horizontal.
Example The data base search and the map can be joined with the load flow program to accom-
plish the engineering application. In Fig. 6, the broken line linking the real-time data base has not been accomplished yet. It will be discussed in the following section. The data base-load f l o w - m a p features are integrated together, and all the process can be completed by a single keystroke. This single-keystroke interrogation scheme is very meaningful to the operator. Figure 7 shows the load flow results on a real feeder map. All values are in per units. T he base values are 1 MVA for the system and 13.8 kV for the voltage. This display is obtained using all the processes discussed in the above sections.
ON-LINE LOAD FLOW For real-time control, accurate system inf o r m a t i o n (voltage, power, current) is essential. It is i m p o r t a n t to have some real-time tool, simulating as closely as possible the actual system profile. On-line load flow is considered the potential tool. As it is a fact t hat the system configuration (physical) is m ore static than the load, it is possible to consider it so while building up the system profile. With the three-phase load flow program m e n t i o n e d above, one possibility is t hat we can use static data for line constants and dynamic data for loads. That is, the load flow will fetch data from both the system data base (line constants) and the real-time data base (load levels). The real-time data base is assumed to store the SCADA measurements. The short-term load forecasting is based on this SCADA information. The broken line in Fig. 6 indicates such an application. This combined data base idea should yield more meaningful results than conventional load flow. If enough measurements are provided, state estimation can be used to generate the system profile. The more measurements available, the m ore accurate are the results one can get. The idea of using state estimation has been investigated for a long time at the transmission level. The application of state estimation to a distribution system has, to our knowledge, never been studied. If there are not sufficient measurements the load flow technique has to be coupled with the state estimator to do the estimation. This may
15
We have to remember here that the socalled 'load forecasting' indicates estimation of 'bus load' used by the load flow program for a radial system. To c o m p u t e bus load, two basic approaches have been proposed [9, 10]: (1) the load is assigned according to historical data; (2) the load is measured directly at each bus. The first method makes use of the daily load curve and the billing data to assign a load level to each bus. The load level can also be assigned according to a historical occupant factor from the substation total consumption measurement. Since dynamic information from the feeder is rare, the terminology of 'real time' will be degraded. The second method needs extra equipment and is obviously uneconomic, at least for the present. (We agree, however, that this m e t h o d would
be what we are going to see in the future. For most utilities, however, we have only the measurements at the substation.
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Fig. 7. (a) A real feeder map. (b) Load flow results o n part of the feeder. - - , line conductor on which are indicated P1 Ql(~b), P2 Q2, and V 0. P1 and P2 are the real power flows, Q1 and Q2 the reactive power flows, V and 0 the voltage magnitude and angle, and ¢ the phase type.
16 provide the best data). A compromise between the two may be acceptable. Another topic concerns the way to select optimum metering points. This is another reason to couple state estimation with the load flow technique. Use of load windows at some buses may be another option with both methods. The above on-line load flow program is an idea obtained from the overall distribution automation structure; it has n o t been studied in detail yet. The load data used in this research are from the m o n t h l y billing data. Although the whole distribution automation system is designed from the point of view of operation, the installation of a real-time system still depends upon whether the real-time data are available or not. Nevertheless, it is a very powerful tool for off-line study and system planning.
APPLICATION OF THE DISTRIBUTION AUTOMATION CONCEPT ON THE FEEDER
Load change and m o t o r starting A m e t h o d similar to voltage and VAR control can be applied. Load unbalance check The status program is the on-line threephase load flow, and the DMP is now an unbalance check program. Interphase switching ability is necessary. The o u t p u t of DMP is a series of line-switching actions. Operators (3) and (4) may be the same person. Load transfer The status program is again the on-line three-phase load flow, but the DMP is now an optimal switching program with its output a series of line-switching actions. The ability to show the multi-feeder on a display screen is required. Operator (3) may change the data base structure interactively according to the DMP decision. He may also bypass the data base by resetting the input data of the three-phase load flow program internally instead. This is a trade-off between accuracy and complexity.
Feeder automation is, in fact, the most fertile area for developing the software. Several interesting examples are considered below at this level. With the scheme designed in Fig. 5, most features can be accomplished interactively.
r
~] Voltage and V A R control This involves capacitor bank control, regulator control, and transformer tap control. Data base records for the status of these devices can be changed interactively by the operator (3). All the functions above can be accomplished easily if the status program is a load flow and has the ability to take care of capacitor banks, regulators, and transformer taps in reading input data. A decision-making program may or may not be necessary here. It has to be noted that this is the linkage between the map features and the data base attributes, so the data-manipulating technique can be greatly simplified. It is the linkage that makes the interactive mode possible. Feeder load management Setting the DMP of Fig. 5 differently, three interesting examples are shown below.
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Fig. 9. An artificial feeder map. The following symbols are used in this Figure and in Figs. 10 and 1 1 : - - , threephase conductor; . . . . , two-phase c o n d u c t o r ; - - ' - - , single-phase conductor; }~, t r a n s f o r m e r ; ~ , regulator;-~, capacitor bank; [], customer load.
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system. This bypassed part is what we are expecting to see in the future. It can be imagined that a similar application can be developed by a system planning group. For example, by drawing a new branch in graphic mode and inserting the related data, a new system profile can be obtained through the interactive feature of the Intergraph/VAX system.
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Figure 8 shows the flow chart of this interactive application. The VAX operation system is used in Virtual Memory System (VMS) mode. In this mode the logic of Fig. 6 is completed in one keystroke. Turning to graphic mode, we can check the status and make decisions. The control signal can be issued to the power system, and the data base can be updated through an interactive non-procedural process. We can go back to VMS mode again to obtain a new system profile. The map of the whole feeder is shown in Fig. 9. Figure 10 is a capacitor bank o n / o f f demonstration example, and Fig. 11 is a regulator-step adj u s t m e n t simulation. Table 1 shows the data sets used in each Figure. These results are obtained through the process shown in Fig. 8 except for the broken line linking the power
Skyrocketing expense and political obstacles have discouraged many utilities from investing in either generation or transmission. More and more effort can be expected to be put into the area of distribution for the next few decades. With the aid of a powerful computer system, all utilities are able to do something in this area. Some are trying to build up a data base system for statistical bulk data management. Some are trying to build up a computer mapping system. More or less every company has gathered some knowledge about data to make another step forward, but the direction ahead is not yet clear. With the existing high technology of the computer industry, what we can do is much more than build a data base or do some mapping. Application to power engineering is in fact a most valuable subject, making use of both data base and mapping systems. With the knowledge accumulated by the power industry today, it is the right time and a good opportunity for utilities to make progress in this direction. This paper sets up an overall distribution automation concept, to point out a direction which can be realized in the immediate future, and to open the door for valuable engineering applications. In addition, the hidden difficulties in interfacing both the data base and computer graphics have been surmounted by the use of the popular VAX/ Intergraph system. This makes the success of the concept within reach. Different graphics ideas have been proposed before [ 1 1 - 1 3 ] ; they are considered to be part of the distribution automation concept. Finally, the conclusions are summarized below: (1) A reasonably good data base is essential. A static system data base is the basic requirement.
19 (2) S C A D A relies o n a g o o d c o m m u n i c a t i o n s y s t e m . A c h e a p a n d reliable c o m m u n i c a t i o n s y s t e m is a l w a y s a p p r e c i a t e d , b u t overeconomizing may create a bottleneck to further automation. (3) M o r e e f f o r t is n e e d e d t o d e v e l o p g o o d d e c i s i o n - m a k i n g p r o g r a m s f o r d i f f e r e n t purposes. (4) T h e d e v e l o p m e n t o f s t a n d a r d i z e d interfaces f o r h a r d w a r e a n d s o f t w a r e will b e n e f i t the automation functions. (5) As we w o r k t o w a r d the final goal o f d i s t r i b u t i o n a u t o m a t i o n t h e r e will a l w a y s be something with a new descriptive name. (6) A bigger ( b e t t e r r e s o l u t i o n ) display screen (or p r o j e c t i o n - s t y l e screen) t h a t is c o m p u t e r o r i e n t e d is desirable. (7) A n i n d e x e d sequential structured graphical d a t a base is helpful. (8) P o t e n t i a l a p p l i c a t i o n s can be e x p l o r e d b y s y s t e m p l a n n i n g engineers t h r o u g h t h e interactive feature. (9) A static d a t a base c a n at least b e n e f i t b o t h s t u d y a n d s y s t e m p l a n n i n g p u r p o s e s , so it is w o r t h while. (10) A similar a u t o m a t i o n c o n c e p t c a n be a p p l i e d o n t h e v a r i o u s p a r t s o f a p o w e r system.
ACKNOWLEDGEMENT Sincere a p p r e c i a t i o n is e x p r e s s e d t o Bill P i p p i n e a n d Travis Besier o f T e x a s Electric Service C o m p a n y , w h o s p e n t t h e i r p r e c i o u s t i m e in p r o v i d i n g t h e a u t h o r s w i t h every c o n v e n i e n c e while t h e y b e c a m e f a m i l i a r w i t h the Intergraph system.
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