Patent GB-788548-A (GB)
Title: A testing arrangement for electric circuit breakers
IPC: G01R31/333
Filed: 1954-12-10
Abstract: 788,548. Testing circuit-breakers. LICEN. TIA PATENT-VERWALTUNGS-GES. Dec. 10, 1954 [Dec. 11, 1953; Dec. 16, 1953; Dec. 21, 1953; Dec. 28, 1953; Jan. 22, 1954; Feb. 10, 1954], No. 35900/54. Class 37. Apparatus for testing circuit-breakers wherein high current and high voltage are successively and respectively applied thereto from an alternating current source connected to the test breaker through an auxiliary breaker which opens together with the test breaker, and from a source of oscillatory voltage of higher frequency but smaller current than the test current which is switched by a spark gap triggered shortly before the last test current wave passes through zero, so as to replace the test current by a further current due to the oscillatory voltage; the auxiliary breaker being reclosed to apply a further test current half-wave if the test breaker arc reignites in response to the high voltage circuit, which circuit is disconnected from the breaker after a small number of half-waves of its reignition current have passed, and the high oscillatory voltage being reapplied to the test breaker shortly before the further test current waveform passes through zero in conformity with the polarity thereof.  In Fig. 1 a high power circuit breaker Sp is connected for test using the Weil methodthrough current limiting choke Lb to a high alternating current generator G over an auxiliary breaker Sh designed.to operate therewith. Shortly before the arc current ik (Fig. 2) at the opened contacts of the test breaker passes through zero a switching spark gap F1 is ignited in response to the high current waveform, to apply to the test breaker contacts a low current is at high oscillatory voltage Ue which is derived from a series resonant circuit LsCs excited by a transformer T energized from generator G in synchronized quadrature therewith, at a higher frequency (determined by Ls Cs), a smaller amplitude, and an instantaneous polarity similar to that of the high current from generator G at interruption. The test breaker contacts are shunted by damping resistance Rd in series with capacitance Ce across which there is developed a steep voltage excursion Ucs. A further switching spark-gap F2 in series with a current breaker S2, and a switching gap F3 in series with a current breaker S3, are shunted across auxiliary breaker Sh, while controllable gaps St2, St3 are connected in series with capacitances Cz2, Cz3 and the triggering electrodes of gaps F2, F3 for excitation, e.g. by impulse generator SG. If in testing breaker Sp, reignition of the gap occurs, due to the application of high voltage Ue, immediately following the extinction of the arc at the zero value of the test current, the second half-wave of the oscillatory current therein triggers spark-gap St2 and in turn spark-gap F2 so as to re-apply the test current from generator G to the test breaker Sp, after which auxiliary breaker S2 opens after one half-wave. If the gap again reignites on application of voltage Ue, spark-gap St3 is triggered similarly to ignite spark-gap F3 to again apply the test current from generator G, after which auxiliary breaker S3 operates as before. Further controllable spark-gaps and auxiliary breakers may be provided, and the gap triggering arrangement H comprises an electrode rod within a spherical insulated electrode and extending into the gap through a hole therein, or two auxiliary gap electrodes within the main gap. Alternatively the auxiliary breaker Sh is replaceable by a known switching gap igniting at the start of each successive test current halfwave and extinguished at the end thereof by a gas blast so that the additional switching gaps and auxiliary breakers are unnecessary. Transformer T may be tuned to mains frequency to increase power supply efficiency, utilizing the transformer secondary inductance and/or additional inductance with the capacitance Cs (Figs. 3, 4, not shown). For D.C. testing (Fig. 5) the oscillatory high voltage is derived from a unidirectional voltage source connected on closure of switches S1a and S2a to charge capacitance Cs, which is connectible by triggered switching spark-gaps F1a, F3a and F2a, F4a respectively to discharge through inductance Ls and the test breaker Sp with successively alternating polarities to create an oscillatory current is superposed therein for a predetermined number of cycles (2) until the auxiliary breaker Sh (Fig. 1) opens, after which the breaker gap Sp is subjected to the voltage across Rd in series with Ce if there is no reignition. On re-ignition, a further half-wave of high test current ik is applied to the test breaker, the capacitance Cs is recharged; and gaps F2a, F4a are controlled to discharge the capacitance Cs reversely into inductance Ls; the oscillatory current being interrupted after a further time interval of two half-waves. Alternatively (Figs. 6, 7, not shown) the switching gap is designed to interrupt the oscillatory current after 3 half-waves and time interval t3; one gap only being required since the odd number of half-waves automatically effects the 180 degrees phase-shift of the oscillatory voltage which is necessary for phase correspondence with the appropriate half-wave of the testing high current. Additional halfwaves of oscillatory current may be obtained by utilizing the preceding half-wave or the collapsing voltage due to the breaker high test current to trigger a control device initiating the appropriate pair of control gaps. The operation of the switching gaps may be initiated by a counter responsive to a predetermined number of half-waves of high current in the test breaker, or by the peak value of the breaker arc voltage at the end of the quench period.