Patent ID: 9037429
Filing Date: 2015-05-19
Classification: G01R

Abstract:
1. A method of providing circuit breaker protection comprising: providing a circuit breaker including a measurement circuit wherein the circuit breaker is responsive to the measurement circuit; sampling a first number of full cycles of a signal at a rate based on a nominal frequency of the signal; converting the samples to a first set of digital samples using an analog to digital (A/D) converter within the measurement circuit; processing the first set of digital samples using a digital signal processor (DSP) within the measurement circuit to identify a first pair of digital samples with each one disposed on either side of a first zero-crossing and a second pair of digital samples with each one disposed on either side of a last full cycle zero-crossing; interpolating the first pair of digital samples and the second pair of digital samples using the DSP within the measurement circuit to determine a position of the first and last zero-crossings relative to each other in time; calculating a preliminary fundamental frequency of the signal using the DSP within the measurement circuit based on the first number of full cycles sampled and the relative position of the first and last zero-crossings; sampling a second number of full cycles of a signal at a rate based on the calculated preliminary fundamental frequency of the signal; converting the samples to a second set of digital samples; processing the second set of digital samples to identify a third pair of digital samples with each one disposed on either side of a third zero-crossing and a fourth pair of digital samples with each one disposed on either side of a final full cycle zero-crossing; interpolating the third pair of digital samples and the fourth pair of digital samples to determine a position of the third and final zero-crossings relative to each other in time; and calculating a final fundamental frequency of the signal based on the second number of full cycles sampled and the relative position of the third and final zero-crossings; and measuring at least one of voltage RMS and current RMS using a sampling rate based on the calculated final fundamental frequency of the signal to tell if there is at least one of an overload and a short circuit condition within the circuit breaker.