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If the reset timer reaches the value set by
Reset delay time
, the operation timer resets and
the
PICKUP
output is deactivated.
Timer calculates the start duration
PICKUP_DUR
value, which indicates the percentage
ratio of the start situation and the set operating time. The value is available in the
Monitored data view.
The activation of the
BLOCK
input resets Timer and deactivates the
PICKUP
and
TRIP
outputs.
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 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. 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.
4.3.4.5
Application
87A, 87B, 87C provides a secure and dependable protection scheme against all types of
faults. The high-impedance principle is used for differential protection due to its
capability to manage the through-faults also with the heavy current transformer (CT)
saturation.
For current transformer recommendations, see the Requirements for
measurement transformers section in this manual.
High-impedance principle
The phase currents are measured from both the incoming and the outgoing feeder sides of
the busbar. The secondary of the current transformer in each phase is connected in parallel
with a protection relay measuring branch. Hence, the relay measures only the difference
of the currents. In an ideal situation, there is a differential current to operate the relay only
if there is a fault between the CTs, that is, inside the protected zone.
If there is a fault outside the zone, a high current, known as the through-fault current, can
go through the protected object. This can cause partial saturation in the CTs. The relay
operation is avoided with a stabilizing resistor (R
s
) in the protection relay measuring
1MAC059074-MB A
Section 4
Protection functions
615 series ANSI
553
Technical Manual
Содержание Relion 615 series
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