Use Of Binary Inputs In Control And Tripping Circuits - Siemens 7SR18 Solkor Manual

7SR18 Applications Guide
3) Set equation E1 to operate virtual I/O V1 in the Output Matrix:
4) Set virtual I/O V1 to operate Inhibit 51-1 in the Input Matrix:
1.2.4

Use of Binary Inputs in control and tripping circuits

Where a binary input is used to as part of a dc control function, for example tripping or closing a circuit breaker, it
may be desirable to provide an enhanced level of immunity to prevent unwanted trips due to induced voltages.
This is most important where cross-site cabling is involved, as this is susceptible to induced voltages and will
contribute to capacitive discharge currents under DC system earth-fault conditions. One method of enhancing the
immunity of the binary input is to switch both positive and negative connections; however this is often not possible
or desirable.
As a guide to suitable degrees of enhanced immunity, we have adopted the parameters laid down in U.K.
standard EATS 48-4. This standard identifies two levels of immunity: -
1. Category ESI 1 may be adopted for connections which do not include significant wiring runs or cabling
outside the relay enclosure.
2. Category ESI 2 should be used for connections which include significant wiring runs or cabling outside
the relay enclosure. This category also gives immunity to capacitive discharge currents.
The following diagrams show the external resistors which should be fitted to allow the binary input to comply with
either of the above categories.
Fitting these components will raise the current required to operate the binary input, and hence makes it less
susceptible to maloperation.
Where required, the minimum pickup delay for the binary input is stated on the diagram.
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