Calculating Settings For Restricted Earth Fault Protection Refpdif - ABB Relion 650 Series Applications Manual

Section 3
RET650 setting examples
The current transformers class is 5P giving a maximum amplitude error of 1 % and
maximum phase displacement of 60 minutes. To assure that the load current does not
cause unwanted operation
10. Set
The unrestrained differential protection function is operated without any stabilization.
The setting principle is that the unrestrained function shall only be able to detect internal
faults. This means that the current setting shall be larger than the largest current
through the transformer at external faults. A very simple way to estimate this current is
as:
IdUnre
GUID-D44EC374-13ED-4E91-A420-F9C7460F71C2 V2 EN-US
If the feeding network is considered and a three-phase-fault at the low voltage side of
the transformer is calculated, the following current results through the transformer (145
kV level):
I
GUID-D49C58EF-F9FD-4BAD-943A-55C186968C2F V2 EN-US
This corresponds to 7.6 times the transformer rated current. In the setting there should
also be consideration to the influence from fault current DC-component.
11. Set
11.1. Set
11.2. Set
11.3. Set
The transformer differential protection also has external/internal fault discrimination,
based on negative sequence current. The settings of
NegSeqROA are defined as advanced and the default values are recommended.
3.1.4 Calculating settings for restricted earth fault protection
REFPDIF
The restricted earth fault protection is applied to the 145 kV winding as shown in figure 12.
IEC09000448 V1 EN-US
Figure 12:
38
IdUnre to 10.0 IBase
1 1
³ × = ×
IBase IBase
e 0.12
k
145
= =
× +
3 ( Z Z )
net T
×
3 ( . 3 5
NegSeqDiffEn , IMinNegSeq and NegSeqROA
NegSeqDiffEn to On (default)
IMinNegSeq to >0.04 IBase (default)
NegSeqROA to 60º (default)
Restricted
earth-fault
protection
Restricted earth fault protection application
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IdMin is set to 0.25 times the rated transformer current.
= ×
8.33 IBase
145
=
1 83 . kA
2
145
+ ×
0 12 . )
60
1MRK 504 124-UEN B
NegSeqDiffEn , IMinNegSeq and
GUID-FBC09EEE-3426-4A18-A23D-CA23BD23E5D7 v2
IEC09000448-1-en.vsd
Transformer protection RET650
Application manual
(Equation 3)
(Equation 4)