Current Transformers

Current Transformers are step up transformer.

Current transformers are used to step down the current rating because lower current rating can only be allowed to pass through ammeter and current coils of wattmeters.

Current transformer is a static device having two windings called primary and secondary, to transfer power from primary to secondary with suitable change in level of current. Current transformer basically has a primary winding with a few turns having large cross-sectional area. This side is connected in series with the line carrying high current. Whereas secondary winding is made up of many turns of fine wire having rating of 5 A current. This end is connected to low range meter such as ammeters and current coils of wattmeters. Current transformers are basically step up transformer because of the principle "higher the voltage, lower the current". If I₁ and I₂ be the current in primary and secondary sides and N₁ and N₂ be the number of turns of primary and secondary winding, Then it is given by. The current transformer's secondary winding should not be kept open. If it is kept open, secondary current will be zero and ampere turns produced by the secondary will be zero. Since the secondary ampere turn oppose the promary ampere turns, the back emf will be zero. Hence, unopposed primary produces heavy flux in the core, which causes excessive core losses and even cause insulation damage to the transformer, which is dangerous while the transformer is in operation.