GB658749A - Commutating and interrupting process, applicable particularly to high tension electric rectifiers and converters - Google Patents

Abstract

658,749. Switching systems; converting. TOULON, P. M. G. Dec. 31, 1947, No. 35103. Convention date, Jan. 8, 1946. [Classes 38 (ii) and 38 (iv)] To prevent sparking at interrupter contacts, more particularly at the brushes of a converter of the rotating brush type, a negative feed-back electric valve system is arranged to suppress the voltage across the contacts just prior to their closing and to suppress the current passing through the contacts just prior to their opening. As shown in Fig. 1 a load 202 is connected for a short period to a source 201 through a switch comprising a fixed contact 204 and a motordriven contact 203, sparking between which, as the moving contact engages and disengages the fixed, it is desired to prevent. For this purpose the contacts are shunted by auxiliary contacts 214, 215 having a slight lead on contacts 203, 204 and in series with a potential divider 216, 217, so that just prior to closing of the main contacts 203, 204 the auxiliary contacts are closed and a fraction of the voltage then across the main contacts appears across 216. After amplification at 219 this voltage is applied over contact 212 of a synchronously driven changeover switch 212, 213 to the grid of a valve 210 the anode current change of which induces in a coupled coil 207 in the load circuit a voltage annulling that across the main contacts. A further amplifier 218, energized by a resistor 206 in the load circuit, is connected to the grid of valve 210 by contact 213 of the changeover switch as the auxiliary contacts 214, 215 separate, whereby the valve supplies to coil 207 a voltage such as to reduce the load current to zero. Fig. 3 shows an A.C. to D.C. converter comprising transformers 5-10, 5<SP>1</SP>-10<SP>1</SP> so connected to a three-phase source 1-4 as to give a twelve-phase output. The secondary winding of each transformer has five equally-spaced tappings and the total sixty tappings are connected to two staggered commutators 19, 20 having thirty segments each. The D.C. output is taken from pairs of main brushes 27, 28, 271, 281, which rotate about the commutators, through valves 29, 30, 291, 30<SP>1</SP>, which are gridcontrolled for current regulation by a controller 28<SP>11</SP> responsive to the voltage drop across shunts in the output conductors. Auxiliary brushes 31, 32, 31<SP>1</SP>, 32<SP>1</SP> leading the main brushes and directly or capacitively engaging the two commutators may also control the device 28<SP>11</SP>. The commutating voltages are supplied by a synchronously-driven generator 33 and injected into the brush leads by transformers 34, 341.