magnitude of all three phase current or voltages goes below
Current block value
and
Voltage block value
respectively, the timer reset state is activated. The reset timer
depends on the
Reset delay time
setting.
The Timer 1 calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operating time. The value is
available in the Monitored data view.
Timer 2
Once activated, the Timer 2 activates the alarm timer. The timer characteristic is
according to DT. When the alarm timer has reached the value set by
Alarm delay
time
in the DT mode, the ALARM output is activated. If a drop-off situation occurs,
that is, a power factor improves and exceeds the
Alarm reset value
in the direction
as defined by
Dir alarm reset value
before the alarm delay is exceeded or either
magnitude of all three phase current or voltages goes below
Current block value
and
Voltage block value
respectively, the timer reset state is activated. The reset timer
depends on the
Reset delay time
setting.
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 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 output is not activated.
4.8.4.6 Application
The MPUPF function can be used to detect loss of excitation or for power factor
correction. Synchronous motors are mostly operated at leading power factor and
its operation as lagging power for extended period can be used an indication of an
out-of-step condition possibly caused by under or loss of excitation. To detect such
a situation, the relay is typically set to operate when the current into a motor lags
more than 30 degrees, that is, a power factor goes below +0.87 lagging.
The function provides alarm facility which can be used as an early indication that
the power factor is moving outside the allowable range; therefore the
Alarm value
setting should be set higher than the
Start value
. The delay time for alarm should
also be set as low as possible, only long enough to prevent spurious activation of
the output.
In a power factor correction application, the ALARM and START outputs can be used
as controls to switch in capacitive loads when the
Alarm value
and
Start value
settings, respectively, are exceeded. The ALARM output is set for a higher value
to add the first corrective load and the START output set for a second stage of
corrective load, if needed. The
Start reset value
and
Alarm reset value
settings allow
their respective outputs to remain activated to maintain the correction after power
factor rises as a result, but to drop out after it reaches a level where corrective
capacitive loading is no longer needed.
Protection functions
1MRS759142 F
1082 REX640
Technical Manual
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