4.5.3.2
Function block
Figure 337: Function block
4.5.3.3
Functionality
The three-phase undervoltage protection function PHPTUV is used to disconnect
from the network devices, for example electric motors, which are damaged when
subjected to service under low voltage conditions. PHPTUV includes a settable value
for the detection of undervoltage either in a single phase, two phases or three
phases.
The function contains a blocking functionality. It is possible to block function
outputs, timer or the function itself, if desired.
4.5.3.4
Operation principle
The function can be enabled and disabled with the
Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of PHPTUV can be described using a module diagram. All the modules
in the diagram are explained in the next sections.
Figure 338: Functional module diagram
Level detector
The fundamental frequency component of the measured three phase voltages
are compared phase-wise to the set
Start value. If the measured value is lower
than the set value of the
Start value setting, the level detector enables the phase
selection logic module. The
Relative hysteresis setting can be used for preventing
unnecessary oscillations if the input signal slightly varies above or below the
Start
value setting. After leaving the hysteresis area, the start condition has to be fulfilled
again and it is not sufficient for the signal to only return back to the hysteresis area.
The
Voltage selection setting is used for selecting the phase-to-earth or phase-to-
phase voltages for protection.
Protection functions
1MRS757644 H
646
620 series
Technical Manual
