Apparatus providing protection and metering in an ac electrical system utilizing a multi-function sampling technique

A circuit interrupter for an electrical system comprising:

• separable contacts for interrupting current in said ac electrical system when opened;
• sensing means sensing waveforms in said ac electrical system including at least one current waveform;
• sampling means sampling said ac waveforms sensed by said sensing means at sampling instants to generate digital waveform samples;
• timing means generating said sampling instants repetitively in pairs with sampling instants in each pair spaced 90 electrical degrees apart, and with delays between successive pairs of samples adjusted to produce a selected equivalent sampling rate after a given number of samples, and with said given number of samples substantially evenly distributed over an equivalent sampling cycle;
• and
• processor means comprising means squaring and summing values of samples in each pair to generate a squared pair sum for each pair of samples, means maintaining a running sum of the squared pair sum for each of the two most recent sample pairs, means repetitively generating an accumulated sum calculated by accumulating a sum of said running sum at every other pair of samples for said given number of samples, and means tripping said contacts open when said running sum exceeds a threshold value representative of an instantaneous trip pick-up value and tripping said contacts open when said accumulated sum after said given number of samples exceeds a long delay threshold value representative of a long delay pick-up value for a predetermined period of time to provide long delay protection.