ABSTRACT This paper presents the development of an algorithm based on ‘Rectangular Wave Transform’ for extracting the desired frequency components from transient power system relaying signals. In this approach the desired frequency components are obtained from data samples using only the arithmetic operations of add, subtract and shift- The algorithm is applied for transmission line distance protection. The algorithm is evaluated, under different fault conditions, using relaying signals obtained from transient analysis conducted on a model 345 kV, 3-phase system.