A current transformer converts a high primary current with a secondary winding around the magnetizable core to a lower secondary current. The current transformer is passive, so there is no external power supply, and the part of the secondary connection constitutes the load of the current transformer. In short, the connecting wires and connected meters constitute the load of the current transformer. In technical terms, this is called VA load (volt-ampere). This load affects the accuracy of the current transformer.
In the design of the current transformer, the internal losses and external loads of the current transformer are considered. Current transformers are used as current sources. Therefore, Midwest current transformer designers take the burden of the current transformer into account.
The IEC 61869-2 standard for current transformers specifies the following for the loading of current transformers:
The measuring transformer is loaded between 25% and 100% of its nominal load. The idea behind this is that when the current transformer is loaded too low, it may no longer meet the rating and can return an overly positive value.
Knowing your burden and calculating your VA is the key to finding the right current transformer for your application.
The VA rating of a current transformer is determined by two simple formulas.