Control And Tripping Circuits - Siemens 7SR224 Technical Manual

7SR224 Argus Applications
1.2.2

Control and tripping circuits

Where a binary input is used to as part of a control function, for example tripping or closing a circuit breaker, it
may be desirable to provide an enhanced level of immunity to prevent maloperation 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.
Where the battery voltage allows its use, the 88V binary input will give an added measure of immunity, compared
to the 19V binary input, due to its higher minimum pickup voltage.
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: Category ESI 1 may be adopted for
connections which do not include significant wiring runs or cabling outside the relay enclosure. 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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