ABB RELION REX640 Technical Manual page 934

Protection functions
Restoring mode
A condition can arise where the restoring operation needs to be canceled. Activating
the BLK_REST input for the "Auto" or "Manual" modes cancels the restoring
operation. In the "Manual" restoring mode, the cancellation happens even if
MAN_RESTORE is present.
Once the RESTORE output command is cancelled, the reactivation of RESTORE is
possible only after the reactivation of the OPERATE output, that is, when the next
load-shedding operation is detected.
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 that selects the blocking mode. The BLOCK input can be controlled
with a binary input, a horizontal communication input or an internal signal of the
protection relay's program. The influence of the BLOCK input signal activation is
preselected with the
The
mode, the operate timer is frozen to the prevailing value, but the OPERATE 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 OPERATE output" mode,
the function operates normally but the OPERATE, OPR_FRQ and OPR_FRG outputs are
not activated.
4.6.2.6 Application
An AC power system operates at a defined rated frequency. The nominal frequency
in most systems in the world is 50 Hz or 60 Hz. The system operation is such
that the operating frequency remains approximately at the nominal frequency value
by a small margin. The safe margin of operation is usually less than ±0.5 Hz.
The system frequency stability is one of the main concerns in the transmission
and distribution network operation and control. To protect the frequency-sensitive
electrical equipment in the network, departure from the allowed band for safe
operation should be inhibited.
Any increase in the connected load requires an increase in the real power generation
to maintain the system frequency. Frequency variations form whenever there are
system conditions that result in an unbalance between the generation and load.
The rate of change of the frequency represents the magnitude of the difference
between the load and generation. A reduction in frequency and a negative rate of
change of the frequency are observed when the load is greater than the generation,
and an increase in the frequency along with a positive rate of change of the
frequency are observed if the generation is greater than the load. The rate of
change of the frequency is used for a faster decision of load-shedding. In an
934
Description
cy has exceeded the
includes a timer with the DT characteristics. When the timer has
reached the set value of the
output is activated if the restoring condition still persists. If the fre-
quency drops below the
output is activated, the reset timer is activated. If the reset timer
reaches the value of the
the
ST_REST
Blocking mode global setting.
Blocking mode setting has three blocking methods. In the "Freeze timers"
Restore start Val setting. The manual restoration
Restore delay time setting, the
Restore start Val setting before the
Reset delay time setting, the timer resets and
start output is deactivated.
1MRS759142 F
RESTORE
RESTORE
REX640
Technical Manual