High voltage network elements are subject to high voltage magnitudes (220KV, 66KV or a minimum of 11kV) and hundreds of amperes are passing through them. Instrument transformers are accustomed cut back the values of volts and current to plain secondary values that are (100v or a 110v) and (1 or 5) amperes. These values are appropriate for protection and measuring relays. Advantage of victimization instrument transformers is isolating the present and voltage coils of relays from high voltages of the power system.
Basic Design of Instrument Transformer
Instrument transformer is analogous to power transformer within the plan of work that depends on, once electrical energy (AC) follow through primary winding of the transformer, this currents creates a magneto motive force (M.M.F.) inflicting an alternating flux within the core, that is translated as a current within the secondary coil of the transformer. This study is concentrated on the sensible read of current transformer, differential between metering and protection cores of current transformer star and open delta of Voltage transformer.
Current transformer consist a minimum of 2 secondary cores. The first core is typically designed for measurements, the second and the third exist if used for cover. The secondary of current transformers are nearly connected in star.
The star purpose of every secondary core should be earthed. All relays of each core are connected asynchronous. From the above figure shows the secondary connection of 1 secondary core of a current transformer and also the relays connected with it.