Detector circuit to be used for measuring current
A detector circuit to be used for measuring current and including a main current transformer and two substantially identical auxiliary current transformers, where magnetomotive forces are induced by a main current, said magnetomotive forces being counteracted by magnetomotive forces induced by a compensating current (i 4 ) in a compensating winding (L 4 ) across at least two annular cores ( 2, 3 ) at the same time as the two auxiliary current transformers are magnetized in antiphase by means of a modulation signal, said circuit further including a synchronous rectifier for providing an adjustment signal for the compensating current (i 4 ). According to the invention, the compensating winding (L 4 ) is formed by a so-called “pilgrim winding”. A pilgrim winding results from one section being wound at a time, and it presents the property that the potential difference between the individual winding layers is smaller than in connection with conventionally wound transformers where one layer is wound at a time in the longitudinal direction of the entire core. As a result the undesirable capacitive currents between the windings have been significantly reduced, viz. the so-called neighbouring effect. In other words, the parasitic capacities between the windings have been reduced. In addition it turned out that the use of such windings implies that the undesirable resonances are elevated to such an extent that they no longer interfere with the measuring procedure.
1. A detector circuit for measuring high current, the circuit comprising:
a main current transformer;
two substantially identical auxiliary current transformers each including an annular core, wherein magnetomotive forces are induced by a main current, said magnetomotive forces being counteracted by magnetomotive forces induced by a compensating current in a compensating winding across at least the two annular cores of the auxiliary current transformers at the same time as the two auxiliary current transformers are magnetized in antiphase by means of a modulation signal; and
a synchronous rectifier for providing an adjustment signal for the compensating current;
wherein the compensating winding for the compensating current across at least the two annular cores is comprised of a continuous conductive element wound to form a plurality of layers of the conductive element which are non-sequentially wound in relation to each other in such a manner that the potential differences between the plurality of winding layers are reduced to a minimum.
2. A detector circuit according to claim 1 , wherein the compensating winding across at least the two annular cores is a pilgrim winding.
3. A detector circuit according to claim 1 , wherein the compensating winding across at least the two annular cores is a sectional winding.
4. A detector circuit according to claim 1 , further comprising:
an AC-pick-up winding wound as a pilgrim winding or a cross-winding so as to reduce the potential difference between winding portions close to each other to a minimum.