ABB RELION 620 Series Technical Manual page 649

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1MRS757644 F

Technical Manual

autoreclose sequence. The low-level blocking is activated by default (Enable block

value is set to "True") and the blocking level can be set with the Voltage block value

Phase selection logic

If the fault criteria are fulfilled in the level detector, the phase selection logic detects

the phase or phases in which the fault level is detected. If the number of faulty phases

match with the set Num of start phases, the phase selection logic activates the Timer.

Once activated, the Timer activates the START output. Depending on the value of the

set Operating curve type, the time characteristics are selected according to DT or

For a detailed description of the voltage IDMT curves, see the

curves for under voltage protection

When the operation timer has reached the value set by Operate delay time in the DT

mode or the maximum value defined by the IDMT, the OPERATE output is activated.

When the user-programmable IDMT curve is selected, the operate time

characteristics are defined by the parameters Curve parameter A, Curve parameter B,

Curve parameter C, Curve parameter D and Curve parameter E.

If a drop-off situation occurs, that is, a fault suddenly disappears before the operate

delay is exceeded, the reset state is activated. The behavior in the drop-off situation

depends on the selected operate time characteristics. If the DT characteristics are

selected, the reset timer runs until the set Reset delay time value is exceeded. If the

drop-off situation exceeds the set Reset delay time, the Timer is reset and the START

output is deactivated.

When the IDMT operate time curve is selected, the functionality of the Timer in the

drop-off state depends on the combination of the Type of reset curve, Type of time reset

and Reset delay time settings.

Protection functions

section in this manual.

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