ABB RELION 620 Series Technical Manual page 677

1MRS757644 F
4.5.8.2
4.5.8.3
4.5.8.4
620 series
Technical Manual
Function block
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Figure 339: Function block
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, if desired.
Operation principle
The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of OEPVPH can be described using a module diagram. All the modules
in the diagram are explained in the next sections.
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Figure 340: Functional module diagram
Section 4
Protection functions
671