ADR233B
Ref ID : ADR233B/IM/PS
Rev No. : 05
Page No. : 133 of 479
2H Diff Threshold
2H current
+
-
&
Diff L1 T
Hr m BL k Mod e
=2H&4H
2HDif-A B
&
2HDif-B B
2HDif-C B
4H Diff Threshold
4H current
+
-
Cr os s Blo cking =
Enabled
Cr os s Blo cking = Timer
or
+
-
t Cro ss
blocking= 0.5s
Time measure from
any p hase 2
nd
and 4
th
hrm detection
&
Figure 9: Harmonic blocking (2
nd
and 4
th
Harmonic selection)
Harmonic blocking logic for B phase and C Phase Also Same like Harmonic blocking logic of A Phase
5th Harmonic Blocking (5th Hrm Diff BLK)
The ADR233B relay provides 5
th
harmonic blocking feature to block the differential tripping
during transformer over excitation condition. The device is determining the fundamental I(fn) and
fifth harmonic Components I (5*fn) of the differential current. If the ratio I (5*fn)/I(fn) exceeds a
specific adjustable value (typical setting 20%) in at least one measuring system, Differential
tripping is Blocked
4.7 Restricted Earth Fault (64R) Protection
Winding-to-core faults in a transformer can be caused by insulation breakdown. Such faults can
have very low fault currents, but they still need to be picked up. If such faults are not identified,
this could result in extreme damage to very expensive equipment. Often the associated fault
currents are lower than the nominal load current. Neither Over Current nor percentage
differential protection is sufficiently sensitive in this case. We therefore require a different type of
protection arrangement. Not only should the protection arrangement be sensitive, but it must
create a protection zone, which is limited to each transformer winding. Restricted Earth Fault
protection (REF) is the protection mechanism used to protect individual transformer winding
sets.
The ADR233B relay is consisting of two different types of Restricted Earth Fault; Low
Impedance REF (also known as Biased REF) and High Impedance REF. Each method
compensates for the effect of through-fault errors in a different ways.
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