To control power flow for multi-terminal high voltage DC (MTDC) grids, the transformations of synchronous reference frames highly relies on the knowledge of the amplitude, phase-angle, and frequency offset of the grid voltage's positive and negative sequence components especially under grid fault conditions. Therefore rapid and accurate detection of the above information are more significant. The existing techniques can only detect partial fault information and are not able to deal with various contingencies simultaneously in terms of non-sinusoidal, asymmetric, phase and amplitude jump, frequency offset and random noise. This paper presents a new rapid grid voltage faults detection method that is capable of tracking signal deviations on the grid-voltage accurately and rapidly even in the case that bus-voltage contains high order harmonics and random noises. Various grid-fault conditions are experimentally generated by a programmable AC source device. The experimental results verify the validity of the proposed method.