possible diagnosis of transformer. It is known for measuring the
transformer impedance that the circuit diagram is constructed
with a resistor of 50 ohms between the terminal of transformer
and the earth and the power source of the function generator is
connected to the other terminal of transformer and the
earth[2][3]. The impedance is derived from the current deduced
from the voltage drop of the resistor and the terminal voltage
drop of the transformer. In the circuit diagram, the current which
flows through the stray capacitance of transformer does not flow
through the 50 ohm resistance. Therefore by the circuit diagram
the impedance cannot be measured correctly in the high
frequency range when the influence by the stray capacitance
becomes large.