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1MRK 505 370-UEN D
The delay characteristics are described in the "
restrictions regarding the choice of reset delay.
For the independent time delay characteristics the possible delay time settings are
instantaneous (1) and IEC (2 = set constant time reset).
For ANSI inverse time delay characteristics all three types of reset time characteristics are
available; instantaneous (1), IEC (2 = set constant time reset) and ANSI (3 = current dependent
reset time).
For IEC inverse time delay characteristics the possible delay time settings are instantaneous
(1) and IEC (2 = set constant time reset).
For the customer tailor made inverse time delay characteristics (type 17) all three types of
reset time characteristics are available; instantaneous (1), IEC (2 = set constant time reset) and
ANSI (3 = current dependent reset time). If the current dependent type is used then settings
pr, tr and cr must be given.
HarmRestrainx : Enable block of step x from the harmonic restrain function (2nd harmonic).
This function should be used when there is a risk if power transformer inrush currents might
cause unwanted trip. Can be set
tPCrvx , tACrvx , tBCrvx , tCCrvx : Parameters for customer creation of inverse time characteristic
curve (Curve type = 17). See equation
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EQUATION1261 V2 EN-US
For more information, please refer to the "
tPRCrvx , tTRCrvx , tCRCrvx : Parameters for customer creation of inverse reset time
characteristic curve (Reset Curve type = 3). Further description can be found in the "
reference manual ".
7.2.3.2
Second harmonic restrain
If a power transformer is energized there is a risk that the transformer core will saturate
during part of the period, resulting in an inrush transformer current. This will give a declining
residual current in the network, as the inrush current is deviating between the phases. There is
a risk that the phase overcurrent function will give an unwanted trip. The inrush current has a
relatively large ratio of 2
restrain signal to prevent this unwanted function.
The settings for the 2
2ndHarmStab : The rate of second harmonic current content for activation of the 2
restrain signal, to block chosen steps. The setting is given in % of the fundamental frequency
residual current. The setting range is 5-100% in step of 1%. The default setting is 20%.
HarmRestrainx : This parameter can be set Off/On , disable or enable the 2
The four-step phase overcurrent protection can be used in different ways, depending on the
application where the protection is used. A general description is given below.
Busbar protection REB670
Application manual
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nd
harmonic component. This component can be used to create a
nd
harmonic restrain are described below.
Technical reference manual ". There are some
Off/On .
30
for the time characteristic equation.
Technical reference manual ".
Section 7
Current protection
(Equation 30)
Technical
SEMOD127941-90 v1
nd
harmonic
nd
harmonic restrain.
155
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