Function Block - ABB 615 series Technical Manual

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Protection functions

Function block

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Function block

Functionality

The overexcitation protection function 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 24 can be described using a module diagram. All the modules in the

diagram are explained in the next sections.

1MAC059074-MB A

615 series ANSI

Technical Manual

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