Patent GB-474140-A (GB)
Title: Improvements in and relating to methods of testing electric circuit breakers
IPC: G01R31/333
Filed: 1937-04-03
Abstract: 474,140. High - tension switches. BRITISH THOMSON-HOUSTON CO., Ltd. April 3, 1937, No. 9534. Convention date, April 3, 1936. [Class 38 (v)] An arrangement for testing a circuit-breaker comprises a relatively low voltage source of current adapted to be short-circuited by the breaker adapted to open the short-circuit, and means for subjecting the breaker to a recovery-voltage of greater magnitude than would be available from the current-source immediately upon interruption of current by the breaker. In Fig. 1, the breaker 11 under test is connected in series with an auxiliary, and preferably similar, breaker 12 across a source 13 capable of supplying full testing current. An autotransformer or, as shown, a two-winding step-up transformer 21 has its secondary 23 connected across breaker 11 so as to supply full voltage to the latter, and suitable apparatus, such as an oscillograph 24, is also provided. With both breakers 11, 12 closed, the desired current is passed through by energizing source 13 and closing switch 14, or vice versa, whereupon both breakers are opened simultaneously. If both finally interrupt the current simultaneously, breaker 11 has interrupted the desired current and been subjected to the desired recovery voltage by winding 23. The Specification points out, with reasons, the importance of simultaneous clearing of the current, and that if simultaneity is departed from, breaker 11 must clear within a very short interval after breaker 12. The method is accordingly well adapted to impulse and cross-blast types of breakers, and if it is applied to other types, a large number of tests should be made and the results discarded where 11 cleared first or 12 cleared too long before 11. In order to reduce the timeinterval, impedances 27, 28 may be arranged in the transformer circuits to hold back the application of the voltage until the breakers are ready to interrupt and thus cause simultaneous interruption. Such arrangement is also shown in Fig. 4, in which a breaker comprises two units 30, 31 with series-breaks arranged in hollow oil-filled insulators, and a common operating mechanism. The current is supplied to the units in series from a transformer 40, across which is the primary 22 of an autotransformer the secondary 23 of which supplies the tested unit, shown at 31, over a spark-gap 45. This gap opens the external circuit to terminal 36, and so the currents in the units are equal and clear simultaneously. The gap is set so as only to break down at a voltage appreciably higher than the arcvoltage, so that it prevents current-flow in its high-voltage circuit while the units shortcircuit the source, but applies the high-voltage immediately the short-circuit current ceases. The gap-resistances may be reduced after it has broken down, by igniting combustible gas supplied from a rubber hose H and nozzle N. The units 30, 31 may be tested in turn by interchanging the connections to terminals 37, 38, and oscillograph-transformers 43, 44 are provided. In a modification of Fig. 1, the short-circuit current may be supplied from a two-winding transformer, Fig. 3 (not shown) and in a further modification, Fig. 2 (not shown) three star-connected switches are tested by a three-phase supply, utilizing an autotransformer to supply each with the necessary recovery-voltage.