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Current Transformer

  • Split core current transformer (CT) (e.g., YHDC SCT-013-030)
  • CTs are comprised of magnetic core, primary and secondary windings.
  • For AC current measurements, the CT "primary" is usually the live or neutral AC wire.
  • The "secondary" is comprised of many turns housed within the CT housing.
  • The gaps in the hinged segment of a split CT introduce inaccuracy
  • "Burden" refers to the load on the secondary side of a CT
  • Burden refers to the function (and location) and not to its construction
  • Burden (load) plays a safety role in circuits and prevents high induced voltages across an infinite (open) burden load.
  • Burden (load) impacts accuracy of CT measurements.

Wikipedia

https://en.wikipedia.org/wiki/Current_transformer

The burden (load) impedance should not exceed the specified maximum value to avoid the secondary voltage exceeding the limits for the current transformer. The primary current rating of a current transformer should not be exceeded, or the core may enter its non-linear region and ultimately saturate. This would occur near the end of the first half of each half (positive and negative) of the AC sine wave in the primary and compromise accuracy.

The secondary of a current transformer should not be disconnected from its burden while current is in the primary, as the secondary will attempt to continue driving current into an effective infinite impedance potentially generating high voltages and thus compromising operator safety. For certain current transformers, this voltage may reach several kilovolts and may cause arcing. Exceeding the secondary voltage may also degrade the accuracy of the transformer or destroy it. Output voltage is limited by core saturation since the primary flux is not canceled by secondary flux when the core is saturated. Because of this, smaller current transformers may not actually incur dangerous voltages when operating nominally. Faster current transients from loads being switched on etc. can however still induce dangerous voltage levels due to high current slope.

The secondary load of a current transformer is termed the "burden" to distinguish it from the primary load.