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What is the real power (in VA) that the current transformer must provide for metering and/or protection devices circuits? How can I estimate its value?

This is the sum of the consumption of the cabling and that of each device connected to the current transformer secondary circuit.
  • Consumption of copper cabling (line losses of the cabling):
Here are estimate values of secondary cabling consumption: 
  • Consumption of metering or protection devices:
Consumption s of various devices are given in the manufacturer's technical data sheet; here are some common values can be used for estimation purposes: 

1) Estimated consumption for metering instruments: 

2) Estimated consumption for protection relays:

Tip: selection of a current transformer rated output (burden) value for metering purpose should be a close as possible to the calculated real output to avoid negative impact on measuring accuracy.
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