Current transformers are used to step down high current to very low current that can be handled comfortably.
WHY CURRENT TRANSFORMERS?
- High currents can not be measured directly using ammeters due to limitations of current carrying capacity of the measuring instruments.
- Also, high currents can not be used in protective relays. To allow high current to pass, larger size of conductor is required .
- This leads to practical difficulties in handling the devices
- The practical solution to this difficulty is to step down the current to a very low value that can be as low as 1 amp or 5 amp.
- Unlike a regular transformer, a current transformer steps down only current.
- Voltage developed in the secondary will be negligibly less
- (ie, current in the secondary x resistance of the winding)
- The basic principle of CT functioning is ampere-turn matching
- AT primary = AT secondary