Abstract: A method of protecting a bus in a three-phase electrical power system comprises the steps of (a) sampling voltage values and current values of each phase of the or each power system element within a predefined protection zone; (b) analysing at least one sampled voltage value of each phase of a power system element within the protection zone to detect when a fault condition arises; (c) on detection of a fault condition, determining whether the fault condition has arisen because of a bus fault; and (d) electrically isolating the bus from the or each power system element within the protection zone when a bus fault is determined so as to clear the bus fault.