ABB RER620, Technical Manual

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1MAC309294-MB F
Section 4
Protection functions
RER620 229
Technical Manual
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 functionality. The operation modes are
controlled by the
BLOCK
input and the Configuration > System > Blocking mode global
setting 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 relay program. The
influence of the
BLOCK
input signal activation is preselected with the Blocking mode
global setting.
The Blocking mode setting has three blocking methods. In the “Freeze timers” mode, the
operate 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
,
OPR_FRQ
and
OPR_FRG
outputs are not activated.
4.4.2.5 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 underfrequency situation, the load shedding trips out the unimportant
Manual In the “Manual” mode, a manual restoration is possible through the
MAN_RESTORE
input or via communication. The
ST_REST
output is activated if the
MAN_RESTORE
command is available and the frequency has exceeded the
Restore start Val
setting.
The manual restoration includes a timer with the DT characteristics. When the timer
has reached the set value of the
Restore delay time
setting, the
RESTORE
output is
activated if the restoring condition still persists. If the frequency drops below the
Restore start Val
setting before the
RESTORE
output is activated, the reset timer is
activated. If the reset timer reaches the value of the
Reset delay time
setting, the timer
resets and the
ST_REST
start output is deactivated.
Restoring mode Description