The design of a largely self-calibratable voltage transformer testing set (VTTS) is described in which the only components that have a first-order bearing on the instrument's errors are transformer devices working at zero burden. The errors of resistance and capacitance components in the circuit are eliminated by a simple setup procedure which may be carried out each time the VTTS is used. The device described, which could be made up largely from components found in a standards laboratory, should be accurate to within 0.1% of the VTTSs indicated error in both ratio and phase, and would be ideal for checking the accuracy of automatic, digital-read-out VTTSs.
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