Analysis and simulation of the IEC 61850 standard reliability

One of the important elements within an electrical system is the electrical substation since it is the sub-system that produces, transforms, regulates and distributes power. Ensuring that this process works properly is key in everything related to the energy industry; this document is an analysis and meticulous study that focuses on comparing the calculation of the reliability of a typical electrical substation, with and without implementing the IEC61850 (GOOSE) standard. The results suggest that when implementing the IEC61850 standard, system reliability is increased by 15%. Keyword— Reliability, double busbar substation, IEC 61850, Monte Carlo simulation.


B. Fault Tree
The Fault Tree (FTA) is a representation of the combination of events that cause the occurrence of an undesirable event. Este diagrama se realiza basándose en combinaciones definidas por operadores de tipo lógico, los cuales se presentan en la Fig. 1. El proceso deductivo continúa hasta que se llega a eventos básicos, los cuales son mutuamente independientes y tienen asociada una probabilidad de ocurrencia [4]. As a quantitative tool, the FTA is widely used because it reduces the possibility of the top event by determining the faults and errors that could cause the top event. Also, it allows analyzing the effects of the change or addition of components to a system, for example, the installation of a high-level alarm system. C. Substation The substation is comprised of a set of computers that control the flow of energy and ensure the safety of the system by automatic protective devices [5]. The configuration of a substation, is the arrangement of electromechanical equipment constituting a connection yard as long as these are referenced to the same voltage level. The reliability of a substation, depends on its protection system operation. The function of a protection system is to reduce the influence of a fault in the electrical system, so as not to affect the operation or the components of the substation, nor to endanger the life of human beings. Taking a basic configuration of a substation, the unwanted event is the fault of the substation. Four basic events can be considered: failure in the transmission line module of the failure in the transformer module, failure in the Busbar module and failure in the circuit module. The occurrence of any of these basic fault events is represented by a type OR gate, the inputs being, each of the aforementioned events. The representation of the fault tree is presented in Fig. 2.

IV. RELIABILITY CALCULATION AND SIMULATION.
To perform the reliability calculations, it should be noted that the Monte Carlo methods encompass a collection of techniques to obtain solutions of mathematical or physical problems through repeated random tests. In practice, random tests are replaced by results of certain calculations performed with random numbers [6]. Generally in statistics, random models are used to simulate phenomena that have some random component.

A. Algorythm
The Monte Carlo simulation algorithm developed is based on the generation of random numbers by the inverse transformation method, which is based on the cumulative frequency distributions for:  Determine the random variables and their cumulative distributions (F).  Generate a uniform random number between 0 y 1.  Determine the value of random variables for the number generated according to classes that are had.  Calculate mean, standard deviation error and perform the histogram.  Analyze results for different sample sizes.  Iterate as many times as samples are needed.

B. Graphic interface
To calculate reliability, a graphic interface was designed with the different modules that comprise the substation.
To perform the corresponding program to calculate the reliability, using MATLAB GUI, the following general steps were taken into account:

C. Analysis of the IEC61850 standard
The substation is formed by a set of computers that control the flow of energy and ensure system security with automatic protection devices [5]. The configuration of a substation is the arrangement of the electromechanical equipment constituting a connection yard and are referenced to the same voltage level; the representation diagram of a double bus substation is presented in Fig. 3. The reliability of a substation depends on the operation of the substation's protection system. The function of a protection system is to reduce the influence of a failure in the electrical system, so that proper operation or components of the substation is not affected, nor jeopardize the lives of human beings [7]. Taking a basic configuration of a double bus substation, the unwanted event is the substation failure. They can be considered as basic events: failure in the transmission line module, failure in the transformer module, failure in the bus module, failure in the circuit module and the communications module. He occurrence of any of these basic fault events is represented by a type OR gate, the inputs being the same, each of the aforementioned events. The representation of the fault tree is presented in Fig. 4. The use of high-speed LAN networks for data transmission considerably reduces the volume of cabling and, thanks to its immunity to electromagnetic interference (in the case of fiber optics), allows its use as close as possible to the primary process. On the other hand, the use of IEDs based on microprocessors, offers new possibilities such as self-supervision, signal analysis, computational facilities for protection and control algorithms, data storage, event handling and failure analysis. The general operation of this standard is presented in accordance with the message that is transmitted from the control center to each of the substations, that is, from the control center the message is sent to each of the control stations, to be transmitted according to the coding established for each of the OMS, by means of electric cable and the TCP / IP protocol. Each one of the OMS that intervene in the process, communicate with each other by the TCP / IP protocol through Fiber Optics, to then communicate with the SICAM PASS which are in charge of converting the TCP / IP protocol to the IEC61850 protocol. The OSM and the IEDs of each of the substation, as shown in Fig. 5. When this message is received by each of the OSM, it begins to transmit among the different OSM belonging to the substation by means of optical fiber, to be sent to all the IEDs that are communicated by this protocol. This being one of the advantages of the IEC61850 standard, since the message is transmitted to all the connected elements and the element that needs it, accepts them and decodes them for its use, delivering a received signal that is sent to the control center, and the element that is not affected by this message, ignores it. The main disadvantage of this Protocol is in the operation by message transmission ring since if any part fails, it interrupts the transmission of the message that is sent from the substation main control center. D. Simulations for calculating reliability To perform the corresponding simulations of the substation operation under study, a graphic interface was implemented in MATLAB, as shown in Fig. 6. Each of the modules that are part of a typical double busbar substation is located in the interface, such as the line module, transformer module, bus module, communications module, circuit module, as well as the spaces for the load and power factors, in addition to the KWh cost.
In each of the modules, you should have the Lambda information and the recovery time where each of the system failures is presented, this information is obtained from international standards such as the GOLD BOOK and / or studies carried out to determine the reliability factors of the substation, as shown in Fig. 7 for the communications module applying the IEC61850 standard [8]. According to studies conducted in this investigation, to implement the standard, the communications module is added, because this standard indicates the protocols that are used in substations when its implementation is done. Therefore, for the values in which differences are presented, we have in Table I, II and III, where the respective values are assigned to lambda and recovery time for the comparison without or with the standard.

E. Economic analysis
To calculate the IRR, we look for the interest rate that makes the flow of money brought to present value equals zero (0). The interest rate at which this occurs is a measure of the totality of the benefits that the investment generates while it is in the project. The decision rules applied are:  If the IRR is greater than the minimum acceptable rate, the project must be accepted.
 If the IRR is equal or similar to the minimum acceptable rate, the decision making is indifferent.
 If the IRR is less than the minimum acceptable rate (Opportunity Rate), the project must be rejected.
 The opportunity rate is understood as the current bank rate.
In the case of the analysis and simulation of the implementation of Standard IEC61850, the financial viability of the project is shown, since it shows that the IRR rate is greater than 1.98% E.A. with which the company would benefit, since it would increase the profitability of their services as well as their users with improved quality of service (see Table VI and VII). V. CONCLUSIONS According to the results of the Monte Carlo simulations of Electrical Substation double busbar that are made by Matlab GUI, designed to develop this study, we can observe from the implementation of the IEC61850 standard, that it increases reliability of the system by approximately 15%, that is, the simulated system without the GOOSE implementation has a 72% reliability and with the implementation of the Standard it has a reliability of approximately 89%. Based on the reduction of the simulated system failures, the system presents increased reliability, resulting in an increase in yearly economic gains, which is determined by calculating the quality indexes. These indexes show that with the implementation of the standard there is a gain of $ 398,085,852.80 pesos per year, that is, approximately a 15% gain versus the system without the implementation. Taking into account the economic projection, it is said that increasing the IRR, project gains are increased, in this system, not having this standard, the IRR is 11.9% and with the implementation of the system, a projection of 12.3% is obtained, so the implementation of the standard is recommended, because it increases the substation economic production annual profit.