GB1482717A - Identification of phases in a three-phase alternating current supply - Google Patents

Abstract

1482717 Measuring phase ELECTRICITY COUNCIL 7 Jan 1976 [23 Oct 1974] 45864/74 Heading G1U To determine which phase of a three-phase supply is connected to a load, to determine distribution of loads amongst the three-phases, an optical pick-up is used to derive a signal from a light source forming at least part of the load, and the output therefrom is compared in phase to a reference signal derived from a known phase of the supply. In monitoring domestic installations, the reference signal may be received by radio, whereas for a localized system e.g. a factory site, the reference signal may be received by a wire or ultrasonic link. Alternatively, phase information may be transmitted at a high frequency signal along one or more phases, and the information detected using an inductive pick-up. To identify which subsystem is supplying the load, a chosen subsystem is instantaneously loaded e.g. by switching a thyristor, to cause a 5-10% drop in the phase voltage. A corresponding drop can be detected in the optical pickup output, and indicated. In normal operation, a phase shifter giving 0‹ or Œ 120‹, is switched until phase equality is detected. Extra phase shift may be provided if the load is not purely resistive.