GB936713A - Improvements in and relating to transformer tap-changing systems - Google Patents

Abstract

936,713. Transformers. BROWN, BOVERI & CO. Ltd. March 26, 1962 [March 28, 19611, No. 11413/62. Class 38 (2). On load tap changing of transformer winding 31 is carried out with current gates 35, 36 connected in opposed parallel relationship, control of these gates being provided by rectified pulses from the pulse generator 37, the rotor of which is mechanically coupled to main switch 34, resistance switch 39, commutator switch 38 and current gate contacts 42, an independent preselector switch 40 also being provided in series with resistance 41. The sequence of operations for transferring load from tap 31c to 31d commences with the pre-selector switch being set at 40b, the main switch 34 then opens and current flows along the shunt path through switches 38, 42. Switch 39 closes, connecting tap 31d through the resistance to both the load and tap 31c, and the current gates each receive a firing pulse which lasts until the contacts 42 open, the arcing which follows at the contacts producing a temporary operating voltage across the current gates and the gate having a favourable instantaneous direction of voltage conducts, thus shorting out switch 42. When the voltage next passes through zero the conducting gate is cut off and the change-over switch passes from 38a to 38b without current flowing. Switch 42 now closes to complete the main shunt path from tap 31d and switch 39 opens to disconnect the resistance, the change-over terminating with the main change-over switch closing on to 34b. The pulses are generated in stator windings 21a, 21b, 22a and 22b of the pulse generator, the rotor being a permanent magnet. A second embodiment (Fig. 2, not shown) is designed to remove sparking at switch 39 and has a second pair of current gates connected in opposed parallel relationship with each other but in series with the resistance 41, the gates being fired by pulses from additional windings in the pulse generator.