The main difference is that their working states during normal operation are quite different, as shown below:
1) The secondary side of a current transformer can be short-circuited, but must not be open-circuited; the secondary side of a voltage transformer can be open-circuited, but must not be short-circuited. The single-phase relay protection tester has complete functions and can complete all the above tests in one operation, with strong applicability. The measurement time, AC/DC voltage and current are all digitally displayed, making readings intuitive and accurate, and the button operation is convenient and flexible.
2) Relative to the load on the secondary side, the primary internal impedance of a voltage transformer is so small that it can be neglected, and the voltage transformer can be considered a voltage source; while the primary internal resistance of a current transformer is very large, so it can be considered a current source with infinite internal resistance.
3) During normal operation, the magnetic flux density of a voltage transformer is close to the saturation value, and it decreases during faults; the magnetic flux density of a current transformer is very low during normal operation, but during short circuits, the primary short-circuit current becomes very large, greatly increasing the magnetic flux density, sometimes even far exceeding the saturation value.
