PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 88 NR 6/2012 55 Petre Lucian OGRUTAN 1 , Lia Elena ACIU 1 , Dan LOZNEANU 1 , Ioan ROSCA 2 , Transilvania University of Brasov, Romania (1), Transilvania Sud Electricity Distribution (2) Consumers protection and monitoring with microcontroller based device for low-voltage distribution systems Abstract. Protection devices against over-voltage and over-currents for low voltage systems are equipped with varistors and gas-discharge tubes around a fuse, having a disconnection time about 200ms. This paper proposes an intelligent protection system that includes a real-time energy distribution monitoring system for the consumer, providing rapid load disconnection/reconnection without any human intervention, which is considered as an important improvement. Streszczenie. Urządzenia chroniące przed przepięciami i przetężeniami w instalacji elektrycznej zawierają warystory, iskierniki oraz bezpieczniki o czasach działania około 200 ms. W artykule przedstawiono inteligentny rozwiązanie ochrony zawierające system monitorowania użytkownika energii w czasie rzeczywistym oraz zapewniające szybkie wyłączenie/załączenie bez ingerencji człowieka (Zastosowanie urządzeń wykorzystujących mikrokontrolery do ochrony i monitorowania instalacji elektrycznej) Keywords: safety, microcontroller, monitoring, low voltage, distribution systems Słowa kluczowe: bezpieczeństwo, mikrokontroler, monitorowanie, instalacja elektryczne Introduction A recent study achieved for the European Community [1] was aimed at investigating the causes of accidental fires in order to establish effective safety provisions for low voltage consumers against such hazards. The study mentions, for instance, a percentage of 31% of fires caused by the electric section of the equipments. Within this context, ascertains that most of the fires were caused by the defects in the electrical system – shortcircuits and overvoltages. Consequently there is a worldwide concern for identifying and applying new methods of protection. The levels of the overvoltages occurring in electrical supply systems are lower than those arising in electrical power transport and distribution systems yet under unfavorable conditions the former can also cause significant equipment damage. A situation specific to low voltage systems is the occurrence of hazardous accidental voltages at the grounding connections of the equipments due to the effects of the carried overcurrents. Under the present conditions of operation of the energy market and due to the increased requirements in terms of the quality of services imposed on electrical energy providers, the need to determine the level of overvoltages becomes increasingly important in distribution and supply systems as well. This provides the opportunity to identify the areas of increased electrocution risk, as well as other potentially hazardous situations to consumers in the investigated low voltage systems. Also, the possibility of hazards due to damages produced in low voltage cable systems cannot be neglected. The computer-assisted simulation of the transient electromagnetic regimes and sequences of such regimes is the only feasible method for performing parametric analyses at the level of accidental voltages, overvoltages and overcurrents in the system. Such parametric analyses allow for determining the level of voltages and currents circulation in any point of the system on a given range of its operating parameters. This is virtually the only solution to anticipate the sensitive areas of potential risk. Knowing the current values in any point of the system allows an adequate planning of the preventive maintenance of grounding connections, of protection systems and points with damaged insulation, especially in cable systems. Knowing the voltage values in any point of the system allows to avoid operation at voltage values that are unacceptable not only to consumers but also to certain system components for a prolonged operation regime, knowing the touch and step voltages in all ground connections of the analyzed system for any operating mode including anomalous situations like broken neutral wires or potential equalization conductors. The measures that can be implemented as following to the performed analyses will produce immediate effects in terms of avoiding unwanted events with respect to electrical safety, reduction of frequency and duration of electrical power outages with the associated technological and economic advantages. Adequate planning of maintenance activities, which follows as a consequence to such analyses, results in enhanced services quality of the provided electrical power. The EMTP-ATP simulation program allows to determine the voltage and current variations occurring in different points of an electrical network, highlighting those locations where an intervention appears necessary by using types of protection devices as proposed in this paper [2]. A single electronic device including embedded systems for overcurrent, overvoltage and user protection against electrocution represents a necessity at this level of modernization [3]. The data exchange with the exterior moves the fuse system into the 21st century by ensuring the facilities for remote control [4]. E.g. a quick and safe fuse which operates at a precise value of the short-circuit current could improve the quality of electrical power by reducing the voltage sags in the system. The paper presents a system for consumer protection against short-circuits and overvoltages that can occur in the low voltage power supply grid. The proposed system was subjected to practical tests for various power factors. Presentation of the protection device The protection device proposed in this paper operates as an electronic circuit breaker based on a microcontroller which provides the possibility of transferring distant events into an event log. Its structure is shown in Fig. 1. The proposed device has the following advantages: -High cut-off speed (maximum 10ms) which is faster than with conventional methods; -Does not require human intervention since after power cut- off in the case of short-circuit or overvoltage, the power supply is automatically restored (for short-circuits only after eliminating the cause); -Due to its two-stage action for the case of occurrence of low-value overvoltages or overcurrents, the average voltage value is subtracted thus preventing the load to be cut-off from the supply. This advantage can be obtained for the triac equipped version only;