ABB 615 Series ANSI, Technical Manual

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Section 4
1MAC050144-MB C
Protection functions
252 615 series ANSI
Technical Manual
Blocking logic
There are three operation modes in the blocking functionality. The operation modes are
controlled by the BLOCK input and the global setting "
Configuration/System/ Blocking
mode " which selects the blocking mode. The BLOCK input can be controlled by a binary
input, a horizontal communication input or an internal signal of the IED program. The
influence of the BLOCK signal activation is preselected with the global setting
Blocking
mode .
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode, the
trip timer is frozen to the prevailing value. In the "Block all" mode, the whole function is
blocked and the timers are reset. In the "Block TRIP output" mode, the function operates
normally but the TRIP output is not activated.
4.2.6.5 Timer Characteristics
24 supports both DT and IDMT characteristics. The DT timer characteristics can be
selected as "ANSI Def. Time" or "IEC Def. Time" in the
Operating curve type setting. The
functionality is identical in both cases. When the DT characteristics are selected, the
functionality is only affected by the
Trip delay time and Reset delay time settings.
24 also supports four overexcitation IDMT characteristic curves: "OvExt IDMT Crv1",
"OvExt IDMT Crv2", "OvExt IDMT Crv3" and "OvExt IDMT Crv4".
Overexcitation inverse definite minimum time curve (IDMT)
In the inverse time modes, the trip time depends on the momentary value of the excitation:
the higher the excitation level, the shorter the trip time. The trip time calculation or
integration starts immediately when the excitation level exceeds the set
Pickup value and
the PICKUP output is activated.
The TRIP output is activated when the cumulative sum of the integrator calculating the
overexcitation situation exceeds the value set by the inverse time mode. The set value
depends on the selected curve type and the setting values used.
The Minimum trip time and Maximum trip time settings define the minimum trip time and
maximum trip time possible for the IDMT mode. For setting these parameters, a careful
study of the particular IDMT curves is recommended.
Once activated, the timer activates the PICKUP output for the IDMT curves. If the
excitation level drops below the
Pickup value setting before the function trips, the reset
timer is activated. If the fault reoccurs during the reset time, the tripping calculation is
made based on the effects of the period when PICKUP was previously active. This is
intended to allow a tripping condition to occur in less time to account for the heating
effects from the previous active pickup period.
The tripping time of the function block can vary much between different
operating curve types even if other setting parameters for the curves were
not changed.