The verification of Rogowski coil linearity from 200 A to greater than 100 kA using ratio methods

Many industrial processes make use of transient currents greater than 10 kA. Among others, these include resistance welding processes and circuit breaker testing. Some applications require measurement of currents to greater than 500 kA. Though the latter special applications may be few in numbers, they often have strategic importance and economic value. Rogowski coils are assumed to be amplitude-linear devices. However, questions do arise regarding linearity due to coil construction practices and the materials selected. This paper describes ratio methods (often known as "boot strapping") to verify Rogowski coil linearity from a current of 12.5 kA to 100 kA. The measurement process utilizes 3 coils and 3 sets of currents that have nominal ratios of 2:1. A measure of coil nonlinearity is derived using the simultaneous solution of 8 ratio-equations.