GB330969A - Improvements in or relating to the control of electrical transformers - Google Patents

Abstract

330,969. Weekes, W. March. 20, 1929. Systems depending on static transformers.-In a supply system including a transformer applicable to supply a direct current circuit through mercury-arc rectifiers, in order to prevent the rush of current when the transformer is re-connected to the load after operation of the automatic cut-outs in the load circuit provision is made for automatically reducing the secondary voltage when the load is above a predetermined amount. This may be effected by choking coils in the primary or secondary circuits which are normally short-circuited by automatic switches controlled in accordance with the load current, and the choking coils may further be arranged to be in circuit on the initial switching-in of the supply. As shown in Fig. 1 applied to a transformer having a star-connected primary 1 the choking coils 4 are arranged in the connections to the starpoint 3 and are adapted to be short-circuited by automatic switches 6. A similar arrangement may be employed with a star-connected secondary winding. In the case of a delta-winding the choking-coils with their automatic short-circuiting devices are included in the line connections. The complete control arrangement employed in connection with the modification according to Fig. 1 is shown in Fig. 4 in which the 6-phase secondary winding supplies a D.C. load circuit 10, 11 through a mercury-arc rectifier 8. A time lag relay 12 is connected across lines 10, 11 and completes the circuit of a relay 15 which in turn completes the circuit of a relay 19, the movement of which controls the automatic short-circuiting switches 6 on the primary side. Thus on switching in a 'reduced voltage is first supplied. If the load-conditions are unsuitable for the full-voltage the relay 22, the winding of which is across a resistance 23, by opening contacts 17 prevents operation of the relay 19 and switches 6. The relay 19 on operation completes a maintaining circuit through contacts 21 under the control of the overload relay 24 so that a reduction of voltage is produced immediately this relay is operated. In a further modification in which choking coils having an intermittent rating may be employed, three-contact automatic switches are employed which after opening the short-circuit around the coils move to a further position in which a lower voltage transformer tapping is connected.