Design, construction, and testing, of voltage transformers

It is the aim of this paper to consider broad principles rather than manufacturing details. The performance characteristics of voltage transformers are deduced from general fundamental principles, and expressions are derived for calculating ratio and phase errors from design data. Two methods are given for determining errors on and desired burden from a knowledge of previously ascertained test data. The first method is based on ordinary graphs of errors against output, and the second method employs a simple geometrical construction based on the transformer vector-diagram. Several questions concerning the construction and practical application of voltage transformers are considered, including typical performance characteristics, voltage transformers for high frequency and high accuracy, winding connections, fuses, limiting resistances, and breakdowns, and a comparison of dry, oil-immersed, and compound-filled types. Testing is subdivided into general routine testing and testing of ratio and phase errors. Descriptions are given of two equipments for testing errors. One equipment employs a resistance potential-divider and is capable of testing ratios up to 200. The other equipment employs as potential divider a high-voltage condenser in series with a resistance and is capable of testing ratios up to 2 200. The paper concludes with some remarks on testing of errors under actual working burden, and on the effect of resistance of secondarv leads on errors.