Application - ABB 615 series Technical Manual

Section 4
Protection functions
4.4.1.5
590
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.

Application

Since the negative sequence current quantities are not present during normal, balanced
load conditions, the negative sequence overcurrent protection elements can be set for
faster and more sensitive operation than the normal phase-overcurrent protection for fault
conditions occurring between two phases. The negative sequence overcurrent protection
also provides a back-up protection functionality for the feeder ground-fault protection in
solid and low resistance grounded networks.
The negative sequence overcurrent protection provides the back-up ground-fault
protection on the high voltage side of a delta-wye connected power transformer for ground
faults taking place on the wye-connected low voltage side. If a ground fault occurs on the
wye-connected side of the power transformer, negative sequence current quantities
appear on the delta-connected side of the power transformer.
Probably the most common application for the negative sequence overcurrent protection
is rotating machines, where negative sequence current quantities indicate unbalanced
loading conditions (unsymmetrical voltages). Unbalanced loading normally causes
extensive heating of the machine and can result in severe damage even over a relatively
short time period.
Multiple time curves and time multiplier settings are also available for coordinating with
other devices in the system.
1MAC059074-MB A
615 series ANSI
Technical Manual