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How a Current Transformer Works:

Current transformers

Primary Winding:

  • The primary winding of the CT is connected to the conductor carrying the current to be measured.
  • This winding usually has a single turn, as it may simply be the conductor itself passing through the CT.

    Core:

  • The CT contains a magnetic core, typically made of laminated silicon steel, which guides the magnetic flux generated by the primary current.

    Secondary Winding:

  • The secondary winding is wound around the core and contains many more turns than the primary winding.
  • The current induced in the secondary winding is proportional to the current in the primary but scaled down by the turns ratio of the transformer.

    Load (Burden):

  • The secondary winding is connected to measuring instruments or protective relays. These devices form the "burden" of the CT.

    Operating Principle:

  • When current flows through the primary winding, it creates a magnetic field in the core.
  • This magnetic field induces a proportional current in the secondary winding, allowing the measurement of the high primary current through the low secondary current.

Applications:
Current transformers are widely used in:

  • Measuring instruments (e.g., ammeters)
  • Protective relays in power systems
  • Monitoring equipment

    Important Points:

    The secondary winding of a CT should never be left open-circuited while the primary current is flowing, as this can cause dangerously high voltages.