Development of harmonic measuring system using PIC

A harmonic measurement has been carried out in a building of a university campus. The measurement and an EMTP simulation make clear that the 7th harmonic is the maximum and it is caused by a resonance between compensation capacitors of ballasts for mercury lamps and an inductance of the distribution line. Time-dependency of the harmonic is also observed. A simple and cost-effective harmonic measuring system using a peripheral interface controller (PICmicro/spl reg/ microcontroller) has been developed for an investigation of the harmonic characteristic. This measuring system has an A/D converter and a radio for synchronizing a clock which is indispensable for a multi-point measurement. To achieve a high accuracy, a fundamental component of the system voltage is removed by a phase locked loop oscillator and a differential amplifier. Another accuracy improving method using a capacitor connected to an outlet is proposed. Because the harmonic current flowing into the capacitor increases in proportion to the order of the harmonics, high-order harmonics can be measured accurately. An estimation method of a line inductance, which is a cause of the resonance, is also proposed.