ABB RELION 620 Series Technical Manual page 466

Section 4
Protection functions
460
To calculate the directional differential current ID_COSPHI, the fundamental frequency
amplitude of both the residual and neutral currents has to be above 4 percent of In. If
neither or only one condition is fulfilled at a time, the cosφ term is forced to 1. After the
conditions are fulfilled, both currents must stay above 2 percent of In to allow the
continuous calculation of the cosφ term.
Second harmonic blocking
This module compares the ratio of the current second harmonic (IG_2H) and IG to the set
value Pickup value 2.H. If the ratio (IG_2H / IG) value exceeds the set value, the BLK2H
output is activated.
The blocking also prevents unwanted operation at the recovery and sympathetic
magnetizing inrushes. At the recovery inrush, the magnetizing current of the transformer
to be protected increases momentarily when the voltage returns to normal after the
clearance of a fault outside the protected area. The sympathetic inrush is caused by the
energization of a transformer running in parallel with the protected transformer connected
to the network.
The second harmonic blocking is disabled when Restraint mode is set to "None" and
enabled when set to "Harmonic2".
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 Minimum trip
time, the TRIP output is activated. If the fault disappears before the module trips, the reset
timer is activated. If the reset timer reaches the value set by Reset delay time, the reset
timer resets and the PICKUP output is deactivated.
The Timer calculates the pickup duration value PICKUP_DUR which indicates the
percentage ratio of the pickup situation and the set trip time. The value is available through
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
operate 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
1MAC504801-IB E
620 series ANSI
Technical Manual