ABB RELION 620 Series Technical Manual page 316

Section 4
Protection functions
310
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.
Voltage level
Voltage high limit
U <
Voltage high limit
U ≥
In this example, U represents the measured input voltage. This voltage step
characteristic is graphically represented in
Effective start value (I> effective)
Start value low
Start value
Figure 156.
1MRS757644 F
620 series
Technical Manual