GB1199016A - Voltage Testing Arrangement - Google Patents

Abstract

1,199,016. Voltage testing. IPA INTERNATIONALE PATENT-UND LIZENZANSTALT. June 19, 1967 [June 17, 1966; Jan. 13, 1967], No.28203/67. Heading G1U. The presence of high voltage on a line 1 is detected using an arrangement including a contact 2 to be brought into contact with the line, a conducting body 4 having a capacity C to earth and an indicating circuit incorporating a current source 11 and indicator 9 in a series path controlled by a trigger relay 10 of thyristor type having two control terminals connected respectively to the contact 2 and the body 4. The impedance between the control terminals (the barrier layer impedance of the thyristor) and the capacity are such that at the instant of contact between the contact 2 and conductor 1 a transitory current oscillation is set up which is so large as to cause the triggering of the relay to cause the indicator to operate, the relay being responsive solely to this oscillation. In a particular embodiment Fig. 4 the control electrode of a thyristor 10 is connected to the conducting body 4, while the cathode is connected via the housing of a buzzer 13 to the probe 2. When the thyristor triggers, current flows from the battery 11 and the buzzer coil 14 opens the contacts 15. A capacitor 16 and resistor 17 take a charging current which prevents the thyristor being extinguished for a short time, so that the opening contacts do not immediately extinguish the thyristor. The standby condition of the circuit is tested by closing the switch 18. This causes the capacitor 19 to charge, and the apparatus operates if in working condition. Furthermore, if the battery is properly charged, steady current will flow through the lamp 20 and Zener diode 21 to light the lamp. The whole arrangement is built into a portable unit Figs. 6 and 7 (not shown). A circuit for use in lower voltage tests incorporates a transistor amplifier stage before the thyristor Fig. 5 (not shown). Other devices are explained suitable for insertion into hollow containers, etc. for detecting voltages therein, and assembly details of apparatus in accordance with the invention and test arrangements therefor are given Figs. 6, 7, 9-12 (not shown). In an alternative form of the invention Fig. 8, the capacitive body 4 is a Faraday cage containing the circuitry of the test arrangement, except the indicator, and the cage is connected directly to one control electrode of the thyristor and to a contact 33 for making contact with the wire 1. The other control electrode is coupled to a plate 2 capacitively coupled to the cage 4, and it is this capacity, together with the barrier layer impedance of the thyristor, which are such that at the instant of contact between the contact 33 and the high voltage conductor a transistory oscillation is set up which triggers the thyristor, the thyristor being responsive solely to this oscillation.