Functionality
30 USER MANUAL FPC 200 - 3/2017
Inrush restraint
Inrush restraint function is a blocking function. The function can block overcurrent or earth fault overcurrent protection
from operating for pre-defined period of time.
2.2.6.1 Functionality
Transformer inrush current includes high 2
nd
harmonic
component. The Inrush restraint function is based on
evaluation of 2
nd
harmonic component present in the
inrush current. Inrush current detection is set for each
monitored current separately as defined in Table 16.
When transformer is energized high amount of 2
nd
harmonic component is present. In order to prevent
unwanted tripping Inrush restraint function can be used.
Another example is in combination with 50N/51N
protection function. When large object (e.g.
Transformer) is energized large amount of transients are
present. Because of that a large zero sequence can be
calculated which can trigger unwanted tripping of
50N/51N protection function. To once again prevent
unwanted tripping Inrush restraint should be used.
In order for inrush restraint to inhibit desired protection
its output should be assigned in parameter Inrush
restraint source which is present in all types of
overcurrent protection [2.2.1, 2.2.2].
2.2.6.2 Monitoring
Monitored currents are different for each protection
function.
Table 16: Monitored currents.
Inrush detection
Inrush pickup
Inrush block
Max. inrush time
t < 20 ms
Figure 2.24: Inrush Restrain characteristic.
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