DC Arc flash calculations for solar farms

Abstract

The NFPA 70E standard -2012 edition and the CSA Z462-12 standard describe the calculations required to determine the approximated incident energy in a DC arc flash. These calculations assume that the power source for the DC system is linear. This paper describes the calculations required to estimate the incident energy in a DC arc flash for solar farms, where the power source is highly nonlinear. The equations required for the calculation are derived from fundamentals and compared to the equations provided by the above standards. The incident energy levels found in a typical solar farm are presented in an example, where the results obtained by the application of the standards and the proposed method are compared. Recommendations to include in the standards the provisions for the calculation of DC arc flash in solar farms are given in this paper.

Arc flash safety concerns for solar panels

“…The results of the maximum IE deployed by a DC arc flash for a PV system presented in the example show that the method described in the standards provide significantly lower IE levels than the method described in [8]; resulting in the potential of serious hazard to the maintenance personnel due to the inappropriate selection of the personal protection equipment.…”

“…There are significant differences between the calculation of the maximum IE as described in [6], [7] and the calculation of the maximum IE in photovoltaic system as described in [8]. The impact of the difference between these two methods is evaluated in the following subsections.…”

“…Following the analysis described in [8], it is possible to estimate the maximwn incident energy in an arc flash for a roof mounted PV system. As shown in (1), the maximum power at the fault Pmax is a function of the maximwn power voltage Vmp and the maximum power current Imp.…”

“…As described in [8], the use of the formulas listed in the current editions of the NFPA 70E and the CSA Z462-12 standards will result in an underestimation of the maximum IE encountered in a PV system. The underestimation error is expressed in (7) and it does not account for the correction for temperature.…”

“…In this particular example, the number of modules connected in series ns is 11. Then, the system voltage is given by (8) and the maximwn power voltage is given by (9). The number of PV modules connected in parallel np is given by (10).…”