1. The current transformer is composed of a closed core and windings.A voltage transformer is a transformer with an iron core.
2. The current transformer can be short-circuited at the second time, but not open;The secondary voltage transformer can be open circuit, but not short circuit.
3. The winding with more turns and fine wire diameter of the current transformer is connected to measuring instrument (ammeter), while the winding with less turns and thick wire diameter of the voltage transformer is connected to measuring instrument (voltmeter).
4. The current transformer with less turns and thick wire diameter is connected in series with the measured circuit as a primary winding, while the voltage transformer with more turns and thin wire diameter is connected in parallel with the measured circuit as a primary winding.
5. Compared with the load on the secondary side, the primary internal impedance of the voltage transformer is so small that it can be ignored. Therefore, the voltage transformer can be considered as a voltage source.However, the primary internal resistance of the current transformer is so large that it can be considered as a current source with infinite internal resistance.
6. The flux density of the voltage transformer is close to saturation value during normal operation, but decreases when fault occurs.The magnetic flux density is very low when the current transformer is working normally, but it increases greatly when the primary short-circuit current becomes very large, sometimes even far beyond saturation.
7. The current transformer is actually a boost transformer working in short circuit condition (because the ammeter is a low resistance meter, the current is very large, so it is equivalent to short circuit.A voltage transformer is essentially a step-down transformer that operates under no-load conditions.