Experimental study of current error of up to 50 hz current-measuring transformer

When using a variable-frequency drive at low and extra-low frequencies, it is difficult to control the current value. Standard current transformers are often used. This paper analyzes the transformer performance at frequencies below the industrial one. The objective is to study operation of the process transformer connected to an adjustable current source experimentally. The paper proves that frequency drop results in excitation current rise, core saturation, and a significant increase of the transformer current error. There are secondary current traces at various degrees of the transformer's core saturation. The authors have studied the effect of both measured current and burden resistance values experimentally on the current-measuring transformer's error within low frequency range. They give some practical advices and solutions related to the use of current transformers when measuring alternating current within the range below 50 Hz.