Application - ABB 615 series Technical Manual

Section 4
Protection functions
4.3.3.5
542
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
TRIP output is not activated. The activation of the output of the second harmonic
blocking signal BLK2H deactivates the TRIP output.

Application

A ground-fault protection using an overcurrent element does not adequately protect the
transformer winding in general and the star-connected winding in particular.
The restricted ground-fault protection is mainly used as a unit protection for the
transformer windings. 80LOZREF is a sensitive protection applied to protect the star-
connected winding of a transformer. This protection system remains stable for all the
faults outside the protected zone.
87LOZREF provides higher sensitivity for the detection of ground faults than the overall
transformer differential protection. This is a high-speed unit protection scheme applied to
1MAC059074-MB A
615 series ANSI
Technical Manual