GB480306A - Improvements in and relating to methods of testing the power of electrical appliances - Google Patents

Abstract

480,306. High tension switches. BRITISH THOMSON-HOUSTON CO., Ltd. Aug. 23, 1937, No. 23071. Convention date, Aug. 21, 1936. [Class 38 (v)] [Also in Group XXXVI] Switches or fuses are tested by means of separate current and voltage sources so arranged that the change in current taking place upon the extinguishing of the arc between the switch contacts causes the test voltage to be impressed on the path of the arc, the release of the voltage impulse being obtained by the employment of the second derivative of the current d2 i.dt<2>. A generator 1 supplies current to the switch 3 to be tested, through choke coils 2, the switch 3 having to undertake the interruption of the short-circuit current. In parallel with the switch 3 is an impulse circuit containing a three-electrode spark-gap 4, 5, 6 and a condenser 7 which is charged from a transformer 9 through a rectifier 8. The spark-gap 4, 5, 6 is so adjusted' that it does not break down under the influence of the voltage on the condenser 7 applied when the switch 3 is closed. In parallel with one of the choke coils 2 is a circuit containing a resistance 10 and a condenser 11. The voltage across the resistance 10 due to the short-circuit current i flowing through the coils 2 and switch 3 is proportional to d<2>i.dt<3>, and is impressed between the electrodes 4, 5 of the spark-gap. The peak value of this voltage, together with the voltage of the condenser 7, is sufficient to break down the spark-gap and allow the condenser voltage to be impressed on the switch 3, which has opened in the meantime. Two separate threeelectrode spark-gaps and two separate impulse systems 7, 8, 9 delivering impulses of opposite polarity may be provided. Ignition takes place only in that spark-gap in which the potential difference is increased by the voltage across the resistance 10. Specification 474,140 is referred to.