Calculating Settings For Four Step Phase Overcurrent Protection, Lv-Side Oc4Ptoc - ABB Relion 650 Series Applications Manual

Section 3
RET650 setting examples
I>: 300 A which corresponds to 45 A on 145 kV level.
I>>: 6 000 A which corresponds to 910 A on 145 kV level.
Characteristic: IEC Normal Inverse with k-factor = 0.25
The setting of the k-factor for the 145 kV phase overcurrent protection is derived from
graphical study of the inverse time curves. It is required that the smallest time difference
between the inverse time curves shall be 0.4 s. With the setting
between the characteristics is about 0.4 s as shown in figure 15.
IEC09000451 V1 EN-US
Figure 15:
3.1.7 Calculating settings for four step phase overcurrent
protection, LV-side OC4PTOC
The 22 kV phase overcurrent protection has the following purpose:
• Main protection for short circuits on 22 kV busbar
• Backup protection for short circuits on outgoing 22 kV feeders (if possible)
The reach of phase overcurrent line protection is dependent of the operation state and the
fault type. Therefore the setting must be based on fault calculations made for different faults,
fault points and switching states in the network. Although it is possible to make manual
calculations of the different faults it is recommended to use computer based fault
calculations. Different time delay principles can be used. This is due to different praxis.
42
Inverse time operation characteristics for selectivity
© Copyright 2011 ABB Power Grids. All rights reserved
1MRK 504 124-UEN B
k1 = 0.15 the time margin
GUID-4159DE32-08C2-424A-920F-1C537BE10EEF v2
Transformer protection RET650
Application manual