P3 binary input threshold

[palak]

Easergy P3 relays binary inputs are rated form 24 to 255 VAC/DC with binary threshold link to order code as 24 VDC/110 VDC/220 VDC. question is even if we select 24 VDC in order code for all application then whatever the control voltage DI will activate so what is the reason or application when we select different threshold voltage.  for 110 VDC system would it be ok to select threshold as 24 VDC or it should be 110 VDC? 

[Rudolf_Simon · Accepted solution]

The need of higher binary input switching thresholds (> 50 % Vaux.nom) is independent from the relay platform.

The technical problem is illustrated in the figure below.  It is of relevance if the station supply battery is either set up with 2 segments and the neutral is grounded via a high resistance, or the DC circuit is equipped with an earth-fault monitoring device.  Then under certain earth-fault conditions (fault location as shown in the figure in the attached pdf) a voltage is present across the binary input of about half nominal battery voltage and a small current flows (practically determined by the resistances of the monitoring circuit and the opto-coupler input).  Under this condition, a wide-range opto-coupler input would pick up. 

One solution to prevent the false operation of the input under this condition is to have an operating threshold above half nominal battery voltage.

Another (‘classical’) solution is to use 2-pole switching on the few critical inputs (like intertripping inputs) – per 2nd sketch in the pdf.

In any case immediate action is recommended in case of bad isolation state of the battery supply system.