US1927479A - Switch controlling means - Google Patents

Description

p 1933- G. H. WHITTINGHAM 1,927,479

SWITCH CONTROLLING MEANS Filed Feb. 8, 1932 Patented Sept. 19, 1933 UNITED STATES PATENT OFFICE SWITCH CONTROLLING MEANS Application February 8, 1932.

2 Claims.

This invention relates to improvements in electromagnetic switches or contactors, adapted for use on alternating current circuits. Contactors are generally designed to suit a voltage in the supply wires which is kept constant except when trouble arises on the power line or at the central station which may cause temporary lowering of the voltage or complete failure of current. As long as the voltage is normal, the usual form of contactor will operate satisfactorily; but if, while the contactor is closed, the voltage dies away on the line to the point where the switch starts to open, introducing a gap in the magnetic circuit, the reactance of the magnet coil will be lessened and the current flowing through the coil will be increased, causing attraction of the armature toward the magnet, with a resulting decrease in current in the coil, and these back and forth fluttering movements of the switch arm will cause burning and perhaps welding of the contacts, if long continued. Again, if current fails in the supply circuit while the contactor is closed, the switch arm will fall to open position and if the current returns to the wires with gradually increasing voltage, the switch arm will approach the closed position before the voltage on the supply circuit becomes normal and will flutter and burn the contacts. In such case, if the subnormal voltage is long continued, the coil of the contactor magnet may be injured by the excess current which it takes, and apparatus, such as induction motors, on the work circuit which the contactor connects to the supply circuit may become overheated and burned out.

By means of the present invention, in case the voltage drops to a predetermined point, the contactor will open without fluttering of the switch arm or burning of the contacts, and if the current on the line fails and then returns, the switch '40 will not close until the voltage of the supply circuit is practically normal, thus preventing injury to the switch contacts and magnet coil and to motors, etc. on the work circuit. In the accompanying drawing, The figure is a diagrammatic view illustrating the preferred form of the invention, and,

Referring to the drawing, L and L indicate supply wires leading from an alternating current source, and a indicates a contactor adapted to complete a circuit from the supply wires to a load such as lamps or an electric motor. The contactor comprises an armature 1 hinged to one end of a U-shaped core 2 of a magnet b and adapted to form a closed magnetic circuit through the core when the con- Serial No. 591,701

tactor closes and the armature engages the opposite end or" the core. One side of the load circuit extends from conductor L through conductor 3 to stationary contact 4, thence through the contactor arm to conductor 5. The other side of the load circuit is indicated at 6, extending from the supply wire L.

The circuit for the coil of the magnet 12 extends from conductor 6 through a switch 7, resistance 8 and conductor 9 to the coil 10 of a relay 0, thence by conductor 11 to the coil 12 of the contactor magnet, thence by conductors 13 and 3 to the side L of the supply circuit. The resistance, relay coil and. the magnet coil of the contactor will thus be normally connected in series. The function of the relay is to close a shunt around the resistance. One terminal of the resistance is connected by conductor 14 to relay contact 15 and the other terminal of the resistance is connected by conductor 16 to contact 17. As shown, 7 the relay comprises an iron core 18, within the coil 10, suspended by a spring 19 from an adjustable supporting screw 20. A metal bridge piece 21 is arranged on the relay core below the contacts 15 and 17. When the coil 10 is energized 0' sufficiently, the core lifts and the part 21 bridges the contacts, thereby short-circuiting the resistance; and when the core drops, the resistance is again placed in series with the coil of the relay and contactor magnet. The amount of resistance 5 in series with the coils may be adjusted as desired by means of a contact arm 22 connected to the shunt conductor 14 and adjustable along the resistance,

The operation of the invention as illustrated in the drawing is as follows: Assuming the line voltage to be normal, when the switch '7 is closed current will flow in series through the resistance 8 and coils 10 and 12. The current value will be below that required for causing the contactor magnet to actuate its armature but it will be suflicient to cause the relay to lift its core and bridge the contacts 15 and 17, thereby shunting the resistance 8. A greater current flow will immediately follow in the coil 12 and the magnet b will attract the armature l, and the armature will close the magnetic circuit through the core 2. This will instantly increase the reactance of the magnet coil 12 and the current flowing through this coil and the relay coil will be reduced to such an extent that the relay core will immediately drop and open the shunt around the resistance 8. Thereafter, as long as the line voltage is normal and the switch '7 remains closed, the resistance 8 will remain in series with the coil of the contactor magnet. It will be seen that the resistance is in series with the coil of the contactor magnet at the start; that it is momentarily cut out to increase the current flow through magnet coil of the contactor so that the magnet will have sufficient strength to close the switch arm, and the resistance is then again inserted in series with the magnet coil, reducing the current flowing through the coil while the switch is closed.

If, now, while the contactor is closed, the voltage on the supply wires is reduced, from any cause, to the point where the magnet will release its armature, the switch arm will drop back to its open position without fluttering and burning of the contacts, because the resistance in series with the magnet coil will prevent the heavy surges of current in the magnet coil which would result from opening the magnetic circuit if theresistance were not present. After the contactor has opened, by reason of lowered voltage, the switch cannot close until the voltage again builds up to practically normal voltage, and during all the time that the voltage is subnormal, the resistance will prevent the magnet coil from receiving excessive current. As the voltage returns to normal, and when within a volt or two of normal, the relay will operate to bridge the resistance and the magnet coil will receive the heavy current required to cause the magnet to close the switch. Immediatelv thereafter, the reactance of the magnet coil will so reduce the current flowing in the relay coil that the relay will be de-energized and open the shunt around the resistance, leaving the latter in series with the magnet coil.

What I claim is:

1. The combination with an alternating current supply circuit, a normally open switch, a magnet for closing said switch and a circuit for the coil of the magnet connected to the supply circuit, of a. resistance in series with said coil sufficient to prevent the magnet from closing the switch while the voltage in the supply circuit is below a predetermined value, and a relay having a coil connected to the supply circuit in series with the coil of said magnet, said relay adapted to cut out the resistance when the voltage approximates said value. to permit the magnet to close the switch, and to re-insert the resistance when the switch has closed.

2. The combination with an alternating current supply circuit, a normally open switch, a magnet for closing said switch, and a circuit for the coil of the magnet connected to the supply circuit, of a resistance in series with said coil suflicient to prevent the magnet from closing the switch while the voltage in the supply circuit is below a predetermined value and a relay having a coil connected to the supply circuit in series with said magnet coil and with said resistance, said relay adapted to cut out the resistance when the voltage approximates said value, to permit the magnet to close the switch, and to re-insert the resistance when the switch is closed.

GEORGE H. WHITTINGHAM.

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