Patent GB-658025-A (GB)
Title: Electromagnetic relay system
IPC: G01R31/02
Filed: 1949-04-23
Abstract: 658,025. Detecting faults. HAIN, F. B. L. April 23, 1949, No. 10815. [Class 37] [Also in Group XXXVII] An electromagnetic relay system for detecting faults in installations is arranged to give responses distinguishing between a small leak, a single lamp in circuit, and a larger load such as a resistance put in circuit by a fire alarm. A relay A, Fig. 1, has three windings 1, 2, 3, mounted on a common iron core, and two armatures of which one is actuated by the windings 1, 2 and the other by the winding 3. A load circuit B is connected by a manual switch 6 either to the A.C. main R or, in the position shown, to the relay A through contacts 6a, 6b, and a D.C. source L such as a rectifier. If there is a small insulation fault in the circuit B, a weak current flows in the windings 1, 2, 3. The winding 1 has a large number of turns and attracts its armature, operating the switch 4 and breaking the circuit at the contact 4a. The windings 2, 3 have insufficient turns to hold the armature attracted, so that the armature vibrates and makes and breaks at the contact 4c the circuit of a relay 10 causing a bell 14 to sound intermittently. If a small load 8a such as a lamp is connected to the circuit B whilst the switch 6 is in the " off " position shown, the winding 1 attracts its armature and operates the switch 4, disconnecting the winding 1 at the contact 4a. Current from the A.C. supply passing through contact 4b and the winding 2 is sufficient to maintain the armature in the attracted position and the bell 14 is sounded continuously. The circuit of the relay 10 may also be opened by a door contact 13 and the bell then sounds continuously. If a greater load is connected to the circuit B, for example a low resistance 9a connected by a fire alarm contact, the A.C. current through the windings 2, 3 is sufficient to cause the winding 3 to attract its armature and operate a switch 5. This interrupts the circuit of a relay 15 at contact 5b and sounds a fire alarm 16. The winding 2 connected to the A.C. supply at contact 4b is at the same time short-circuited by the contact 5a. The relay system is also arranged to indicate faults in three-phase motor or other A.C. load circuits C, D. The switch 11 controlling the circuit C has auxiliary contacts 11r, 11s, 11t, which are closed when the switch is opened and through which each phase is connected to the relay A through a contact 6d of the switch 6 and a resistance 17 to protect the winding 3 against short-circuit currents. The switch 12 controlling the circuit D is similarly provided with auxiliary contacts 12s, 12t. A rotary multiple switch E comprises a series of cams 18 ... 24 driven by a motor 25 and operating switches 18a ... 24a in succession so that the relay circuit is connected successively to the three phases of the load circuit C. The relay circuit also responds to insulation faults in the circuit D during the same intervals as in the phases S, T of the circuit C. The contact 24a actuated by the last cam 24 controls the connection of the negative terminal of the rectifier L to earth. By observing on a dial 27 during which of the cyclic intervals the bell 14 or alarm 16 is sounded, the faulty phase may be determined. The relay A is shown in Fig. 2. An H-shaped iron core 31 has a high resistance winding 33, corresponding to 1, Fig. 1, on one leg 32 and a winding 35 of lower resistance corresponding to 2, Fig. 1, on the adjacent leg 34. The other two legs 36 each carry one half of a low resistance winding 37, corresponding to 3, Fig. '1. The legs 32, 34 attract a straight bar armature 38 fixed to a U-shaped support 39 which is carried by a pivoted axle 40. The armature 38 is provided with projecting blades 41 which enter recesses 42 in the pole faces as the armature is attracted, in order to reduce the reluctance. The axle 40 carries a mercury switch 43 which corresponds to the switch 4, Fig. 1. The legs 36 attract an armature 44, similar to the armature 38, carried by a U-shaped support 45 which is mounted on an axle 46. The armature 44 is also provided with a contact bridge 47 which in the attracted position engages two contacts 48, forming the contact 5a of switch 5, Fig. 1. The armatures 38, 44 are interconnected by links 49, 50 and a lever 51 pivotally mounted in the casing. The link coupling maintains the armature 38 in its attracted position when the armature 44 is in its attracted position, even though the armature 38 is not attracted. The link 49 is connected to the support 39 of the armature 38 by means of a slot-and-pin joint 52, so that attraction of the armature 38 does not cause the armature 44 to be positively moved into its attracted position.