Calculating General Settings; Calculating Settings For Step 1 - ABB Relion 650 Series Applications Manual

Section 3
RET650 setting examples
locations, different switching states in the system and different earth-fault types. Below one
example of setting of residual overcurrent protection for a line in a meshed solidly earthed
system is given.
If there is no generation at the low voltage side of the generator the transformer can only feed
earth-fault currents as long as any of the non faulted lines are still in operation. If there is
generation connected to the low voltage side of the transformer the transformer can feed 145
kV earth-faults alone.
The residual overcurrent protection has the following purpose:
• Fast and sensitive protection for earth-faults on the 145 kV busbar
• Backup protection for earth-faults in the 145 kV transformer winding
• Backup protection for earth-faults on the 145 kV lines out from the substation
• Sensitive detection of high resistive earth-faults and series faults in the 145 kV network
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. Different time delay principles can be used. This is due to different praxis.
The following principle for the residual overcurrent protection is proposed:
• Step 1 (
directional function. This step gives fast trip for the busbar earth-faults and some earth-
faults on the lines.
• Step 2 (
the 145 kV lines out from the substation. Step 2 has non-directional function. The function
has a delay to enable selectivity to the line protections.
• Step 3 (
and series faults in the network. Step 3 has non-directional function. The function has a
longer delay to enable selectivity.
3.1.8.1

Calculating general settings

The settings are made in primary values. These values are given in the base settings in Global
base 1.
1. Set
2. Set
3. Set
3.1.8.2

Calculating settings for step 1

Set operating residual current level and time delay
1. Set
Faults are applied at the 145 kV busbar as shown in figure 18.
46
IN1> ) with high current setting and a short delay (about 0.4 s). Step 1 has non-
IN2> ) with a current setting, if possible, that enables detection of earth-faults on
IN4> ) with a current setting that enables detection of high resistive earth-faults
GlobalBaseSel to 1
DirMode1 , DirMode2 and DirMode4 to Non-directional
DirMode3 to Off
IN1> to 650% of IBase , corresponding to 1553 A
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Transformer protection RET650
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