What is the difference between "Sum 3I" and "Input Io" when setting the ANSI 50/51N protection in a Sepam relay?

FA179989

13/05/2020

Issue              
The residual CT is wired to the Sepam but how to make sure its not using the calculated version for protection?

Product Line                   
Sepam 20 Series
Sepam 40 Series
Sepam 60 Series
Sepam 80 Series

Resolution
When setting the ANSI 50/51N protection, the Sepam relay provides 2 different options for residual current type: "Sum 3I" and "Input Io".


The residual current type depends on the wiring of the current APS_SENSORS to the relay. If, for example, the relay is wired with a standard 3-phase current connection without wiring the Ir input of the CCA634 or using a CSH zero-sequence ct, the "Sum 3I" option needs to be selected. The measurement of the 3-phase currents allows the "calculation" of residual current.

* Note: A 2-phase current connection will not calculate residual current.

If, for example, the CCA634 Ir input is wired or a CSH zero-sequence ct is used, the Sepam will "measure" the residual current and "Input Io" needs to be selected when configuring 50/51N.