12. INSTRUMENT TRANSFORMERS
It is not practicable to conned instruments and meters directly to the lines in high voltage circuits. Instead instrument transformers are used. The following are the two basic advantage inherent in this method:
(i) Standard rated instruments may be used.
(ii) Operating personnel coming in contact with the instruments are not subjected to high voltage and current of the lines, and so there is less danger to them. Even with a low-voltage system, instrument transformers are used for measuring large currents, so that heavy leads to the instrument panel and to the ammeter and other current terminals are avoided.
The principle of the instrument transformer is fundamentally the same as that of the power transformer. The instrument transformers are classified as follows: