Technical description
2 Protection functions
2.12 Line differential protection
LdI> (87L)
VM59.EN001
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81
Figure 2.12-7 Up to 16 event stamped binary signals
Parameters of the line differential protection stage LdI> (87L):
Parameter
Value/unit
Description
Setting
values
dI> pick-up
I
n
Basic setting for lower phase
currents
Start of slope
I
n
Phase current limit for
applying linear threshold
characteristics
Slope
%
Linear characteristics slope
CT primary
(remote END)
[10 ..
20000]
CT ratio of the other unit
Default 500
Recorded
values
TCntr
Trip counter (Trip) reading
LdI> status
Protection state
Synchronized
Synchronization status
In VAMP59 current comparison is based to nominal primary
currents of both ends. In line or cable differential protection
“nominal primary” value should be the same the “CT primary”
value.
When it comes to transformer protection it is normal that
nominal current of the transformer differs of the CT nominal
which is higher. To ensure correct differential calculation it is
important to know the nominal current of the other end as well.
When there is transformer on the line or VAMP59 is used
mainly to transformer differential protection, it is possible to
select correct connection group and whether the relay is on
high voltage (HV) or low voltage side (LV).
