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.
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 operation 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
operation 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.
4.5.5.5
Application
47U, 27PS can be applied for protecting a power station used for embedded generation
when network faults like short circuits or phase-to-ground faults in a transmission or a
distribution line cause a potentially dangerous situations for the power station. A network
fault can be dangerous for the power station for various reasons. The operation of the
protection can cause an islanding condition, also called a loss-of-mains condition, in
which a part of the network, that is, an island fed by the power station, is isolated from the
Section 4
1MAC059074-MB A
Protection functions
638
615 series ANSI
Technical Manual
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