ABB RELION RET670 Applications Manual page 447

1MRK 504 163-UUS A
Transformer protection RET670 2.2 ANSI
Application manual
X = X + X
0E 0 m0
EQUATION554 V1 EN-US
Check the reduction of a reach for the overreaching zones due to the effect of the zero
sequence mutual coupling. The reach is reduced for a factor:
Z 0
m
= -
K 0 1
× + +
2 Z 1 Z 0 R
f
EQUATION1426 V1 EN-US
If the denominator in equation
real and imaginary part of the reach reduction factor for the overreaching zones can be
written as:
( )
×
X m 0 Re
( )
= -
Re K 0 1
( )
2
+
Re B Im
EQUATION1427 V2 EN-US
( )
×
( ) X m 0 Im
=
Im K 0
( )
2
+
Re B Im
EQUATION1428 V2 EN-US
Parallel line is out of service and grounded in both ends
Apply the same measures as in the case with a single set of setting parameters. This
means that an underreaching zone must not overreach the end of a protected circuit for
the single phase-to-ground faults.
Set the values of the corresponding zone (zero-sequence resistance and reactance)
equal to:
2
æ X
m0
× ç
R = R 1 + ------------------------- -
0E 0
2
è
R + X
0 0
EQUATION561 V1 EN-US
2
æ X
m0
×
X = X ç 1 – ------------------------- -
0E 0
2 2
è
R + X
0 0
EQUATION562 V1 EN-US
354 is called B and Z0m is simplified to X0m, then the
B
( )
2
B
B
( )
2
B
ö
÷
2
ø
ö
÷
ø
Section 8
Impedance protection
(Equation 353)
(Equation 354)
(Equation 355)
(Equation 356)
GUID-EC052207-C9AF-47EC-999A-BD485378FD9E v1
(Equation 357)
(Equation 358)
441