Pin Sensor for Interior Induction Measurements in Transformer Cores

This paper concerns, the problem to assess 3-D distributions of magnetic induction in soft magnetic systems like machine cores of transformers or generators. Within bulk material, estimations of distributions are restricted to numerical methods like FEM, the application of sensors being hard. On the other hand, in laminated material, the conventional method is to use single-turn search coil sensors arranged in holes through the laminations. As drawbacks, the method is extremely laborious, and it causes artifacts due to the formation of interlaminar air gaps. This paper presents a completely novel alternative that is applicable in systems of both laminated and bulk material. Instead of single holes, measurement channels (e.g., 3 mm width) are established through the whole system. A soft magnetic pin (e.g., 2.5 mm diameter) with pickup coil is used as an a priori calibrated dummy sensor. It determines an induction profile along the channel in a fully automatic way. The effectiveness is demonstrated for the case of a 3-phase transformer core. Induction profiles through a core-limb of three packages of different width are presented in correlation with corresponding loss profiles, as detected in an analogous way.