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2 Functions
Figure 2-17
Logic diagram of the unbalanced load protection
2.10.2 Setting Notes
The unbalanced load protection is only in effect and accessible if address 117
General
UNBALANCE LOAD is set to Enabled during configuration. If the function is not re-
quired Disabled is set.
The address 1701 UNBALANCE LOAD serves to switch the unbalanced load protec-
tion ON or OFF or to block only the trip command (Block relay).
The maximum permissible, continual negative phase-sequence current is important
for the thermal model. For machines of up to 100 MVA with non-salient pole rotors, this
typically amounts to a value in a range from 6 % to 8 % of the nominal machine current,
and with salient-pole rotors at least 12 %. For larger machines and in cases of doubt,
please refer to the instructions of the machine manufacturer.
It is important to note that the manufacturer's data relate to the primary values of the
machine, for example, the maximum permissible continuous inverse current is re-
ferred to the nominal machine current. For settings on the protective relay, this data is
converted to the secondary inverse current. The following applies
with
I
I
I
72
Permissible thermal inverse current of the motor
2 perm prim
Nominal current of the machine
N Mach
Primary nominal current of the current transformer
N VT prim
7UM61 Manual
C53000-G1176-C127-3
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