2
145 145
1.83
3 ( )
145
3 (3.5 0.12)
60
net T
I kA
Z Z
= = =
× +
× + ×
GUID-662F8080-2FA3-47D9-B030-CDB4D502DB53 V2 EN (Equation 1)
The dynamic overreach, due to fault current DC-component, shall be considered in
the setting. This factor is less that 5 %. The setting is chosen with a safety margin of
1.2:
I
set
≥ 1.2 · 1.05 · 1 830 = 2 306 A
SettingPickup = 1000 % of IBase
3.1.4 Calculating settings for four step phase overcurrent protection
3-phase output, HV-side, OC4PTOC (51_67)
The phase overcurrent protection is difficult to set as the short circuit current is highly
dependent of the switching state in the power system as well as the fault type. In order to
achieve setting that assure a selective fault clearance, a large number of calculations have
to be made with different fault locations, different switching states in the system and
different fault types.
The 145 kV phase overcurrent protection has the following tasks:
• Backup protection for short circuits on the transformer
• Backup protection for short circuits on 22 kV busbar
• Backup protection for short circuits on outgoing 22 kV feeders (if possible)
Although it is possible to make hand calculations of the different faults it is recommended
to use computer based fault calculations.
The following principle for the phase overcurrent protection is proposed:
• Only one step (step 1) is used. The time delay principle is chosen according to
network praxis, in this case inverse time characteristics using IEC Normal inverse.
3.1.4.1 Calculating general settings
1. Set GlobalBaseSel to 1
For the (HV) winding data should be related to Global base 1
2. Set DirModeSel1 to Non-directional
The function shall be non-directional
3. Set Characterist1 to IEC Norm.inv.
1MRK 511 286-UUS A Section 3
REC650 setting examples
43
Application manual
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