ABB RELION 620 Series Technical Manual page 298

Section 4
Protection functions
292
Level detector
The calculated positive-sequence voltage is compared to the set Pickup value setting. If
the value drops below the set Pickup value, the level detector enables the timer. The
Relative hysteresis setting can be used for preventing unnecessary oscillations if the input
signal slightly varies from the Pickup value setting. After leaving the hysteresis area, the
pickup condition has to be fulfilled again and it is not sufficient for the signal to only return
to the hysteresis area.
The level detector contains a low-level blocking functionality for cases where the
positive-sequence voltage is below the desired level. This feature is useful when it is
wanted to avoid unnecessary pickups and trips 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 PICKUP output. The time characteristic is
according to DT. When the operation timer has reached the value set by Trip delay time,
the TRIP output is activated if the undervoltage condition persists. If the positive-
sequence voltage normalizes before the module trips, the reset timer is activated. If the
reset timer reaches the value set by Reset delay time, the trip timer resets and the PICKUP
output is deactivated.
The timer calculates the pickup duration value PICKUP_DUR, which indicates the ratio
of the pickup situation and the set trip time. The value is available in the monitored data
view.
Blocking logic
There are three operation modes in the blocking function. The operation modes are
controlled by the BLOCK input and the global setting in 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 protection relay's
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, but the TRIP output is not deactivated when
blocking is activated. 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.
1MAC504801-IB E
620 series ANSI
Technical Manual