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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a secondary arc extinction device in a
multi-conductor transmission line electric power system in which an
electrostatic coupling between the lines is strong and problems are
thereby caused.
2. Description of the Prior Art
The above-noted problems are that the arc generated by back flashover at
the installation of the insulator for the transmission line (which is
hereinafter referred to as "secondary arc") is not extinguished to disable
the reclosing at a high speed or it is impossible to take a sufficient
non-voltage period of time by the fact that the induction electric current
or the induction voltage is supplied from the whole phase or the whole
line due to the electrostatic coupling even after the circuit breakers at
both ends of the transmission line are interrupted when there is caused a
short circuit due to the damage caused by lightning or the like at the
insulator installation.
Nextly described with the aid of FIGS. 1, 2a, 2b, 3 and 4 is the
conventional electric power transmission line system. Specifically, a
power transmission line (R, S & T phases) is considered wherein the fixed
reactor with zero phase, i.e., the reactor between the neutral point of
the star-connection and ground, compensation is provided as shown in FIG.
1. In FIG. 1,
Y.sub.ca : power transmission line a phase ground admittance,
Y.sub.cb : power transmission line b phase ground admittance,
Y.sub.cc : power transmission line c phase ground admittance,
Y.sub.cab : power transmission line a-b phase interphase admittance
Y.sub.cbc : power transmission line b-c phase interphase admittance
Y.sub.cca : power transmission line c-a phase interphase admittance
Y.sub.La : .omega..La: reactor a phase admittance,
Y.sub.Lb : .omega..Lb: reactor b phase admittance,
Y.sub.Lc : .omega..Lc: reactor c phase admittance,
Y.sub.g : .omega..Lg: neutral point reactor admittance,
L.sub.a : reactor a phase reactance,
L.sub.b : reactor b phase reactance,
L.sub.c : reactor c phase reactance,
L.sub.g : neutral point reactor reactance,
In addition, the reactor with zero phase compensation which is shown in
FIG. 2(a) can be resolved into components between lines, as well as ground
components as shown in FIG. 2(b). In FIG. 2(b), if it is assumed that
m=Y.sub.La +Y.sub.Lb +T.sub.Lc +Y.sub.g, each admittance will be obtained
as the following:
Y.sub.Lab =Y.sub.La .multidot.Y.sub.Lb /m
Y.sub.Lbc =Y.sub.Lb .multidot.Y.sub.Lc /m
Y.sub.Lca =Y.sub.Lc .multidot.Y.sub.La /m
Y.sub.ag =Y.sub.a .multidot.Y.sub.g /m
Y.sub.bg =Y.sub.b .multidot.Y.sub.g /m
Y.sub.cg =Y.sub.c .multidot.Y.sub.g /m
On the other hand, as shown in FIG. 3, there is considered a state in which
the a phase circuit breaker CB is opened after an a phase ground
short-circuit problem has occurred. Then, an induced electric current
i.sub.a flows into the problem point A from the other whole phases b and
c, not undergoing a fault by way of Y.sub.cab and Y.sub.cca. In addition,
the condition of the recovery voltage v.sub.r and the secondary arc
current i.sub.a for the continuation of the secondary arc is dependent
upon the weather conditions, the primary arc current, the time, the design
of the insulator of the line, etc. In other words, it becomes possible to
extinguish the secondary arc if it becomes possible to limit the secondary
arc current and the recovery voltage in a range which either the recovery
voltage v.sub.r or the secondary arc current i.sub.a is small.
However, the induction via the power transmission line phase ground
admittances Y.sub.caa', Y.sub.cab' and Y.sub.cac' from the whole
transmission line is received in the case of a juxtaposed pair of
transmission lines as shown in FIG. 4, but it is difficult to compensate
for the capacitance between the lines with the reactor which is
constituted as shown in FIG. 1.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a novel
secondary arc extinction device in an electric power system in which it is
possible to shorten the period of time for extinction of secondary arcs
caused by all kinds of problems.
Another object is to provide a new and improved power transmission system,
especially a UHV system, provided with active countermeasures for the
extinction of secondary arcs.
These and other objects are achieved according to the invention by
providing a novel secondary arc extinction device in an electric power
system in which the reactance value of each phase reactor is made variable
in a continuous manner by effecting thyristor phase control and the
star-connection reactor which has a reactor between the neutral point of
the star-connection reactor and ground (as seen from the system, and which
is hereinafter referred to as "reactor with zero phase compensation"), and
in which the reactance value of each phase reactor is capable of being
controlled to the most optimum reactance value for extinction of secondary
arcs. Contrary to the conventional system in which highspeed multi-phase
reclosing is carried out with nothing as a countermeasure, the present
invention provides an active countermeasure for extinction of secondary
arcs in the UHV power transmission system, versus the mere provision of a
fixed reactor with zero phase compensation as is otherwise conventional.
Briefly, in accordance with one embodiment of this invention, a secondary
arc extinction device in an electric power system is provided which
includes a bus bar; an electric power line connected to the bus bar;
protective relaying means connected to the bus bar; a transformer having a
primary winding and a secondary winding, one terminal of the primary
winding being connected to the electric power line; first reactance means
connected between the other terminal of the primary winding of the
transformer and ground; second reactance means connected to the secondary
winding the transformer; and means for controlling the second reactance
means in response to the protective relaying means.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention will be readily obtained as
the same becomes better understood by reference to the following detailed
description when considered in connection with the accompanying drawings,
wherein:
FIG. 1 is a circuit diagram of a conventional electric power transmission
line with a fixed reactor with zero phase compensation;
FIGS. 2(a) and 2(b) are respectively circuit diagrams of a part of FIG. 1
and an equivalent circuit of a portion of the circuit of FIGS. 2(a);
FIG. 3 is a diagram showing when an a phase 1 ground short-circuit occurs
in the conventional electric power transmission line;
FIG. 4 is a diagram showing when an a phase 1 ground short-circuit occurs
in the conventional juxtaposed multi-line power transmission system;
FIG. 5 is a circuit diagram showing one embodiment of secondary arc
extinction device in accordance with the present invention;
FIGS. 6(a) and 6(b) are circuit diagrams of electric power transmission
lines employing the active countermeasures of the present invention;
FIG. 7 is a block diagram of one embodiment of a control device shown in
FIG. 5; and
FIG. 8 is a block diagram of another embodiment of a control device shown
in FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention shortens the period of time for extinction of
secondary arc with the reactor with zero phase compensation by producing
parallel resonance in the circuits of Y.sub.cca and Y.sub.Lca, Y.sub.cab
and Y.sub.Lab respectively in the circuit which is shown in FIG. 3, so
that the impedance becomes infinite, thereby making zero the electric
current between the (A) point and ground and the recovery voltage, or
making them approach zero. In other words, it becomes possible to make
zero both the secondary arc current and the recovery voltage in the
transmission line of one line by choosing the reactance of the reactor in
such a way that the capacitance between the lines and the reactor between
the lines resonate in parallel.
The continuous control of the reactive power is also the continuous control
of the reactance value. The continuous reactance control ability of the
thyristor phase control reactor is utilized according to the present
invention.
Referring now to the drawings, wherein like reference numerals and letters
designate identical or corresponding parts throughout the several views,
and more particularly to FIG. 5 thereof, one embodiment in accordance with
the invention will be explained with reference to the accompanying
drawings.
FIG. 5 shows an example of a secondary arc extinction device in an electric
power system in accordance with the present invention. In FIG. 5, there is
provided a thyristor phase control reactor with zero phase compensation at
a service entrance of an electric station, a substation or a connection
station between the bus bar and the line. This reactor is capable of
varying the reactance value of each phase in a continuous manner by
effecting the phase control of the thyristor.
A protective relay LINE PRO, as well known, generates a trip signal (dotted
line) to be transmitted to a circuit breaker CB in response to outputs
from a current transformer CT and a potential transformer PD when a ground
fault occurs in a range to be protected.
As described in FIGS. 1 and 2, one terminal of the primary windings of
transformers TR for dropping voltage are connected to each phase line
(only one phase R is shown in FIG. 5 for the sake of brevity) as a
star-connection. Between the neutral point of the star-connected
transformers TR and ground a reactor L.sub.g is provided.
The secondary winding of the transformer TR is connected to a series
connection of a phase reactor RE and anti-parallel connected thyristors
THY and a filter F.
A control device CONTROL receives outputs from the current transformer CT,
the potential transformer PD, the protective relay LINE PRO and an
auxiliary contact (b contact, not shown) of circuit breaker CB. Control
device CONTROL generates a signal to change the conduction angle of
thyristor THY to a predetermined value so as to produce parallel
resonance, e.g., in the circuits of Y.sub.cca and Y.sub.Lca, Y.sub.cab and
Y.sub.Lab in FIG. 3 when a fault occurs, as described hereinafter with
regard to FIGS. 7 and 8 in more detail.
When a fault occurs, the reactance of the transformer TR of each phase is
controlled by the thyristor THY so as to change the reactance to a
predetermined value.
As a result, it is possible to extinguish the secondary arc so that the
capacitance between the lines and the controlled reactance between the
lines resonate in parallel.
For example, the thyristor phase control reactor with zero phase
compensation is constituted in such a way that only the interphase
capacitance of its own line is compensated for as shown in FIG. 6(a) or in
such a way that even the capacitance between the lines is compensated for
as shown in FIG. 6(b). In addition, in a juxtaposed multicircuit power
transmission system, all capacitance, (interphase capacitance, the
capacitance between the link shown in FIG. 6B) are used to match the
parallel resonance condition.
FIG. 7 is a example of the above mentioned control means CONTROL in
accordance with which the troubled phase is identified at PHASE SELECTION
portion by the operative condition of the circuit breaker CB or the
operative condition of the protective relay LINEPRO of a line or a
troubled phase selection relay such as over current relay OC, undervoltage
relay UV or the like and the gate ignition angle of the thyristor THY is
determined at the GATE CONTROL portion so as to transmit an ignition
signal to the thyristor THY. Now, if a gate ignition angle is set in
advance which is in correspondence with the most suitable reactance value
of each phase which is capable of compensating for the interphase
capacitance or the capacitance between the lines by the condition of the
troubled phase, it becomes possible to instantaneously respond in
determining the ignition angle of the thyristor gate at the GATE CONTROL
portion. In other words, the PHASE SELECTION portion functions to select
the reactance value (ignition angle) in advance in response to the kind of
faults and kind of transmission system.
Thus, the secondary arc extinction device in an electric power system is
constituted in such a way that a thyristor phase control reactor with zero
phase compensation is provided at a service entrance of a line in an
electric place, a trouble phase is identified by a trip signal condition
of a protective relay LINE PRO for a line or by the operative condition of
a relay OC, UV for selecting a trouble phase or by the operative condition
(b contact, not shown) of the circuit breaker CB and a reactance value of
each phase is controlled to be a predetermined value so as to match the
parallel resonance condition above-described.
Therefore, it becomes possible to make short the period of time for
extinction of the secondary arc in the power transmission system and
furthermore, the reclosing is made possible if the means for extinction of
secondary arc as mentioned above is employed. Although it is impossible to
gather together the reactors for reactive power control of the system at
the service entrance of the line in the case of the fixed reactor, it
becomes possible to do so in accordance with the device of this invention
because the reactance value is made variable. In addition, it is possible
to constitute as a combination of a thyristor phase control reactor and a
circuit breaker switching control capacitor, in other words, to constitute
in combination with the capacitor equipment. Therefore, it is possible to
provide the reactive power control means in such a way as to be gathered
together at the service entrance of the line, which will also become
possible to be used at the time when any trouble is caused for the line so
as to shorten the period of time for extinction of the secondary arc. In
addition, since it is possible to use the floating capacitance of the line
as the advance capacitance by controlling the reactor current, it becomes
possible for the electric station as a whole to save the capacitor, which
is quite advantageous from an economical viewpoint.
Another embodiment of a secondary arc extinction device in accordance with
the present invention will be explained with reference to FIG. 8, wherein
the output of the ground protective relay GND LINE PRO and the output of
"OR" gate OR are supplied to an "AND" gate AND.
The "AND" gate AND is employed for prohibiting the operation of thyristor
THY in the event of an interphase short-circuit. In other words, even if
the output of current transformer CT is generated when the interphase
short-circuit occurs ground protective relay GND LINE PRO does not
function.
Therefore, when the interphase short-circuit occurs, thyristor THY, i.e.,
reactance value of each phase is not controlled in the FIG. 8 embodiment.
The present invention is not limited to the above mentioned embodiments but
may be varied and carried out in various manners without varying the gist
of the invention.
In accordance with the present invention as mentioned above, since a
thyristor phase control reactor with zero phase compensation is provided
at a service entrance of a line in an electric installation, a problem
phase is identified by a trip signal condition of a relay for protecting a
line or by the operative condition of a relay for selecting a problem
phase or by the operative condition of a circuit breaker, and a reactance
value of the reactor of each phase is controlled to a predetermined value
which is most suitable for producing parallel resonance, it becomes
possible to provide a means for extinction of a secondary arc in an
electric power system which is very reliable and in accordance with which
it is possible to make short the period of time for extinction of the
secondary arc irrespective of the cause thereof.
Obviously, numerous additional modifications and varitions of the present
invention are possible in light of the above teachings. It is therefore to
be understood that within the scope of the appended claims, the invention
may be practiced otherwise than as specifically described herein.
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