Detecting A Transition; Transition Detection - GE MiCOM P40 Agile Technical Manual

Application Notes
MiCOM P40 Agile P442, P444
• Power System Frequency is being measured and tracked (48 samples per cycle at 50
or 60 Hz).
No fault is detected:
• all nominal phase voltages are between 70% and 130% of the nominal value.
• the residual voltage (3V0) is less than 10% of the nominal value
• the residual current (3I0) is less than 10% of the nominal value + 3.3% of the
maximum load current flowing on the line
The measured loop impedance is outside the characteristics, when these requirements are
fulfilled, the superimposed values are used to determine the fault inception (start), faulty
phase selection and fault direction. The network is then said to be "healthy" before the fault
occurrence.
2.2.2

Detecting a Transition

To detect a transition, the MiCOM P442 and P444 compares sampled current and voltage
values at the instant "t" with the values predicted from those stored in the memory one
period and two periods earlier.
G
Figure 5:

Transition detection

Gp(t) = 2G(t-T) - G(t-2T) where Gp(t) are the predicted values of either the sampled current
or voltage
A transition is detected on one of the current or voltage input values if the absolute value of
(G(t) - Gp(t)) exceeds a threshold of 0.2 x IN (nominal current) or 0.1 x UN / √3 = 0.1x VN
(nominal voltage)
With: U = phase-to-phase voltage
V = phase-to-ground voltage = U / √3
G(t) = G(t) - Gp(t) is the transition value of the reading G.
The high-speed algorithms will start if either U OR I is detected on one sample.
T
G(t-2T)
t-2T
2T
G(t-T)
t-T t
P44x/EN AP/Hb6
(AP) 5-17
G(t)
Gp(t)
Time
P3034ENa