4.5.7.2 Function block
Figure 494: Function block
4.5.7.3 Functionality
The overexcitation protection function OEPVPH is used to protect generators
and power transformers against an excessive flux density and saturation of the
magnetic core.
The function calculates the U/f ratio (volts/hertz) proportional to the excitation
level of the generator or transformer and compares this value to the setting limit.
The function starts when the excitation level exceeds the set limit and operates
when the set operating time has elapsed. The operating time characteristic can be
selected to be either definite time (DT) or overexcitation inverse definite minimum
time (overexcitation type IDMT).
This function contains a blocking functionality. It is possible to block the function
outputs, reset timer or the function itself.
4.5.7.4 Analog channel configuration
OEPVPH has two analog group inputs which must be properly configured.
Table 840: Analog inputs
Input Description
I3P Three-phase currents
U3P Three-phase voltages
See the preprocessing function blocks in this document for the possible
signal sources.
There are a few special conditions which must be noted with the configuration.
Table 841: Special conditions
Condition Description
U3P connected to real measurements The function can work with at least one volt-
age channel connected (A, B or C according
to
Phase selection
“1”, “2” or “3”) if
Voltage
selection
is set to "phase-to-earth".
The function can work with any two voltage
channels connected (AB, BC or CA according
Table continues on the next page
1MRS759142 F Protection functions
REX640
Technical Manual
885
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