ABB RELION REX640 Technical Manual page 931

Protection and control

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1MRS759142 F

The df/dt detection module includes a timer with the DT characteristics. Upon

detection of df/dt, operation timer activates the ST_FRG output. When the timer

has reached the value set by

if the df/dt condition still persists. If df/dt becomes normal before the module

operates, the reset timer is activated. If the reset timer reaches the value of the

Reset delay time setting, the timer resets and the ST_FRG output is deactivated.

Load-shedding control

The way of load-shedding, that is, whether to operate based on underfrequency

or high df/dt or both, is defined with the

operation modes for the

and "Freq< OR df/dt".

Once the selected operation mode conditions are satisfied, the START and OPERATE

output signals are activated.

When the START output is active, the percentage of the elapsed delay time can be

monitored through START_DUR which is available as monitored data.

Technical Manual

Operate Tm df/dt , the OPR_FRG output is activated

Load shed mode user setting. The valid

Load shed mode settings are "Freq<", "Freq< AND df/dt"

Protection functions