Page 130 IM02601004E www.eaton.8 Setup on the Web Server PagesSUBCYCLE DISTURBANCEThe Power Xpert Meter captures subcycle disturbances with its regular metering hardware, whichsamples at 30.72 ksps. You can set the dv/dt Threshold and Absolute Threshold for Van, Vbn, Vcn,Vab, Vbc, and Vca. In addition, you can select the kind of action that will occur when one of thethresholds has been reached; Capture Waveform, Capture Parameters and/or Send E-mail.The Absolute Threshold Voltage setting is intendedto trigger on Voltage spikes that exceed the normalpositive and negative peak values, which are typi-cally 1.4 times the rms line-to-ground Voltage. It isimportant to set this threshold safely above the ex-pected peaks. The Setup page suggests a thresholdthat is 20% above the Nominal L-L Voltage (dividedby the PT ratio). For example, a 120V/208V systemhas a 120V rms and 170V peak (line-to-ground), andso a 250V threshold is appropriate (i.e. 208 + 20%).The dv/dt Threshold setting is entered in dv while thedt is fixed at the hardware sampling rate. The Setuppage suggests an aggressive threshold. Specifically,the setup page suggests a threshold that is 5% ofthe Nominal L-L Voltage (divided by the PT ratio).To calculate the volts per microsecond, multiply the threshold Volts by 0.03072. For example, if thedv/dt Threshold is set at 20V, the Volts per micro second would be 0.744 (i.e. 20V x 0.0372 Msps =0.744 V/ microsecond).A 30.72 ksps sampling rate and a pure 120V sine wave would result in a dv of 1.5V per sample atthe zero crossing. A disturbed waveform would have a much higher dv/dt.Note: To notify Power Xpert software of subcycle disturbances, select the Send Web ServicesNotification box.
