Device, system, and method for performing an online-update of a two-port equivalent
A device or system for use with an electric power system is provided. The electric power system has a first bus, a second bus, a third bus, a first line between the first and second buses, and a second line between the third bus and one of the first and second buses. The device or system is operative to determine, responsive to at least one trip event, one or several updated impedances of an equivalent model across a line.
1 . A method of determining updated impedances of an equivalent model across a transmission line for an electric power system, the electric power system comprising a first bus, a second bus, a third bus, a first line between the first and second buses, and a second line between the third bus and one of the first and second buses, the method comprising:
receiving, by a substation system, measurements comprising voltage measurements for one or several of the buses and switch status information;
determining, by the substation system, responsive to at least one trip event, one or several updated impedances of the equivalent model from the received measurements and impedances of the equivalent model obtained before the at least one trip event, wherein the substation system determines the one or several updated impedances of the equivalent model responsive to a trip of a shunt element at the third bus using the following quantities obtained from measurements:
a shunt current through the shunt element at the third bus prior to the trip of the shunt element, the shunt current being obtained from a shunt current measurement prior to the trip or being determined computationally, and
a change in voltage at the second bus in response to the trip of the shunt element,
wherein the substation system determines the one or several updated impedances of the equivalent model responsive to a trip of a shunt element at the third bus using measurements of changes in voltages at the first and third buses in response to the trip of the shunt element; and
performing a protection function using the updated impedances of the equivalent model, wherein the protection function comprises at least one of
setting operational characteristics of a distance relay,
locating a fault on the transmission line, or
setting power swing blinders.
2 . The method of claim 1 , wherein determining the one or several updated impedances of the equivalent model only utilizes substation process bus level measurements, and the impedances of the equivalent model before the at least one trip event.
3 . The method of claim 2 , wherein all measurements used for determining the one or several updated impedances of the equivalent model are obtained in a neighborhood of the first line.
4 . The method of claim 1 , wherein the updated impedances of the equivalent model comprise an updated first equivalent source impedance, an updated second equivalent source impedance, and an updated equivalent transfer path impedance.
5 . The method of claim 3 , wherein the substation system is operative to determine the one or several updated impedances without a re-computation of a full bus impedance matrix of the electric power system.
6 . The method of claim 1 , wherein the measurements are obtained at a substation level in the substation system.
7 . The method of claim 1 , wherein the one or several updated impedances of the equivalent model are updated impedances of the equivalent model of a two-port equivalent across the first line subsequent to the at least one trip event, and wherein the impedances of the equivalent model before the trip event comprise impedances of the equivalent model of the two-port equivalent prior to the at least one trip event.
8 . The method of claim 1 , wherein determining the one or several updated impedances of the equivalent model comprises:
determining at least one matrix element of a bus impedance submatrix using the measurements;
performing series and/or shunt branch modifications of the bus impedance submatrix to determine matrix elements of a modified bus impedance submatrix; and
determining the updated impedances of the equivalent model of the two-port equivalent using the modified bus impedance submatrix.
9 . The method of claim 8 , wherein the bus impedance submatrix is
Z
(
m
n
p
)
=
(
Z
m
m
Z
m
n
Z
m
p
Z
n
m
Z
n
n
Z
n
p
Z
p
m
Z
p
n
Z
p
p
)
,
wherein the substation system determines Z np =Z pn using the measurements,
wherein the substation system determines at least Z mm , Z mn , Z nm , and Z nn from impedances of the equivalent model of the two-port equivalent before the at least one trip event and modification calculations,
wherein Z ij designates the impedance of the equivalent model between two nodes i and j selected from {m, n, p}, wherein m designates the first bus, n designates the second bus, and p designates the third bus.
10 . The method of claim 9 , wherein the substation system determines the modified bus impedance submatrix
Z
(
mnp
)
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=
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Z
mm
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Z
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Z
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Z
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Z
nn
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Z
np
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Z
pm
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Z
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Z
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)
from the bus impedance submatrix Z(mnp) by performing series branch modifications comprising removing the branches between nodes m and p and between nodes m and n,
wherein the substation system determines the updated impedances of the equivalent model of the two-port equivalent such that they fulfill
Z
s
M
=
Z
mm
″
Z
nn
″
-
Z
mn
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Z
nm
″
Z
nn
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-
Z
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,
Z
s
N
=
Z
mm
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Z
nn
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-
Z
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Z
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Z
mm
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-
Z
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,
Z
tr
MN
=
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mm
″
Z
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Z
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Z
nm
″
Z
mn
″
.
wherein Z sM is an impedance of a first source of the two-port equivalent, Z sN is an impedance of a second source of the two-port equivalent, and Z tr MN is an impedance of a transfer path between the first source and the second source.
11 . The method of claim 1 , wherein the substation system determines the one or several updated impedances of the equivalent model responsive to a trip of the second line.
12 . The method of claim 11 , wherein the substation system determines the one or several updated impedances of the equivalent model responsive to a trip of the second line using measurements of:
a change in voltage at the second bus in response to the trip of the second line; and
a current on the second line at the first bus before the trip of the second line.
13 . The method of claim 12 , wherein the substation system determines the one or several updated impedances of the equivalent model responsive to a trip of the second line using the following quantities obtained from measurements:
(i) changes in voltages at the first and third buses in response to the trip of the second line; or
(ii) a current of the second line at first bus before the trip of the second line.
14 . A substation system for use with an electric power system, the electric power system comprising a first bus, a second bus, a third bus, a first line between the first and second buses, and a second line between the third bus and one of the first and second buses,
wherein the substation system comprises an interface to receive measurements comprising voltage measurements for one or several of the buses and switch status information;
wherein the substation is operative to determine, responsive to at least one trip event, one or several updated impedances of an equivalent model from the received measurements and impedances of the equivalent model obtained before the at least one trip event, and trigger a protection function using the updated impedances of the equivalent model;
wherein the substation system determines the one or several updated impedances of the equivalent model responsive to a trip of a shunt element at the third bus using the following quantities obtained from measurements:
a shunt current through the shunt element at the third bus prior to the trip of the shunt element, the shunt current being obtained from a shunt current measurement prior to the trip or being determined computationally, and
a change in voltage at the second bus in response to the trip of the shunt element,
wherein the substation system determines the one or several updated impedances of the equivalent model responsive to a trip of a shunt element at the third bus using measurements of changes in voltages at the first and third buses in response to the trip of the shunt element; and
wherein the protection function comprises at least one of
setting operational characteristics of a distance relay,
locating a fault on the transmission line, or
setting power swing blinders.
15 . An electric power system, comprising:
a first bus;
a second bus;
a third bus;
a first line between the first and second buses; and
a second line between the third bus and one of the first and second buses; and
the substation system of claim 14 to determine updated impedances of the equivalent model of a two-port equivalent from the received measurements and base impedances of the equivalent model.
16 . An electric power system, comprising:
a plurality of substations, each comprising a substation system according to claim 14 ; and
a central entity communicatively coupled to the substation systems and operative to coordinate the substation systems and/or to combine updated impedances obtained from different substation systems.