The testing of instrument transformers

The determination of the ratio and phase angle of instrument transformers has now become a very important part of the work of electrical testing laboratories. The method now almost universally used in accurate work depends upon the potentiometer principle. Various modifications of this method have been suggested and used^∗. A modification of the method has recently been developed at the Bureau of Standards which, while involving no entirely new principles, possesses some distinct advantages over any of these.