ABB Relion 620 Series - Page 745

The function contains a blocking functionality to block function outputs, timer or
the function itself.
4.8.3.4 Operation principle
The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of DQPTUV can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 388: Functional module diagram
Under voltage detection
Under voltage detection compares the fundamental frequency component of all
three phase-to-phase voltages with the set Voltage start value . When all three
phase-to-phase voltages are lower than the set Voltage start value , the Under
voltage detection module sends an enable signal to the Timer indicating an
undervoltage condition at the grid connection point.
Reactive power monitoring
This module calculates and monitors the reactive power based on positive
sequence current and voltage. The use of a positive sequence component makes
the determination of power insensitive to a possible asymmetry in current and
voltages. When the reactive power exceeds Min reactive power and flows in the
operating area, the module sends an enable signal to the Timer indicating that the
reactive power is being consumed at the grid connection point. A slight tilt in the
curve can be obtained by the setting Pwr sector reduction .
To avoid false tripping, reactive power calculation is blocked if the magnitude of
positive sequence current is less than the set Min PS current .
The magnitude of calculated reactive power Q is available in the Monitored data
view.
1MRS757644 H
Protection functions
620 series
Technical Manual
745