Current Transformers

Current Transformer

What is Current Transformer & Why is it used?

  1. It isolates the protection system from high voltages and currents, resulting in the reduction of the and cost of protection equipment
  2. The output of a Current Transformer is standard (i.e. 1A or 5A) which eliminates the need for protection equipment relays having diversified operating values.
Construction of current transformer

Working Principle:


Based on Function:

  • Measurement CT:
  • Protection CT: ​

Based on Construction: ​

  • Bar Type Current Transformer:
  • Wound Current Transformer: ​
  • Toroidal/Window Current Transformer:

Connections of CTs: ​

Polarity of CT: ​

Grounding of CT:

Burden of a CT: ​

Burden of current transformer
90% OFF — Power System Protection Fundamentals

CT Ratio:

Transformer Ratio =Primary Current/Secondary Current

Errors in a CT:

Current Ratio Errors​

Ratio Error =KtIs / IpIp

Phase Angle Error

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AllumiaX Engineering

AllumiaX Engineering

Leaders in Industrial & Commercial Power Systems Engineering