762,603. Sparking preventing in switches; oil-break switches; protective cut-out systems; automatic circuit - breakers. F. K. G. F. KESSELRING GERATEBAU AKT.-GES. March 25, 1954 [March 25, 1953; June 20, 1953; Aug. 29, 1953; Dec. 17, 1953; Feb. 22, 1954], No. 8809/54. Class 38(5) To prevent 'sparking at the contacts of a switch s, Fig. 1, an impulse is fed to the switch in opposition to the main current I from a shunt circuit including a condensor c, resistance R and inductance L, by the closing of an auxiliary switch sc at. or about the instant when switch s is opened, the maximum value of the impulse current being at least 80 per cent of the momentary value of the main current and the half-value duration of the impulse being at the most 1 millisecond. Suitable means are provided for charging the condenser. In a D.C. arrangement (Fig. 2, not shown) the condenseris replaced by a battery. An A.C. arrangement wherein the impulse current is made proportional to the instantaneous value of the main current is shown in Fig. 7, the condenser c being charged through a current transformer 2 connected in the main circuit across a resistor 1. Any residual current flowing through the impulse circuit may be broken by the switch sc or a residual current switch s1 which is closed with switch s. A resistance r in parallel with a switch s brings the residual current into phase with the generator voltage and the recovery voltage to aid interruption by switch s1. Also any residual magnetic energy in the circuit is converted into heat in the resistance r. The resistor 1 may be placed by an inductance in parallel with which is a resonant circuit tuned to main frequency. Alternatively a D.C. generator may charge the condenser, the excitation thereof being effected by the main current. A constant value of condenser voltage may be used and the constants c, L and R adapted to the instantaneous value of the main current so that the amplitude of the impulse current automatically adapts itself to the momentary value of the main current. Thus in the D.C. arrangement shown in Fig. 8, the inductance L comprises one winding 22 of a choke 20, another winding 23 being connected in the main circuit and the condenser c being charged from a battery, so that the higher the main current, the higher premagnetization of the choke and the smaller the effective inductance. In the A.C. arrangement shown in Fig. 9, a condenser 54 is charged with a voltage proportional to the main current through a current transformer 51 and is connected, through electrodes 51 of a quadruple spark gap, in parallel with the primary winding 63 of a transformer 62. The auxiliary electrodes 58 of the spark gap are connected to the ends of a choke 59 in the main circuit and the secondary winding 64 of transformer 62 has tappings a1...a4 connected to one side of impulse condensers c1...c4 which are charged from a constant source 66 and are connected in series with spark gaps F1...F4 and inductances L1...L4. On opening of the switch s, gap 57 breaks down and condenser 54 disdischarges through winding 63. According to the magnitude of the discharge, a corresponding number of the gaps F1...F4 will be bridged with consequent discharge of the relevant condensers so'that an impulse proportional to the main current is produced. The spark gaps may be quenched with the arcs at switch s or a residual current will flow which may be broken by switches sl, spark gap 57 may be set so that it breaks down at a predetermined value of the main current or is triggered by electrodes 58 at a particular rate of charge of main current, switch being simultaneously tripped. Figs. 10 and 11 show a further arrangement wherein switch s is contained in a casing 119, preferably liquid filled, together with condenser c, inductance L and switch s1. Switch s comprises a liquid or gas-filled casing 86 carrying fixed contacts 89, 90. The bridging contact 91 is operated by a plunger 92 passing through a partition 93 above which is a spring- loaded piston 97 movable with the plunger, the spring holding the switch closed. Plunger 92 is operated by a lever 108 and rod 113. Condenser c is separately charged and inductance L forms one winding 84 of a choke having a premagnetizing winding 84a in the main circuit so as to produce an impulse current proportional to the main current. Actuation of rod 113 manually or electromagnetically opens switch s and bridge 91 engages contacts 102, 103 connected to electrodes 94, 95 of a spark gap F. This completes the impulse circuit through the main contacts 89, 90 and continued rotation of lever 108 causes its outer end to depress a plunger 107 to open the contacts 104. 106 of the auxiliary switch s1 and interrupt the residual current. In the case of a short-circuit, gap F is triggered by an auxiliary electrode F1 and the arc set up across electrodes 94, 95 heats the air below plunger 97 which drives the latter upwards to open switch s and close the impulse circuit. Switch s1 may be subsequently opened by energizing actuating coil 116. Means for limiting the voltage at the condenser in a highly inductive circuit may be provided comprising, for example, a spark gap in parallel therewith so that when, after opening of the main switch, the condenser voltage rises to a predetermined amount, the gap breaks down, the residual current being broken by the gap or the auxiliary switch (Figs. 13-15, not shown). Fig. 16 shows a D.C. circuit wherein, a horn gap 231 shunts condenser 230 and series resistor 232. The auxiliary switch 226 is interconnected with the main switch 223 and is closed before the latter opens. In Fig. 17, the main switch 243 is operated by a coil 247 energized from the impulse circuit when the auxiliary switch 248 closes. With moderate inductance in the main circuit excessive voltage at condenser 255 is prevented by resistance 256 but with high inductance horn gap 258 breaks down and places resistance 257 in circuit, a magnetic blow-out coil 259 in this case assisting quenching of the arc. Automatic interruption is effected by a current transformer 253 in the main circuit, the secondary winding being connected to an ignition electrode 250 in the auxiliary switch. An arrangement for preventing reversal of polarity of the condenser in an A.C. circuit after it has discharged is shown in Fig. 18. The condenser 280 is shunted by a switch 284 linked to the main switch 273. As the latter opens and the condenser discharges, switch 284 closes almost immediately and cuts out the condenser. The residual current is broken by auxiliary switch 277. A further arrangement suitable for a D.C. circuit is shown in Fig. 19. Current passes to the main switch 302 through a holding winding 305, thence through a choke 316 and the primary winding of a current transformer to the load 323. The condenser 313 is connected in parallel with the supply through a charging resistor 314 and the negative plate is connected to the auxiliary switch 307, a holding winding 310 of which is connected in parallel with a resistor 312 in the main circuit. The current transformer assists charging of the condenser through a rectifier 322 in the event of a large rate of charge of current so that the impulse current may be of the same order as the main current. On discharge of the condenser by closure of switch 307 either manually or by winding 310, the current through the main switch is reduced so that the holding winding 305 releases and the arc is quenched. The residual current is broken by switch 307. A rectifier 324 may replace choke 316 if no reversal of current is desired through the main switch. Figs. 22, and 23 show arrangements -wherein ion an A.C. system automatic opening of the main switch is effected when the main current reaches predetermined positive or negative value. In Fig. 22 the main switch 404 has an operating winding 408 connected to a multiple spark gap 411...414 having auxiliary electrodes 415...418 connected to the secondary windings 423 and 424 of chokes 419, 420 having premagnetizing windings 421, 422 and being subjected to the field produced by the main current. Thus an excessive positive value of current overcomes the premagnetization of choke 419 and the voltage induced in winding 423 triggers auxiliary spark gaps 415, 417 and discharges the separately charged condenser 409 through spark gap 414, coil 408 and the main contacts 405, 406. An excessive negative value of main current causes choke 420 to trigger gaps 416, 418 and the condenser is discharged in the opposite direction. An auxiliary switch 425 in parallel with load may be used for arbitrary opening of the main switch, the current flowing on closure of the former being sufficient to cause one of the chokes to trigger the spark gap. In Fig. '23 which is equally applicable to a D.C. system, a component of the main current, determined by a variable resistor 443, operates an oscillating switch 451. If the current exceeds a predetermined value in either direction the arms 452, 453 of switch 451 will engage one of the pairs of contacts 458, 459, or 456, 457 and discharge condenser 447, which is charged from a supply 450, through the operating winding 436 and contacts of the main switch 432. The impulse current may be superimposed on the main A.C. current near a passage of the latter through zero whereby a weak-current condition is produced during which the switch is opened. Thus in the circuit for a synchronously controlled switch shown in Fig. 28, condenser 507 connected across an inductance 514 is charged to a voltage proportional to the main current, and the voltage across the inductance and resistance 513 is impressed through a transformer 517 and battery 519 on the grid 512 and anode of a triode 509 in the impulse circuit. As the main current increases the grid 512 is negatively biased but as the current falls the sign of the voltage drop across induc