| Current Transformers (CT) |
Potential Transformer (PT) |
| Reduce the main power line current to be measured by normal range instruments i.e. current is stepped down from ptimary to secondary |
Reduce the main power line voltage to be measured by normal range of instrument. i.e., voltage is stepped down from primary to secondary |
| Primary winding of CT is connected in series with the main power line to sense current |
Primary winding of PT is connected across the main power line to sense current |
| Primary winding has less number of turns as compared to the secondary winding |
Primary winding has more number of turns as compared to the secondary winding |
| CT secondary side should never be open circuited while energized, to restrict accidental over-voltage |
PT secondary can be safely open circuited even if the PT energized, since secondary voltage is always restricted by the turn ratio |
| In many cases, such as in bar type, in single primary winding type and in clamp-on type CT, the primary winding is nothing but main power line conductor itself |
In all the PTs, separate primary as well as secondary windings are necessary. Primary winding terminals are connected across the main power line |
| While using CT for measurement of power, secondary winding is connected in series with the coil of wattmeter |
While using PT for measurement of power, secondary winding is connected in parallel with the coil of wattmeter |
