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It is observed that the inverter fault current in such system strongly depends on several aspects: 1) Fault type and location 2) Neutral grounding techniques and 3) Grid strength. This paper presents the comprehensive fault analysis in a smart urban distribution grid integrated solar PV system. Therefore, in order to combine the effects on the fault level by these two streams, we have considered IEC 60909 standards for the calculation of SC current by upstream conventional grid while the contribution by the solar PV inverters connected downstream grid is considered under assumptions given in. The total fault level is the phasor sum of the maximum current from the conventional upstream grid and the solar PV connected at the distribution level, including power electronic interface. The limitation of established standards is that they emphasizes mainly on the fault contribution by conventional power system and provides no guidelines for interfacing inverters. There are various recognized standards for conventional SC studies such as IEC and ANSI/IEEE standards. Such situation may cause the undesirable islanding, problem of protection coordination, threat to the reliability of system and impedes the process of integration.
Iec 60909 0 2016 changes free#
The SC current contribution of a single PV inverter unit may not be large, because of its small size and transient free behavior in comparison to rotating machines, but the large scale integration of solar PV at various places of the network can cause the total fault level exceeds the designed fault level of the system. Addition of solar PV in the conventional system affects the designed fault level of the system.
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Existing distribution grid has a designed SC capacity of the protective equipment, which ensures that the equipment is able to interrupt or withstand the SC current reasonably. The significance of these impacts depends on the level of integration, one such alarming and often overlooked impact which poses a serious challenge in the process of integration, is the change in SC level of the system. The solar PV impacts on the distribution system are addressed as voltage variation, voltage unbalance, harmonics, reverse power flow, change in short circuit level and protection malfunction. The integration of solar PV in the downstream of radial distribution system changes the electrical characteristics of network and introduces critical challenges. The integration of more and more renewable energy sources like solar PV is expected in future power grid, therefore a proper planning study is required at the time of integration to ensure the reliable operation of the system. Such situation has to be managed to ensure the protection coordination and reliability of the system. Moreover, the varying network conditions also alter the SC current and fault level of the system. It is found that, with solar PV integration, the major change in fault level occurs due to the three phase fault then followed by double line to ground and other faults.
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Paper also reports that the grid strength and neutral grounding techniques significantly affect the inverter SC current. The network is analyzed according to IEC 60909 standard and the alteration in SC current and fault level by the inverters is reported. In order to investigate the issue, a generic urban distribution feeder is modeled, which supplies power to the loads of varying nature. The aim of this paper is to analyze the short circuit (SC) behavior and variation in fault level due to solar PV inverters in a smart distribution network.