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1MRK 505 370-UEN D
available: IEC and ANSI. It is also possible to programme a user defined inverse time
characteristic.
Normally it is required that the phase overcurrent function shall reset as fast as possible when
the current level gets lower than the operation level. In some cases some sort of time delayed
reset is required. Therefore three different kinds of reset time characteristics can be used.
For some protection applications there can be a need to change the current pick-up level for
some time. A typical case is when the protection will measure the current to a large motor. At
the start up sequence of a motor the start current can be significantly larger then the rated
current of the motor. Therefore there is a possibility to give a setting of a multiplication factor
to the current pick-up level. This multiplication factor is activated from a binary input signal to
the function.
Power transformers can have a large inrush current, when being energized. This phenomenon
is due to saturation of the transformer magnetic core during parts of the period. There is a
risk that inrush current will reach levels above the pick-up current of the phase overcurrent
protection. The inrush current has a large second harmonic content. This can be used to avoid
unwanted operation of the protection. Therefore the Four step phase overcurrent protection
(OC4PTOC) function have a possibility of second harmonic restrain if the level of this harmonic
current reaches a value above a set percentage of the fundamental current.
7.2.3
Setting guidelines
The parameters for the four step phase overcurrent protection function (OC) are set via the
local HMI or Protection and Control IED Manager (PCM 600).
Common base IED values for the primary current (
power (
GlobalBaseSel : Selects the global base value group used by the function to define IBase , UBase
SBase . Note that this function will only use IBase value.
and
The following settings can be done for the four step phase overcurrent protection.
Operation : Off/On
IBase : Base current in primary A. This current is used as reference for current setting. It can be
suitable to set this parameter to the rated primary current of the protected object.
2ndHarmStab : Operate level of 2
current. The setting range is 5-100% of IBase in steps of 1%. Default setting is 20%.
HarmRestrainx : Disabled/Enabled , enables blocking from harmonic restrain.
7.2.3.1
Settings for each step (x = 1-4)
Characteristx : Selection of time delay characteristic for step x. Definite time delay and
different types of inverse time delay characteristics are available according to table 28.
Busbar protection REB670
Application manual
A typical starting time delay of 24ms is subtracted from the set trip time delay,
so that the resulting trip time will take the internal IED start time into
consideration.
SBase ) are set in global base values for settings function GBASVAL.
IBase ), primary voltage ( UBase ) and primary
nd
harmonic current restrain set in % of the fundamental
Section 7
Current protection
SEMOD127939-1 v1
SEMOD127941-4 v4
SEMOD127941-18 v4
153
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