The invention relates to a fast testing instrument of the
variable ratio and the polarity of a
current transformer and a testing method thereof. According to the invention, not only can the time for testing the
variable ratio and the polarity of the
current transformer be shortened from about 50min to about 25min, but also the invention has the advantages of small size, convenience in carrying, high in measuring accuracy, safety and reliability. The testing method comprises the following steps: the
voltage outputted by a
volt-
ampere tester is inputted to a
volt-
ampere voltage input end of the tester, an exciting
voltage U2 is outputted to a secondary coil of the
current transformer by S1 and S2; a primary side of the current
transformer is inputted to the input end of a primary voltage U1 of the testing instrument;
volt and
ampere are inputted to the output end of the exciting voltage U2, and then a small current
transformer is connected in series and is used for monitoring volt-ampere current I; U2, I and U1 are respectively sampled by a corresponding range switching circuit, a corresponding buffering and amplifying circuit and an corresponding AD, and are transmitted to a CPU (
Central Processing Unit) by optoelectronic isolation; the CPU measures amplitudes of three paths of signals; and the U2 and the U1 are also changed into square
waves through a waveform converting circuit, the square
waves are transmitted to the CPU through the opoelectronic isolation to be used for measuring the
phase difference of the U2 and the U1, so as to judge the polarity of the current
transformer.