AUTOMATION PLANNING OF LOOP CONTROLLED DISTRIBUTION FEEDERS M. Sperandio(1), E.A.C. Aranha Neto(1), J. Coelho(1), F. Trevisan(1) E.T. Sica(1), C.C.B. Camargo(1), R. Ramos(2) (1)
Electrical Systems Planning Research Laboratory (LabPlan/UFSC), Brazil (2) Central Electrical of Santa Catarina (CELESC), Brazil
This paper presents a methodology for the automation planning of loop controlled distribution feeders considering multiple criteria, like supply quality indices and feeder priority. The objective is to determine a list of interconnected feeders where which will receive three automated switches, one normally open (tie-line) and two normally closed, attending to the tradeoffs stipulated by the decision maker.
The fault detection, isolation, and service restoration is the most cost-effective distribution automation project [2,3]. It comprehends the loop controlled distribution feeders, which must have at least three automated switches, one tie-line normally open (NO) and two normally closed (NC) in each feeder. The switches are controlled by the distribution automation system (DAS) by a communication channel, as shown in Figure 1.
Keywords: automated switches, supply quality, distribution systems 1. Introduction It is known that about 80% of the customer service interruptions are due to failures in the distribution network, so the automation together with the operational evolution, speeds up the process of systems restoration under fault. Consequently, this improves the continuity indicators and the customer's satisfaction, because of the reduced needs of in loco maintenance that can be affected by traffic jams, long distances and unfavorable accesses. However, the costs associated with automation are still very high, and a strategic evaluation is necessary [1]. Although the feeder switches automation is very attractive, the decision about the acquisition of this type of equipment and the planning for its allocation requires the consideration of multiple criteria, like the influence of a switch’s position over the reliability indices SAIDI (System Average Interruption Duration Index), SAIFI (System Average Interruption Frequency Index) and ENS (Energy Not Supplied). There are also some customers that must be prioritized, such as essential services and industries, which usually conflict with the minimization of the technical indices. Meanwhile, it is very important to verify if the switches’ maneuver will not infringe the loading and voltage restrictions of the feeders. An innovative aspect of this methodology is the use of system reconfiguration as an initial step for establishing candidate positions to receive the automated switch. The goal is to optimize installation investments, minimizing the allocation cost and maximizing the quality and reliability of the system.
Figure 1- Automated loop controlled distribution feeders The problem is to define the position of the NCs switches in each loop, and then choose which loops will be automated amongst a distribution network area. 2. Methodology The methodology is divided in three modules, Reconfiguration, Reliability and Multicriteria (Figure 2). It starts with the decision about the area intended to be automated, so the feeder’s information is gathered from the utility’s database, where are the georeferenced electrical network, the failures event log, customer’s informations, etc. Then, interconnected feeders are grouped, and load flow studies will determine the candidate points (CP) and its respective load transfer capacity (LTC), so that none maneuver infringe any restriction. After that, the failure rates and repair times are determined for each interval between electrical points, and faults are simulated to calculate the reliability indices (SAIDI, SAIFI and ENS) for each CP [4]. Finally, the decision maker sets the tradeoffs in the multicriteria tree in order to define the CP that will receive the NC automated switch, and a list with the loop controlled distribution feeders’ priority [5]. So, the decision maker has a ranking of the most influential feeders that attend his requirements.
• • • • • • •
Decision Maker
Feeders data
Reconfiguration Module
CP- Canditate Points
CP’s LTC
Electrical Network Cables; Manual Switches; Fuses; Transformers; Customers; Capacitor Banks; Voltage Regulators.
Another search is conducted in the operations and maintenance database to acquire information concerning equipments’ faults. With this, the failure rates and repair times are calculated to be employed in the computation of reliability indices.
Reliability Module
SAIDI / SAIFI / ENS of CPs
Tradeoffs
Multicriteria Module List of Prioritary Loops
Figure 2- Methodology 3. Software A software was implemented from the methodology, including the three modules to perform all described tasks. The object oriented modeling was used, facilitating the programming and maintenance of the application. This also allows the use of code parts for development of other programs. The computational language was C++ with containers and classes of STL standard library, facilitating the implementation of structures such as lists, tables, vectors and matrices. The method requires a lot of matrices multiplications and demands a heavy computational burden, so a sparse matrix storage was adopted. The graphic interface is independent from the program’s data structure and was developed with the visual component library (VLC). As the main code is decoupled from the graphics, it is possible to introduce improvements easily into the user interface. 3.1 Data The data processed by the planning software is extracted from the distribution utility database. There are different tables with information about each network equipment involved in the process, all with georeferenced position. The main data tables acquired are:
After all feeders’ data are imported, they are loaded for processing the network connectivity and to set up the reachability matrix for each feeder. This matrix is used to find out if a customer is located up or down stream of a faulted sector, and if there is any protection equipment between them. Sometimes the database is corrupted or incomplete, making necessary to verify if the orientation of the circuit graph is radial, with the substation as the only source, and if all points are connected. Any inconsistency is reported for subsequent correction. There is also acquired information about the feeder’s cables impedance, for load flow calculations, and a table with a classification of the feeders established by the utility’s Emergency Load Shedding Plan. This table has four classes: • • • •
A: Susceptible to shedding; B: Not recommended for shedding; C: Personal risk or public security loads; CE: Special loads, must not be shed.
This classification is considered in the multicriteria module, where a tradeoff between them must be set. Thus, the planner can assign his priorities as he feels necessary. 3.2 Load Model In the program there is a form for configuration of the load modeling, where the following parameters can be set for each feeder: • • • •
Base Voltage; Demand Factor; Power Factor; Load coefficients.
The load coefficients are the percentiles of constant power (pCTE), constant current (iCTE) and constant impedance (zCTE) that compose the polynomial equations of active (P) and reactive (Q) power, as shown in equation (1).
2 ⎧ ⎡ ⎛V ⎞ ⎤ V ⎪ P = P0 ⎢ p CTE + iCTE + z CTE ⎜⎜ ⎟⎟ ⎥ V0 ⎪⎪ ⎢⎣ ⎝ V0 ⎠ ⎥⎦ ⎨ 2 ⎡ ⎛V ⎞ ⎤ V ⎪ ⎜ ⎟ ⎢ Q Q p i = + + z 0 CTE CTE CTE ⎜ ⎪ ⎟ ⎥ V0 ⎢⎣ ⎝ V0 ⎠ ⎥⎦ ⎩⎪
(1)
The values of P0 and Q0 are obtained from the installed power of the distribution transformers together with the power and demand factors of each feeder. V and V0 are the voltage variables used in the power flow calculations. This process will result in the candidate points to receive the NC automated switch, guaranteeing that no restriction will be infringed in a load transfer maneuver for the parameters set.
A reduction of the ENS is an energy revenue obtained by the company, because less customers were affected by a long energy fault due to a fast maneuver of the automated feeders loop, and is direct related to the feeder’s load and failure rate. On the other hand, the LTC is an idle capacity, or a strategic reserve that the network operator can use to balance the load between feeders seeking to minimize losses. 3.4 Tradeoffs The tradeoffs of a multicriteria model represent the loss of performance that an alternative must suffer over the criterion to compensate the performance gain in another criterion. The grades of each criterion can be adjusted through the multicriteria decision tree (Figure 3).
According to the load parameters and the network impedance more or less candidate points can be tested. If no candidate can be obtained, the feeders loop will be marked as unfeasible in the ranking list. The program also shows which restriction was infringed, voltage or current, and the point where it occurs. 3.3 System Indices The multicriteria module is built by criteria that allow measuring the performance of each configuration alternative of the distribution network, evaluated in the objective and sub-objectives. The attribute is constituted by impact levels, where each impact level is seen as the representation of the potential action performance (configuration alternative of the distribution network) in the considered criterion, for example: the SAIDI and SAIFI indices. The impact levels are arranged in terms of preference, and the most attractive level corresponds to an action whose performance is the best possible, for instance: the smallest possible SAIDI index. In another way, the least attraction corresponds to an action whose performance is the worst acceptable. The attribute module is used to the determination of the candidate points from a load condition and for the calculus of the attributes for each candidate point. The attributes computed are the following: • • • •
SAIDI (h/y); SAIFI (fails/y); ENS (kWh/y); LTC (kW).
The SAIDI and SAIFI information are associated to sets of consumers (districts), and a feeder can supply more than one of these sets. If a feeder crosses more than one district, there will be information for the SAIDI and SAIFI of this feeder for each set.
Figure 3- Multicriteria decision tree Each criterion can receive a value between 1 and 10 so that the degree of importance is defined for each objective and sub-objective. According to the values set, one or other criterion will be prioritized and will change the global value of the alternatives and consequently the ranking order. Inside the SAIDI and SAIFI criteria a value must be set for each district included in the planned area, so a tradeoff is defined amongst them. Thus, the decision maker can highlight some districts as his preference to receive the automated feeders loops, but they will not necessary be the first ones in the final rank. All values set in the decision tree are saved in a user profile, so that the adjustment of those parameters is kept and can be recovered with the opening of the profile. When a new profile is created the default value for all parameters is 1. 3.5 Ranking the Alternatives After all information about the attributes has been calculated and the tradeoffs were set in the decision tree, or loaded from a profile of a previous session, it is possible to rank the alternatives of automation of loop controlled feeders.
A list is generated with each feeders loop, represented by the name of both feeders and the number of the NO tie-switch, followed by each feeder’s switch NC selected position (FS1 and FS2) and the mulcriteria global value. This value is a performance index of each alternative, reflecting the tradeoffs provided by the planner (Figure 4).
4. Conclusions This work was developed in a partnership between the university and the local distribution utility as a decision aid software for the automation planning of loop controlled distribution feeders. The use of multiple criteria such as the reliability indices SAIDI, SAIFI and ENS together with customer priority and reserve capacity was necessary to attend to different company’s policies. Extensive calculations are performed without simplifications to assure that the feeders loop can afford the tasks of load transfers, and the customers are assisted with proper power quality. All data used in the development process was from the real network of a south brazilian distribution utility.
Figure 4- List of loops priority There are also two types of icons to indicate if the alternative is feasible. An alternative is unfeasible if no candidate point was found, due to voltage or load restrictions, or if there is another alternative with the same feeder with a higher global value, them it is marked with a red X. Otherwise, a feasible solution is marked with a green V. 3.6
Switches Positions Visualization
As the data come from a georeferenced database, the software can plot the feeders loop and the respective position determined to the installation of the automatic switches (Figure 5).
The feeders’ automation is a complex decision that affects both the planning and operation of the distribution system. Thereby, the optimization of automation investments is aimed, maximizing the increase of power quality and reliability, according to the company’s proceedings. References [1] M. Sperandio, E.A.C. Aranha Neto, J. Coelho, R. Ramos, “Analysis of Automated Distribution Systems Schemes”, In: CEE-2005 - 1st International Conference on Electrical Engineering, cod.6w47, Coimbra - Portugal, Outubro, 2005. [2] P. Dondi, Y. Peeters, and N. Singh, “Achieving Real Benefits by Distribution Automation Solutions.” Proc. of the 16th CIRED. Amsterdam-Netherlands, v.482, p.5.8, 2001. [3] Chun-Lien, S. and Jen-Ho, T. “Economic Evaluation of a Distribution Automation Project”, Industry Applications Society, IEEE-IAS annual meeting, v.3, p.1402-1409, 2006. [4] E.A.C. Aranha Neto, M. Sperandio, J. Coelho, R. Ramos, E.T. Sica, C.C.B. Camargo, “Planejamento da Alocação de Chaves Automatizadas Considerando os Índices de Confiabilidade e Qualidade”, XVII SENDI - Seminário Nacional de Distribuição de Energia Elétrica, Belo Horizonte, IT-0276, 2006.
FS1
FS2
[5] E.T. Sica, E.A.C. Aranha Neto, M. Sperandio, C.C.B. Camargo, J. Coelho, R. Ramos, “Modelaje Multicriterio y Sistema de Apoyo a la Decisión y Ubicación de Llaves en la Red de Distribución”, CIDEL - Congreso Internacional de Distribución Eléctrica, Buenos Aires, 2006.
NO
Author address Mauricio Sperandio Figure 5- Switches Positions Visualization The window shows the feeders with different colors, and the protected area between the two NC switches can be highlighted to view the customers that can be assisted by both feeders.
[email protected] www.labplan.ufsc.br LabPlan – EEL / CTC / UFSC Campus Universitário – Trindade Florianópolis/SC CEP 88040-900 Brazil
