A METHOD AND A SYSTEM FOR SYNCHRONIZING MULTI-PHASE ELECTRICAL POWER SYSTEMS

Since the introduction of numerical protections, Fourier Filtering has been used extensively in power system measurements used for metering, control and protection assuming steady state frequency condition. This method is not accurate when the frequency rapidly varies. An example application when precise measurement of voltage, frequency and phase angle is important under rapidly varying frequency condition is changing over a load bus from one source to another with spinning down induction and synchronous motors. The method proposed below uses signals in real time which reflect the true status of the system at every instant of measurement. The method is applicable for multi-phase systems wherein at least two phases information of a multi-phase system in time domain can be directly measured. Assuming the motor bus voltage and frequency would go down exponentially, it is possible to predict exact advance angle compensating CB closing by using Taylor series expansion, limiting to typically second or third order. This method not only uses third order modeling but also continuously evaluates the error between calculated advance angle and the measured angle and compensates for it. This method greatly reduces any errors not only in advance angle calculation but also averages out the measurement errors introduced in instantaneous measurement method indicated above, in presence of harmonics and other noise signals.