High-Set Function; Circuitry Fail Alarm; Figure 41: Transformer Biased Tripping Characteristic - GE P642 Technical Manual

P64x
V03110

Figure 41: Transformer biased tripping characteristic

Once the differential and bias currents are calculated, the following comparisons are made and an operate/
restrain signal is obtained:
For the flat slope range: 0 ≤ I
I ≥ I + transient bias
diff s1
For the K1 slope range: I
I ≥ K1.I
diff bias max
For the K2 slope range: I
I ≥ K1.I + K2(I
diff s2
3.7.1

HIGH-SET FUNCTION

The High Set 1 algorithm uses a peak detection method to achieve fast operating times. The peak value is the
largest absolute value of differential current in the latest cycle. Since the High Set 1 algorithm uses a peak
detection method, Is-HS1 is set above the expected highest magnetizing inrush peak to maintain immunity to
magnetizing inrush conditions. For a High Set 1 trip, two conditions must be fulfilled:
The peak value of the differential current is greater than Is-HS1 setting.
●
The bias characteristic is in the operate region.
●
If the differential current is above the adjustable Is-HS1 threshold, the device will trip if in the Operate region, but
not in the restrain region. However, second harmonic blocking and overfluxing blocking are NOT taken into
account. The High Set 1 resets when the differential and bias currents are in the restraint area.
If the differential current is above the adjustable Is-HS2 threshold, bias current is not taken into account and the
device will trip regardless. As with High Set 1, second harmonic blocking and overfluxing blocking are NOT taken
into account. The High Set 2 element resets when the differential current drops below 0.95*Is-HS2.
3.7.2

CIRCUITRY FAIL ALARM

The circuitry fail alarm logic requires the following settings:
Circuitry Fail: to enable or disable the function
Is-cctfail: to define the minimum differential threshold
K-cctfail: to define the slope gradient
P64x-TM-EN-1.3
Idiff/Inom
Is-HS2
Is-HS1
Operate region
Is1
≤ I /K
bias max s1 1
/K ≤ I ≤ I
s1 1 bias max s2
+ transient bias
≤ I ≤ I /K2
s2 bias max s-HS2
- I ) transient bias
bias max s2 +
Chapter 6 - Transformer Differential Protection
Restraint region
K2
K1
TC and CT errors
Is2 Ibias /Inom
111