ABB RELION REF615R, Technical Manual

Page: 237 / 664

After leaving the hysteresis area, the pickup condition has to be fulfilled again and it is not
sufficient for the signal to only return back to the hysteresis area.
The Voltage selection setting is used for selecting the phase-to-ground or phase-to-phase
voltages for protection.
For the voltage IDMT mode of operation, the used IDMT curve equations contain
discontinuity characteristics. The
Curve Sat relative setting is used for preventing
unwanted operation.
For more detailed description on IDMT curves and usage of Curve Sat
Relative setting, see the IDMT curves for under voltage protection section
in this manual.
The level detector contains a low-level blocking functionality for cases where one of the
measured voltages is below the desired level. This feature is useful when unnecessary
pickups and trips are wanted to avoid during, for example, an 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 setting.
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.
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 IDMT
curves for under voltage protection section in this manual.
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
1MRS240050-IB C
Section 4
Protection functions
REF615R 231
Technical Manual