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How do I select the proper rated output (burden) value of my voltage transformer?

Sometimes one can select a relatively high value of rated output (burden) for a given voltage transformer as it is commonly thought the better choice when we are not sure about the typical burdens (loads) connected to our voltage transformer secondary. 

IEC 61869-3 gives the standard values for rated output (burden) for a given voltage transformer: 

In many cases where devices connected are mainly of micro-processor based protection /metering equipment, the overall burden can only be a few VAs; in other words a burden range (I) voltage transformer is considered adequate in many cases. 

It is important to know that using an "oversized" voltage transformer rated output (burden) has a negative impact on accuracy thus increasing the error of the measurements.
The below highlights provides the limits of error which IEC 61869-3 specifies for each burden range. 


Finally, it is important not to oversize your voltage transformer too far beyond the actual need for rated output in order to avoid increase of errors at a lower value of burden applied. 
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