ABB RELION REX640, Техническое руководство, Страница: 761 / 1960

Timer
Once activated, the timer activates the
START
output. The time characteristic is
according to DT. When the operation timer has reached the value set by
Minimum
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 function. 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 OPERATE
output" mode, the function operates normally but the
OPERATE
output is not
activated.
4.3.5.6 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 protection relays have
their minimum sensitivity in the range of 5 to 10 percent. The level for HREFPDIF
is dependent on 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 protection relay's
possibility to detect the earth faults. Such faults are then only detected by the
restricted earth-fault function.
The restricted earth-fault protection relay is connected across each directly or to
low-ohmic earthed transformer winding. If the same CTs are connected to other
protection relays,, separate cores are to be used.
1MRS759142 F Protection functions
REX640
Technical Manual
761