Tailoring a spectral line detection system for applications in dissolved gas analysis

Abstract

In the process of developing a simple and highly sensitive dissolved gas analysis (DGA) sensor system, applicable for surveillance of the operating conditions of high-voltage equipment, a systematic optimization strategy has been conducted to allow detecting low concentration levels of DGA target molecules, by use of the harmonic detection technique, without use of long interaction length, multipass cells. Gas phase experiments were carried out by use of carbon monoxide — one of the target molecules in DGA— as a model to evaluate the limitations in detection sensitivity imposed by electronic noise, etalon effects, optical interference noise and mode hopping in the system’s optical assembly. By properly setting up the electronic detection system and designing the optical circuit and measurement cell, it was possible to detect a minimum carbon monoxide concentration of 90 ppm with a single pass, 25.4 cm cell, around the 1568 nm absorption line of the gas. This detection sensitivity, together with the simplicity of the measurement principle, allows establishing the proposed configuration as a feasible alternative for practical use in real-time, DGA of insulating oils of high-voltage transformers.