Second Harmonic Blocking Logic (Poc Input); Figure 76: 2Nd Harmonic Blocking Logic (Poc Input) - GE MiCOM P40 Agile Technical Manual

Chapter 6 - Current Protection Functions
15.2

SECOND HARMONIC BLOCKING LOGIC (POC INPUT)

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

Figure 76: 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.
150
&
harm / IA fund
nd
&
harm / IB fund
nd
&
nd harm / IC fund
&
1
&
&
&
&
I2H Any Start
IA2 H Start
IB2 H Start
IC2H Start
P14xEd1-TM-EN-1
P14x