Table 587:
Pickup duration value
Operation mode in use
Available pickup duration value
Freq<
ST_DUR_UFRQ
Freq>
ST_DUR_OFRQ
df/dt
ST_DUR_FRG
The combined pickup duration
PICKUP_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 function. The operation modes are
controlled by the
BLOCK
input and the global setting in
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, but the
TRIP
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 TRIP output" mode, the function operates normally but the
TRIP
output is not activated.
4.6.1.5
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
consumption. In this case, the available generation is too large compared to the power
demanded by the load connected to the power grid. This can occur due to a sudden loss of
a significant amount of load or due to failures in the turbine governor system. If the
situation continues and escalates, the power system loses its stability.
The underfrequency is applicable in all situations where a reliable detection of a low
fundamental power system voltage frequency is needed. The low fundamental frequency
Section 4
1MAC059074-MB A
Protection functions
682
615 series ANSI
Technical Manual
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