Application - ABB RED615 Technical Manual

1YHT530004D05 D
4.3.4.5
615 series
Technical Manual
operate time, the OPERATE output is activated. If the fault disappears before the
module operates, the reset timer is activated. If the reset timer reaches the value set
by Reset delay time, the operation timer resets and the START output is deactivated.
The timer calculates the start duration value START_DUR, which indicates the
ratio of the start situation and the set operation time. The value is available in the
monitored data view.
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 IED 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
OPERATE output" mode, the function operates normally but the OPERATE output
is not activated.

Application

In solidly earthed systems, the restricted earth-fault protection is always deployed
as a complement to the normal transformer differential protection. The advantage
of the restricted earth-fault protection is its high sensitivity. Sensitivities of close to
1.0 percent can be achieved, whereas normal differential IEDs have their minimum
sensitivity in the range of 5 to 10 percent. The level for HREFPDIF is dependent of
the current transformers' magnetizing currents. The restricted earth-fault protection
is also very fast due to the simple measuring principle as it is a unit type of protection.
The differences in measuring principle limit the biased differential IED's
possibility to detect the earth faults. Such faults are then only detected by the
restricted earth-fault function.
The restricted earth-fault IED is connected across each directly or to low-ohmic
earthed transformer winding. If the same CTs are connected to other IEDs, separate
cores are to be used.
Section 4
Protection functions
433