Patent GB-190520269-A (GB)
Title: Electric Mains Telephone and Fault Detector, for use on Continuous Current Mains of Electric Light System
Inventor: CARR IVAN ARTHUR
Filed: 1905-10-07
Granted: 1906-09-27
Abstract: 20,269. Carr, I. A. Oct. 7. Testing.-Relates to arrangements for telephonic communication and for indicating and testing faults on two- or three-wire continuous-current lighting-systems. The circuits of both the transmitter and receiver are connected inductively with the line-wires. Call signals between the central and out stations may be made by the line current, or by the microphone battery when the line current is off. Fig. 1 shows the circuit arrangements at the central station, and Fig. 2 those of a portable or out-station apparatus. The receivers K are in series with the secondaries of two induction coils L, M, the primaries of which are in the microphone and line circuits respectively. At the central station the neutral bar of the dynamo is earthed through the primary of a transformer S the secondary of which is in circuit with the relay R controlling the call or alarm bell E<2>. At the out station, the call-bell E<1> is in shunt with the socalled liquid transformer D, comprising lead plates in dilute sulphuric acid. C', C', C<3> indicate fuses, B<1>, B<2> incandescent lamps, and A<1>, A<2> G, F<1>, F<2>, T switches. The switches G are normally on their centre contacts, and the switches A' closed. To call the central, the switch G is placed on the right stop, and the switch A<2> closed, current then flowing from the outer wire through switches A<2>, A<1>, and earth to central and through the primary of the coil S to the neutral bar, thus inducing a current in the secondary and ringing the bell E<2>. When a fault occurs, current flows in the same way from the grounded outer wire through the primary, thus ringing the bell E<2>. To distinguish a telephone call from a fault alarm, the switch T is opened; if it is a fault the current will flow through the terminal N, switch A', lamp B<2>, and the switch G to the neutral wire, lighting the lamp B<2>. The degree of brilliancy of the lamp gives approximately the size of the fault. A call can also be made by placing the switch G on its right stop and pressing the button H, thus connecting the microphone battery I to earth and to the neutral wire. When the central calls the substation, current flows from the neutral wire through the switch G, Fig. 2, lamps B<2>, and the "transformer " D to earth, ringing the bell E<1>. For telephonic communication, the switches G are placed on their left stops. The current induced in the secondary of the coil L by the microphone current in turn induces current in the primary of the coil M, this current flowing through the switch G to the neutral wire, and thence through the switch G at the other station and coil M to earth. In order to test the neutral wire for a fault, the switch T is put off and the switch A<2> on. If there is a fault, current flows from an outer wire through the switch A<2> and lamp B<1> to earth, the lamp B<1> only lighting up. If there is no fault, current flows through the switch A', lamps B<1>, B' in series, and switch G and back to the neutral wire, both lamps lighting up. When the telephonic communication is interrupted due to faults, signals can be sent to out stations by means of the switch T.