When a line, transformer, or feeder blackout occurred in the power system, service restoration was managed to optimal radial topology to restore maximum out-of-service loads with less switch operation and return the system to a healthy operation. This paper presents a new improved sequential opening branch (ISOB) algorithm to propose a solution for service restoration in power distribution systems by considering On-Load Tap Changer (OLTC) and Capacitor Bank (CB) operation at two different load levels with normal load and heavy load. The proposed method aims to minimize the percentage of voltage deviation index which is a measure of how much the voltage on a feeder deviates from the nominal voltage as the objective function. To ensure that the voltage levels remain within acceptable limits during service restoration, several tests are carried out on IEEE 33-bus and a 70-node system for multiple-fault scenarios.