A Methodology for Testing of Substation Functional Circuits

Transcription

1 A Methodology for Testing of Substation Functional Circuits GERMANO LAMBERT-TORRES CARLOS HENRIQUE VALÉRIO DE MORAES LUIZ EDUARDO BORGES DA SILVA JAMIL HADDAD Itajubá Federal University Av. BPS, 1303 Pinheirinho Itajubá/MG BRAZIL ANDRE ENDRIGO SUZUMURA CINTRA EDP-Bandeirante Power System Rua Bandeira Paulista, 530 São Paulo/SP BRAZIL Abstract: - This paper has developed a methodology for testing of substation functional circuits from the utility company. This methodology allows making all possible combinations of the functional circuits, aiming to find whether there is any fault, bad operation or project mistake in these circuits. The fundamental idea is that this set of tests, automatically made by a computer package, provide the elimination of any type of wrong action of these circuits, which generate the undesirable system breakdown and problems regarding the rate of steady power supply. This joint project has been developed between EDP-Bandeirante Power System and Federal University at Itajuba with practical and education purposes. Key-Words: - Power System Operation, Functional Circuits, Decisions Support, Heuristic Search Techniques, Intelligent Systems. 1 Introduction The electric power systems operation is becoming more complex everyday. The community usually expects to have lower breakdown rates. Because of this the substation operation become of major importance. Mistakes in substations have a direct effect for the power users and should be prevented at any cost. Otherwise, the electric systems automation, reducing the operator s actions, is actually an irreversible process all over the world. One of the most frequent problems that are happening in the substations, mainly because of its complexity increase, whether because of its size or by the operational requirements for new configurations, is tight up to the functional circuits for the protection, command and control. Before a new configuration comes into operation it is necessary making previous tests. For that purpose, experienced maintenance technicians with sound knowledge of tests criteria and interlock procedures for the several substation configurations are called. These technicians generate tests to check whether there are not problems into these new configurations. However, some configurations may not be tested, because of their great number. This result that an automatic testing program, that ensures the all the possible test combinations, may be very useful, in helping to reach better reliability process. In addition to this difficulty, there are also the losses that the utility companies have with the cost of the retirement system, which have been reducing the capacity and know-how available. This project presents the use of Expert Systems [1] and Heuristic Search Techniques [2] for making functional tests programs in command circuits. This program analyzes the circuit s functionality, so as detects possible project mistakes. The techniques like the expert systems and searching techniques make possible to explore a new world through computer program with non-algorithm structures (said intelligent). Intelligent systems have been to create computational programs to help or train students, operators or engineers [3]. It should be noticed that the intelligent systems tend to be complementary to the existing systems, and not to substitute them. 2 Computer Structure Used There is a great class of problems in power systems that human experts using their know-how are solving so far, or together with results obtained using analytical methods. This class of problems has a great potential for the application of Expert Systems and usually presents one or more of the following characteristics: - it is not possible the use of a mathematic model that at least roughly represents the actual situation; - the problem is such that some restrictions are not

2 properly specified and cannot be mathematic represented; - an algorithm form cannot express the solution methodology used by the operators. These three characteristics are present in this problem. The methods of heuristic searching are used for the solution of problems, for finding the solution in a space of possible states considering evaluation function. They may be described independent of any task or domain of problems in particular way [4]. One of the scientific contributions from this project was testing the many existing search techniques, making a competition between them, checking for the case of the functional circuits, the one(s) that presented the best performance. The following techniques were tested: (a) Initial Search in Depth: It consists, in the beginning; to develop the more early generated knots. Starting from the first successor knot it is determined their respective successor knots, and so on goes the process until the solution be found. If the solution is not achieved in the route passed through, and the route has to have one end, the search begins once more at a next superior level in the search tree, starting from a successor knot not yet searched. This process is characterized by the thorough search for the solution, and only arrives to an efficiency and viable degree in case the search tree be small and of little depth. (b) Initial Search in Wide: It consists in searching a solution at each generated successors level. A new level of successor knots only is generated if the solution is not found through the analysis of all the existing knots in the present research level. This process is recommended when the search tree, independently of the depth, has a small branching factor. (c) Ordered Search in Depth: It consists in directing the search among the knots more early generated, after the knot that for some heuristic rule, be considered more promising for obtaining a solution for the problem. If no solution is found checking this knot, the second more promising knot is chosen, and so on. This process presents a good performance when there is a way for the evaluation of the distance of the present state up to the solution and, among a set of o possibilities, what is the more promising. (d) Searching First for the Best: It consists in choosing the most promising knot among all the not yet checked knots from the searching tree. The movement is always made starting from the knot nearer to the solution, allowing for shorter driven routes. This process, just like the one presented in the previous item, presents a good performance when there is a way for evaluating the distance from the present state up to the solution, and among a set of possibilities, what is the more promising. (e) Search for The British Museum Algorithm : It is made up by developing first all the possible routes, and only after that, choosing the best. Its use is limited to the cases where the search trees have both small depth and wide. (f) Search "Branch and Bound": Comprises in having in each knot a measurement of the displacement effort made since the starting knot, to choose among all the existent open knots, that which presents the smaller effort measurement. This process also presents a good performance but when there is a way for evaluating the effort made for the displacement already done, and the effort to be made for reaching the solution. (g) Simulated Annealing: the algorithm for simulated annealing search combines the strategy of search in amplitude with search in depth, starts the search in amplitude up to a point from which the strategy is changed for search in depth. These seven alternatives were implemented and tested for the problem of searching for the functional circuits. Some ways were given up very fast because they presented poor results, and some new variants were used. The best alternative was (d) Searching First for The Best together with some heuristic rules. Initially this algorithm was written in Turbo- Prolog and C Language, so as the heuristic rules. In the last version of the computer package this alternative was rewritten and optimized in Visual Basic, including the decision-take heuristic rules and the searching control rules for having more speed, reliability and operation stability to the project and product. 3 The Computer Package Because the functional circuits analysis is basically an exercise of logics and enumeration, the methodology of functional circuits analysis and tests methodology was developed through logic circuits and introduced into a computer package, generating a flexible product that may be used in several situations. This computer package has two main parts: the Logical Program and the Functional Program. The first program has the function of mounting the inside logic of the equipments that will be used by the functional circuit, while the second simulates a substation functional circuit. Inside and in one visible way for the user, the computer programs have an intensive generation of search trees, which are developed according the requirements found by program searching for one

3 solution. Many searching algorithms were tested aiming to find those that were showing the best performance for the present problem. Because of the facility for implementation and for making changes during the test phase, these algorithms were implemented in Turbo-Prolog and C Language, according its type. Several tests were made and after the choice, they were re-programmed in Visual-Basic (language used for writing the interface with the user) to increase the processing speed and preventing against possible compatibility problems between the languages. 3.1 Logic Program The first step of the logic program was to set up the components individual logics that would be used for the mounting of the functional circuits. Following elements were set up: AND Logic door AND; OR Logic door OR; XOR Logic door OR-EXCLUSIVE; NOT Logic door NEGATION; INPUT Entry signal sent by coils; MEASURE Entry signal resulting from measurements or events, in the field; OUTPUT Out signal for contacts; EDGE + - Positive logic level transition (from 0 to 1 ); EDGE - Negative logic level transition (from 1 to 0 ); TIMER Timer; LATCH RS Storing door of type in/out. Having these elements, it is possible to mount logic structures representing the actions into substations. One example could be the command digital circuit for a circuit breaker, as shown in Figure 1. Figure 1 Command digital circuit of a circuit breaker. The above circuit simulates the signal for Trip and Close from one circuit breaker, and still, when there is a fault, both signals are inhibited and the circuit breaker remains blocked in its present state. Figure 2 Window for mounting of step-by-step cycles. Originally, the man-machine interface has been written in Portuguese. Figure 3 Logic Program main window. It was decided also to make analysis step-by-step aiming to make possible, in a definite timing, to check the functional circuit under analysis, against many inputs (which actually would come out from substation). Each step represents one permanent condition from signals states considered during a 10 milliseconds period. The maximum simulation time allowed is milliseconds. Figure 2 shows a window for this type of entry. An example of the window from this program is found on Figure Functional Program The Functional Program presents the following main window for user, as shown on Figure 4. In the main window, the user also has a tool bar with buttons, for the access of some program functions, all doing the same function as the respective commands from the menu: New, Open, Save, Cut, Copy, Paste, Clean, Entry Events, Execute and Simulation Results. For mounting a digital relay scheme the user has a toolbar on the left of desktop with following objects: Gnd Grounding; Vdc Voltage DC source.

4 of a window with a circuit already set up is shown in Figure 7. Figure 4 Main window of Functional Program. On this toolbar there are three buttons with following functions: Add Equipment Add one equipment into equipments library starting from an engraved model.rel ; Edit Equipment Edit equipment from the equipment library; Remove Equipment Remove equipment from the equipments Clicking the first button from the toolbar the following window will be shown, as presented in Figure 5. Figure 5 Adding a new element in the functional circuit. The equipments type list to be added presents many types already recorded into the Functional Program Library, and still presents all the digital circuits exported by the Logic Program for the Functional Program. Figure 7 Example of a functional circuit. For analyzing a functional circuit work the user should first to fill up the entry events table, accessing this function in the menu, or button (see Figure 8). In this figure 8, it is shown the entry table for the many equipments introduced into present functional circuit, and always the equipment name is placed first in parentheses, and after, the type of the equipment. Following, it is presented the event starting time and ending time. On this window the user has four buttons: Add Add entry event for analysis; Edit Edit entry event for analysis; Remove Remove entry event for analysis; Out Leaves from entry events window. Figure 8 Entry events table. Figure 6 A new element added into equipments library. The user should but digit the code in use by the company to name the element, and click button OK for adding to the toolbar, Figure 6. An example For user to define a new entry event he should access the function Add and the following window will show up (see Figure 9). First the user will select the entry to be used from the list of all the circuit entries. Following he should enter with the timing for the beginning and ending of the event, always taking into consideration multiple values of the simulation

5 step. Each step represents a permanent condition of the considered signals states during 10 milliseconds. Figure 9 Entry Event. For executing the logic simulation of the digital relay work the user should access the function on the menu or go through the corresponding button (see Figure 10). Figure 10 Simulation control. Through the simulation control window the user may go step-by-step during the program execution, clicking in the button Next, or going right to the end of the last event using the button End, or still Delete the present simulation. Figure 11 Simulation results. After the end of the simulation a window will be presented with the simulation results (see Figure 11). On this window the user may select which measurers and coils he wants to see, and then click the button Make Report so as to be presented the window of Figure 12, with all the events happened in the selected items. 4 Tests Many tests have been made with the computer package to check the performance of its answers. Figure 12 Report of selected items events Simultaneous and individual mistakes were introduced on purpose into the functional and logic circuits, aiming to check the program answers. An example is found as follows for the Functional Program, where is given the control functional circuit of a bay, comprising the breaking switch (SE1) circuit break (DJ1) and breaking switch (SE2). For this set of equipments the developed functional circuit, already with the interlocking logics is presented in the Figure 7. The above circuit simulates the existing interlocking into a bay comprising break switch, circuit breaker and break switch, where it is not possible neither to open nor to close the break switches while the circuit breaker is closed. The table of used entry events is shown bellow. The result is shown in Figure 13. Time [ms] ON OFF ON Break OFF Break Conclusions This paper presents a computer program that allows testing the functional circuits for protection, command and control of substations from the EDP- Bandeirante power system utility. This program has a friendly interface with the user, generating a conclusive report about eventual substation restrictive configurations. This program uses search techniques for

6 (a) (b) (c) (d) (e) (f) (g) (h) (i) typical elements of the functional circuits, so as a test manual aiming the development and up-to-date of the professionals. (j) Figure 13 Functional Circuit (a) 0 10 [ms]; (b) [ms]; (c) [ms]; (d) [ms]; (e) [ms]; (f) [ms]; (g) [ms]; (h) [ms]; (i) [ms] and (j) [ms]. generating all possible combinations of substation configurations, in such a way that it is possible the evaluation of the reliability of its control, command and protection functional circuits. A laboratory for testing the many functional circuits configurations also was assembled. This lab also may be used for teaching purposes, has the 6 References [1] G. Lambert-Torres, G.M. Ribeiro, C.I.A. Costa, A.P. Alves da Silva & V.H. Quintana - Knowledge Engineering Tool for Training Power-Substation Operators, IEEE Transactions on Power Systems, Vol. 12, No. 2, pp , April [2] K.Y. Lee & M.A. El-Sharkawi Evolutionary Computation Techniques for Power System Optimization, IFAC Press, pp , [3] C.-C. Liu et al. - Testing and Maintenance Procedures for Expert System in Power System Operation and Planning, Electra, No. 173, pp , Aug [4] B. Valiquette, G. Lambert-Torres & D. Mukhedkar - An Expert System Based Diagnosis and Advisor Tool for Teaching Power System Operation Emergency Control Strategies, IEEE Transactions on Power Systems, Vol.6, No.3, pp , August 1991.