AQ: Current transformer selection
When you want to select current transformer with appropriate rated power for your power system, you need to consider that value of rated power of selected current transformer should be higher from sum of values of load and Joules’ losses which are a consequence of flow current through conductors which connect current transformer with relay.
So, if you have a long distance between current transformer and relay, then you need to consider one of two following manners for solving this problem:
1. replacing existing current transformer with current transformer with higher power,
2. replacing existing conductors with conductors with lower cross-section.
This solution is a consequence of necessity for reducing of Joules’ losses which are a consequence of flow current through conductors which connect current transformer with relay. If you have conductors whose value of rated current is 5A, you will have Joules’ losses P=R*I^2=R*5^2=25*R. Otherwise, if you have conductors whose value of rated current is 1A, you will have Joules’ losses P=R*I^2=R*1^2=R.
On this way, Joules’ losses in your selected conductors will be reduced 25 times and selected current transformer will be unloaded by reducing additional load.
