Definite Time Characteristics - ABB 615 series Technical Manual

1MAC059074-MB A
Section 11
11.1
11.1.1
615 series ANSI
Technical Manual
General function block features

Definite time characteristics

Definite time operation
The DT mode is enabled when the Operating curve type setting is selected either as "ANSI
Def. Time" or "IEC Def. Time". In the DT mode, the TRIP output of the function is
activated when the time calculation exceeds the set Trip delay time.
The user can determine the reset in the DT mode with the Reset delay time setting, which
provides the delayed reset property when needed.
The Type of reset curve setting has no effect on the reset method when the
DT mode is selected, but the reset is determined solely with the Reset
delay time setting.
The purpose of the delayed reset is to enable fast clearance of intermittent faults, for
example self-sealing insulation faults, and severe faults which may produce high
asymmetrical fault currents that partially saturate the current transformers. It is typical for
an intermittent fault that the fault current contains so called drop-off periods, during which
the fault current falls below the set start current, including hysteresis. Without the delayed
reset function, the operation timer would reset when the current drops off. In the same
way, an apparent drop-off period of the secondary current of the saturated current
transformer can also reset the operation timer.
General function block features
Section 11
1073