Patent GB-648045-A (GB)
Title: Improvements in electromagnetic interrupters and circuits therefor
IPC: H02M7/62
Filed: 1948-11-12
Abstract: 648,045. Converting ; supply systems for space-discharge lamps. ERICSSON TELEPHONES, Ltd., WILMAN, C. V., and DIXEY, K. H. Nov. 12, 1948, No. 29389. [Classes 38 (ii) and 38 (iv)] A circuit fed from a direct-current source is periodically modified at interrupter contacts to produce an alternating-current in a load circuit including one or more gaseous discharge tubes, capacitors, and inductors, the load circuit forming a series-resonant circuit adapted to modify the wave-form of the alternating current therein and thereby to limit the current at the contacts at the instants of make and/or break, one or more relays being provided and adapted to operate automatically a pre-determined time after the connection of the directcurrent source to the interrupter contacts to modify the capacitance and/or inductance of the load circuit and thereby to maintain the said modified wave-form of the alternating current and the consequent limitation at the instants of make and/or break both before and after the gaseous discharge tubes strike. When contacts S1, S2, are closed, alternate currentpulses are supplied from a battery to the primary winding of a transformer TRA through vibratory contacts VB1, VB2, a time-delay relay A being simultaneously energized. The secondary circuit of the transformer comprises discharge lamps LPA, LPB, which are initially shunted by inductors LX, LY. The natural frequency of the transformer secondary circuit circuit is initially arranged so that the duration of a half-cycle of oscillation is substantially equal to the make-period of the vibratory contacts, the half-cycles being maintained in phase with the make-periods by means of the current-pulses supplied through the transformer TRA. When the lamps strike inductors LX, LY are short-circuited, the relay A being adjusted to operate substantially at this instant to energize a relay B which closes self-maintaining contacts B1, and then opens contacts B3 to de-energize the relay A. Contacts B2 are also closed to remove condenser C1 from the transformer secondary circuit and so compensate for the short-circuiting of inductors LX, LY, the natural frequency of the circuit being maintained at its initial value. The voltage applied to the load circuit is also reduced by the short-circuiting of a portion of the transformer secondary winding through contacts B2. Whilst the wave-form of the voltage applied to the primary winding of the transformer is substantially rectangular, that of each current-pulse in the secondary circuit is substantially sinusoidal, the reflected impedance in the primary circuit modifying the current-pulses passing through contacts VB1, VB2, so that their wave-form is approximately sinusoidal. The current passing through the vibratory contacts is thus of minimum value at the moment of making and breaking. One, for example the inductor LM, or a number of the inductors in the secondary circuit, may be saturable so as to have a non-linear relation between the inductance and the applied voltage. The capacitor C1 may be replaced by an inductor, capacitors being substituted for inductors LX, LY. The transformer TRA may be dispensed with. The Provisional Specification refers to the delayed switching operation being effected by a number of relays acting in sequence, any or all of which may be of the thermal, dash-pot, or telephone exchange types regulated by resistors, neon lamps, capacitors, or like devices.