GB482033A - Improvements in or relating to the impulse voltage testing of electrical apparatus - Google Patents

Abstract

482,033. Detecting faults. SIEMENSSCHUCKERTWERKE AKT.-GES. Aug. 18, 1937, No. 22683. Convention date, Aug. 25, 1936. [Class 37] Electrical apparatus such as transformers, reactance coils, condensers, cables, and the windings of generators and motors are tested by an impulse voltage whilst subjected at the same time to one or more other voltages, for example the normal operating voltage, auxiliary spark gaps controlled by the impulse voltage being employed for producing predetermined operative conditions in the apparatus to be tested and in the sources of voltage. A testing impulse voltage is applied to one of the high tension secondary windings U, V, W of a threephase transformer whilst the normal operating voltage is being produced in them by excitation of the low-tension primary windings (not shown). In order to reproduce the most unfavourable conditions, the impulse voltage should reach the winding V to be tested at the moment when the phase voltage of this winding attains its maximum value and is of opposite polarity to the impulse voltage. The impulse voltage generator Cs may be, as shown, of the Marx type consisting of condensers which are charged in parallel through resistances from a source Lq and then connected in series through spark gaps and discharged to the apparatus to be tested. In order to obtain the correct polarity, the initiating spark gap F1, F2 has three electrodes, the central one being connected to the junction between two seriesconnected condensers K charged by the operating voltage Uph of the winding V under test. At the moment when the operating voltage Uph reaches its maximum value with a polarity opposite to that of the impulse the spark gap F1 breaks down and the impulse voltage enters the winding V through a resistance R1 and a discharge spark gap SF, which may have needlepoint electrodes by means of which the magiiitude of the impulse voltage is adjusted. An auxiliary spark gap HF1 is such that it permits the impulse voltage to pass freely to the winding V, but prevents the operating voltage Uph from passing across it to the impulse circuit. The windings U, W to which the impulse voltage is not applied are earthed through spark gaps HF2, HF3 and a resistance, the spark gaps being broken down simultaneously with, or slightly before, the entry of the testing impulse into the winding V. This is effected by means of an auxiliary circuit containing a three-electrode spark gap F3, F4 and a condenser CH, the gaps being so adjusted that F3, F4 break down immediately after F1, F2 and an auxiliary impulse is applied to the gaps HF2, HF3. In order to prevent the windings U, W from being stressed by the auxiliary impulse, the spark gaps HF2, HF3 may be three-electrode gaps, the auxiliary impulse being applied to the central electrode. If the voltage of the charging source is not high enough to provide the auxiliary voltage, the auxiliary circuit may also contain an auxiliary impulse generator. The impulse circuit may be connected to the spark gaps HF2, HF3 through a Tesla transformer. In another arrangement, the auxiliary impulse voltage is tapped off from the discharge resistance R2 of the main impulse generator Cs. The polarity of this impulse may be reversed by a combination of a spark gap, condenser, and resistance. The auxiliary spark gaps controlled by an auxiliary voltage may be used for other switching operations such as the parallel or series connections of the high-potential windings with the low-potential windings or the connection of condensers, cables, excess voltage arresters &c. to a winding to be tested.