Electric-lighting system.

Application filed October 26, 1910. Serial No. 589,254.

To all whom it may concern:

Be it known that we, Edgar Booth and Norman Russell Booth, subjects of His Majesty the King of Great Britain, residing at Halifax, in the county of York, England, have invented a new and useful Improvement in Electric-Lighting Systems, of which the following is a specification.

It has been proposed to arrange electric incandescent lamps connected in series in such manner that when a lamp of the series becomes inoperative the circuit is automatically completed through a shunt circuit to such lamp thereby maintaining the flow of current to the remaining lamps in the series. This has been effected by interposing in some part of such shunt circuits metal pieces which are separated by insulating material which will withstand the electro-motive force thereat when the lamps are in a normal operation but which on an increase of electro-motive force thereat owing to a lamp becoming inoperative will be destroyed and then contact will be made between the metal pieces so as to conduct the current through the shunt circuit and the remaining lamps of the series are maintained in operation. Now in an arrangement of this kind all that has hitherto been relied upon to break down or destroy the insulating material in the shunt circuit is the above referred to increase of electro-motive force in such circuit consequent upon a lamp of the series becoming inoperative and in practice it has been found to be very difficult to so arrange the metal pieces and the insulating material separating them that in every case this rise of electro-motive force shall be sufficiently great to break down or destroy the insulating material and thus establish the shunt circuit, so that this arrangement has been unreliable in operation. It has also been proposed to produce a rise of potential sufficient to insure the breaking down of the insulation by placing the lamps in series with the secondary circuit of an induction coil the primary coil of which is arranged to be momentarily traversed by a current from the mains upon the failure of a lamp.

According to the present invention a single circuit self-induction coil is employed and the necessary rise of potential is produced by the “ extra current ” induced by the instantaneous and complete interruption automatically or otherwise of a circuit shunting the lamps and in which the self induction coil is included as hereinafter explained with reference to the accompanying drawings.

The improvements comprising the present 6C invention are illustrated by way of example in the accompanying drawing, in which—

Figure 1 is a diagrammatical representation of a system of installation: and Fig. 2 is also a diagrammatical representation of a 65 modified arrangement.

Referring particularly to the drawings. Fig. 1 illustrates four incandescent lamps a arranged in series in the usual manner across the mains g and h each lamp having a shunt 0 circuit d containing metal pieces k k which are prevented from coming into metallic contact by the insulating material m which preferably consists of a piece of paper, c is a shunt wire across the mains g and h Ίξ> containing a resistance r and a switch s by means of which the shunt circuit c may be broken or interrupted. It is essential for the successful breaking down of the insulating body m that the break in the shunt cir- 80 cuit should be as instantaneous as possible and a simple and efficient way of doing this is to break such circuit at two or more points simultaneously. In Fig. 1, the switch s is shown to break simultaneously at two 85 points viz:—at t and v. n is an electromagnet and is common to 'both the circuit comprising the lamps a in series and the shunt circuit c. When the lamps a are in a normal operation the switch s is open and 90 consequently the shunt circuit e is not completed. On the series circuit being interrupted by reason of one of the lamps a becoming inoperative, the shunt circuit c is completed and broken by closing and open- 95 ing the switch s and as the electro-magnet n is also contained in this circuit, on breaking it the “extra current” above referred to is produced. The effect of breaking this shunt circuit at two or more points simultaneously ¹⁰⁰is to prevent the “ extra current ” from arcing across the points of interruption and to force it to pierce and break down the insulating material m separating the metal pieces k k thereby allowing them to come ¹⁰⁵into contact and thereby reestablishing metallic continuity in the circuit comprising the lamps in series. It will be readily xinderstood that the shunt circuits may include a body r' the resistance of which is ap- ¹¹⁰proximately equal to the resistance of the filament to which it forms a shunt but such

1,024,495 resistance should preferably be a non-inductive resistance. The function of these resistances r' one of which is thrown into the circuit when insulating pieces k are broken down is to choke the current so that no injurious impulses can injure the lamps which are still lighted.

By means of the above described arrangement metallic continuity in the series circuit may be immediately reestablished on a lamp becoming inoperative by operating the switch s as above described, but it has the disadvantage that it is not automatic and all the lamps in the series are liable to be extinguished until the switch s is so operated. The following arrangement obviates this latter disadvantage and automatically reestablishes continuity in the series circuit upon a lamp becoming inoperative.

Referring to Fig. 2, this again illustrates four incandescent lamps a arranged in. series across the mains <7 and h each lamp as before having a shunt circuit d containing metal pieces k k separated by insulating material in, and resistance r'. c is the shunt circuit across the mains g and h containing the resistance r, and n is the electro-magnet common to both the circuit comprising the lamps a in series and the shunt circuit c. f is an iron armature attached to a spring I and to which latter is also attached the contact piece j. The normal position of the contact piece j by reason of the spring I is in contact with and bridging the terminals t and v.

The manner of operation is as follows:—· On supplying current to the mains g and h if there is continuity in the series circuit, as the electro-magnet n is contained in such circuit, the armature f is attracted to it and the shunt circuit c is broken simultaneously at t and v. Let it now be assumed that the filament of one of the lamps a breaks. The series circuit being thereby interrupted the armature f is released and the contact piece j again comes into contact with and bridges the terminals t and v. This establishes the shunt circuit c and as the electro-magnet n is also contained in this shunt circuit it is again excited and the armature f is attracted. This has the desired effect of breaking the shunt circuit at two points simultaneously viz:—at t and v, the extra current is produced and as hereinbefore de scribed breaks down the insulating material 55 in the circuit which forms a shunt to the lamp the filament of which, has broken. Metallic continuity in the series circuit having been reestablished the armature f remains attracted to the magnet n by the cur- 60 rent flowing through the series circuit and the shunt circuit c remains broken.

The thickness of the insulating material and of the pieces of metal separated thereby are shown increased in both the figures in 65 order to better illustrate them.