Calculating Settings For Step 2 - ABB Relion 650 Series Applications Manual

Section 3
RET650 setting examples
The time delay must be chosen so that the blocking signal shall be able to prevent
unwanted operation at feeder short circuits. 0.1 s should be sufficient.
3.1.7.3

Calculating settings for step 2

The first requirement is that the phase overcurrent protection shall never trip for load current
during the extreme high load situations. It is assumed that the transformer shall be able to be
operated up to 130 % of the rated power during limited time. Further shall the protection
resetting ratio be considered. The resetting ratio is 0.95. The minimum setting can be
calculated as follows:
³
I 1.3
pu
GUID-4D6B62EC-32DC-433E-B1C8-D23E8D06D017 V1 EN-US
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 16.
145kV
3
IEC09000452 V1 EN-US
Figure 16: Fault calculation for phase overcurrent protection
The following fault is applied: phase-phase-earth short circuit. In this calculation should the
short circuit power in the feeding substation be minimized (the source impedance
maximized).
1. Set
2205 A primary current.
The longest 22 kV feeder has the impedance Z = 3 + j10 Ω. The external network has the
maximum source impedance Zsc = j10 Ω (145 kV level). This impedance is transformed to
22 kV level:
Z
GUID-BA67F1FC-2DCE-4E04-BBB3-FABB86FDEA3A V1 EN-US
The transformer impedance, referred to 22 kV level, is:
The phase-to-phase fault current can be calculated:
I
sc ph
GUID-BAA8989B-EF8F-4277-9B2B-EBBCA35ED7C2 V1 EN-US
44
×
1 60 1000
× × =
2155 A
×
0.95
3 22
RET650
Ph-Ph
3
1
I2> to 140 % of IBase
2
æ ö
22
= × = W
j 10 j 0.23
ç ÷
sc ,22
è 145 ø
3 22000 / 3
= ×
2
+ + +
2 j 0.23 j 0.97 3
© Copyright 2011 ABB Power Grids. All rights reserved
I>
22kV
1 1
=
949 A
j 10
1MRK 504 124-UEN B
GUID-F2126B37-2182-406B-B8B2-6DF26A78409A v2
(Equation 14)
IEC09000452-1-en.vsd
(Equation 15)
(Equation 16)
Transformer protection RET650
Application manual