Correct Answer - Option 3 : Measurement of high alternating voltages
In high voltage A.C. circuits, the measurement cannot be done by using the method of extension of ranges of low range meters by providing suitable shunts.
In such conditions, specially constructed accurate ratio transformers are used. These transformers are used to isolate the instruments from high current and high voltage A.C. circuits.
These are generally classified as
(i) Current transformer - large alternating currents can be measured
(ii) Potential transformer - High voltages can be measured
