Importance

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Abstract

A transformer ground fault protector is provided and includes sensing means in the form of at least one conductive plate adjacent but spaced from the output of each secondary winding in a transformer having its secondary windings connected in series and at the midpoint of the series circuit to ground. The at least one conductive plate forms a capacitive circuit with the windings and provides an output voltage when the secondary windings are energized and unbalanced. The output voltage generated by the at least one conductive plate in normal operation of the transformer, is substantially equal to zero volts. However, when a fault occurs in the transformer, the output voltage induced in the at least one conductive plate has a magnitude greater than zero. The resultant voltage in turn is conveyed to a comparator which compares the magnitude of the resultant voltage with a predetermined threshold voltage. When the resultant voltage is greater than the predetermined threshold voltage, the comparator provides a positive output voltage which is used to bias a switch connected in series with the transformer primary winding to an open condition thereby to isolate the primary welding from its power supply. An LED is illuminated when the primary welding is isolated from the power supply to provide a visual indication of the transformer fault condition.

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First Claim