GE MiCOM P40 Agile Technical Manual page 154

Chapter 6 - Current Differential Protection
Using the Inrush Restraint setting you can choose what will happen to differential characteristic in the presence of
second harmonic current:
If set to Disabled, the characteristic will not be modified,
●
If set to Restraint, the characteristic will be restrained if the second harmonic component is above a
●
user set threshold.
If set to Blocking, the protection will be blocked
●
The Restraint and Blocking modes are qualified by other settings outlined below. In both cases an
unbiased high-set current differential element becomes visible.
Note:
You must set Compensation to Transformer before the Inrush Restraint setting becomes visible.
Note:
When used, the Inrush Restraint function must be enabled at all ends to avoid possible maloperation.
Note:
There is an Inrush Detection setting in the SUPERVISION column of the menu. The Inrush Detection setting is only visible if
the Inrush Blocking'in the CURRENT DIFF column is not being used. The function asserts the same DDB outputs as Inrush
Restraint and can be used to control other protection elements during magnetising inrush conditions. The output of Inrush
Detection does not, however, affect the Current Differential protection.
10.3.1.1 SECOND HARMONIC RESTRAINT
If the Inrush Restraint setting is set to Restraint, then a percentage of the second harmonic component of the
input signal is added to the bias quantity used in the current differential characteristic.
The amount of additional bias to be added into the calculation is defined by the following expression:
Additional bias = Ih(2) Multiplier * 1.414 * largest 2nd harmonic current
You can set Ih(2) Multiplier between 1 and 20 according to your application.
Note:
Where Inrush Restraint is used to restrain operation, it must be used at all terminals in the scheme to avoid possible
maloperation.
10.3.1.2 SECOND HARMONIC BLOCKING
If the Inrush Restraint setting is set to Blocking, then the operation of the current differential elements will be
blocked if magnetising inrush is detected.
Magnetising inrush is considered to be present if the level of phase current is above 5% In AND the ratio of
harmonic to fundamental in that phase exceeds the Ih(2) %> value which you set.
Detection of magnetising inrush forces a phase block signal to block local and remote ends.
You can choose whether to block just the affected phase, or to block all three phases using the Ih(2) CrossBlock
cell. If you disable Ih(2) CrossBlock, only the affected phase is blocked. If you enable Ih(2) CrossBlock, all phases
are blocked.
10.3.1.3 HIGH SET DIFFERENTIAL
It is possible for current transformers (CTs) to saturate under heavy internal fault conditions. CT saturation, like
magnetising inrush, is characterised by significant second harmonic components. The protection is required to
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P543i/P545i
P54x1i-TM-EN-1