Patent GB-498570-A (GB)
Title: Improvements in and relating to devices for testing the performance of circuit-interrupters in opening electric circuits
IPC: G01R31/333
Filed: 1938-02-28
Abstract: 498,570. Indicating faults ; electricity supply; switches. BRITISH THOMSONHOUSTON CO., Ltd. Feb. 28, 1938, No. 6313. Convention date, Feb. 27, 1937. [Class 37] [Also in Groups XXXV and XXXVII] A circuit arrangement for testing the performance of circuit-interrupters in opening circuits at high apparent power on a low-power source (i.e. simulating actual fault conditions), comprises two or a multiple of two surge generators of opposite polarities arranged to be released one at a time in succession at each interruption to simulate the actual recovery voltage produced under actual operating conditions. Releasing means for the generators comprises voltage-impulse producing means responsive to sudden cessation of current through the interrupter, and a pair of discharge tubes have control electrodes influenced by the voltage impulse produced to initiate the discharge of one or the other of the tubes according to the polarity of the impulse. A voltage-responsive connection from each discharge tube to a control electrode of a separate surge generator releases the surge on initiation of the discharge. The arrangement comprises in general a low-voltage source 12 earthed at 29 and capable of supplying normal load to the contacts 19 of the breaker 11 under test ; one or more successively-released surge generators 13 &c. one of which is released after each current interruption in cases where the current is re-established, to simulate a given recovery-voltage transient; valve-apparatus 17 for tripping the surge-generators ; and an inductive coupling 18, condenser 48, and resistance 49 for triggering the valve-apparatus 17 when the rate of change of current alters from a high value approaching the zero of the cycle) to zero (as the current remains zero). Four surge generators 13 .. 16 of similar character, but of alternately-opposite polarity are shown, the selection of the appropriate one depending on which of the valves comprising the apparatus 17 is triggered, which in turn depends on the direction of the interruptedbreaker current. The breaker has an operating mechanism 22, back contacts 51 preferably adapted to close to complete the valve-triggering circuit before the contacts 19 separate, and preferably-synchronized oscillographs 24, 26 for current and voltage measurement, the source 12, if of insufficient reactance, being protected against the generated surges by a reactance 23. Each generator 13 &c. comprises condensers 30 .. 34 connected in shunt to a slow source of charging current of moderately-high voltage, such as the A.C. source 35, and rectifier 36 which is connected with due regard to the polarity desired for the surge generator, for example, the side 38 of condenser 34 is positive, whereas the side 38 of condenser 34<1> of 16 is negative. When released, the condensers all discharge in series through discharge gaps 40 and an external gap 41 connected to the high-voltage contact of the breaker 11, an inductance 45 and resistance 46 preventing the surge from tripping the other generators. The wave-form of the generated surge may be adjustable by means of variable circuit-constants and added capacity &c. When a generator has been released, an electromagnetic switch 72 or 73 having an armature 75 and a deadcentre spring 79, changes over to the next one of the same polarity by means of its contact 76 ready for a further surge if the current in the breaker 11 is re-established. The last pair of generators (15, 16 in Fig. 1) energize windings 83 which restore the switches 72, 73 to their original positions. The lower contacts 77 of 72, 73 connect the appropriate valve of apparatus 17 to the gap 40 or 40<1> of generator 13 or 14, whereas the upper contacts 78 connect those valves to the next pair of generators 15, 16, respectively. The gaps, 40, 40<1> are connected over condenser 68 to the anode 60 of valve 53, and over condenser 70 to the cathode 64 of valve 54, respectively, the grids 62, 65 of these valves being suitably biassed. A condenser 50 and inductance 49b prevent operation by, for example, the brief passage of current through zero during the arcing-period, and a high resistance 52 prevents accumulation of stray charges on grid 62. When the mechanism 22 opens the contacts, 19, either the voltage on grid 62 will be raised, or the voltage on cathode 64 will be lowered, depending on the polarity of the voltage induced across resistance 49. In the former case, the potential of electrode 69 is lowered and gap 40 breaks down, so causing all the gaps of generator 13 to break down and hence also gap 42, whereas in the latter case the potential of electrode 71 of gap 40<1> is raised. In a four-generator arrangement, instead of the bridge 76 of switch 72 being retracted by a winding 83 energized by the switch 81, an arrangement as shown in Fig. 4, may be used, in which the discharge-current in generator 15 attracts an armature 86 on the opposite end of rod 80 to that carrying armature 75, the dead-centre spring 79 maintaining the movable parts in their extreme positions. Instead of a single apparatus 17 supplying a number of pairs of surge-generators in succession, each pair of surge-generators may have its own apparatus, the individual apparatus being switched in succession by switches similar to 72, Fig. 2 (not shown). In Fig. 3 (not shown) both valves 53, 54 are connected so as to be operated by raising the potentials with respect to earth of their grids, which are connected to the ends of a resistance similar to 49, the mid point of which is earthed and connected directly to one of the valve-cathodes. In Fig. 5 (not shown), three-electrode discharge gaps are used in alternate surge-generators 14, &c. with suitably-modified valve connections, the intermediate electrode being connected to the anode of one valve and to the mid-point of a resistance, the ends of which are connected to the outer electrodes of the discharge gap. Fig. 6 shows an arrangement suitable for use where high surge voltages are not required. Two condensers 126, 127 constitute the surgegenerators and are controlled by two threeelectrode gaps 128, 129, the middle electrodes of which are connected to the respective anodes 60, 63, so that, when either valve becomes conducting, the middle electrode drops in potential and initiates a discharge. Specification 480,306 is referred to.