Energy Measurement in Split-Phase Systems Using 78M6612

Abstract: This document discusses energy measurement in split-phase systems. A split-phase electricity distribution system is a 3-wire single-phase distribution system, commonly used in North America for single-family residential and light commercial (up to about 100kVA) applications. A 3-wire system, using a distribution transformer with a single-phase input (primary) winding, is common in countries with a standard phase-neutral voltage of 120V.

This article analyzes three different load cases:
  • Line1/Neutral + Line2/Neutral: balanced load (case 1)
  • Line1/Neutral + No load on Line2: unbalanced load (case 2)
  • Line1/Neutral + Line2/Neutral + Line1/Line2: unbalanced load (case 3)
A firmware load for the 78M6612 energy-measurement IC was developed to implement split-phase measurement for two independent phases with a phase offset of 120° or 180°. It implements 4 channels (2I and 2V) and measures RMS for each channel as well as power for two phases. Two voltage dividers and two current transformers as sensors are required.