Functions
2.30 100-%-Stator Earth Fault Protection with 3rd Harmonics (ANSI 27/59TN 3rd Harm.)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
221
Figure 2-96 3. harmonic secondary voltage as a function of the active power referred to S
N device
(extrapo-
lation of this voltage and final characteristic)
With 100 % active power the extrapolated value is (U
3H1
) 12.7 V.
With 50 % active power the value is (U
3H2
) 7.5 V.
The setting value is thus calculated as follows:
At address 5207 U0 3.H.(V/100%) – 10.4 is set. The pickup value in address 5203 U0 3.HARM> must like-
wise be extrapolated to 100 %. If you choose 14.0 V for it, we obtain a pickup value of 14.0 V – 5.2 V = 8.8 V
for 50 % active power (referring to S
N device
). The resulting active power dependent characteristic is shown in
Figure 2-96. It lies above the extrapolated measured values.
If cos ϕ = 0.8 and the generator is run at this nominal value, the active power P
N Gen
= S
N Gen
·cos ϕ = 5.27
MVA · 0.8 = 4.22 MW (80 % S
N Gen
) and P
N Gen
/ S
N device
= 4.22/5.46 = 77.3%.
The resulting pickup value is 14.0 V – 10.4V/100 % (100% -77.3 %) = 14.0 V – 2.36 V = 11.64 V.
As described under the side title „Operating Range“, the characteristic must be limited by defining the minimum
possible active power. Since the 3rd harmonic has been measured in Figure up to P = 20 %, and the behaviour
is still almost linear, a setting of parameter 5205 P min > = 30 % · P
N Gen
/ S
N device
= 0.3 · 4.22/5.46 = 23 % is
possible with a selected safety margin of 10 %.
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