Evaluation of the efficiency of a low voltage autotransformer

Abstract

In many developing countries, low-voltage autotransformers are commonly used in residential settings to compensate for persistent voltage irregularities in the electrical distribution network. Despite their widespread use, few studies have systematically evaluated their performance and efficiency under typical operating conditions. This study presents the design, construction, and experimental evaluation of a low-voltage autotransformer rated at 1580 VA. The design equations were derived from Faraday's Law, and the equivalent circuit parameters were obtained through open-circuit and short-circuit tests. The efficiency was measured using a power network analyzer under resistive and non-resistive loads and compared with values calculated analytically from the equivalent circuit. The study also incorporated uncertainty analysis in both experimental and analytical procedures. Results showed that the autotransformer reached an efficiency of 98.0 % under nominal load and exceeded 90.0 % efficiency at just 10.7 % of the demand coefficient. Furthermore, the all-day efficiency remained stable between 96.5 % and 96.8 % across real residential demand profiles, confirming consistent energy performance under variable load conditions. The differences between measured and calculated efficiencies were below 1 percentage point in all cases, and validation was confirmed using uncertainty propagation, mean absolute error (MAE), and root mean square error (RMSE). These findings reinforce the reliability of the analytical model and highlight the high efficiency of these devices as voltage-regulating elements when properly designed.