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Section 7: Common Functions
7.1
Binary Inputs
Each Binary Input (BI) can be programmed to operate one or more of the relay functions, LEDs or output relays.
These can be used to bring such digital signals as Inhibits for protection elements, CB position status and trip
circuit supervision status etc. into the Relay.
Alarm and Tripping Inputs
A common use of binary inputs is to provide indication of alarm conditions, fault conditions or switching
operations. The Binary Inputs can be mapped to LED(s), waveform storage trigger and binary outputs.
The inputs can also be mapped as 'General Alarms' – this allows user defined text to be displayed on the LCD
when the BI is energised. Inputs used in this way are programmed using:
INPUT CONFIG>INPUT MATRIX>General Alarm n – Assigned to BI.
INPUT CONFIG>GENERAL ALARMS>General Alarm n – 16 character string.
The Effects of Capacitance Current
The binary inputs have a low minimum operate current and may be set for instantaneous operation. Consideration
should be given to the likelihood of mal-operation due to capacitance current. Capacitance current can flow
through the BI, for example if an earth fault occurs on the dc circuits associated with the relay. The binary inputs
will be less likely to mal-operate if they:
1
Have both the positive and negative switched (double-pole switched).
2
Do not have extensive external wiring associated with them e.g. if the wiring is confined to the
relay room.
Where a binary input is both used to influence a control function (e.g. provide a tripping function) and it is
considered to be susceptible to mal-operation the external circuitry can be modified to provide immunity to such
disturbances, see Figure 7-1.
AC Rejection
The default pick-up time delay of 20ms provides immunity to ac current e.g. induced from cross site wiring.
©2013 Siemens Protection Devices Limited
Chapter 7) 7SR23 DAD Applications Guide
Chapter 7 Page 39 of 42
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