GB268365A - Means for keeping the degree of insulation of the oil of oil-filled electric apparatus continuously under observation - Google Patents

Abstract

268,365. Kocsis, B. March 29, 1926, [Convention date]. Resistances, measuring; phase differences and power factors, measuring.-In order to keep under continuous observation the dielectric strength of the insulating oil of transformers, oil switches, &c., a condenser C1 is provided of which the dielectric is formed of the oil under test and the coatings are of such a size that a measurable current flows under normal circumstances and at such a distance apart that no discharge can occur between them. The ratio of the watt component of the current through the condenser C1 to the wattless charging current may be measured by means of a Sheering bridge, of which the condenser C1 forms one arm, a condenser C2 of known capacity forms a second arm, and a variable resistance R3 and fixed resistance R4 shunted by a variable condenser C4 form the other two arms. Current is supplied from a transformer T. The dielectric strength of the oil is determined from the power-factor of the condenser C1 so measured. In place of the Sheering bridge, the current passing through the condenser C1 may be measured by means of a milliammeter. On the dielectric strength of the oil diminishing, the charging current decreases only inappreciably, but the watt component increases considerably so that the deflection of the instrument is inversely proportioned to the resistance of the oil. The transformer winding or the container wall may form one plate of the condenser C1. A resistance or choking-coil may be provided in circuit with the condenser.