Difference Between Current Transformer (CT) & Potential Transformer (PT)

Key Differences between Current and Potential Transformer

1. The current transformer transforms the high value of current into the low value so that it can conveniently measure by the instrument whereas the potential transformer converts the high value of voltage into low value.
2. The primary winding of the current transformer is connected in series with the transmission line whose current is to be measured whereas the potential transformer is connected in parallel with the line.
3. The core of the current transformer is built up with the laminations of the stainless steel. The core of the potential transformer is made up with high operating core operating at low flux densities.
4. The primary winding of the current transformer carries the current which is to be measured whereas the primary of the potential transformer carries the voltage.
5. The primary winding of the current transformers has a small number of turns, whereas in potential transformer the primary winding has a large number of turns.
6. The secondary of the current transformer has a large number of turns, and it cannot be open circuited when it is under the services. The secondary winding of the potential transformer has a small number of turns, and it can be open circuit during the services.
7. The normal range of the current transformer for measuring the current is 5A or 1A whereas the standard voltage at the secondary winding of the potential transformer is up to 110V.
8. The transformation ratio of the current transformer is always remained high, whereas for the potential transformer its remains low.
   • Note: The transformation ratio of the current and the voltage transformer is defined as the ratio of the rated primary voltage to the rated secondary voltage.
9. The input of the current transformer is the constant current, whereas the input of the potential transformer is the constant voltage.
10. The primary winding of the current transformer does not depend on the burden of the secondary winding of the transformer; it depends on the current flows in the primary windings whereas the primary of the potential transformer depends on the burden of the secondary winding.
    • Note: Burden is the secondary load on the transformer.
11. The primary winding of the current transformer is directly connected to the full line current whose current is to be measured whereas in potential transformer the full line voltage is directly connected to the primary terminal.
12. The impedance of the primary winding of the transformer is very low as compared to the secondary winding whereas in a potential transformer, the impedance of the primary winding is high.
    • Note: Impedance is the opposition of the current offered by the circuit when the voltage is applied across them.
13. The current transformer is mainly used for measuring such magnitude of current that the meter or instrument cannot conveniently be measured whereas the potential transformer is used for measuring the high voltage of the current.