GB773466A - A pulse echo fault locator - Google Patents

Abstract

773,466. Pulse echo testing systems. HARTMAN & BRAUN AKT.-GES. Aug. 10, 1955 [Aug. 10, 1954], No. 23036/55. Class 40(7) A pulse echo test equipment for detecting faults in an electric transmission line includes a device for measuring the time taken for a pulse to reach a fault and return wherein a steady current is caused to flow through a suitable measuring instrument from the time of transmission of a pulse to the time of the return of the first echo pulse. The current is switched on and off by means of grid controlled thyratron valves. In the embodiment shown the transmitting circuit consists of a condenser C<SP>1</SP> which is charged from a D.C. source when spherical electrodes K<SP>1</SP> and K<SP>2</SP> are in contact. Movement of electrode K<SP>1</SP> over into contact with electrode K' against the action of spring F causes a pulse to be applied to line L the polarity of which is dependent on the position of reversing switch, u. Positive pulses are applied to the line to check for an open circuit fault and negative pulses to test for a short. In either case the arrangement. of the earth points, resistor R<SP>1</SP> and potentiometer a is such that the transmission to be applied to the indicator unit from the slider of potentiometer a and the appropriate echo pulse applies a positive impulse over he same line. Before operation none of the cathode coupled thyratron valves T<SP>1</SP>, T<SP>11</SP> or T<SP>111</SP> is conducting. The negative impulse corresponding to the transmission of a pulse does not affect T" but its application to differentiating circuit b causes a sufficient positive pulse to be applied to the grid of T<SP>1</SP> to initiate a discharge. Current then flows through ammeter D, ballistic galvanometer measuring instrument G, screened grid valve SR, thyratron T<SP>1</SP> and cathode resistor e. Arrival of an echo pulse has no effect on T<SP>1</SP> but causes T<SP>11</SP> to fire. Current through T<SP>11</SP> increases the potential drop across e sufficiently to cut off T<SP>1</SP> and terminate the current flow through the measuring instrument. T" itself is subsequently cut off by the termination of the discharge from capacitor f. The valve SR stabilises the current flow through the measuring instruments and its anode and screen grid potentials are chosen to suppress any slight residual discharge that may otherwise pass when the thyratron T<SP>1</SP> is nominally non- conductive. A compensating circuit g is connected across galvanometer G to prevent errors arising due to the time of growth and decay of current in the galvanometer coils. To protect the galvanometer against overloading it is provided with an elastic limit contact z which when closed initiates the firing of thyratron T<SP>111</SP> which terminates the current flow through T' in the same way at T<SP>11</SP>.