Drawback of Using Double Core Current Transformers in Static Watt-Hour Meters

This article deals with dual core current transformers that are used in some modern static watt-hour meters where they should substitute the more expensive DC tolerant current transformer with linear hysteresis loop. It describes the problem of power consumption measurement on inductive or capacitive loads where some DC magnetic field is applied. In this case the core with high permeability is saturated and operating point is moved on hysteresis loop of low permeability core. Then additional errors occur and the sign of the error can be both positive and negative depending on load type. Dimension of errors can be in order from units up to tens of per cents and it relies on power factor and DC magnetic field. Explanation of this problem is described in the article as well as some results of measurements and comparison with theoretical computation.