ABB REQ650 - Calculating Settings for Pole Discordance Protection

3.1.7 Calculating settings for four step residual overcurrent
protection 3I0> EF4PTOC
The purpose of the delayed residual overcurrent protection is:
• Backup protection for earth faults on the whole line length
• Backup protection for earth faults in the remote busbar
• Backup protection for earth faults in other lines from the remote substation or
own substation, when possible
The reach of residual 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 hand calculations of the different faults, it is recommended to use computer
based fault calculations. Due to different practices, different time delay principles can
be used.
The following principle for the phase residual overcurrent protection is proposed:
• One delayed step used as line backup protection. It should be set to assure
selectivity to line protection. Directional function forward is used.
• One delayed step used as backup protection of the own busbar. It should be set to
assure selectivity to line protection. Directional function reverse is used.
• A long time delayed step covering further parts of the system and detecting high
resistive faults. This step should have a time delay longer than 1.2 s. Non-
directional function is used.
3.1.7.1 Calculating general settings
1. Set GlobalBaseSel to 1.
The settings are made in primary values. These values are given in the base
settings in Global base 1.
3.1.7.2 Calculating settings for step 1
The protection shall be able to detect all earth faults within the defined protected zone.
In this case, it is required, that the protection shall detect single-phase earth at the most
remote point of the protected line. A single-phase earth, as shown in figure
17, at the
remote line end and high source impedance results in the following fault current to the
protection:
0
3 1.6 87I kA= Ð - °
EQUATION2348 V1 EN
1MRK 505 291-UEN A Section 3
REQ650 setting examples
53
Application manual