ABB REG670 Applications Manual page 263

1MRK 502 071-UEN -
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
2
U
Z = ------ -
loadmin
S
EQUATION571 V1 EN
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:
U
min
--------------------- -
Z =
load
×
3 I
max
EQUATION574 V1 EN
Minimum voltage U
min
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.
 
RFPEZx 0.8 Z
load
EQUATION792 V2 EN
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.

  
RFPEZx 0.8 Z cos


load min
EQUATION578 V5 EN
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.
RFPPZx  
1.6 Z
load
EQUATION579 V3 EN
and maximum current I
max
 
2 R Zx R Zx 1 0

 
sin
 
2 X Zx 1 X Zx 0
Section 8
Impedance protection
(Equation 140)
(Equation 141)
are related to the same operating
(Equation 142)




(Equation 143)
(Equation 144)
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