The AC current transformer designed for precise measurement of AC current is used to convert AC primary current into a proportional AC voltage signal or a lower proportional AC current signal level, suitable for microprocessor based systems. The VA (Voltage Amperage) burden, applied to the secondary output of AC current transformers, can have a significant impact on the accuracy performance of AC current transformers. In order to achieve the required accuracy level for a specific application, the primary to secondary ratio of the AC current transformer must be carefully matched with the VA load of the monitoring device to provide optimal accuracy performance.

Secondary load of AC current transformer

The secondary burden or impedance on the AC current transformer directly affects the accuracy performance of the AC current transformer. The overload of the secondary coil of the AC current transformer will seriously affect the accuracy performance of the AC current transformer. Careful consideration should be given to the interface between monitoring equipment and current transformers to ensure optimal accuracy performance.

Exchange secondary voltage

For typical AC current transformers with AC voltage secondary signals, maintaining a secondary load of ≥ 10000 ohms is usually sufficient to ensure optimal accuracy performance. The power consumption from the secondary coil of the AC current transformer is minimized.

AC current secondary

For current transformers with AC current secondary signals, secondary burden is crucial for the accuracy performance of the current transformer.

For the purpose of this article, we will discuss the CTSB0816 split core current transformer, which has a 5A secondary output signal at rated primary current. This example will compare two CTSB0816 open type current transformers of the same model, each configured with a different rated primary current:

CTSB0816-500A/5A type, with a rated primary current of 500A, and a secondary signal at a rated primary current (500A) of 5A,

CTSB0816-5000A / 5A， The rated primary current is 5000A, and the secondary signal is at 5A rated primary current (5000A).

The comparison between the two models shows that there is a significant difference in the burden required to meet specific accuracy levels of performance.In this example, to achieve an accuracy level of 0.5 for CTSB0816-500A/5A, the secondary burden must be less than 2.5VA, while the secondary burden for CTSB0816-5000A/5A must be less than 20.0VA.When calculating the load (VA) of a current transformer, not only should the burden of the measuring equipment be considered, but also special consideration should be given to the lower VA load, i.e. the length of the wire from the current transformer to the measuring equipment.For the CTSB0816-500A/5A configuration, the impedance of the current transformer coil (inductance and resistance) and the length of the wire from the current transformer to the measuring device may seriously affect the accuracy performance.