Figure 165: Functional module diagram
Effective start value calculator
The normal starting current above which the overcurrent protection starts is set
through the
Start value
setting. The Effective start value of the current may need
to be changed during certain conditions like magnetizing inrush or when the
terminal voltages drop due to a fault. Hence, the effective start value calculator
module dynamically calculates the effective start value above which the overcurrent
protection starts.
Four methods of calculating the effective start value are provided in PHPVOC. These
can be chosen with the
Control mode
setting to be either "Voltage control", "Input
control", "Volt & Input Ctrl" or "No Volt dependency".
The calculated effective start value per phase, EFF_ST_VAL_A, EFF_ST_VAL_B,
EFF_ST_VAL_C, is available in the Monitored data view and is used by the Level
detector module.
All three phase-to-phase voltages should be available for the function to
operate properly.
Voltage control mode
In the Voltage control mode, the Effective start value is calculated based on the
magnitude of input voltages U_AB, U_BC and U_CA. The voltage dependency is
phase sensitive, which means that the magnitude of one input voltage controls
the start value of only the corresponding phase, that is, the magnitude of voltage
inputs U_AB, U_BC and U_CA independently control the current start values of
phases A, B and C.
Two voltage control characteristics, voltage step and voltage slope, can be achieved
with the
Voltage high limit
and
Voltage low limit
settings.
The voltage step characteristic is achieved when the
Voltage high limit
setting is
equal to the
Voltage low limit
setting. The effective start value is calculated based
on the equations.
Protection functions
1MRS757644 H
328 620 series
Technical Manual
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