JPS57138117A - Current transformer - Google Patents

Abstract

PURPOSE:To fulfill a monitoring function at all times by forming a circuit using differential output from the current transformer and output with an AC separate power supply applied to the current transformer as trouble detecting output. CONSTITUTION:When current flow through the primary winding 1 of the current transformer and AC having frequency sufficiently higher than the sampling frequency of a sampler 4 are supplied to a coil 6 wound on a core 2 through a switch 8 from an AC current source 7, the quantity of electricity proportional to magnetomotive force interlinking with the core 2 is drawn out of a magnetic flux detector 3. The sampler 4 samples the output of the detector 3 at the period of T sec, and outputs it as the secondary output of the current transformer. The switch 8 functions at the period of T sec only for the time of less than a period when the sampler 4 is opened, and conducts the action of on-off. The output of the detector 3 is differentiated by a differentiator 5, and the terminal voltage of the winding 6 is subtracted in an adder 9. When the detector 3 gets trouble, the conversion constant changes, and voltage corresponding to the change is outputted from the adder 9 and supplied to an alarm device and a controller.