Calculating Settings For Step 4 - ABB REC650 Applications Manual

Section 3
REC650 setting examples
3.1.5.3
48
2
æ ö
22
= × =
Z j 10
ç ÷
sc ,22
è 145 ø
GUID-A4805F4D-20EC-4B39-A39D-925513515FA5 V1 EN
The transformer impedance, referred to 22 kV level, is:
2
22
= × =
Z j 0.12
T ,22
60
GUID-CB0D94B6-5BFA-42EB-AE4A-B0EE898A0D78 V1 EN
Calculation of a phase-to-phase short circuit at this busbar:
3 22000 / 3
= ×
I
sc ph 2
+
2 j 0.23
GUID-846C7A33-F976-45DF-95E9-75124D6A24D2 V1 EN
The setting is chosen to 5 IBase which corresponds to 7 875 A primary current.
2. Set t1 to 0.1 s
The time delay must be chosen so that the blocking signal shall be able to prevent
unwanted operation during feeder short circuits. 0.1 s should be sufficient.

Calculating settings for step 4

The first requirement is that the phase overcurrent protection shall never trip for load
current during extreme high load situations. It is assumed that the transformer shall be able
to be operated up to 130% of the rated power during the limited time. The protection
resetting ratio of 0.95 shall also be considered. The minimum setting can be calculated as
follows:
×
1 60 1000
³ × × =
I 1.3 2155
pu
×
0.95
3 22
GUID-4D6B62EC-32DC-433E-B1C8-D23E8D06D017 V1 EN
The next requirement is that the protection shall be able to detect all short circuits within
the defined protected zone. In this case it is required, if possible, that the protection shall
detect phase-to-phase short circuit at the most remote point of the outgoing feeders as
shown in figure 8.
W
j 0.23
W
j 0.97
=
9167 A
j 0.97
A
1MRK 511 286-UUS A
(Equation 7)
(Equation 8)
(Equation 9)
(Equation 10)
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