The impact of PV generation and load types on the impedance relays during both balanced and unbalanced faults

Abstract

Photovoltaic (PV) power generation and the types of connected loads both have an effect on protective impedance relays’ readings. This paper investigates this effect in a real distribution system installed in the State of Kuwait. It is found that, both the dynamic loads and the PV plants have considerable effects in the relay impedance value which vary according to the load type, PV connection and fault locationplace. Both single phase to ground fault (unsymmetrical fault) and three phase fault (symmetrical fault) are investigated. When single line to ground fault occurs at the PV bus (far from relay location), the dynamic loads increase the relay impedance while the PV plant decreases the relay impedance. When a single phase to ground fault occurs at the relay bus (load bus), the dynamic load decreases the relay impedance and the PV plant increases it. For a three-phase to ground fault at the relay bus, both dynamic load percentages and PV plant power generation have no effect on the protective relay impedance readings. At this condition, the relay impedance totally depends on the fault resistance. The main finding of this paper is that both the load type (especially dynamic load) and the PV plant have dominant effects on the protective impedance relay reading and setting. The distribution system planners and operators must consider the PV plant and types of load during designing, setting and adjusting the protective impedance relays. The most important point in this paper is considering real case study. This means that, the obtained results are more realistic than the assumed system in the other research. If the fault occurs at the location of the PV system’s bus when no PV power is generated, the dynamic load causes the relay impedance to increase, while connecting the PV decreases the relay impedance. The relay’s resistance and reactance increase from 0.3153Ω and 1.4950Ω, to 0.3456Ω and 1.6617Ω respectively when the dynamic load increases from 25% to 90% of the total load at constant high fault resistance. The relay resistance and reactance decrease from 0.2849Ω and 0.3443Ω (without PV plant), to 0.2195Ω and 0.3137Ω (with PV), respectively. When the dynamic load percentage increases from 25% to 90%, the resistance and reactance of the relay decrease from 1.0488Ω and 0.0051Ω, to 0.9526Ω and 0.0008Ω, respectively. This phenomenon is valid for all expected fault resistances. When considering constant dynamic load percentage and constant fault resistance, the relay resistance and reactance increase from 1.375Ω and 0.0022Ω (without PV) to 1.5745Ω and 0.0726 Ω (with PV), respectively. Based on those results, the impedance relay setting must be adjusted according to the percentage of the dynamic loads percentage, the PV penetration level, and the fault location.