Zone Reach Setting Higher Than Minimum Load Impedance - ABB REG670 Applications Manual

1MRK 502 071-UEN -
8.2.3.8
[4] RLdRv=RLdRvFactor*RLdFw
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
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
Equation 76 is applicable only when the loop characteristic angle for the phase-to-
phase faults is more than three times as large as the maximum expected load-
impedance angle. For other cases a more accurate calculations are necessary
according to equation 77.

 
 
RFPPZx 1.6 Z

load min
IECEQUATION2307 V2 EN

Zone reach setting higher than minimum load impedance

The impedance zones are enabled as soon as the (symmetrical) load impedance
crosses the vertical boundaries defined by RLdFw and RLdRv
ArgLd. So, it is necessary to consider some margin. It is recommended to set RLdFw
and RLdRv to 90% of the per-phase resistance that corresponds to maximum load.
< ×
RLdFw 0.9 R
load min
IECEQUATION2419 V2 EN
< ×
RLdRv 0.9 R
load min
IECEQUATION2420 V2 EN
The absolute value of the margin to the closest ArgLd line should be of the same order,
that is, at least 0.1 • Z
load min
The load encroachment settings are related to a per-phase load impedance in a
symmetrical star-coupled representation. For symmetrical load or three-phase and
phase-to-phase faults, this corresponds to the per-phase, or positive-sequence,
impedance. For a phase-to-earth fault, it corresponds to the per-loop impedance,
including the earth return impedance.

R1Zx
 
 
cos sin


X1Zx
.
Section 8
Impedance protection
(Equation 76)
(Equation 77)
[4]
or the lines defined by
(Equation 78)
(Equation 79)
209