In the power grid, on power lines, noise and signals of different kinds are transmitted. Some of the siganls are wanted, others are not. For all the signal types it is important to know how they propagate on the power grid. In this report different mathematical or computational methods are discussed with special emphasis on a simple but accurate method proposed by Arne Brejning Dalby. This method is compared (theoretically) with other methods, some employed in commercially available computer programs.A number of examples demonstrate the feasibility of the method and the advantages that can be obtained using the method.