Figure 3.37-2 The phase A initial condition
This module calculates the ratio of the second harmonic (I_2Hp) and fundamental frequency (Ip)
phase currents. The calculated value is compared to the set Start value. If the calculated value
exceeds the set Start value, the protection is initial.
The output of the phase specific level detector is activated when the fundamental frequency
current Ip exceeds 0.04In.
Figure 3.37-3 The inrush operation condition
Once activated, the timer runs until the set Operate delay time value. The time characteristic is
according to DT. When the operation timer has reached the Operate delay time value, the H2Blk
output is activated. After the timer has elapsed and the inrush situation still exists, the H2Blk signal
remains active until the I2H_p/Ip ratio drops below the value set for the ratio in all phases, that is,
until the inrush situation is over. If the drop-off situation occurs within the operate time up counting,
the reset timer is activated. If the drop-off time exceeds Reset delay time, the operate timer is
reset.
The binary input Blk can be used to block the function. The activation of the Blk input deactivates
all outputs and resets internal timers.
3.37.3 Application Scope
Transformer protections require high stability to avoid tripping during magnetizing inrush
conditions. A typical example of an inrush detector application is doubling the start value of an
overcurrent protection during inrush detection
Other applications of this function include the detection of inrush in lines connected to a
transformer.
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