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More and more photovoltaic (PV) power is being connected to electricity grid every year. Most PV units are installed at a low-voltage distribution level. According to the current standards for small scale PV integration, PV systems are basically the devices of real power generation and do not generally regulate voltages at the point of common coupling. Moreover, PV generation highly depends on weather conditions, so its power varies all the time throughout a day. Therefore, with increase in PV penetration distribution networks may experience significant PV power fluctuations within a short period of time caused by fast moving clouds. This can result in considerable voltage variations that may lead to undesirable under/over voltages and unacceptable voltage imbalance levels. This paper investigates phase voltage variation sensitivities to PV power fluctuations in an unbalanced distribution network. Asymmetrical line mutual couplings are considered. Mathematical explanations of unbalanced phase voltage variations are reported in this paper.