Section 4 1MAC309294-MB F
Protection functions
220 RER620
Technical Manual
The module calculates the start duration (START_DUR) value which indicates the
percentage ratio of the start situation and set operate time (DT). The start duration is
available according to the selected value of the Operation mode setting.
Table 235: Start duration value
The combined start duration START_DUR indicates the maximum percentage ratio of the
active protection modes. The values are available via 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 relay 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
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 output is not activated.
4.4.1.5 Application
The frequency protection function uses the positive phase-sequence voltage to measure the
frequency reliably and accurately.
The system frequency stability is one of the main principles in the distribution and
transmission network maintenance. To protect all frequency-sensitive electrical apparatus
in the network, the departure from the allowed band for a safe operation should be
inhibited.
The overfrequency protection is applicable in all situations where high levels of the
fundamental frequency of a power system voltage must be reliably detected. The high
fundamental frequency in a power system indicates an unbalance between production and
Freq> OR df/dt A parallel operation between the protection methods is enabled. The START output is
activated when either of the measured values of the protection module exceeds its set
value. A detailed information from the active module is available at the STR_OFRQ and
STR_FRG outputs. The shortest operate delay time from the set
Operate Tm Freq
or
Operate Tm df/dt
is dominant regarding the OPERATE output. The time characteristic is
according to DT. The characteristic that activates the OPERATE output can be seen
from the OPR_OFRQ or OPR_FRG output. If the frequency gradient restores before the
module operates, the reset timer is activated. If the timer reaches the value set by the
Reset delay Tm df/dt
setting, the operate timer resets and the STR_FRG output is
deactivated. If the frequency restores before the module operates, the reset timer is
activated. If the timer reaches the value set by the
Reset delay Tm Freq
setting, the
operate timer resets and the STR_UFRQ output is deactivated.
Operation mode in use Available start duration value
Freq<
ST_DUR_UFRQ
Freq>
ST_DUR_OFRQ
df/dt
ST_DUR_FRG
Operation mode
Description
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