| 摘要 |
1,102,017. Checking faults in multi-wire lines. INTERNATIONAL STANDARD ELECTRIC CORPORATION. June 18, 1965 [June 20, 1964], No. 25868/65. Heading G1U. [Also in Division H4] In a method of checking multi-wire connecting lines, such as used in an automatic telephone exchange, for earth faults, short circuits between wires of the line, or excessively low leakage resistances from wire to earth or between wires, the n different phases derived from a multi-phase alternating current generator G are applied to the n wires of a line 1 to be checked when the line is not in use, each phase being applied to a different wire, and the currents which flow in the wires and also in the neutral phase of the multi-phase A. C. are individually monitored. An indication of the nature of any fault which may be present is provided in accordance with the monitored currents. End to end conductance may also be checked. The phases from the generator G are connected to the telephone line 1 via the capacitors C and switches Vbl, the other ends of the line being connectable via the switches Vb2 and matching resistors R 1 -R n to earth. The currents in the various phases are monitored via the transformers U 1 -U n , while the current in the neutral phase M p is monitored by the transformer U o . The transformers are connected via amplifiers to an evaluating circuit A. To test for short circuits and leak currents either between a wire and ground or between wires, the switch Vb2 is left open. If current is detected in any one wire and in the neutral phase, a short circuit to ground is indicated, if it is detected in two wires, a shunt between these wires is indicated. To check the line for adequate conductance, the resistors H 1 -R n are switched into circuit via Vb2. If all wires are of proper condition, the generator feeds a symmetrical load and no neutral or zero current flows. If one wire is interrupted, no output is derived from its transformer and a fault is indicated. Faults which occur symmetrically on all wires may be detected by providing the generator with excess phases which are loaded correctly. Arrangements for testing three wire lines using fewer amplifiers than in the arrangement of Fig. 1 but involving more complicated transformers are discussed, Figs.2 and 3 (not shown). |
