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A method and apparatus are provided for detecting a fault condition on a power system. By rectifying power system phase voltages to produce a rectified waveform, and filtering the rectified waveform or a representation of the rectified waveform through a finite gain synchronous band pass filter to g

A method and apparatus are provided for detecting a fault condition on a power system. By rectifying power system phase voltages to produce a rectified waveform, and filtering the rectified waveform or a representation of the rectified waveform through a finite gain synchronous band pass filter to generate a synchronous band pass filter output waveform that indicates the magnitude of a predefined harmonic frequency component, a fault condition on a power system can be identified.

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1. A method for detecting a power system fault, the method comprising: rectifying power system phase voltages to produce a representation of a rectified waveform;filtering the representation of the rectified waveform through a finite gain synchronous band pass filter to generate a synchronous band p

1. A method for detecting a power system fault, the method comprising: rectifying power system phase voltages to produce a representation of a rectified waveform;filtering the representation of the rectified waveform through a finite gain synchronous band pass filter to generate a synchronous band pass filter output waveform that indicates a magnitude of a predefined harmonic frequency component; andpost-processing the synchronous band pass filter output waveform to generate a fault detector output signal by comparing a waveform that indicates the magnitude of the predefined harmonic frequency component to an imbalance reference value to determine if a fault is present on a power system. 2. The method of claim 1, further comprising pre-processing a rectified waveform to generate the representation of the rectified waveform. 3. The method of claim 1, wherein the finite gain synchronous band pass filter comprises matched low pass filters. 4. The method of claim 1, further comprising filtering the representation of the rectified waveform through a plurality of finite gain synchronous band pass filters to generate a plurality of synchronous band pass filter output waveforms that indicate the contribution of an associated plurality of predefined harmonic frequencies of a power system frequency. 5. The method of claim 4, wherein the plurality of synchronous band pass filter output waveforms further indicate whether a fault occurred on the primary or secondary side of a transformer. 6. An apparatus comprising: a rectifying element configured to rectify power system phase voltages to produce a representation of a rectified waveform;a finite gain synchronous band pass filter configured to filter the representation of the rectified waveform to generate a synchronous band pass filter output waveform that indicates a magnitude of a predefined harmonic frequency component; anda post-processing element configured to generate a fault detector output signal from the synchronous band pass filter output waveform by comparing a waveform that indicates the magnitude of the predefined harmonic frequency component to an imbalance reference value to determine if a fault is present on a power system. 7. The apparatus of claim 6, further comprising a pre-processing element configured to generate a representation of the rectified waveform from the rectified waveform. 8. The apparatus of claim 6, wherein the finite gain synchronous band pass filter comprises matched low pass filters. 9. The apparatus of claim 6, further comprising a plurality of finite gain synchronous band pass filters configured to filter the representation of the rectified waveform to generate an associated plurality of synchronous band pass filter output waveforms that indicate the contribution of an associated plurality of predefined harmonic frequencies of a power system frequency. 10. The apparatus of claim 9, wherein the plurality of synchronous band pass filter output waveforms further indicate whether a fault occurred on the primary or secondary side of a transformer. 11. An apparatus comprising a processor, the processor configured to: receive a representation of a rectified waveform;filter the representation of the rectified waveform such that an output waveform has a finite gain as a frequency of a power system changes and such that the output waveform indicates the magnitude of a predefined harmonic frequency component; andgenerate a fault detector output signal by comparing the output waveform that indicates the magnitude of the predefined harmonic frequency component to an imbalance reference value to determine if a fault is present on a power system. 12. The apparatus of claim 11, wherein the processor is further configured to receive a rectified waveform to generate a representation of the rectified waveform. 13. The apparatus of claim 11, wherein the processor is further configured to filter the representation of the rectified waveform such that a plurality of output waveforms have a finite gain at various frequencies and indicate the magnitude of a plurality of predefined harmonic frequency components. 14. The apparatus of claim 13, wherein the processor is further configured to determine from the plurality of output waveforms whether a fault occurred on the primary or secondary side of a transformer. 15. A method for detecting a power system fault, the method comprising: rectifying power system phase voltages to produce a representation of a rectified waveform; andfiltering the representation of the rectified waveform through a plurality of finite gain synchronous band pass filters to generate a plurality of synchronous band pass filter output waveforms that indicates the contribution of an associated plurality of predefined harmonic frequencies of a power system frequency. 16. The method of claim 15, wherein the plurality of synchronous band pass filter output waveforms further indicate whether a fault occurred on the primary or secondary side of a transformer. 17. An apparatus comprising: a rectifying element configured to rectify power system phase voltages to produce a representation of a rectified waveform, anda plurality of finite gain synchronous band pass filters configured to filter the representation of the rectified waveform to generate an associated plurality of synchronous band pass filter output waveforms that indicate the contribution of an associated plurality of predefined harmonic frequencies of a power system frequency. 18. The apparatus of claim 17, wherein the plurality of synchronous band pass filter output waveforms further indicate whether a fault occurred on the primary or secondary side of a transformer.