Windows-based Educational Software for Calculating Reliability in Interconnected Power Systems M. Hosseini-Firouz
M. Fotuhi-Firuzabad
Islamic Azad University Ardabile Branch Iran
[email protected]
Department of Electrical Engineering Islamic Azad University Science and Research Branch Tehran, Iran
[email protected]
load requirements),using forced outage rate (FOR), failure rate (λ), and repair rate (µ), this educational software can calculate reliability indices for a determined load capacity. FOR, λ, and µ can be calculated as follows: 1 λ= (1) m
Abstract_ this paper presents a graphical package to facilitate the teaching and learning of power system reliability, and it can calculate the reliability in hierarchical level 1 (HL1) and hierarchical level 2 (HL2). This graphical software has been developed in MATLAB 7 environment and it creates a simple environment for the user and it includes different combinations of interconnected power systems. In order to calculate the reliability indices and complete capacity outage probability table (COPT) in considered system, one can select each one of these combinations and enter the input information. In interconnected power systems, there are no limitations due to the number of generating units and used transmission lines.
µ=
1 r
FOR =
Index Terms—power system reliability, interconnected systems, power system education, graphical software.
(2)
λ λ+µ
(3)
Where r: mean time to repair m: mean time to failure
1.INTRODUCTION ADEQUACY EVALUATION of power generation systems is usually concerned with assessing the ability of the generation facilities to meet the system load requirements. In this assessment, the associated transmission and distribution facilities are assumed to be fully reliable and capable of transmitting and distributing the generated energy to the customer load points. In its simplest form, the capacity model and the load model are convolved to create a risk model which defines the reliability performance of the generating system in terms of reliability indices [1, 2]. The two most commonly specified indices are the loss of load expectation (LOLE), and the loss of energy expectation (LOEE) [1]. Long-term capacity expansion planning is based on one or both of these indices. In addition, power generation costs are also considered in the capacity planning. The determination of unit additions in the future is based on an acceptable level of risk (LOLE and/or LOEE) and on the rate of load growth expected for the planning horizon. The planning procedure for the expansion of generating capacity by adding new units, based on the criterion that a certain risk level should not be exceeded, is selected largely by economic considerations. (F&D) is among other indices of reliability the frequency and duration, and this software is capable of calculating these indices together with complete (COPT). In (HL1), (in which, only the ability of the generation facilities to meet the system
2. SOFTWARE DESCRIOTION IN (HL1) It is easy to use this software, and in order to calculate the reliability in (HL1), it is enough to select its radio button (see fig 1). Then a menu is opened (see fig 2), Clicking on system A button opens a menu, like the one shown in fig. 3 and system A input data should be entered in. In part (number of units) from figure 3 the number of those units of generating are entered that are of the same capacity as units as well as FOR, λ, and µ . Unit capacity, amount of these quantities, and load capacity are entered in parts (unit capacity, FOR, λ, and µ, and load), respectively. At the next stage, through clicking on the Apply button these inputs are registered and then by clicking on the next button the information about the next units is entered. This will be repeated until information about all units are entered. After completing the task, we can exit this menu. It should be noted that there are no limitations in calculations, due to the number of generating units and used transmission lines. After this stage in menu of fig. 2, and clicking on Run button, the program will be executed and the complete COPT together with reliability indices calculated.
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Fig.1. Menu for selecting the state of interconnected systems (HL1) and (HL2)
Fig 2
Fig. 3. menu for entering the input data of load and generating systems.
2
Fig .4
3. SOFTWARE DESCRIOTION IN (HL2) In this (HL2) different combinations of interconnected power systems have been prepared into the software, from among which we can choose our favorite system and calculate the reliability indices for the chosen interconnected system by entering the related information. As it can be see from fig.1, generally there are three choices for interconnected systems: The first case- shows systems that have been connected to each other in series. Here, a system assists another one in the direction of arrows through transmission line and the system that receives assistance, can receive it only from one direction. The second case- shows systems that have been connected to each other in series but the system which receives assistance can receive it from systems of two directions and systems assistance to the system which receives it, takes place in the same direction as the arrows and through the transmission line. The third case- shows systems that have been connected to each other in a triangle form and in this case assistance from one system to another can be transmitted through two ways by transmission line and in the same direction as the arrows. Selecting the first case and clicking on Next button will open fig.4 menu in which different combinations of systems that have been connected to each other in series, have been shown. By selecting each one of these combinations, systems related to that combination will be activated and by clicking on these systems or transmission lines, a menu will be opened in which these systems input information and transmission lines will be arrived.
Fig.5. The menu related to transmission line input information Considering fig 5, one can enter information in transmission line menu as follows: In part number of tie number of those transmission lines are entered that both their capacity and FOR, λ, and µ are the same and in the part related to FOR, λ, and µ the amount of these quantities are entered. If the line is reliable, 0 is replaced with the amounts FOR, λ, and µ. In the next stage by clicking on Apply button these inputs are registered and then
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complete COPT, in series state for the system which receives assistance and it is shown in two cases: before receiving assistance and after that. By considering this, we can see that how much the reliability indices have been developed after receiving the assistance.
by clicking on Next unit button the next transmission lines information are entered and this will be repeated until the information about all transmission lines have been entered. When this was completed we can click on OK button and exit the menu. After these step, by clicking on Run button the program will run and its result include reliability indices and
Fig .6
Fig .7
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By selecting the second case in fig 1, menu in fig. 6 is opened in which some combinations of interconnected systems are shown and their situation is such one that a system in them can receive assistance in the same direction as arrows from two directions and by transmission lines and other systems, and after selecting the considered combination and entering the input information of the systems and transmission lines and running the program, reliability indices and complete COPT for considered system, in two cases, before and after receiving assistance from systems and transmission lines of the two directions are obtained. Considering the obtained results, we can see that how much the reliability indices have been developed after receiving the assistance from two directions. By selecting the phase three in fig. 1 the menu shown in fig. 7 is opened in which some combinations of interconnected systems are shown and their situations are such ones that if input information of A and A1 are equally selected, then a triangle combination is created in which a system can transmit its assistance through two different paths in the same direction as the arrows to the considered system through other systems and transmission lines. It is after selecting the considered combination and entering the input information of the systems that and transmission lines and running the program that reliability indices and complete COPT for considered system are shown in three phases. One of them is before receiving assistance and the second is after that through systems and the first path’s transmission lines, and the third phase, after receiving assistance through systems and the second path’s transmission lines. By comparing the obtained results we can find out in which cases reliability indices have been better than others.
4. EDUCATIONAL OBJECTIVES where the power engineering students are required to use the software in order to understand the basics of generating capacity reliability assessment and determine the reliability indices such as loss of load expectation (LOLE) and loss of energy expectation (LOEE) and the frequency and duration (F&D). The software can be a useful tool: . to introduce the student to the basic concepts of reliability assessment and capacity planning to both of generating systems and transmission systems; . to enable the student to interactively create and utilize different types of interconnected systems models; . to make the student appreciate the effects of various pertinent factors such as unit size, unit forced outage rate (FOR), system peak load, maintenance scheduling, unit addition and removal, load forecast uncertainty, etc.; 5. SAMPL STUDY CASES -The first case (HL2) The package is used to evaluate the reliability of a relatively small generating systems. The system consists of six units, with an installed capacity of 75 MW. The maximum total demand is 100 MW. The generation data is given in table 1. Fig. 8 shows reliability indices and complete COPT fir this system
Table 1: generation data for the test system Number Unit System of Unit capacity FOR (MW) A
5 1
10 25
λ
µ
0.02 0.01 0.49 0.02 0.01 0.49
Fig 8 . Complete COPT table together with reliability indices -The second case (HL2) Here, the software is evaluated in evaluating the reliability of an interconnected power system. This system has been shown in fig. 9.
The aim in this interconnected system is system A’s assistance to system C through two directions: One time, directly through Tie 3 and another time through Tie 1, Tie 2, and B system. The information about given system in fig. 9 is similar to that of system A in table 1 and maximum required load for system A is 50MW and for systems B and C is 75MW. In such a case only system A can receive 25MW assistance. The information of each one of the three lines is similar and it has been shown in table 2.
System C Tie 3
System A
Tie 2
System B
Tie 1 Fig. 9 A sample for an interconnected system
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The point that comes from obtained results is that, LOLE, and Average Duration quantities are reduced after C system receives assistance from A system. In other words, C system has been more reliable. On the other hand, by comparing Fig.11 and 12 we come to the conclusion that the transmission of A system’s assistance to C system through Tie 3 have been better than that of Tie 1 and Tie 2, because it has reduced LOLE and Average Duration amount a lot. In this example each three lines had been selected equally, and if the capacity and FOR of the lines were different from each other, other results might be obtained. Finally, this software contains different combinations of interconnected power system and this allows students to know more about reliability in both HL1 and HL2 by using them.
Table 2: Transmission lines information Tie
1,2,3
Number Tie of tie capacity FOR lines (MW)
2
20
λ
µ
0.02 0.01 0.49
When the program was run, the complete COPT together with reliability indices for C system are obtained in three cases: C system has not received assistance from any system that have been shown in fig. 9. C system has received assistance only from system A through Tie 3 line, and this has been shown in fig. 10. C system has received assistance from system A through Tie 1, Tie 2, and B system. This has been shown in fig. 11.
Fig. 10: Complete COPT and reliability indices for C system
Fig. 11: Complete COPT and reliability indices for C system after receiving assistance from A system through Tie 3
Fig. 12: Complete COPT and reliability indices for C system after receiving assistance from A system through Tie 1 and Tie 2.
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reliability indices in HL1, and this can be effective in learning and teaching the reliability.
6. CONCLUSION In this paper, a package of software in windows environment for evaluating the reliability of capacity generating and transmission systems in interconnected power systems has been described (HL2).This software can calculate risk indices (such as LOLE, LOEE and F&D) in designing the production capacity and power systems transmission, and contains different combinations of interconnected power systems and allows the reliability indices to be calculated in different combinations of interconnected powder systems, and the effect of these combinations as well as the effects of changes in units and lines sizes, FOR, and the time required for repairing units and transmission lines in reliability indices to be observed. By using this software, one also can calculate
REFERENCES [1]
R. Billinton and R. N. Allan, Reliability Evaluation of Power Systems, Plenum Press, Second Edition, (1996). [2] R. Billinton and R. N. Allan, Reliability Evaluation of Engineering systems: Concepts and Techniques, Plenum Press, Second Edition, New York, (1992). [3] Saleh Aboreshaid, Omar Basoudan, “Graphical User Interface For Teaching Power System Reliability”, IEEE Electrical and Computer Engineering, pp. 1211-1216,May 1999. [4] L. GOEL and G. SHRESTHA, “Windows-based Educational Software for Power Generating Capacity Reliability Assessment and Expansion Planning” , Int. J. Engng Ed. Vol. 14, No. 5, pp. 356±366, 1998.
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