ABB RELION REX640 Technical Manual page 532

Section 4
Protection functions
526
Voltage start value
Maximum
healthy-state
Uo
GUID-08EC8DF9-03C9-4AFB-BF61-9EDA74BC6B49 V1 EN
Figure 287: Example of selection of setting Voltage start value to maximize the
earth-fault detection sensitivity based on the resonance curve
calculated by the coil controller
There are three MFADPSDE instances (stages) available. The
sensitivity of different stages should be selected differently. For
example, stage 1 could have the highest Voltage start value and the
shortest Operate delay time. Thus it would fulfill the requirements for
protection operation speed by providing fast operation for low-ohmic
earth faults. Stage 2 should have lower Voltage start value and longer
Operate delay time compared with stage 1. This stage would fulfill the
requirements for protection sensitivity (in terms of fault resistance
value). Stage 3 could be used to detect high-ohmic earth faults and
generate alarms for them. To maximize the earth-fault detection
sensitivity of stage 3, Voltage start value should be selected based on
the network's resonance curve (see
Such coordination of different protection stages enables:
• Indication (but no tripping) of transient, self-extinguishing earth faults, where the
zero-sequence voltage may temporarily rise to a high value and then decay slowly
away. This can be achieved by monitoring the START outputs. Delayed operation
Resonance Curve
Uo [%]
20 40
68 A
1MRS759142 C
Margin of
few %
60 80 100
Figure 287).
Technical Manual
lcoil: A
120
REX640