تجزیه و تحلیل عملکرد از ماهواره در مدار پائین زمین برای برقراری ارتباط سیستم قدرت

In this paper the main performances of communication services based on low earth orbit satellites (LEOs) have been analyzed in order to evaluate their suitability for a typical set of power system monitoring functionalities. As an experimental test bed, an intelligent electronic device (IED) for remote monitoring and protection of power components equipped with a bi-directional communication system based on the LEO satellites of the Globalstar® consortium has been prototyped. Thanks to the adoption of this facility the main parameters characterizing the performance of the satellite TCP/IP services have been evaluated. They comprise in particular the connection time, the degradation of service and data latency for both packet and asynchronous data services. The experimental results obtained show that the application of LEO satellites based communication technologies exhibits a set of intrinsic advantages that could be particularly useful in several fields of power system communication.

The increase in the growth of information and communication technology (ICT) could play a strategic role in the attainment of the new targets induced by the liberalized electricity market. In particular, amongst the possible solutions available, the employment of satellite based technologies appears to be particularly suitable since it could make possible the realization of advanced, high value communication services such as: • sophisticated metering; • remote control and supervision; • interactive e-commerce and trading applications. Without requiring the construction of complex and expensive infrastructure and assuring, at the same time, a set of intrinsic advantages such as wide area coverage, easy access to remote sites, cost independent of distance, low error rates and adaptable to changing network patterns. Moreover, satellite based technologies are considered a key factor in lowering the degree of vulnerability of complex interactive networks and critical infrastructures as far as the electric power grids and transportation networks are concerned [1], [2] and [3]. On the other hand, the main factors that in the past have limited the application of satellite based technologies in power system communication have been recurring leasing cost of services and intrinsic time delay. Nowadays the large number of satellite service providers in conjunction with the continuous lowering of the cost driving factors characterizing the new technologies are driving satellite communications to become competitive with other wireless based services. At the same time the recent launch of low earth orbiting (LEO) satellites, characterized by an orbital period of much shorter than a day, permits large reduction of communication time delay. These technologies have been successfully applied to support a wide range of advanced telecommunication services such as wireless Internet [4] and high-speed terrestrial/satellite networks [5]. Nevertheless, to the best of our knowledge, the application of LEO satellites based telecommunication technology has not so far been explored in the literature on power system communication. With this paper, we intend to fill this gap. The paper analyses the performance of LEO satellites based communication services in order to establish their suitability for a typical set of monitoring and supervision functionalities required by power system utilities. In particular, after a comparative analysis of the latest data services offered by the main system providers, the LEO satellites based data services furnished by the Globalstar® consortium have been adopted as reference in our experimental activities. The performance of these services have been tested by an experimental test bed consisting of a prototype IED that integrates advanced modeling methodologies and LEO satellites based TCP/IP communication services for the remote monitoring and protection of power components. Thanks to the adoption of this facility the main parameters characterizing the data link performance have been considered. They comprise in particular the connection times, the degradation of services and the data latency. These experimental activities have been developed connecting the IED to the Internet by the Globalstar® satellite gateway and submitting multiple queries to the remote device by a web connected host server. As far as the connections modalities of the host server, several kinds of Internet connections, based on both Local Area Networks and private Internet Service Provides (ISP), have been explored. In the latter case both wired (analog modem connected to a Public Switched Telephone Network (PTSN)) and wireless technologies (based on satellite and GPRS data links) have been considered for the Server/ISP connection. The analysis of the results obtained shows LEO satellites based communication systems, compared with geo-stationary satellite (GEO) based services, are characterized by a set of intrinsic advantages that could be particularly useful in power system communication such as rapid-connecting packet data, asynchronous dial-up data availability, reliable network services and reduced overall infrastructure support requirements. The outline of the paper is as follows: an analysis of the existing literature on satellite based technologies applied to power system communication is given in Section 2. In Section 3, a comparative analysis between the main LEOs based communication services is presented. Section 4 describes the main features of the experimental test bed adopted to assess the performance of LEOs based data services and presents a discussion of the experimental results. Conclusions and future work are summarized in Section 5.

In this paper the main performances of low earth orbit satellites based communication services for power system communication have been analyzed. To address this problem an experimental test bed based on an IED equipped with a bi-directional satellite communication system for remote monitoring and protection of power components has been prototyped. Thanks to the adoption of this facility several figures of merit characterizing the main performances of the satellite based TCP/IP services have been analyzed. These experimental activities have been developed connecting the IED to the Internet by the Globalstar® satellite gateway taking into account several web based connections for the host server. These comprised, in particular, Internet connections based on both enterprise Local Area Networks and private ISP. In the latter case both wired and wireless technologies have been considered for the Server/ISP connection. The results obtained show the application of LEOs based communication technologies allows system operators to overcome some of the intrinsic limitation of the classic geo-stationary satellite based communications exhibiting a set of intrinsic advantages particularly useful in power system communication as rapid-connect packet data, asynchronous dial-up data availability, reliable network services, reduced overall infrastructure support requirements. As far as the data latency, the LEOs based communication services have exhibited better performances compared to other satellite based communication technologies, mainly due to the orbital period being much shorter than a day. Anyway the measured values appear not directly suitable for high performance-time critical applications. All these factors make the employment of LEOs based communication services very promising in several fields of power system communication as far as automation, remote monitoring and supervision are concerned.