Loading...
Please wait, while we are loading the content...
Assessment of Short Circuit Power Levels in Hv and Mv Networks with Respect to Power Quality
| Content Provider | Semantic Scholar |
|---|---|
| Author | Allegranza Ardito, Alessandro Deberardinis, Ettore Delfanti, Maurizio Loschiavo, Luca |
| Copyright Year | 2007 |
| Abstract | The Italian Regulator (AEEG Autorita per l’energia elettrica e il gas) is paying great attention to voltage quality and has started up a research task in the framework of the Public Interest Energy Research Project named "Ricerca di Sistema" (Italian Ministry for Productive Activities Decree of 28 February 2003) aimed to the monitoring of representative portions of the MV network. Moreover, the Italian Regulator has requested the calculation of the minimum short circuit power (hereinafter, Ssc) levels on the EHV and HV transmission network (Resolution n. 250/04), as Ssc represents a meaningful and synthetic parameter for the robustness of the electric network if related to the customers characteristics in terms of disturbing emissions. A simple method to correlate rapid voltage changes caused by rapid variations of loads (f. i. motor starting) with Ssc in the connection site has been set up. Based on this method, a criterion for the classification of HV and MV customers and substations is proposed: this criterion leads to a direct correlation between the customers and substation rated power and Ssc in the point of common coupling (PCC). An example of the application of the methodology to the real short circuit power data coming from HV networks is also reported. INTRODUCTION The power supply quality is attracting growing attention from regulators in the international context. As far as electric systems are concerned, customer requirements are getting harder to meet, especially in highly industrialized countries. On the other hand, distribution networks are increasingly characterized by potentially disturbing loads at any voltage level (f.i. due to the massive development of power electronics). Load requirements are getting huger, with reference to both the continuity of the power supply (the most important parameter in an economic sense) and to the voltage waveform [1]. As in case of the continuity of power supply, the level of voltage quality is determined by the interaction between the distribution networks and the customers connected. In the first case (i.e. continuity of power supply, on which the Italian regulator was mainly focused so far), the situation has considerably improved thanks to the interaction between distributors and customers towards a better network management (operating strategies, network automation, protections selectivity, etc.). As far as the second case is concerned (i.e. voltage quality, on which AEEG has now begun to focus), Ssc is considered an important parameter for power quality (as far as transmission networks are concerned, the Italian regulator has already planned to publish the minimum conventional levels of Ssc for the busses of the Italian transmission network with Resolution n. 250/04 [2]). Without entering into more specific matters, the present paper will outline the reasons why attention has been focused on Ssc with reference to power quality. In particular, it is appropriate (and technically feasible, as described below) to correlate the variations in operating conditions due to the “ordinary” load variability to the capacity of the network of facing such variability without an excessive reduction of the voltage value in the connection point. With good approximation, the rapid voltage variations related to the above-mentioned phenomena can reach different values according to the network Ssc levels. DEFINITIONS AND POSSIBLE USES OF SHORT CIRCUIT POWER The short circuit power Ssc of a network point P is usually obtained by multiplying the threephase short circuit current Isc by the nominal voltage between phase and phase of the system (Un) and by factor √3: 3 sc n sc S U I = ⋅ ⋅ (1) According to the above definition, the short circuit power Ssc at a PCC can be used to obtain the network impedance from the point itself (Zsc): 2 sc n sc Z U S = (2) Generally speaking, it is possible to define different values of short circuit current (and of short circuit power) according to the different aims. The present paper, which makes reference to the document [3] published by CEI 136 working group (a project group established by the AEEG Resolution n. 136/04, referring to guidelines for the connection to the HV and MV networks) defines the following values: 1. Maximum threephase short circuit power (aimed at devices sizing). It is the value of the short circuit current as planned by system operators and adopted in order to choose the short-circuit withstand level of the equipment. 2. Maximum operating threephase short circuit power in |
| Starting Page | 1 |
| Ending Page | 6 |
| Page Count | 6 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.cired.net/publications/cired2007/pdfs/CIRED2007_0161_paper.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
