The EM3550 and it's EM35xx family can directly accept Rogowski ct's, but how does this effect the CT ratio programmed in the meter?
This version of Rogowski CT I am dealing with can accept values from 20-5000 Amps but I am not exactly sure how this scales to our meter.
The default programmed CT ratio in an EM35xx is 100:5, does this need to be modified for proper operation?
I was not aware that you could use Rogowski CT's with this range. The output from this coil I a voltage proportional to the current, so there would need to be a selection in the meter between current (Normal CT's) and voltage to enable the scaling on voltage to current.
The only thing that I have been looking at is a converter for Rogowski outputs into a current that our meters can accept.
Here is a link to the Phonix Contact coils and converters. But I have not had a project yet that I can try these out on.
Here is the knowledge base article on the EM35xx meters and the Rogowski CT's http://www.powerlogic.com/kbarticle.cfm?myrequest=FA233732.en_US
I think these particular meters can only accept rogowski ct's, as there is not an internal setup feature that I have found to switch between the two types of CT.
When programming the EM3500's, there are 2 CT parameters to set up:
CT V - CT Input Voltage: 1.0V or 0.33V.
CT SZ - CT Size: in Amps. Maximum is 32000 Amps.
Only the EM35xxA (Part number must end with "A" aka "A" version) works with the U018 Rogowski Rope CTs. The regular EM35xx meters will not accept the U018 Rogowski Rope CTs.
When programming the EM35xxA, the meter will not ask for the CT output voltage as the U018 Rope CTs are the only type it will accept. Since CT range covers 20A to 5000A, you will only program the CT size corresponding to the service. It is recommended to use the Rope CTs for 400A and above applications.
Why wouldn't you set the CT scale to 5000A since that corresponds to the .33V output on the secondary side. Does the meter internally correct for this?