I I I I I
LOC C LOC C LOC A LOC B LOC C
− − − − −
= − × + +
_ _ _ _ _
1
3
GUID-D5203A0B-D0A0-4147-B1F0-06C2B78B288B V1 EN
Fail safe function
To prevent malfunction during communication interference, the operation of 87L is
blocked when the protection communication supervision detects severe interference in the
communication channel. The timer reset stage is activated in case the stabilized stage is
started during a communication interruption. The protection communication supervison
is connected internally from PCS to 87L (dotted OK line).
PROT_ACTIVE
BLOCK
Protection
communication
supervision
(PCS)
AND
OK
Operation ”Test/blocked”
Operation ”Off”
GUID-A0935D4B-06D6-4384-8652-3E7D28D839D8 V1 EN
Figure 232: Operation logic of the fail safe function
The function can also be set into “test/blocked” state with the Operation setting. This can
also be utilized during the commissioning.
The BLOCK input is provided for blocking the function with the logic. When the function
is blocked, the monitored data and measured values are still available but the binary
outputs are blocked. When the function is blocked, the direct inter-trip is also blocked.
The PROT_ACTIVE output is always active when the protection function is capable of
operating. PROT_ACTIVE can be used as a blocking signal for backup protection
functions.
Timer
Once activated, the timer activates the STR_LS_LOC output. Depending on the value of
the set Operating curve type, the timer characteristics are according to DT or IDMT. When
the operation timer has reached the value set with the Trip delay time in the DT mode, the
maximum value defined by the inverse time curve, the OPR_LS_LOC output is activated.
When the operation mode is according to IDMT, Low trip value is used as reference value
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 479
Technical Manual
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