Analysis of Grounding Grids Connection Between Photovoltaic Farm and Its Substation

Photovoltaic (PV) farms often surround their supporting substations, which are sometimes built in mountainous regions with high soil resistivity. When the farm and the substation are independently grounded, if there is a fault in the substation, the grounding system of the PV farm will collect most of the fault currents from the substation, which can generate a very high potential difference between the two grounding systems, and give rise to very high step voltages and touch voltages which are hazards to personnel safety and reliable equipment operation. This paper discusses this issue in depth based on numerical simulation of the grounding systems of a PV farm and its 220 kV substation. The grounding resistance, step voltage, touch voltage, and the ground potential difference in the grounding grid are considered, especially in the PV farm. The dangerous place and the mechanism are discussed. The measures to protect the device in the PV farm are investigated. The research finds that if the two grounding system are interconnected, all of the parameters decrease greatly. Therefore, interconnection two grounding system is necessary even they belong to different companies.

I. Introduction

The grounding systems play an essential role in ensuring the reliable operation of the photovoltaic (PV) farm and substation, and the safety of personnel [1]. In China, PV farm and the supporting substation belong to different companies and each company wants its own grounding system not to be connected to other grounding systems. However, due to the very high soil resistivity in mountainous areas, the ground impedance of the substation is very high, as well as the potential gradient if there is a fault in the substation. Since the huge PV farm surrounds the substation, its grounding system will collect most of the fault currents from the substation, which can generate a very high potential difference between the two grounding systems, and give rise to very high step voltage and touch voltage. Accordingly, the grounding systems cannot ensure the reliable operation of the PV farm and substation, and the safety of personnel.