CURRENT TRANSFORMER....

400 kv, 3000/1A CT at site after erection

CT junction box

        Current transformer is also same as the power transformer with slight difference,current transformer is not used for step up or step down  of voltage levels as in case of power transformers.It is mainly used for step down the current levels. Generally in transmitting of power is done at high currents and voltages,but our ammeters and energy meters are does not with stand such high currents, on other hand protective devices like relays are also unable to with stand the high currents.
         So by step down the current with certain ratio and that value is used for protection and metering,then by multiplying with that factor we can get the real values that in line.
         So generally secondary current range is 1A or 5A. And primary current was is in order of 1000 amps.
 MAIN DIFFERENCE between POWER TRANSFORMER and CURRENT TRANSFORMER
  In power transformer primary current depend upon secondary current, but in current transformer primary current will depend upon on only load not on secondary burden or secondary current.

CT at 765kv site at India

working at CT secondary box in site (India)

      DIFFERENT TESTS OF CURRENT TRANSFORMER....

1. INSULATION RESISTANCE...

2.POLARITY...

3.RATIO TEST...

4.WINDING RESISTANCE...

5.KNEE POINT VOLTAGE TEST...(for PS class only)