ABB RELION REX640 Technical Manual page 539

1MRS759142 C
REX640
Technical Manual
fault. MFADPSDE can then adapt to a fault direction change more rapidly if a single-
phase earth fault persists in the system after the other faulty feeder has been tripped
(the cross-country fault has been transformed into a single-phase earth fault).
The direction of MFADPSDE is supervised by a settable current magnitude threshold,
setting Min operate current. The operate current used in the magnitude supervision is
measured with a special filtering method, which provides a stable residual current
estimate regardless of the fault type. This estimate is the result of the fundamental
frequency admittance calculation using the CPS technique. The stabilized current
value is obtained (after conversion) from the corresponding admittance value by
multiplying it by the system nominal phase-to-earth voltage value. The equations for
calculating the stabilized values of the fundamental frequency admittance and the
corresponding current are given below.
1
I
3
⋅
1 1
0 CPS
Y Y
Re

= =
o stab o stab
1
U 
−
0 CPS
GUID-8F62CA80-71E2-449F-A405-483A0F909C4F V1 EN
Stabilized fundamental frequency admittance estimate, which is the result of the fundamental
1
Y frequency admittance calculation using the CPS technique
o stab
Fundamental frequency zero-sequence current phasor calculated using the CPS technique
1
I
0
CPS
Fundamental frequency zero-sequence voltage phasor calculated using the CPS technique
1
U
0
CPS
Real part of stabilized fundamental frequency conductance estimate
1
G
o stab
Imaginary part of stabilized fundamental frequency susceptance estimate
1
B
o stab
1 1 1
I G j B
( )
= + ⋅ ⋅
o stab ostab ostab
GUID-DAB61C38-DA83-47FE-96B9-9E705824880E V1 EN
Stabilized fundamental frequency residual current estimate, which is obtained (after
1
I conversion) from the corresponding admittance value by multiplying it by the system
o stab
nominal phase-to-earth voltage value
Real part of stabilized fundamental frequency residual current estimate
1
I
o Cosstab
Imaginary part of stabilized fundamental frequency residual current estimate
1
I
o Sinstab
U System nominal phase-to-earth voltage value
baseres
The main advantage of the filtering method is that due to the admittance calculation,
the resulting current value does not depend on the fault resistance value, that is, the
estimated current magnitude equals the value that is measured during a solid earth
1 1
j Y G
Im
  
+ ⋅ =
o stab ost
  
1 1
U I j I
= + ⋅
baseres oCosstab oSinsta
Section 4
Protection functions
1
j B
+ ⋅
a a b ostab
b b
(Equation 85)
(Equation 86)
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