1. A method for obtaining signal outputs signifying fault determinations of an electrical signal, represented by x(k), wherein said electrical signal has different states, with a state being defined by a constant amplitude (A) and a constant phase (0) relative to a given amplitude and phase reference, and each of said different states being caused by a raw event representing a disturbance in said electrical signal, comprising the steps of: detecting the actual state of said electrical signal; detecting the raw event causing a change of the state of said electrical signal; said steps of detecting the state and raw event including the step of sampling the electrical signal and operating with a truncated general Fourier series with an exponentially decreasing constant part to obtain an estimated error signal according to the equation: ##EQU4## where, N=the number of terms in the truncated Fourier series; .omega.=the basic angular frequency of the input signal: T.sub.s =the sampling time; and deriving an estimation error signal: EQU x(k)=x(k)-x(k) as a difference signal between the actual electrical signal and said estimated error signal; detecting the occurrence of a raw event at sample k=h from said difference signal x(k) and the estimated coefficients a and b in a decision logic circuit when ##EQU5## where .delta. is an accuracy coefficient depending on the desired accuracy in the step of detecting the raw event; detecting the amplitude (A) and phase (0) for each state of the different states of said electrical signal and which comprises samples k.sub.1 to k.sub.2 according to: ##EQU6## where: m-(k.sub.1 +k.sub.2)/2 and the event .increment.A and .increment..phi. according to: ##EQU7## supplying the states A, .phi., k=1, k=n and the events .DELTA.A, .DELTA.A, and k=h as respective signal outputs for determination of electrical faults on said electrical signal.