Protection Communication Signalling Supervision; Inter-Trip Elements; Internal Inter-Trip Elements (87R-N); External Inter-Trip Elements (85S-N, 85R-N) - Siemens 7SR18 Solkor Manual

3.1.3

Protection Communication Signalling Supervision

The 'Prot'n Comms Disturb' output is raised for any protection communication signalling disturbance
detected. This can be for a CRC error on the frame, a missed frame, a frame out of sequence,
etc. This output is fleeting and will be cleared when authentic communication has been re-established.
The 'Prot'n Comms Alarm' is more of a persistent output. If there is a prolonged disturbance detected
the alarm output will be raised after the 'Prot'n Comms Alarm Delay'. Differential protection is inhibited
during periods of disturbance or when the relays are not synchronised.
'Prot'n Comms In Sync' is raised when there are no communication disturbances and both devices are
now synchronised.

Figure 3.1.3-1 Logic Diagram: Protection Communications Signalling Supervision

3.2

Inter-Trip Elements

There are several types of Inter-Trip elements, internal and external.
3.2.1

Internal Inter-Trip Elements (87R-n)

The line differential elements 87L-1 and 87L-2 each have their associated inter-trip element e.g. 87R-1 & 87R-2.
These are used to ensure both ends of a feeder are cleared when internal fault differential protection has
operated. When an internal fault occurs, even if it is fed largely from one end, the differential comparators at both
ends operate identically and trip their respective circuit-breakers. To ensure tripping at both ends, an inter-trip,
using the above elements, is sent between the local and remote relays.
3.2.2

External Inter-Trip Elements (85S-n, 85R-n)

Six external inter-trip channels are provided designated 85S-n sending & 85R-n receiving. These are of the Direct
Inter-trip type and are independent of the differential protection. They are driven from mapped binary inputs or
internal user programmable logic. At the receiving end the inter-trip follows the status of the sending end binary
input or programmable logic. They can be used as direct control or permissive control via programmable logic to
control features or operate any user selected contact. Inter-trip channels are especially useful to apply Start,
Inhibit, Lockout logic to a Feeder Autoreclose scheme to allow sequenced closing of the circuit-breakers.
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7SR18 Description Of Operation
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