Patent GB-904829-A (GB)
Title: Improvements in or relating to the testing of high-voltage switches
IPC: G01R31/333
Filed: 1958-12-23
Abstract: 904,829. Testing high - voltage electric switches. SIEMENS-SCHUCKERTWERKE A.G. Dec. 23, 1958 [Dec. 23, 1957; March 28, 1958; March 31, 1958], No. 41541/58. Class 37. [Also in Group XL (a)] In a method of testing high-voltage switches there is connected in series with the switch a second auxiliary switch the current through which is interrupred simultaneously with that of the switch to be tested. A high-current source feeds both switches at a high-voltage which supplies the re-striking voltage. Immediately following the passage through zero of the current supplied by the high-current source the highcurrent circuit first supplies a re-striking voltage with the desired waveform at the appropriate voltage frequency and the damping and the high-voltage source is only subsequently connected. In this way the switch can be loaded approximately as if it had been tested with the short-circuit current at the rated voltage of the switch, the re-striking voltage meeting the requirements arising under actual operating conditions. Fig. 1 shows an apparatus for testing a switch 1 which is connected in series with auxiliary switch 2, the two switches being connected in the secondary of a transformer 3 which is fed from a test generator 6 which forms the high-current source and supplies the required short-circuit current at a lower voltage than the rated voltage of the switch. The resistor 7 and capacitor 8 adjust the natural frequency damping of the high-current circuit to produce the desired rise of the voltage after the current has passed through zero. The highvoltage circuit consists of a capacitor 10 which is charged from a D.C. supply and discharged through the controlled spark-gaps 12 and 13 so that when these gaps are triggered a highvoltage circuit produces a waveform having the desired rise and shape for the correct loading of the switch. The spark-gaps 12, 13 are fired by a pulse derived from the current transformer 16 and control device 17 so that the gaps fire at about the passage through zero of the highcurrent circuit. In operation the switches 1, 2 are closed and then the switch 5. Short-circuit current flows through switches 1, 2 which receive the circuit breaking signal simultaneously. After the first passage of the current through zero both switches are re-ignited by the restriking voltage or other means, this condition being maintained until the maximum quenching distance of the switch is reached. Thus as the current passes through zero a re-striking voltage is set up in the high-current circuit, which by suitable choice of network 7, 8 and of the voltage of the high-current source corresponds to the rise of the required re-striking voltage. Capacitor 10 has a large value so that it acts substantially as a D.C. source. As shown in Fig. 2, where b represents the re-striking voltage supplied by the high-current source, the voltage set up at the series arrangement of network 14, 15 is shown at c, so that when at point D the voltages b and c are of equal value, spark gap 13 fires and the actual re-striking voltage obtained is that represented by the thick line of Fig. 2. Other desired waveforms of re-striking voltage may be obtained as described in connection with Figs. 3, 4, 5, not shown. Testing of the switch may also be effected by setting the contact members of switches 1, 2 to a maximum quenching distance and bridging each switch by means of an ignition wire. When the current is switched on, an arc is set up at both switches and interrupt action is then started. A non-uniform distribution of the re-striking voltage can be effected by connecting an impedance in parallel with one of the two switches it then being possible to effect ignition of both switches with a relatively small testing voltage until a maximum quenching distance is reached. A rectifier instead of an impedance could be used for this purpose. The method may be applied to testing the switch at its capacity for brief interruption, the two switches 1, 2 are re-closed after a short currentless break following the first interruption. In this case the direct voltage of capacitor 1 is present at switch 1 and may be adapted to the peak value of rated alternating voltage of the switch. The capacitor is then discharged very rapidly so that the spark gap 13 is extinguished. The initial conditions are thus restored as the spark gap has already been distinguished and the fresh interruption can be carried out. In the apparatus shown in Fig. 6 the spark gap 13 of Fig. 1 is replaced by a threeelectrode spark gap 30, the disposition of the electrodes is such that spark-over takes place when the re-striking voltage produced by generator 6 and the switch 1 has approximately the same value as the voltage set up at the network 14, 15, so that at this time the voltage derived from network 14, 15 is connected in parallel with the switch 1 through the arc and the voltage provided by the high-current source is succeeded by the voltage supplied by the highvoltage source, Fig. 7 (not shown), and the switch is loaded with a re-striking voltage corresponding to the actual operating conditions. In this arrangement no special control devices for the spark gaps are required. In a further arrangement of testing apparatus using three electrode spark gaps, Fig. 8 (not shown), only the arc between one pair of electrodes constitutes the connection between the high-current and the high-voltage circuit so that the response voltage of the gap of the other pair of electrodes is not impaired by this arc. Various types of threeelectrode spark-gaps are described, Figs. 9-11 (not shown) (see Group XL (a)). In the arrangement shown in Figs. 12, 15 the high-voltage source is currentless before connection to the switch 1 to be tested. In Fig. 12 the waveform of the re-striking voltage of the switch 1 is adjusted after interruption of the short-circuit current with the aid of inductor 4, resistor 107, capacitor 108 and resistor 109, so that it corresponds to the waveform of the re-striking voltage which would be set up in the mains or to a voltage curve required to meet test requirements. The required test is produced by superimposition of the voltage of the high-current circuit and that of the high-voltage circuit after ignition of the spark gap 112, as described in connection with Fig. 13 (not shown). In all the arrangements described the capacitor 10 charged with direct current may be replaced by generator of the same frequency as the highcurrent generator and run synchronously with it, or an existing high-voltage supply system may be employed, the phase position being such that the spark gap 12 or 112 is ignited in the region of the maximum of the high-voltage generator. Specification 788,548 is referred to.