Fast Fault Detection and Location of a Zonal Marine Power System: Using Active Impedance Estimation

On marine distribution systems traditional protection schemes often fail to provide the necessary reliability and discrimination. In this paper, a novel protection scheme for a zonal system, as proposed for marine applications, is presented based on active impedance estimation. The power system impedance is measured by injecting a very short current transient onto the network via a coupling inductance and analysing the transient response to this using the measured voltages and currents. Wavelet analysis is used in the data processing to estimate the system impedance over a broad frequency range; the identified impedance can be used for fault discrimination. The speed, accuracy and range of validity of such an approach are fully explored. It is shown that this scheme provides a useful compliment to traditional protection strategies and can also provide the necessary back up protection during extreme protection failure.