Why are current transformers used in power system?
Protective relays coils and measuring instruments such as an ammeter, watt meter and energy meter are very sensitive devices and cannot be directly connected to the line carrying high magnitudes of current. So, we have to reduce the magnitude to a lower value and equivalent to the measurable capacity of those instruments. For this purpose, Current transformers are used. The primary of the current transformers are connected in series to the lines and the instruments are connected across the secondary terminals.The readings made by the instrument will be proportional to the actual value and depends on the transformer ratio of the transformer used.