Recently, utility-scale photovoltaic (PV) plants in remote areas are drastically increasing due to abundant and low-priced land. These remote areas are usually connected to zone substations through long weak feeders with open-delta step voltage regulators (SVRs) installed in the middle to regulate downstream voltages. However, frequent PV and load power fluctuations can lead to undesirable voltage variations and hence excessive tap operation issues. Currently, it is not clear about the percentage of responsibility by load or PV fluctuations to excessive tap operations. In this article, a novel method based on line-to-line voltage sensitivity and time series evaluation is proposed to respectively quantify the interactions between PV/load fluctuations and tap operations. The accuracy of this method is firmly validated with the measured data from a real-life unbalanced distribution network with high PV penetration. Further, this proposed method is implemented to statistically quantify the causes of excessive tap operations with half-year field data under the support of the local utility and the PV plant owner. The investigation results can provide valuable insights for utilities to better manage the voltage profiles and tap maintenance for remote distribution networks with high PV penetration.