The Vanguard(Doble Company), USA ATRT-03A is a battery-powered, microprocessor-based, automatic, three-phase, transformer turns-ratio tester. This lightweight, portable, battery-powered unit is designed for testing transformers at utility power substations. The ATRT-03A determines the transformer turns ratio using the IEEE C57.12.90 measurement method. The transformer turns ratio (ranging from 0.8 to 15,000) is determined by precisely measuring the voltages across the unloaded transformer windings. To ensure accuracy, the ATRT-03A?s measuring circuitry self-calibrates before each measurement. It requires neither adjustment nor temperature compensation. The ATRT-03A?s turns-ratio measurement accuracy is 0.1% or better.