EQUATION571 V1 EN (Equation 140)
Where:
U is the minimum phase-to-phase voltage in kV
S is the maximum apparent power in MVA.
The load impedance [Ω/phase] is a function of the minimum operation voltage and the
maximum load current:
Z
load
U
min
3 I
max
×
----------------------
=
EQUATION574 V1 EN (Equation 141)
Minimum voltage U
min
and maximum current I
max
are related to the same operating
conditions. Minimum load impedance occurs normally under emergency conditions.
To avoid load encroachment for the phase-to-earth measuring elements, the set
resistive reach of any distance protection zone must be less than 80% of the minimum
load impedance.
EQUATION792 V2 EN (Equation 142)
This equation is applicable only when the loop characteristic angle for the single
phase-to-earth faults is more than three times as large as the maximum expected load-
impedance angle. For the case when the loop characteristic angle is less than three
times the load-impedance angle, more accurate calculations are necessary according
to equation
75.
min
21 0
0.8 cos sin
21 0
load
RZx R Zx
RFPEZx Z
XZx XZx
EQUATION578 V5 EN
(Equation 143)
Where:
ϑ is a maximum load-impedance angle, related to the maximum load power.
To avoid load encroachment for the phase-to-phase measuring elements, the set
resistive reach of any distance protection zone must be less than 160% of the minimum
load impedance.
EQUATION579 V3 EN
(Equation 144)
1MRK 502 071-UEN - Section 8
Impedance protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 257
Application manual
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