Evaluation of RMS Current in AC Power Wires Using a High-Speed Infrared System

This paper presents a new method of the effective value (RMS) of alternating current (AC) in power wires based on infrared radiation (IR) measurement using a high-speed medium wavelength infrared (MWIR) camera. The method called “2-ω” involves measurement of the 100 Hz harmonic of temperature (T100) and is supported by signal analysis in the frequency domain. The article discusses the issue of non-sinusoidal alternating current, which causes much more difficult analyzes compared to sinusoidal current with a frequency of 50/60 Hz. The simulation and measurement results for different current shapes obtained in typical power systems like: a phase-controlled switching regulator, half-wave and full-wave rectifiers, and finally the nonlinear distortion of the AC current due to saturation of the magnetic core, are presented and confirm the linear relation of T100 ~ I2RMS. The main advantage of proposed method is the independence of the measurement results from environmental conditions.