| 摘要 |
A circuit interrupter (1) samples waveforms in a protected circuit (3) by taking samples in pairs (P1, P2) spaced 90 electrical degrees apart. The sum of the squares (S2) of samples in each pair, which is representative of the RMS value of the fundamental frequency of the waveform, is used for instantaneous protection (55) by comparing a running sum (S4) of the squares for the two most recent pairs of samples to a threshold representative of the instantaneous trip pick-up value. This sum of the squares (S4) of successive two pairs of samples is also used for short delay protection (61). A delay between successive pairs of samples is varied to produce a selected equivalent sampling rate after a given number of samples. Samples accumulated at this equivalent sampling rate, which is sixty-four samples per cycle in the preferred embodiment, are used for long delay protection (69) and metering. <IMAGE> |
