ABB 615 series Technical Manual page 626

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Protection functions

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 pickup phases, the phase selection logic activates the Timer.

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

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

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 Trip delay time in the DT mode or

the maximum value defined by the IDMT, the TRIP output is activated.

When the user-programmable IDMT curve is selected, the trip 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 trip delay is

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

selected trip 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 PICKUP output is deactivated.

When the IDMT trip time curve is selected, the functionality of the Timer in the drop-off

state depends on the combination of the Type of reset curve and Reset delay time settings.

1MAC059074-MB A

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615 series ANSI

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