A DC controlled reactor using thyristors

Saturable reactors are used widely to obtain an inductance dependent on the dc current in the control winding. These saturable reactors generate harmonics that may cause undesired harmonic resonances. This paper develops an inductor arrangement that generates negligible harmonics and the inductance varies almost linearly with dc voltage. The arrangement basically consists of a binary arrangement of inductors and a vernier inductor. The vernier inductor is used to provide smooth transition between discrete switching of the binary inductors. A control scheme using analogue and digital techniques is developed to monitor the firing of the thyristors for the switching arrangement. The system is analyzed and the experimental results are compared with the theoretical results. The system developed has maximum utilization of the thyristors and the maximum inductive kVA that can be controlled is limited by maximum available ratings of the thyristors.