Method and system for determining location of phase-to-earth fault
View Patent ↗A method and system for determining a location of a phase-to-earth fault in a line of an electric network, the electric line comprising two or more sections ( 30 a, 30 b, 30 c ), the system being configured to determine, at a measuring point, a reactance of a fault loop; determine a faulted section of the electric line to be a section closest to the measurement point of all such sections for which a sum of a positive sequence reactance and an earth return path reactance of the section in question and positive sequence reactances and an earth return path reactances of sections, if any, between the measurement point and the section in question is greater than or equal to the determined reactance of the fault loop; and calculate a distance between the measuring point and a point of fault on the basis of the reactance values.
1. A method for determining a location of a phase-to-earth fault in a three-phase electric line of an electric network, the electric line comprising two or more sections, each section having a predetermined positive sequence reactance and an earth return path reactance, the method comprising:
detecting a phase-to-earth fault on the electric line;
identifying a faulted phase of the electric line;
determining, at a measuring point, a reactance of a fault loop formed by the phase-to-earth fault,
determining a faulted section of the electric line to be a section closest to the measurement point of all such sections for which a sum of a positive sequence reactance and an earth return path reactance of the section in question and positive sequence reactances and an earth return path reactances of sections, if any, between the measurement point and the section in question is greater than or equal to the determined reactance of the fault loop; and
calculating a distance D between the measuring point and a point of fault according to the following formula:
D=D p +(( X Loop −X P )/ X F )· D F , where
X Loop =reactance of the fault loop
X P =sum of the positive sequence reactances and the earth return path reactances of sections, if any, between the measurement point and the faulted section of the electric line,
X F =sum of the positive sequence reactance and the earth return path reactance of the faulted section of the electric line,
D P =sum length of the sections, if any, between the measurement point and the faulted section of the electric line, and
D F =length of the faulted section of the electric line.
2. The method of claim 1 , wherein the reactance of the fault loop is determined according to the following formula:
X Loop =dpu ·( X 1 +X N ), where
dpu
=
Im
(
U
_
X
)
·
Re
(
I
_
X
)
-
Re
(
U
_
X
)
·
Im
(
I
_
X
)
Im
(
Z
_
1
·
I
_
X
)
·
Re
(
I
_
X
)
-
Re
(
Z
_
1
·
I
_
X
)
·
Im
(
I
_
X
)
-
Re
(
Z
_
N
·
I
_
N
)
·
Im
(
I
_
X
)
+
Im
(
Z
_
N
·
I
_
N
)
·
Re
(
I
_
X
)
where
U X =phase voltage phasor of the faulted phase of the line
Z 1 =positive sequence line impedance
R 1 =positive sequence line resistance
X 1 =positive sequence line reactance
X N =earth return path reactance of the line
I X =phase current phasor of the faulted phase of the line
Z N =earth return path impedance of the line
Z 0 =zero sequence line impedance
R 0 =zero sequence line resistance
X 0 =zero sequence line reactance
I N =earth return path current phasor.
3. The method of claim 1 , wherein the faulted section of the electric line is determined by comparing stepwise, section by section, starting from the section closest to the measurement point, the sum of positive sequence reactance and an earth return path reactance of the section in question and positive sequence reactances and an earth return path reactances of sections, if any, between the measurement point and the section in question with the determined reactance of the fault loop until said sum exceeds or equals the determined reactance of the fault loop.
4. The method of claim 1 , wherein when the electric line comprises parallel branches and the faulted section of the electric line has been determined to be located on a section of such a branch, an alternative faulted section and distance between the measuring point and a point of fault is determined for each parallel branch thereof.
5. A system for determining a location of a phase-to-earth fault in a three-phase electric line of an electric network, the electric line comprising two or more sections, each section having a predetermined positive sequence reactance and an earth return path reactance, the system being configured to:
detect a phase-to-earth fault on the electric line;
identify a faulted phase of the electric line;
determine, at a measuring point, a reactance of a fault loop formed by the phase-to-earth fault,
determine a faulted section of the electric line to be a section closest to the measurement point of all such sections for which a sum of a positive sequence reactance and an earth return path reactance of the section in question and positive sequence reactances and an earth return path reactances of sections, if any, between the measurement point and the section in question is greater than or equal to the determined reactance of the fault loop; and
calculate a distance D between the measuring point and a point of fault according to the following formula:
D=D p +(( X Loop −X P )/ X F )· D F , where
X Loop =reactance of the fault loop
X P =sum of the positive sequence reactances and the earth return path reactances of sections, if any, between the measurement point and the faulted section of the electric line,
X F =sum of the positive sequence reactance and the earth return path reactance of the faulted section of the electric line,
D P =sum length of the sections, if any, between the measurement point and the faulted section of the electric line, and
D F =length of the faulted section of the electric line.
6. The system of claim 5 , wherein the system is configured to determine the reactance of the fault loop according to the following formula:
X Loop =dpu· ( X 1 +X N ), where
dpu
=
Im
(
U
_
X
)
·
Re
(
I
_
X
)
-
Re
(
U
_
X
)
·
Im
(
I
_
X
)
Im
(
Z
_
1
·
I
_
X
)
·
Re
(
I
_
X
)
-
Re
(
Z
_
1
·
I
_
X
)
·
Im
(
I
_
X
)
-
Re
(
Z
_
N
·
I
_
N
)
·
Im
(
I
_
X
)
+
Im
(
Z
_
N
·
I
_
N
)
·
Re
(
I
_
X
)
where
U X =phase voltage phasor of the faulted phase of the line
Z 1 =positive sequence line impedance
R 1 =positive sequence line resistance
X 1 =positive sequence line reactance
X N =earth return path reactance of the line
I X =phase current phasor of the faulted phase of the line
Z N =earth return path impedance of the line
Z 0 =zero sequence line impedance
R 0 =zero sequence line resistance
X 0 =zero sequence line reactance
I N =earth return path current phasor.
7. The system of claim 5 , wherein the system is configured to determine the faulted section of the electric line by comparing stepwise, section by section, starting from the section closest to the measurement point, the sum of a positive sequence reactance and an earth return path reactance of the section in question and positive sequence reactances and an earth return path reactances of sections, if any, between the measurement point and the section in question with the determined reactance of the fault loop until said sum exceeds or equals the determined reactance of the fault loop.
8. The system of claim 5 , wherein when the electric line comprises parallel branches and the system has determined the faulted section of the electric line to be located on a section of such a branch, the system is further configured to determine an alternative faulted section and distance between the measuring point and a point of fault for each parallel branch thereof.
9. The system of claim 5 , wherein the system comprises a protective relay.
10. A computer program product comprising computer program code, wherein execution of the program code in a computer causes the computer to carry out the steps of the method according to claim 1 .