ABB RELION 620 Series Technical Manual page 657

1MRS757644 F
620 series
Technical Manual
Level detector
The fundamental frequency component of the measured single-phase voltage is
compared phase-wise to the set value of the Start value setting. If the measured value
is lower than the set value of the Start value setting, the Llevel detector activates the
Timer module. The Relative hysteresis setting can be used for preventing unnecessary
oscillations if the input signal slightly varies above or below the Start value setting.
After leaving the hysteresis area, the start condition has to be fulfilled again and it is
not sufficient for the signal to only return to the hysteresis area.
The Voltage selection setting is used for selecting phase-to-earth or phase-to-phase
voltages for protection.
For the voltage IDMT operation mode, the used IDMT curve equations contain
discontinuity characteristics. The Curve Sat relative setting is used for preventing
unwanted operation.
For a more detailed description of the IDMT curves and usage of
Curve Sat Relative setting, see the IDMT curves for undervoltage
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 can be used when
wanting to avoid unnecessary starts and operates 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.
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
IDMT.
For a detailed description of the voltage IDMT curves, see the IDMT
curves for undervoltage protection section in this manual.
When the operation timer has reached the value set by Operate delay time in the DT
mode or the maximum value set by the IDMT operate time curve, the OPERATE
output is activated.
When the user programmable IDMT operate time 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 operation
delay is exceeded, the reset state is activated. The behavior in the drop-off situation
depends on the selected operation time characteristics. If the DT characteristics are
selected, the reset timer runs until the set Reset delay time value is exceeded. If the
Section 4
Protection functions
651