ABB Relion REG670, Technical Manual

Page: 455 / 1298

8.14.6 Monitored data
Table 246: VRPVOC Monitored data
Name Type Values (Range) Unit Description
IMAX REAL - A Maximum phase current
magnitude
UUMIN REAL - kV Minimum ph-to-ph
voltage magnitude
8.14.7 Operation principle
8.14.7.1 Measured quantities
The voltage-restrained time overcurrent protection VRPVOC function is always
connected to three-phase current and three-phase voltage input in the configuration
tool (ACT), but it will always measure the maximum of the three-phase currents and
the minimum of the three phase-to-phase voltages. If frequency tracking mode for
preprocessing blocks is used, then the function operates properly in wide frequency
range (e.g. 10-90 Hz).
8.14.7.2 Base quantities
GlobalBaseSel defines the particular Global Base Values Group where the base
quantities of the function are set. In that Global Base Values Group:
IBase shall be entered as rated phase current of the protected object in primary
amperes.
UBase shall be entered as rated phase-to-phase voltage of the protected object in
primary kV.
8.14.7.3 Overcurrent protection
The overcurrent step simply compares the magnitude of the measured current quantity
with the set start level. The overcurrent step starts if the magnitude of the measured
current quantity is higher than the set level.
Voltage restraint/control feature
The overcurrent protection operation is made dependent of a measured voltage
quantity. This means that the start level of the overcurrent step is not constant but
decreases with the decrease in magnitude of the measured voltage quantity. This
feature affects the start current value of both definite time and inverse time IDMT
overcurrent protection; in particular the overcurrent with IDMT curve operates faster
during low voltage conditions. Two different types of dependencies are available:
• Voltage restrained overcurrent (when setting parameter VDepMode = Slope ); the
start level of the overcurrent stage changes according to the Figure 208 . The
voltage restrained characteristic is defined by the two points: (0.25* UBase ;
1MRK502052-UEN B
Section 8
Current protection
449
Technical manual