High voltage network components are subject to high voltage magnitudes (220 kV, 66 kV or at least 11 kV) and hundreds of amperes are passing through them.
Instrument transformers are used to reduce the values of volts and current to standard secondary values which are (100 v or 110 v) and (1 or 5) amperes.These values are suitable for protection and measuring relays.
Advantage of using instrument transformers is isolating the current and voltage coils of relays from high voltages of the power system.
Basic Idea of Instrument Transformer
Instrument transformer is similar to power transformer in the idea of work which depends on, when alternating current (AC) follow through primary winding of the transformer, this currents creates a magne-motive force (M.M.F.) causing an alternating flux in the core, which is translated as a current in the secondary winding of the transformer.
This study is concentrated on the practical view of current transformer, differential between metering and protection cores of current transformer, stare and open delta of Voltage transformer.