CT Burden Question

[podobing]

I have encountered a situation with a resistance grounded system that has a 25 ampere neutral grounding resistor. There is a 25:5 CT in series with the resistor to measure ground fault current. The CT secondary is connected to three CO-11 relays that are connected in series using 300 feet of #12 AWG wire (total length). Each relay is set on the 0.5 ampere tap, and each relay is set at a different time dial setting. On one side, my gut tells me that there is too much burden connected to this CT, but on the other side, I only need to obtain 0.5 amperes for proper relay operation. Can someonse shed some light on this problem for me?
Regards,
Dave

 

[dpc]

The burden for the 0.5 A tap may be pretty high depending on the relay tap range. The burden is a function of the tap settings. In addition, the accuracy class for a 25/5 CT is probably very low if it even has a relaying accuracy. Plus you have three relays to drive. But the max current is going to be 25 A.

To really analyze this, you will need the CT excitation curve, or at least the accuracy class of the CT. The relay burden data should be readily available.