Second Harmonic Blocking Logic (Poc Input); Application Notes; Setting Guidelines; Figure 71: 2Nd Harmonic Blocking Logic (Poc Input) - GE P24DM Technical Manual

P24xM
13.2

SECOND HARMONIC BLOCKING LOGIC (POC INPUT)

IA fundamental IA fundamental
I>Lift 2H I>Lift 2H
Low current (hard-coded) Low current (hard-coded)
IA 2ndHarm IA 2ndHarm
2ndHarm Thresh 2ndHarm Thresh
IA fundamental IA fundamental
I>Lift 2H I>Lift 2H
Low current (hard-coded) Low current (hard-coded)
IB 2ndHarm IB 2ndHarm
2ndHarm Thresh 2ndHarm Thresh
IC 2ndHarm IC 2ndHarm
I>Lift 2H I>Lift 2H
Low current (hard-coded) Low current (hard-coded)
IC 2ndHarm IC 2ndHarm
2ndHarm Thresh 2ndHarm Thresh
V00626

Figure 71: 2nd Harmonic Blocking Logic (POC Input)

The function works by identifying and measuring the inrush currents present in the phase currents at switch on. It
does this by comparing the value of the second harmonic current components to the value of the fundamental
component. If this ratio exceeds the set thresholds, then the blocking signal is generated. The threshold is defined
by the 2ndHarm Thresh setting.
We only want the function to block the protection if the fundamental current component is within the normal
range. If this exceeds the normal range, then this is indicative of a fault, which must be protected. For this reason
there is another settable trigger I>lift 2H, which when exceeded, stops the 2nd harmonic blocking function.
13.3

APPLICATION NOTES

13.3.1

SETTING GUIDELINES

During the energization period, the second harmonic component of the inrush current may vary. The second
harmonic level may be different for each phase, which is why phase segregated blocking is available.
If the setting is too low, the 2nd harmonic blocking may prevent tripping during some internal faults. If the setting
is too high, the blocking may not operate for low levels of inrush current which could result in undesired tripping of
the overcurrent element during the energization period.
P24xM-TM-EN-2.1
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nd
IA 2 harm / IA fund
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IB 2 nd harm / IB fund
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IC 2 harm / IC fund
nd
Chapter 6 - Current Protection Functions
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1
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I2H Any Start I2H Any Start
IA2H Start IA2H Start
IB2H Start IB2H Start
IC2H Start IC2H Start
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