Circuit interrupter providing protection and waveform capture for harmonic analysis

摘要

A circuit breaker (1) with a digital trip unit (15) has a protection mode (89) and a waveform capture mode (87) of operation. In the protection mode (89), an equivalent sampling technique based upon pairs of samples spaced 90 electrical degrees apart with a pattern of delays between pairs is used to digitize the waveforms in the protected electrical system (3). Synchronous sampling is used in the waveform capture mode (87). The value of each sample is monitored (77, 79) in the waveform capture mode (87) and a transfer is made back to the protection mode (89) if a threshold value indicating an overcurrent condition is exceeded. The percentage total harmonic distortion, and per harmonic distortion for harmonics, up to and including the 27th are sequentially presented on a display (21) on the front panel of the circuit breaker (1) and can be transmitted along with the raw waveform data to a remote processor. <IMAGE>