Application - ABB RELION 620 Series Technical Manual

1MAC504801-IB E
4.6.4.5
620 series ANSI
Technical Manual
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.

Application

87 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.
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
branch. R increases the impedance of the protection relay; hence the name high-
s
impedance differential scheme.
Protection functions
) in the protection relay measuring
s
Section 4
469