Function Block; Functionality; Operation Principle - ABB RELION 620 Series Technical Manual

Section 4
Protection functions
4.2.6.2
4.2.6.3
4.2.6.4
296

Function block

GUID-C6ADAB46-AACD-44FA-BCFB-8EF872CB171B V1 EN
Figure 134: Function block

Functionality

The overexcitation protection 24 is used to protect generators and power transformers
against an excessive flux density and saturation of the magnetic core.
The function calculates the V/f ratio (volts/hertz) proportional to the excitation level of the
generator or transformer and compares this value to the setting limit. The function picks
up when the excitation level exceeds the set limit and trips when the set tripping time has
elapsed. The tripping 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 "Enable" and "Disable".
The operation of the overexcitation protection can be described using a module diagram.
All the modules in the diagram are explained in the next sections.
1MAC504801-IB E
620 series ANSI
Technical Manual