ABB RELION REX640 Technical Manual page 544

Section 4
Protection functions
538
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Figure 293: Example of interpretation of network damping value, I_DAMPING,
calculated by the coil controller
For example, if the resistive current of the parallel resistor is 10 A (at primary voltage
level), then a value of 0.5 · 10 A = 5 A could be used for setting Min operate current.
The network damping value, I_DAMPING, calculated by the coil
controller can be used as a base for setting Min operate current.
If Operating quantity is set to "Adaptive", the setting value Min operate current is also
applicable if the coil is disconnected and the network becomes unearthed. In this case,
the current magnitude supervision is automatically based on the amplitude of
The selected setting value must never exceed the ampere value of the parallel resistor
in order to allow operation in the faulty feeder. In case of smaller ampere value of the
parallel resistor, for example 5 A, the recommended security factor should be larger,
for example 0.7, so that sufficient margin for CT and VT errors can be achieved.
If Operating quantity is set to "Amplitude", the Min operate current setting should be
selected based on the capacitive earth-fault current values produced by the
background network in case of a solid earth fault with a security margin.
The main task of the current magnitude supervision module is to
secure the correct directional determination of an earth fault so that
only the faulty feeder is disconnected or generates alarms. Therefore,
the threshold value Min operate current should be selected carefully
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REX640
Technical Manual