Note: Descriptions are shown in the official language in which they were submitted.
CA 02325101 2000-11-03
1197-2
METHOD OF CALCULATING SURGE PROPAGATION SPEED AND SYSTEM FOR
LOCATING FAULT POINTS BY THE USE THEREOF
BACKGROUND OF THE INVENTION
The present invention relates to a method of calculating
surge propagation speed and a fault point location system. More
particularly, the present invention relates to a method to
calculate surge propagation speed at the time of locating a surge
and a fault point locating system which is able to accurately
identify a fault point by obtaining the surge propagation speed
at the time of locating a surge.
Heretofore, when a fault occurs along the way of a power
transmission line and distribution line (hereinafter designated
a "transmission and distribution line" for both lines), a method
is known by which the fault point on the transmission and
distribution line is determined in accordance with a difference
in surge detection time at two substations situated across the
fault point (Japanese Patent Publication No. 51274 of 1988, etc.)
In the foregoing method, a fault location is identified based on
the times at which a surge is detected at each of the two
substations, the distance between the two substations, and the
speed at which the surge propagates in the transmission and
distribution line (hereinafter designated the "surge propagation
speed" ) .
The surge propagation speed changes due to conditions of the
transmission and distribution line per se (e.g. differences in
overhead distribution lines or distribution cables, differences
1
CA 02325101 2000-11-03
in ground resistance rates, etc.), weather conditions, and so on.
For this reason, in many of the prior art methods of location,
values of surge propagation speed that were obtained beforehand
by actual measurements were used as estimate values. Providing
that the distances between substations were short, the errors
introduced by performing fault point location with such estimated
values were regarded as negligible in many cases.
SUMMARY OF THE INVENTION
Depending on the conditions of transmission and distribution
line or weather, the differences between the values of surge
propagation speed at the time of surge identification and those
of the estimated surge propagation speed were so large that , in
some cases, the errors in surge identification were no longer
negligible. In addition, if the distances between substations
were long, the errors in surge identification were no longer
negligible in some cases.
It is therefore an object of the present invention to
provide a method of calculating surge propagation speed which
derives the surge propagation speed at the time of surge
identification. Another object of the present invention is to
provide a fault point location system which accurately identifies
fault locations by obtaining accurate surge propagation speeds.
A method of calculating surge propagation speed expressed in
the first aspect of the invention is a method of calculating
surge propagation speed in a fault point location system
comprising:
substations 1 installed along transmission and distribution
lines for sending surge detection time information along the
transmission and distribution lines to a master station 2; and
2
CA 02325101 2007-12-28
the master station 2 for locating a fault point on the basis
of the surge detection time information;
characterized in that
the surge propagation speed is obtained on the basis of the
detection times of a surge current or a surge voltage at the
first substation positioned adjacent to a fault point along the
transmission and distribution lines and another substation
positioned next to the first substation together with a length of
the transmission and distribution lines between the first and
other substations.
The fault point location system expressed in the second
aspect of the invention is a fault point location system
comprising:
substations 1 installed along transmission and distribution
lines for sending surge detection time information along the
transmission and distribution lines to a master station 2; and
the master station 2 for locating a fault point on the basis
of the surge detection time information;
characterized in that: each of the substations 1, that
functions as a clock, is capable of receiving radio waves from a
global positioning system (GPS) satellite and identifying the
time held by the GPS satellite to synchronize its own time with
the time held by the GPS satellite, detects surge currents or
surge voltages occurring along the transmission and distribution
lines in which the particular substation 1 is installed,
determines the surge detection time at which the surge current or
surge voltage is detected, and transfers the surge detection time
to the master station 2 through a communication network; the
master station 2 receives the surge detection time from the
substation 1 via the communication network, identifies the
3
CA 02325101 2007-12-28
location where a fault has occurred on the transmission and
distribution line based on the difference of the surge detection
times from two of the substations 1 positioned at each end of the
fault section, the length of the transmission and distribution
line of the fault section, and the surge propagation speed; and
the surge propagation speed is obtained on the basis of the
surge detection times at the first substation positioned adjacent
to a fault point along the transmission and distribution lines
and another substation positioned next to the first substation
together with the length of the transmission and distribution
lines between the first and other substations.
The master station 2, as indicated in the third Claim of the
invention, uses the surge detection time tl at the first of a
pair of substations situated across the fault point along the
transmission and distribution lines, the surge detection time t2
at the other substation of the pair, the surge propagation speed
v, and the length L of the transmission and distribution line
between the pair of substations to obtain the distance L1 from
the first substation to the fault point along the transmission
and distribution line according to the equation L1 = (L + (tl -
t2) x v) / 2.
Furthermore, the master station 2, as indicated in the
fourth aspect of the invention: uses the surge detection time tl
at a substation closest to the source-side end of the
transmission and distribution line, the surge detection time t2
at a substation positioned at the far end of the transmission and
distribution line, the surge propagation speed v, and the length
L of the transmission and distribution line between the pair of
substations to obtain the distance L1 from the substation closest
to the source-side end to
4
CA 02325101 2000-11-03
the fault point along the transmission and distribution line
according to the equation Ll = (L +(tl - t2) x v) / 2; and
further uses the surge detection time t3 at the first of a
pair of substation situated across the fault point found as per
the calculation above, the surge detection time t4 at the other
substation of the pair, the surge propagation speed v, and the
length L' of the transmission and distribution line between the
pair of substations to obtain the distance L3 from the first
substation to the fault point along the transmission and
distribution line according to the equation L3 =(L' + (t3 - t4)
X v) / 2.
As per the method, calculating surge propagation speed of
the first aspect of the invention and a fault point location
system of the second aspect of the invention, surge propagation
speed at the time of surge identification is found and then the
surge propagation speed is used in identifying a fault point. It
is possible to obtain the accurate location of fault points even
under varying conditions such as of the transmission and
distribution line and weather, etc.
In a fault point location system of the third and the fourth
aspect of the invention, because of the provision of a master
station in the system, it is possible for the master station to
identify a fault point based on surge detection time information
from each substation. Additionally, by providing a master station
which is separate from any substations and which is installed on
the transmission and distribution lines and has the
responsibility of locating fault points to the equipment of the
master station, it is possible for each substation to be compact
and easy to install.
CA 02325101 2000-11-03
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an explanatory diagram showing the relationship
between a master station and substations.
Fig. 2 is an explanatory diagram illustrating components of
a substation.
Fig. 3 is an explanatory diagram illustrating components of
a master station.
Fig. 4 is an explanatory diagram of the principle of
identifying fault points.
Fig. 5 is a diagrammatic representation for explaining the
method of determining the surge propagation speed.
Fig. 6 is a diagrammatic representation for explaining the
method of determining the surge propagation speed.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be explained below by referring
to Fig. 1 through Fig. 6.
(1) The configuration of the fault point location system.
As shown in Fig. 1, the fault point location system of an
embodiment of the present invention comprises:
substations 1 which are installed at each steel tower or
pole along transmission and distribution lines and
a master station 2 which is installed at a service office or
branch office of a power company and which identifies points of
fault on the basis of information from substations 1.
(a) Substations
As shown in Fig. 2, a substation 1 is provided with a GPS
antenna 111, a GPS receiver 112, an oscillator 121, a reference
clock 122, a time synchronization correcting circuit 123, a zero-
phase current transformer (ZCT) 131, a filter circuit 132, a
6
CA 02325101 2007-12-28
surge signal detection circuit 133, a surge detection time
holding circuit 134, a central processing unit 141, and a
communication interface 142.
The ZCT 131, the filter circuit 132, the surge signal
detection circuit 133, the surge detection time holding circuit
134, and a part of the central processing unit 141 correspond to
a "surge detection means 13". Additionally, the central
processing unit 141 and the communication interface 142
correspond to a "surge information transmitting means 14b".
Further in a likewise concept, the GPS antenna 111 and the
GPS receiver 112 together can be regarded as a "GPS receiving
means 11" and the oscillator 121, the reference clock 122, and
the time synchronization correcting circuit 123 together can be
considered as a"time measuring means 12".
Each component will be explained below.
(i) ZCT 131
The ZCT 131 is mounted to the steel tower of a transmission
and distribution line to detect surge signals (surge currents)
that occur at the time of a fault and then send them to the
filter circuit 132. If surge voltages are to be detected as surge
signals, a voltage detector such as a PT or PD will be used.
(ii) Filter circuit 132
The filter circuit 132 filters signals, which the sensor 131
has detected, to remove unnecessary commercial frequency
components that are not surge signals and allows only the surge
signals to pass through and are sent to the surge signal
detection circuit 133.
7
CA 02325101 2000-11-03
(iii) Surge signal detection circuit 133
The surge signal detection circuit 133 detects the level of
a surge signal and then determines that a surge occurred if the
signal level exceeds a surge-acknowledging level, whereupon
outputting a time holding signal to the surge detection time
holding circuit 134.
(iv) Surge detection time holding circuit 134
At the time when a time holding signal is output from the
surge signal detection circuit 133, the surge detection time
holding circuit 134 holds the time of the reference clock 122 and
outputs it as the surge detection time to the central processing
unit 141.
(v) GPS antenna 111 and GPS receiver 112
The GPS antenna 111 receives radio waves from a GPS
satellite and send them to the GPS receiver 112. Then, the GPS
receiver 112 extracts, as a synchronization signal, the
information of the standard time held by the GPS satellite from
the radio waves and then outputs the signal to the time
synchronization correcting circuit 123.
(vi) Time synchronization correcting circuit 123
In accordance with the synchronization signal that is output
by the GPS receiver 112, the time synchronization correcting
circuit 123 synchronizes the time of the reference clock 122 with
the standard time held by the GPS satellite.
(vii) Reference clock 122
The reference clock 122 outputs the reference time to the
surge detection time holding circuit 134.
8
CA 02325101 2000-11-03
(viii) Oscillator 121
The oscillator 121 outputs the reference time signal for
measuring the time to the reference clock 122.
(ix) Central processing unit 141
The central processing unit 141 sends the surge detection
time that is output by the surge detection time holding circuit
134 to the master station 2 via the communication interface 142.
(x) Communication interface 142
The communication interface 142 relays communication signals
between the central processing unit 141 and the commercial
telephone network so that the central processing unit 141 can
communicate with the master station 2 using the public data
network.
(b) Master station
As shown in Fig. 3, a master station 2 comprises a
communication interface 21, an auxiliary storage unit 222, a
central processing unit 23, a CRT 241, a printer 242, and a
keyboard 25.
The communication interface 21 can be regarded as a
"substation surge information receiving means 21b".
Likewise, the central processing unit 23 can be regarded as
a "fault location identifying means 23c" which identifies fault
locations based on the surge detection time and surge propagation
speed.
9
CA 02325101 2007-12-28
The central processing unit 23 also can be regarded as a
V%surge propagation speed calculation means 23d" which calculates
surge propagation speed based on the surge detection time.
Reference character 21a is substation location information
receiving means, reference character 22 is map information
storage means, and reference character 23a is transmission and
distribution line map information preparing means.
Further, the cathode ray tube (CRT) 241 and the printer 242
can be regarded as "information output means 24" which output the
results of fault location. The keyboard 25 as an "input means".
Each component will be explained below.
(i) Communication interface 21
The communication interface 21 relays communication signals
to and from the substations 1. Precisely, it converts signals
transmitted from the substations 1 via a public data network to
supply them to the central processing unit 23.
(ii) Central processing unit 23 (a personal computer, a
workstation, etc.)
The central processing unit 23 receives the location
information and the surge detection time, which are transmitted
by each substation 1, via the communication interface 21, and
performs the fault point location processing, which will be
described later.
Fault points obtained by processing the fault point location
is output to the CRT 241 or the printer 242 together with
transmission and distribution line map data stored in the
auxiliary storage unit 222.
(iii) Auxiliary storage unit 222 (a hard disk, etc.)
CA 02325101 2000-11-03
The auxiliary storage unit 222 stores the surge detection
time and the location information transmitted by each substation
1, the fault points calculated by the central processing unit 23,
and the transmission and distribution line map data necessary for
the central processing unit 23 to perform processing.
The transmission and distribution line map data includes
such data as the locations of poles and steel towers, and the
distances between the poles (steel towers), etc.
(iv) Printer 242
Following the command by the central processing unit 23, the
printer 242 prints out a transmission and distribution line map
data or the results of fault location, which are sent by the
central processing unit 23.
(v) CRT 241
Following the command of the central processing unit 23, the
CRT 241 displays a transmission and distribution line map or the
results of fault location, which are sent by the central
processing unit 23.
(vi) Keyboard 25 (input means)
The keyboard 25 is used to input drawing data, etc.
necessary for creating transmission and distribution line maps.
The drawing data outputs such data as the locations of poles
and steel towers, and the distances between the poles (steel
towers), etc.
(2) Processing of surge propagation speed calculation.
11
CA 02325101 2000-11-03
The calculation method for surge propagation speed processed
by the surge propagation speed calculation means 23d will be
explained below. When a fault occurs many possible configurations
of transmission and distribution lines can be considered but they
can be categorized into cases (a) and (b) below.
(a) In the case where substations are positioned on a straight
line as shown in Fig. 5, substations 1A, 1B, 1C are installed in
such an order on a piece of transmission and distribution line
and a fault occurs at the point P between substations 1B and 1C.
When a surge is caused because of a fault, the surge
propagates along the transmission and distribution line from the
fault point P to and through the substations 1C, 1B, and 1A in
the said order. For this reason, if the distance LõB between the
substations 1A and 1B is given, the surge propagation speed võ,,
between the substations 1A and 1B can be computed Formula (1)
shown below.
vAB = LAU ...
tA-ta
vAB : surge propagation speed between the substations 1A and 1B
L,O distance between the substations 1A and 1B
t,, : surge propagation time at the substation 1A
tg : surge propagation time at the substation 1B
(b) In the case where substations are positioned on branched
lines as shown in Fig. 6, a branch-off point R is introduced on
the transmission and distribution line with substations 1D, 1E,
and iF positioned on each of the branched pieces of transmission
and distribution line and a fault occurs at the point P between
the branch-off point R and the substation 1F.
12
CA 02325101 2000-11-03
When a surge is caused because of a fault, the surge
propagates along the transmission and distribution lines from the
fault point P to and through the substations 1F, as well as the
branch-off point R, and substations 1D and 1E. At this time, if
the distance L,, between the substation 1D and the branch-off
point R and the distance L,, between the substation 1E and the
same are found and the two distances L,, and LR, are not equal,
speed v.E of the surge propagating from the branch-off point R to
both substations 1D and 1E can be computed according to Formula
(2) shown below.
Further, the sections between the branch-off point R, for
which the surge propagation speed vRDE is determined when the
substations 1D, 1E are adjacent to the section, which includes
the fault point P, between the branch-off point R and the
substation 1F, and the conditions of transmission and
distribution lines, as well as the weather conditions, are found
to be similar. For this reason, the surge propagation speed vRDF,
can be regarded as a close approximation of the surge propagation
speed vRF between the branch-off point R and the substation iF.
Therefore, the surge propagation speed v.E that is obtained can
be used as the surge propagation speed v which will be used for
identifying the location of the fault point P.
v _ (Lnx~'LRr) (LEx~'Lxp) _LnR-L~ ...~2)
RDB -
tD _ tE tD _ tE
vjwE : surge propagation speed between the branch - off point R and the
substations 1A and 1B
LDR : distance between the substations 1D and the branch - off point R
Lm : distance between the substations 1E and the branch - off point R
Lm : distance between the branch - off point R and the fault point P
tD : surge propagation time at the substation 1D
tE : surge propagation time at the substation 1E
13
CA 02325101 2000-11-03
By processing the calculation of surge propagation speed
according to the aforesaid method for surge propagation speed to
accurately determine the surge propagation speed v at the time of
fault point location, errors in the location of fault points can
be reduced.
(3) Processing in the fault point location system
Procedures for identifying the location of a fault when one
occurs on the transmission and distribution line will be
explained below. First, determination of the surge detection time
by a substation will be explained in the paragraphs under (a),
which is followed by the explanation of fault point location by
the master station in the paragraphs under (b).
(a) Determination of a surge detection time by a substation.
The procedure for determining a surge detection time by the
central processing unit 141 of a substation 1 will be explained
below.
A substation receives surge currents that occur at the time
of a fault with the ZCT 131, detects the surge currents with the
filter circuit 132 and the surge signal detection circuit 133,
and outputs a surge detection signal to the surge detection time
holding circuit 134. The substation, then, holds the reference
time at which a surge detection signal is received in the surge
detection time holding circuit 134, and outputs the reference
time to the central processing unit 141 as a surge detection
time, followed by the central processing unit 141 which
automatically transfers the data of the detection time of the
surge detection signal together with the substation number to the
master station as fault information.
14
CA 02325101 2000-11-03
(b) Fault point location by the master station.
An explanation of the principle and the procedures of
locating a fault point performed by the central processing unit
23 of the master station 2 will be provided below. First the
principle of locating a fault point will be explained in the
paragraphs under (i), and subsequently the procedures of locating
a fault point will be explained in the paragraphs under (ii).
(i) Principle of locating a fault point
A diagram of the principle of locating a fault point is
provided in Fig. 4.
Occurrence of a ground fault within the section between
substations (1) and (2) causes a travelling wave (a surge) to
develop as shown in Fig. 4. The length of time required for
detecting this travelling wave at substations O and is
proportional to distance L1 and L2 from the point where the fault
has occurred to each substation assuming that the propagation
speed v of the travelling wave propagating along the transmission
and distribution line is constant.
That is, if the distance L between substations (1) and and
the propagation speed v of the travelling wave are known and the
difference in the length of time detected at substations and
is accurate, the equation "L1 = (L +(tl - t2) x v) / 2",
shown in Fig. 4, allows for determination of the distance L1 from
the substation (1) to the fault point.
"Propagation speed v of the travelling wave" at the time of
fault point location can be determined according to the
aforementioned processing of surge propagation speed calculation.
CA 02325101 2000-11-03
In the fault point location system of the present
embodiment, the length L of a transmission and distribution line
segment between substations (positioned at the source side and
the end of the transmission and distribution line) which examine
surge detection time differences is determined by calculation and
stored in memory beforehand. This length L may be either
manually input or determined by a means such as automated
measurement utilizing GPS.
In addition, under the assumption that the transmission
distribution line segment between substations adjacent to each
other is almost straight, the positional information of both
substations (longitude, latitude, and altitude) can be used to
calculate the length of the transmission and distribution line
segment between the two substations.
For the length of the transmission and distribution line
across substations not adjacent to each other, adding each line
segment between any two adjacent substations that exist between
the first two substations provides the target length L.
(ii) Procedure of locating a fault point
The central processing unit 23 of the master station 2, in
advance, calculates and stores in memory the length L of
transmission and distribution line between the substation closest
to the source-side end and each substations positioned at each
end of the transmission and distribution network.
Then the central processing unit 23 selects a combination of
the substation 1 closest to the source-side end of the
transmission and distribution line and another substation 1
closest to the ends of the trunk line and the spur lines to
16
CA 02325101 2000-11-03
locate a fault point based on the difference in surge detection
times at both substations.
That is, the central processing unit 23 uses a surge
detection time tl at a substation on the source side, a surge
detection time t2 at a substation positioned at the far end of
the transmission and distribution line, surge propagation speed
v, and the length L of the transmission and distribution line
between the two substations to obtain the distance L1 from the
substation on to the source side to the location where a fault
occurred along the transmission and distribution line according
to the equation L1 = (L +(tl - t2) x v) / 2.
Then, if further substations 1 are found near and across the
located fault point, the reliability of the fault point location
can be increased by locating the fault point again based on the
difference of surge detection times at these substations.
Such a procedure of locating a fault point may be executed
by an operator manually inputting necessary information for the
central processing unit 23 every time a fault point location is
performed or a software program may be created so that the
central processing units 23 automatically handles the processing.
In this procedure, an accurate time difference will not be
obtained unless the reference time at the substation on each side
has been synchronized with each other, wherein, as described
above, time at each substation is synchronized to correct at any
time by synchronizing the reference time at each substation with
the reference time sent from a GPS satellite.
(iii) Displaying a fault location
17
CA 02325101 2000-11-03
The central processing unit 23 of the master station 2,
after identifying a fault point location, displays transmission
and distribution line map information which is stored in the
auxiliary storage unit 222 and the located fault point on the
screen of the CRT 241 in order to notify the operator of the
location of fault occurrence. Additionally, it causes the
printer 242 to print out such information according to the
operators command.
(4) Operating the fault point location system
Substations 1 will be mounted on poles (steel towers)
supporting transmission and distribution lines and operated
continuously 24 hours a day so that a fault can be detected at
any time.
Master station 2 may be installed, for example, at a service
office or branch office of a power company and operated only
while an operator is available or 24 hours a day to quickly
identify a fault point whenever a fault occurs.
(5) Effects of the fault point location system
The fault point location system of the present embodiment,
having a combination of the time measuring means 12 and the GPS
receiving means 11 within a substation to synchronize the
substations with one another and maintain accurate time, the
location of a fault point (distance from a substation to the
fault point) is identified on the basis of a time difference of
surge signals reaching substations positioned on both sides of a
fault point (on the source side and the end of the transmission
and distribution line). Additionally, the surge propagation speed
is determined based on time differences between surge signals
reaching each of the substations, and such surge propagation
18
CA 02325101 2000-11-03
speed is used to identify the location of a fault point,
therefore enabling accurate fault point location under varying
conditions such as of the transmission and distribution line or
weather.
[Others]
In the present invention, without being limited to the
aforementioned preferred embodiment, various types of embodiments
are possible according to the purpose, use, etc. That is, in the
present embodiment, substations used for obtaining surge
propagation speeds are those positioned adjacent to a fault
point, however speed values can be calculated using a substation
separated by several other substations. Likely, a pair of
substations used for calculation does not need to be those
adjacent to each other but rather other substations can be
positioned between them. By extending the distance between
substations, as illustrated here, time differences of surges
reaching the substations increase, which makes determination of
surge propagation speed easier.
Public networks such as the cellular phone system, PHS
(Personal Handy-phone System), or public telephone network can be
used for the transfer of information from the substations to the
master station, or a dedicated network (of metal cables, optical
fibers, radio waves, etc.) installed along transmission and
distribution lines can also be used. Additionally, modulated
signals can be propagated through the transmission and
distribution lines.
Furthermore, embodiments of the storage means of the map
data of the transmission and distribution line map information
are not limited to using an auxiliary storage unit and storage is
19
CA 02325101 2000-11-03
possible on other recording media such as magnetic disks, optical
disks (CD-ROM, DVD, etc.), magneto-optical disks. Likewise, it
can be so arranged that map data is downloaded from a WWW site
which manages a map information system on the Internet and is
retrieved on-line. It will be possible to obtain the most up-to-
date map information if data is downloaded from the server via
the Internet or retrieved on-line, in which case maintaining ones
own map information will no longer be necessary.
