Calculating Settings For Four Step Phase Overcurrent Protection, Hv-Side, Oc4Ptoc; Calculating General Settings; Calculating Settings For Step 1 - ABB Relion 650 Series Applications Manual

Section 3
RET650 setting examples
Setting
3.1.6 Calculating settings for four step phase overcurrent
protection, HV-side, OC4PTOC
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 of the fault type. In order to
achieve setting that assure 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 have 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)
The reach of phase overcurrent line protection depends on 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 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.
3.1.6.1

Calculating general settings

1. Set
The settings are made in primary values. These values are given in the base settings in
Global base 1.
2. Set
The function shall be non-directional
3. Set
For the choice of time delay characteristic IEC Normal inverse is used in this network.
3.1.6.2

Calculating settings for step 1

1. Set
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:
40
IP>> = 1000 % of IBase
GlobalBaseSel to 1
DirMode1 to Non-directional
Characterist1 to IEC Norm.inv.
I1> to 140% of IBase (334 A primary current)
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Transformer protection RET650
Application manual