**1. Introduction**

In the last decades there has been a gradual increase of the industrial park in several coun‐ tries which demands energy, especially electric power. This situation caused a considerable expansion of the sector responsible for generation and distribution of electric power in a very short period of time. The rapid expansion caused a significant increase of generation sources and of distribution branches of electric power which originated enormous and com‐ plex agglomerates with interconnections among themselves and with a certain degree of de‐ pendence and vulnerability.

This complexity of electric power systems brought up technical needs and technological challenges in order to obtain efficient methods to monitor the variables of the electric quanti‐ ties which express the operational normality state of the networks. Together with the need of energy production the priority, the sentiment of priority given to the extraction forms and the correct usage of energy by mankind came up. This sentiment brought up new public policies of generation and distribution of electric power. Currently, the laws concerning this issue have concentrated on the supervision of the concessionary companies which are re‐ sponsible for the provision of electric power, making sure that these companies offer energy with a high-quality level to the consumers. Besides these obligations, the utilities companies

© 2012 Da Silva Filho et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Da Silva Filho et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

also have the need of markets and because of that they have big interest in the moderniza‐ tion of the management, monitoring and control of their power systems. Due to these facts, a huge effort and investment of the concessionary companies in the research are which deals with the quality of electric energy offered to consumers has been verified [1].

A typical transmission system has three phase conductors to take the electric current and transport power. Each phase of the transmission line is built with two, three or four parallel

Electric Power System Operation Decision Support by Expert System Built with Paraconsistent Annotated Logic

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It is well known that operation failures in an electric power system are unavoidable and there are a large number of reasons why these interruptions happen. This situation is due to the natural conditions of an electric power system in which failures may happen because of internal or external causes, such as consequences of environmental physical phenomena which are beyond the physical specifications of the electric systems or even human error [3].

There also is a fundamental limitation on the electricity distribution: with few exceptions, electric power cannot be stored which means that it must be generated as it is demanded. That being so, an electric power system must provide electric power with safety and with acceptable tolerance ranges either for a normal load or for a demand condition of maximum load or of peak [1][2]. Since the demand periods of peak load, due to the several types of industry or to different types of housing, are different from region to region, this natural

In certain regions industries can be more productive in certain times of the day and show a drop in demand because of lunch time, so the demanded energy has variations during the day. In highly densely populated regions where there is a lot of night life businesses, the en‐ ergy demand is larger in the evening and also depends on the day of the week and even on

Besides this problem particular to each industrial park or city, another factor to consider is the climate of the region where these industries or residences are located. In regions with very hot weather, turning on air conditioning system in the hottest period of the year, the ener‐ gy demand values are higher in the late afternoon. For regions with very cold weather the en‐ ergy demand has different effects on the global load of the electric power system because in the coldest period of the year heaters are turned on in the morning and in the evening.

These situations of difficult control makes power or demand for electric energy vary and be‐ sides, the capacity of a transmission line to transport electric power is limited by physical and electrical parameters of its conductors. In order to avoid interruptions these conductors of electric energy in any load conditions must be sufficient to respond to the demand within

Transmission lines are subject to environmental adversities including large temperature var‐ iations, high winds, storms, etc. Thunders that fall on transmission towers cause high vol‐ tages and propagating waves in the transmission lines which usually cause the destruction of isolators and as a consequence of that the protection relays interrupt the power transmis‐

limits such that their safety relays will not be activated.

condition of electricity brings up a problem of generation control and transmission.

conductors separated approximately by 1.5 ft (0.5 m) [3][7].

**1.2. Main Problems of an Electric Power System**

the season of the year.

sion through the networks [7].

One of the indexes which measure the quality of electric power offered to consumers is ob‐ tained by the number of outages or failures in the energy distribution of the electric power system (and time length) in a certain period of time. When an electric power system is over‐ loaded, it is possible that its equipments may be disconnected by relays which act as protec‐ tion, causing the interruption of electric power in certain areas covered by its transmission networks.

That being so, it is very important to research new methods that effectively evaluate the state of outage risk due to overloads in the system because it is extremely important, in or‐ der to decrease indexes of energy interruption to consumers, to manage the power loads with permanent monitoring of the distribution lines of electric power. However, in the case of an interruption, it is also fundamental to make decisions quickly and safely in order to reconnect systems after an outage.

#### **1.1. Electric Power System Overview**

A typical electric power system can be divided in generation and systems of transmission, sub-transmission and distribution. The transmission system interconnects generating sta‐ tions to large substations located near load centers generally using aerial electric transmis‐ sion lines. The sub-transmission system distributes energy to an entire district and usually uses aerial electric transmission lines. The distribution system transports energy from the lo‐ cal substation to individual houses, using aerial or underground transmission lines [7]. A typical electric power system can be seen in Figure 1.

**Figure 1.** Simplified picture of a typical electric power system.

A typical transmission system has three phase conductors to take the electric current and transport power. Each phase of the transmission line is built with two, three or four parallel conductors separated approximately by 1.5 ft (0.5 m) [3][7].

#### **1.2. Main Problems of an Electric Power System**

also have the need of markets and because of that they have big interest in the moderniza‐ tion of the management, monitoring and control of their power systems. Due to these facts, a huge effort and investment of the concessionary companies in the research are which deals

One of the indexes which measure the quality of electric power offered to consumers is ob‐ tained by the number of outages or failures in the energy distribution of the electric power system (and time length) in a certain period of time. When an electric power system is over‐ loaded, it is possible that its equipments may be disconnected by relays which act as protec‐ tion, causing the interruption of electric power in certain areas covered by its transmission

That being so, it is very important to research new methods that effectively evaluate the state of outage risk due to overloads in the system because it is extremely important, in or‐ der to decrease indexes of energy interruption to consumers, to manage the power loads with permanent monitoring of the distribution lines of electric power. However, in the case of an interruption, it is also fundamental to make decisions quickly and safely in order to

A typical electric power system can be divided in generation and systems of transmission, sub-transmission and distribution. The transmission system interconnects generating sta‐ tions to large substations located near load centers generally using aerial electric transmis‐ sion lines. The sub-transmission system distributes energy to an entire district and usually uses aerial electric transmission lines. The distribution system transports energy from the lo‐ cal substation to individual houses, using aerial or underground transmission lines [7]. A

with the quality of electric energy offered to consumers has been verified [1].

networks.

30 Advances in Expert Systems

reconnect systems after an outage.

**1.1. Electric Power System Overview**

typical electric power system can be seen in Figure 1.

**Figure 1.** Simplified picture of a typical electric power system.

It is well known that operation failures in an electric power system are unavoidable and there are a large number of reasons why these interruptions happen. This situation is due to the natural conditions of an electric power system in which failures may happen because of internal or external causes, such as consequences of environmental physical phenomena which are beyond the physical specifications of the electric systems or even human error [3].

There also is a fundamental limitation on the electricity distribution: with few exceptions, electric power cannot be stored which means that it must be generated as it is demanded. That being so, an electric power system must provide electric power with safety and with acceptable tolerance ranges either for a normal load or for a demand condition of maximum load or of peak [1][2]. Since the demand periods of peak load, due to the several types of industry or to different types of housing, are different from region to region, this natural condition of electricity brings up a problem of generation control and transmission.

In certain regions industries can be more productive in certain times of the day and show a drop in demand because of lunch time, so the demanded energy has variations during the day. In highly densely populated regions where there is a lot of night life businesses, the en‐ ergy demand is larger in the evening and also depends on the day of the week and even on the season of the year.

Besides this problem particular to each industrial park or city, another factor to consider is the climate of the region where these industries or residences are located. In regions with very hot weather, turning on air conditioning system in the hottest period of the year, the ener‐ gy demand values are higher in the late afternoon. For regions with very cold weather the en‐ ergy demand has different effects on the global load of the electric power system because in the coldest period of the year heaters are turned on in the morning and in the evening.

These situations of difficult control makes power or demand for electric energy vary and be‐ sides, the capacity of a transmission line to transport electric power is limited by physical and electrical parameters of its conductors. In order to avoid interruptions these conductors of electric energy in any load conditions must be sufficient to respond to the demand within limits such that their safety relays will not be activated.

Transmission lines are subject to environmental adversities including large temperature var‐ iations, high winds, storms, etc. Thunders that fall on transmission towers cause high vol‐ tages and propagating waves in the transmission lines which usually cause the destruction of isolators and as a consequence of that the protection relays interrupt the power transmis‐ sion through the networks [7].

#### **1.3. The voltage variation and Overcurrent as Overload Risk Factors**

According to what was seen, in an electric power system the loads represented by the elec‐ tric power consumers, such as electric machines of industries, lighting systems, heating de‐ vices of residences and refrigeration systems of businesses, are not static. They are constantly changing, being turned on and off with value variations which may lead to over‐ load. The overloads are outage risks for the whole system because it increases the intensity of the electric current (overcurrent) in the lines and can heat the conductors, increasing their temperature and causing permanent damage with the interruption of energy transmission.

the system, which requires a sophisticated AI based control to assure capable and efficient control of the generation according to the demand. These actions which modify the opera‐ tional state of the electric power systems at any time must be controlled in order to provide

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Nowadays, the software SCADA is installed in the electric power systems. SCADA stands for Supervisory Control and Data Acquisition and provides in real-time large amounts of in‐ formation about values related to electric quantities of the electric power system which can be obtained from points of the transmission network. Such quantities are, for example, volt‐ age, current and potency. The information obtained by the SCADA system are used as input for the analysis systems and decision-making [1][8][9]. However, due to the large amount of information received by the control centers, interference and natural failures in the synchro‐ nization of the transmission, it is not always that the information brought for analysis by SCADA are complete. Because of that, a databank is created and contains ambiguous, vague and contradicting data. Due to the nature of these data a human operator could be led to make false interpretations or even make wrong decisions which could lead to huge losses and delay of the system restoring [1] with damage to the quality index desired. That being so, it became very urgent to have computational treatment with expert systems dedicated to interpretation, data analysis and the presentation of suggestions as a way of supporting the

Artificial Intelligence research oriented to electric power systems has as its goal to find ways of designing new computational tools for the support of decision-making of the team re‐ sponsible for the correct operational action. However, due to the large number of electric keys (breakers that modify the system's topology), to variations on the values of loads and to other several factors inherent to an electric power system, there are many difficulties to find efficient ways. The methods which use conventional binary classical logics to analyze data from the electric power system with the capability of offering suggestions for the opti‐ mized restoring after a failure has not provide good results. One of the difficulties found in the design of models based in classic logics is its condition of being defined by rigid binary laws which lead to equations which are extremely complex to reproduce models. Besides, these equations almost always lead to a combinatorial explosion. Due to this aspect, in this area of artificial intelligence, projects designed with the goal of analysis and decision-mak‐ ing based in classic logics has found many difficulties. It is verified that the low efficiency showed by these projects which use classic logics comes up when a large amount of data has to be computed. These data almost always have redundancies which bring up incomplete‐ ness and contradiction invalidating important information for the analysis. Some classic works use complex algorithms with good results but the computation time is very high making the response time long which is unfeasible in real conditions where an electric pow‐ er system always demands quick and direct actions in order to avoid bigger damages.

power transference in a safe and coordinated way.

operation of electric power systems.

**2.1. Expert Systems structured in non-classical logics**

The existence of load variations requires precise equipments which adjust the voltage in the line, because the overload causes the voltage outage. The voltage variation can aggravate the electric power system state with emergence of large intensities in distribution branches. Because of that, the decrease value or the voltage outage (under-voltage) and the intensity value of the electric current (overcurrent) are two important risk factors to the monitoring of transmission lines of electric power. That being so, the monitoring of the ranges of voltage outage and of maximum current of an electric power system are used as a diagnosis of over‐ loads. In order to increase the quality index these two factors must be constantly monitored because if they both are out of the ranges specified in their projects the possibility of discon‐ nection of the electric power system will be higher.
