CA1044320A - Method of reducing current unbalance in a three-phase power transmission line operating with one faulty phase - Google Patents
Method of reducing current unbalance in a three-phase power transmission line operating with one faulty phaseInfo
- Publication number
- CA1044320A CA1044320A CA225,315A CA225315A CA1044320A CA 1044320 A CA1044320 A CA 1044320A CA 225315 A CA225315 A CA 225315A CA 1044320 A CA1044320 A CA 1044320A
- Authority
- CA
- Canada
- Prior art keywords
- line
- phase
- wire
- transformer
- earth
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
Abstract of the Disclosure A method for reducing current unbalance in the electric system of a three-phase A.C. power transmission line operating in an incomplete phase regime unsing the wires of said line and transformers electrically coupled thereto. According to the present invention disconnected wire of the line operating in the incomplete phase regime is earthed at one end thereof and a suitable alternating voltage source is connected at the other end thereof to increase the currents flowing through the transformer neutrals, thus reducing current unbalance in the electric system. An embodiment of the invention provides for the use of a lighting protection wire rope instead of the wire in case the latter is broken.
Description
- lQ~320 The present invention relates to the art of electric power transmission and more precisely to a method of reducing current unbalance in a three-phase power transmission line operating with one faulty phase; the method ca~,be advantageously used in 110 - 500 kV A.C. power transmission lines.
Damage to the insulation of overhead power trans-mission lines caused by short circuits is quite common at the present time. Most short circuits are caused by atmospheric phenomena, such as thunderstorms, strong winds, snowfall, and the like.
The time required to repair the damage caused to the insulation is determined by the time required for the repair proper, the time for bringing the repair crew to the site of damage, as well as the time for detecting the ~' -location of the fault, the greatest part of the time being consumed by the process of detecting the point of fault and the process of bringing the repair crew and the equipment needed to the site of fault.
IIt should also be noted that very often weather con-ditions present additional hazards preventing these operationsfrom being performed in a shortest possible time with the result that repairs take from a few hours to a few days.
''' ~: ' .~.,~ . .
, If the consumer was supplyed by the damaged line only, he will be deenergized for the duration of repairs, In case the additionally available power sources are not sufficient to provide power to all the region involved, partial restrictions are imposed on the consumers until the fault is eliminated.
Any reqtriction of power consumers results in losses which are incurred to the industrial enterprises in the region affected for the duration of said restriction.
It is therefore common practice at present, in case of a sustained one-phase short circuit in the line to continue operating it with two conductors only while carrying out necessary repairs. The process of operating with two conductors is often termed in the literature as a two-phase operating mode or an incomplete phase regime of the line.
The term "incomplete phase regime" will be used here-inbelow in the sense of operating a line with two conduc~ors only.
The incomplete phase regime, howeve~, if fraught with the following disadvantage.
The power transmitted through the line is limited by the current unbalance appearing in the stator windings of current generators, synchronous condensers, synchronous and asynchronous motors, as well as by the unbalance of illumination and household loads. The term "current unbalance" for example in an electric ~ i ..
, .
~;94~
machine serves to designate the ratio of negative sequence current to the positive sequence current in the machine.
The value of current unbalance is subject to ~ -specification and is determined in turn by the design features of electric machines and apparatuses and their op ration ~
conditions. - ;
In order to reduce the value of current unbalance when operating under the conditions of incomplete phase regime use is often made of a prior art method wherein the disconnected damaged line is grounded fro~ both ends thereof.
The above method can be used provided the short circuit is not accompanied by a line break and the wire insulation re- ~-lative to earth can sustain the voltage induced by the two remaining conductors which carry current. ~-As a rule a short circuit in the lines rated at 220 kV -and higher is not accompanied by a break of wire and after the short circuit is deenergized the wire insulation relative to earth is capable of sustaining a voltage which is 25 to 50 percent of the rated voltage.
The above method for reducing current unbalance permits J' ~ ' increasing the power transmitted over the line which operates under the conditions of incomplete phase regime by 6 to 8% ~;
as compared with the conventional incomplete phase regime operation of the line.
.: -.-:
'' ~ ' '' ~, , .. . .
-3- ~
L044;~'Z~
However, the present method of reducing current unbalance permits only a negligible increase of transmitted power. Moreover, as stated earlier, the method requires pre-conditions, such as absence of a broken wire, while the in-sulation at the point of fault must not be damaged by the vol-tage induced by the current in the sound wires.
These requirements tend to cause problems when using the method for 110 kV lines, which lines are generally made with conductors of a rather small cross-section, which often break as a result of a short circuit.
The object of the present invention is to provide a 1.4- to 1.6 -fold increase of po~er transmitted over a line operating in the incomplete phase regime as compared with conventional incomplete phase regime of the power line, the current unbalance thereof being equal.
Another object of the present invention is to reduce current unbalance in case the faulty wire in the line is broken or its insulation relative to earth is not capable of sustaining the voltage appearing in it when the wire is earthed from both ends thereof.
These objects are achieved in a method for reducing ^- `
current unbalance in a three-phase alternating current power transmission line operating in an incomplete phase regime, wherein use is made of the wires of this line and transformers electrically coupled thereto, comprising the following steps: providing an electrically closed loop made up of the line operating in an incomplete phase regime, a wire which is insulated relative to earth and disposed in a parallel manner along the whole length of said line, and neutral wires of said transformers, connecting said electrically closed loop to a source of alternating -~ -voltage, which is operating in step with the electrical system --into which system said line is connected, selecting a required phase and value of voltage of said source to provide a required -increase of current flowing through the neutral wires of said transformers.
Current unbalance in an electrical system can be reduced as a result of increasing the currents flowing through the neutral wires of transformers which are electrically connected to the line operating in the incomplete phase regime.
Since the power transmitted over a line operating in the incomplete phase regime is restricted by the value of current unbalance, the method according to the present invention permits said power to be increased 1.4 to 1.6 times as compared to conventional incomplete phase regimes, the value of current unbalance being equal.
The disconnected wire of said line, grounded from one ~-end is advantageously used as the wire that is insulated relative ~ -to earth and disposed along the entire length of the line ,:
'~'~''' '' , , .
;': .
1044~0 operating in the incomplete phase regime, whereas said alternating voltage source is conveniently provided by a transformer arranged on the opposite end of said disconnected wire, one winding of aid transformer being connected between the disconnected wire and earth and the second winding being connected to the phase or line voltage of the electric system to which said line is connected.
The disconnected wire can be used also when the short circuit did not result in a broken wire and the insulation at the point of fault can sustain the voltage induced by the current in the live wires of the line. As a rule, this is the case with lines rated at 220 kV and higher. Therefore, a disconnected wire is recommended for use in case of lines rated at 220 kV and higher which operate in the incomplete phase regime.
The method according to the present invention can be advantageously used by the provision of a single-phase or three-phase transformer at one end of the line, or a single-phase -or three-phase autotransformer.
In view of the fact that the transformer or autotrans-former are used as a source of e.m.f. and it is basically im-material whether the function is performed by a transformer or a~ autotransformer, the term "transformer" will be used through-out hereinbelow. It is, however, understood that an auto-transformer can be used as a source of e.m.f. for the purpose.
- ^ - - ,^ -. - .-. .. . . , ~
, ~432(~
The idea of using a transformer as a voltage source can al~ays be easily reduced to practice since a line usually ; connects two sub-stations where stand-by transformers are gene-xally available, or there is always a possibility to unload one of the transformer of the sub-station.
On the other hand there is no difficulty in providing a special transformer at one of the sub-stations, which can also be used for normal operation of the electric system when it is -used in parallel to increase the reliability of electric system as a whole.
Voltage across one winding of said transformer must be within 15 to 35% of the rated voltage of the line, whereas the voltage of the second winding must correspond to one of the rated'voltages of the sub-station where it is installed. In -case the transformer is of a multi-winding type, the voltage of at least one of the windings thereof must correspond to one of the rated voltages of the sub-station where it is installed.
The present invention also envisages earthings at the ends of the three-phase line. At present all 110-500 kV lines are provided with such earthings at the beginning and the end of the line. - ~-The function of a wire which is insulated relative -to earth and disposed along the entire length of the line ~ ~ ;
operating in the incomplete phase regime can be advantageously performed , ~04~3~¢~
by the lightning protection wire rope which is insulated relative to earth along its entire length and earthed at one of its ends, while the function of said alternating voltage source can be performed by a transformer located at the opposite end of said wire rope, one of the transformer windings being connected between the earth and the wire rope, whereas the second winding is con-nected to the phase or lin,e voltage of the electric system to which said power transmission line is connected.
Short circuits occurring on 110 kV lines often result in wire breaks, therefore a disconnected wire of the line can be used for the purpose only after checking it for breakage.
Otherwise the purpose is advantageously achieved by using the lightning protection wire rope of the power transmission line.
Since the present method involves application of voltage to the wire rope, the insulation thereof must naturally withstand the voltage i~pressed. A lightning protection wire rope is easily insulated against 10 - 25 kV current. It is common practice at present to insulate the wire rope relative to earth, the wire rope being grounded at one point only, at other
Damage to the insulation of overhead power trans-mission lines caused by short circuits is quite common at the present time. Most short circuits are caused by atmospheric phenomena, such as thunderstorms, strong winds, snowfall, and the like.
The time required to repair the damage caused to the insulation is determined by the time required for the repair proper, the time for bringing the repair crew to the site of damage, as well as the time for detecting the ~' -location of the fault, the greatest part of the time being consumed by the process of detecting the point of fault and the process of bringing the repair crew and the equipment needed to the site of fault.
IIt should also be noted that very often weather con-ditions present additional hazards preventing these operationsfrom being performed in a shortest possible time with the result that repairs take from a few hours to a few days.
''' ~: ' .~.,~ . .
, If the consumer was supplyed by the damaged line only, he will be deenergized for the duration of repairs, In case the additionally available power sources are not sufficient to provide power to all the region involved, partial restrictions are imposed on the consumers until the fault is eliminated.
Any reqtriction of power consumers results in losses which are incurred to the industrial enterprises in the region affected for the duration of said restriction.
It is therefore common practice at present, in case of a sustained one-phase short circuit in the line to continue operating it with two conductors only while carrying out necessary repairs. The process of operating with two conductors is often termed in the literature as a two-phase operating mode or an incomplete phase regime of the line.
The term "incomplete phase regime" will be used here-inbelow in the sense of operating a line with two conduc~ors only.
The incomplete phase regime, howeve~, if fraught with the following disadvantage.
The power transmitted through the line is limited by the current unbalance appearing in the stator windings of current generators, synchronous condensers, synchronous and asynchronous motors, as well as by the unbalance of illumination and household loads. The term "current unbalance" for example in an electric ~ i ..
, .
~;94~
machine serves to designate the ratio of negative sequence current to the positive sequence current in the machine.
The value of current unbalance is subject to ~ -specification and is determined in turn by the design features of electric machines and apparatuses and their op ration ~
conditions. - ;
In order to reduce the value of current unbalance when operating under the conditions of incomplete phase regime use is often made of a prior art method wherein the disconnected damaged line is grounded fro~ both ends thereof.
The above method can be used provided the short circuit is not accompanied by a line break and the wire insulation re- ~-lative to earth can sustain the voltage induced by the two remaining conductors which carry current. ~-As a rule a short circuit in the lines rated at 220 kV -and higher is not accompanied by a break of wire and after the short circuit is deenergized the wire insulation relative to earth is capable of sustaining a voltage which is 25 to 50 percent of the rated voltage.
The above method for reducing current unbalance permits J' ~ ' increasing the power transmitted over the line which operates under the conditions of incomplete phase regime by 6 to 8% ~;
as compared with the conventional incomplete phase regime operation of the line.
.: -.-:
'' ~ ' '' ~, , .. . .
-3- ~
L044;~'Z~
However, the present method of reducing current unbalance permits only a negligible increase of transmitted power. Moreover, as stated earlier, the method requires pre-conditions, such as absence of a broken wire, while the in-sulation at the point of fault must not be damaged by the vol-tage induced by the current in the sound wires.
These requirements tend to cause problems when using the method for 110 kV lines, which lines are generally made with conductors of a rather small cross-section, which often break as a result of a short circuit.
The object of the present invention is to provide a 1.4- to 1.6 -fold increase of po~er transmitted over a line operating in the incomplete phase regime as compared with conventional incomplete phase regime of the power line, the current unbalance thereof being equal.
Another object of the present invention is to reduce current unbalance in case the faulty wire in the line is broken or its insulation relative to earth is not capable of sustaining the voltage appearing in it when the wire is earthed from both ends thereof.
These objects are achieved in a method for reducing ^- `
current unbalance in a three-phase alternating current power transmission line operating in an incomplete phase regime, wherein use is made of the wires of this line and transformers electrically coupled thereto, comprising the following steps: providing an electrically closed loop made up of the line operating in an incomplete phase regime, a wire which is insulated relative to earth and disposed in a parallel manner along the whole length of said line, and neutral wires of said transformers, connecting said electrically closed loop to a source of alternating -~ -voltage, which is operating in step with the electrical system --into which system said line is connected, selecting a required phase and value of voltage of said source to provide a required -increase of current flowing through the neutral wires of said transformers.
Current unbalance in an electrical system can be reduced as a result of increasing the currents flowing through the neutral wires of transformers which are electrically connected to the line operating in the incomplete phase regime.
Since the power transmitted over a line operating in the incomplete phase regime is restricted by the value of current unbalance, the method according to the present invention permits said power to be increased 1.4 to 1.6 times as compared to conventional incomplete phase regimes, the value of current unbalance being equal.
The disconnected wire of said line, grounded from one ~-end is advantageously used as the wire that is insulated relative ~ -to earth and disposed along the entire length of the line ,:
'~'~''' '' , , .
;': .
1044~0 operating in the incomplete phase regime, whereas said alternating voltage source is conveniently provided by a transformer arranged on the opposite end of said disconnected wire, one winding of aid transformer being connected between the disconnected wire and earth and the second winding being connected to the phase or line voltage of the electric system to which said line is connected.
The disconnected wire can be used also when the short circuit did not result in a broken wire and the insulation at the point of fault can sustain the voltage induced by the current in the live wires of the line. As a rule, this is the case with lines rated at 220 kV and higher. Therefore, a disconnected wire is recommended for use in case of lines rated at 220 kV and higher which operate in the incomplete phase regime.
The method according to the present invention can be advantageously used by the provision of a single-phase or three-phase transformer at one end of the line, or a single-phase -or three-phase autotransformer.
In view of the fact that the transformer or autotrans-former are used as a source of e.m.f. and it is basically im-material whether the function is performed by a transformer or a~ autotransformer, the term "transformer" will be used through-out hereinbelow. It is, however, understood that an auto-transformer can be used as a source of e.m.f. for the purpose.
- ^ - - ,^ -. - .-. .. . . , ~
, ~432(~
The idea of using a transformer as a voltage source can al~ays be easily reduced to practice since a line usually ; connects two sub-stations where stand-by transformers are gene-xally available, or there is always a possibility to unload one of the transformer of the sub-station.
On the other hand there is no difficulty in providing a special transformer at one of the sub-stations, which can also be used for normal operation of the electric system when it is -used in parallel to increase the reliability of electric system as a whole.
Voltage across one winding of said transformer must be within 15 to 35% of the rated voltage of the line, whereas the voltage of the second winding must correspond to one of the rated'voltages of the sub-station where it is installed. In -case the transformer is of a multi-winding type, the voltage of at least one of the windings thereof must correspond to one of the rated voltages of the sub-station where it is installed.
The present invention also envisages earthings at the ends of the three-phase line. At present all 110-500 kV lines are provided with such earthings at the beginning and the end of the line. - ~-The function of a wire which is insulated relative -to earth and disposed along the entire length of the line ~ ~ ;
operating in the incomplete phase regime can be advantageously performed , ~04~3~¢~
by the lightning protection wire rope which is insulated relative to earth along its entire length and earthed at one of its ends, while the function of said alternating voltage source can be performed by a transformer located at the opposite end of said wire rope, one of the transformer windings being connected between the earth and the wire rope, whereas the second winding is con-nected to the phase or lin,e voltage of the electric system to which said power transmission line is connected.
Short circuits occurring on 110 kV lines often result in wire breaks, therefore a disconnected wire of the line can be used for the purpose only after checking it for breakage.
Otherwise the purpose is advantageously achieved by using the lightning protection wire rope of the power transmission line.
Since the present method involves application of voltage to the wire rope, the insulation thereof must naturally withstand the voltage i~pressed. A lightning protection wire rope is easily insulated against 10 - 25 kV current. It is common practice at present to insulate the wire rope relative to earth, the wire rope being grounded at one point only, at other
2 points the wire rope is connected to the ground via spark gaps.
A wire rope which insulated relative to earth achieves a number of objects, such as the melting of ice on the rope, it can also be used for the purpose of establishing communication, etc.
"
A wire rope which insulated relative to earth achieves a number of objects, such as the melting of ice on the rope, it can also be used for the purpose of establishing communication, etc.
"
3~ZI~
Since the wire rope used in the method according to the present invention will carry current whose magnitude determines the effect of current unbalance reduction in the electric syste~, the wire rope is preferably made of aluminum. This can be easily provided on newly erected power transmission lines.
The electric closed loop is preferably made by directly `-connecting one of the ends of a disconnected wire of the line operating in the incomplete phase regime to the neutral wire of -at least one of the transformers which have electrical connection -to said line, the neutral wire of said transformer being dis- ;~
connected from earth, and another transformer being used as a `
source of said alternating voltage, the other transformer being -located on the other end of s~id disconnected wire and having one of its windings connected between the disconnected wire and `
earth, while the other winding is connected to the phase or line voltage of the electric system to which said power transmission -~;
line is connected. -;
The neutral wire of st transformers is generally rated at a certain voltage, depending on the rated voltage of the transformer. This makes it possible to disconnected the neutral -wire from earth in order to reduce in the electric system short circuit currents to earth. Insulated transformer ,,, ~Og43;20 neutrals permits the voltage to be regulated also by means of booster transformers.
Insulated transformer neutrals offer a possibility of using the present method, provided the disconnected wire of - the line is connected directly to the neutral wire of trans-former windings having electrical connection to the line which operates in the incomplete phase regime.
The only limitation placed upon the method of connecting transformer neutrals to the disconnected wire resides in the fact that the value of voltage must not exceed the level of in-sulation of the neutral. A spark gap must be connected to pre-vent voltage build-up during transient processes between the neutral and earth.
In addition to that said electric loop is pre-ferably made by directly connecting one of the ends of said lightning protection wire rope which is electrically insulated relative to earth along the entire length thereof, to the neutral wire of at least one of the transformers having electrical connection to said line, the neutral wire of said transformer being dis-connected from earth, while said source of alternating voltageis provided by a transformer located at the opposite end of said lightning protection wire rope, one of the windings of said transformer being connected between said wire rope and earth, and the other winding being connected to the phase -10~
~443ZO ~:
or line voltage of the electric system to which said line is connected.
Thus the method according to the present invention can be widely used on 110-500 kV lines operating in the in-complete phase regime, thereby increasing the power transmitted over these lines when operating in the above mode. -Taking into consideration the fact that single- -phase short circuits are a common occurrence in these lines ~-(from 0.3 to 0.7 times per 100 km per year), it will be appreciated that the economic effect of the proposed method will be quite substantial.
other objects and advantages of the proposed method will become apparent from the following detailed description ,-thereof taken in conjunction with the accompanying drawings, wherein:
Figure 1 illustrates a current vector diagram of a three-phase line operating in an incomplete phase regime ~' (with phase "a" wire deenergized), Figure 2 shows a transformation diagram of zero sequence currents through a three-phase transformer with a unity transformation ratio' Figure 3 is the same as Figure 2 for first sequence currents, Figure 4 illustrates the vector diagram of phase currents on the transformer side, the transformer windings being delta-connected, Figure 5 shows the schematic diagram of a three- ;~
phase line operating in the incomplete phase regime, wherein one of the ends of the deenergized wire is earthed, according to the invention, A ~:
~ .. . .
. . .. .. , ~ . . . .. ~ ~ . .
;34~
Figure 6 same as Figure 5, when the deenergized wire is connected to the neutral of the transformer windings electrically connected to the line operating in the incomplete phase regime, according to the invention, Figure 7 illustrates the schematic diagram of a three-phase line operating in the incomplete phase regime and a trans-mission sub-station, for the case when a single-phase trans-former is used as said voltage source and a deenergized wire of the line, earthed at the receiving sub-station is used as said wire;
Figure 8 same as Figure 7, for the case when a lightning protection wire rope is used as said wire and a stand-by three-phase transformer is used as said voltage source;
Figure 9 illustrates the diagram for connecting a de-energized line wire to the transformer neutral, Figure 10 illustrates the aiagram for connecting a lightning protection wire rope to the transformer neutral.
Referring now to the Figures, Figure 1 illustrates a current vector diagram in the wires of a three-phase line operating in the incomplete phase regime. Since any one of the three wires can be damaged and thus deenergized and the phenomena occurring in the line will be the same irrespective of which of the wires is deenergized, the processes occurring in the line operating in the incomplete phase regime will be explained here-inunder for the case when phase A is deenergized.
~. .
~)44~Z~ ~
The symbol ib in Figure 1 indicates the current in phase "B" of the line, whereas 9ymbol iC indicates the current in phase "C" of the line.
A system of two currents can be represented as a sum of currents of two systems of symmetric components. Let us -define one system as zero sequence currents and the other - as first sequence currents. The zero sequence currents are equal to half the sum of the phase "B" and "C" currents each. For phase "B" the first sequence currents are equal to half the difference between the phase "s" and "C" currents, whereas for phase "~" they are equal to half the difference between phase ~ -C and B currents.
Denote the zero sequence currents by symbols iob for phase "B" and ioC for phase "C", whereas the first sequence currents will be denoted by symbols iib and iiC respectively.
Since the transformer windings (Figure 2) are connected in series with the line, they carry currents iob, ioC, and iic, which currents are transformed by the transformer. The currents in the second winding of the transformer are denoted as Iob, Ioc~ Iib' Iic-The zero sequence currents as well as the first sequence currents are transformed through a star-delta-connected trans-former in a different way.
Figures 2 and 3 illustrate the transformation of zero and first sequence currents through a transformer with a ;~
~43,~
unity transformation ratio, and connected to star with an earthed neutral and delta.
When phase "A" (Figure 2) is disconnected from the line coupled to the star-connected windings of the transformer, the resistance of delta-connected winding of the transformer between phases "A" and "C" is very high, therefoxe all the current IOb which this winding carries will flow in the reverse direction in phase "A" of the load, whereas the current I
oc in phase "C" flows without changing its direction in phase "C"
of the load.
The first sequence currents are transformed in a diff-erent manner. Referring to Figure 3, consider that since for the first sequence currents, as well as for the zero sequence currents, the resistance of phase "A" winding connected to the delta circuit of the transformer is by two orders higher than the resistance of the other delta windings, the current in phase "A" winding is practically zero. Therefore the first sequence current in phase "B", Iib flows in the reverse direction in the phase "A"
load. The "C" phase current, IiC, flows without changing its direction in the phase "C" load, whereas the "B" phase current of the load is equal to the sum of phase "B" current, Iib and phase "C" current, IiC, taken with a reverse sign, that is the phase "B" current, Iib of the load is equal to double current ib ,' ', ~: ' .:
-14- ~
326;~
The sum of first and zero sequence currents of the load are true currents flowing in the load phases. They are illustrated in Figure 4.
Symbol Ia denotes phase "A" current of the load, symbol Ib is phase "B" current of the load, and symbol Ic is phase ,~
"C" current of the load.
Current Ib of phase "B" equals to double first sequence current. Current Ic of phase C is equal to current ic of -~
phase "C". Current Ia of phase "A" is equal to the value of current ib and is opposite to it.
As seen from Figure 4, current unbalance can be reduced by increasing current IOb to I'ob and current IoC to current I'oC, without changing the first sequence currents. The line -~
currents IOb and IoC are equal to currents iob and ioC, respect-' ively.
In other words, if we increase zero sequence currents iob and ioC in the line, without changing the first sequence currents iib and iiC, the current unbalance will be decreased.
Current unbalance is known to decrease until the angle of 20 currents iib and iiC in the line operating in the incomplete phase regime, reaches 60. Further, the unbalance tends to increase with the angle decreasing.
Thus in summary it may be said that in operating a line in the incomplete phase regime we can reduce current unbalance by increasing zero sequence currents io~ and ioC in the line phases. ~-:': " ..
: : . . . . ., . . .: - . .
~344;~0 Figures 5 and 6 schematically represent power trans-mission lines operating in the incomplete phase regime using the ~ethod according to the present invention.
In these Figures, 1 indicates a three-phase line operating in the incomplete phase regime, with a deenergized wire 2 of phase "An. The line 1 is supplied by a generator system 3, with a transformer 4 connected to the opposite end of the line.
A voltage source 5 is connected to the deenergized wire 2 from the side of the generator system 3, said voltage source being synchronously coupled with the generator system 3. The wire 2 is earthed from the other end thereof with earthing 6. :~
In Figure 6 the neutral of transformer 4 is disconnected from earth by means of a disconnector 7, whereas the wire 2 is connected to the neutral of transformer 4.
As seen from Figure 5, the voltage source 5 connected -to the deenergized wire 2 of line 1 operating in the incomplete pha~e regime, offers an additional electrical closed loop for the zero sequence currents iob and ioC to flow in the line 1.
Current i2 in the wire 2, impressed by the voltage f ~ ~ ~
source 5 will partially flow through the neutral of transformer ~. :
Since the wire rope used in the method according to the present invention will carry current whose magnitude determines the effect of current unbalance reduction in the electric syste~, the wire rope is preferably made of aluminum. This can be easily provided on newly erected power transmission lines.
The electric closed loop is preferably made by directly `-connecting one of the ends of a disconnected wire of the line operating in the incomplete phase regime to the neutral wire of -at least one of the transformers which have electrical connection -to said line, the neutral wire of said transformer being dis- ;~
connected from earth, and another transformer being used as a `
source of said alternating voltage, the other transformer being -located on the other end of s~id disconnected wire and having one of its windings connected between the disconnected wire and `
earth, while the other winding is connected to the phase or line voltage of the electric system to which said power transmission -~;
line is connected. -;
The neutral wire of st transformers is generally rated at a certain voltage, depending on the rated voltage of the transformer. This makes it possible to disconnected the neutral -wire from earth in order to reduce in the electric system short circuit currents to earth. Insulated transformer ,,, ~Og43;20 neutrals permits the voltage to be regulated also by means of booster transformers.
Insulated transformer neutrals offer a possibility of using the present method, provided the disconnected wire of - the line is connected directly to the neutral wire of trans-former windings having electrical connection to the line which operates in the incomplete phase regime.
The only limitation placed upon the method of connecting transformer neutrals to the disconnected wire resides in the fact that the value of voltage must not exceed the level of in-sulation of the neutral. A spark gap must be connected to pre-vent voltage build-up during transient processes between the neutral and earth.
In addition to that said electric loop is pre-ferably made by directly connecting one of the ends of said lightning protection wire rope which is electrically insulated relative to earth along the entire length thereof, to the neutral wire of at least one of the transformers having electrical connection to said line, the neutral wire of said transformer being dis-connected from earth, while said source of alternating voltageis provided by a transformer located at the opposite end of said lightning protection wire rope, one of the windings of said transformer being connected between said wire rope and earth, and the other winding being connected to the phase -10~
~443ZO ~:
or line voltage of the electric system to which said line is connected.
Thus the method according to the present invention can be widely used on 110-500 kV lines operating in the in-complete phase regime, thereby increasing the power transmitted over these lines when operating in the above mode. -Taking into consideration the fact that single- -phase short circuits are a common occurrence in these lines ~-(from 0.3 to 0.7 times per 100 km per year), it will be appreciated that the economic effect of the proposed method will be quite substantial.
other objects and advantages of the proposed method will become apparent from the following detailed description ,-thereof taken in conjunction with the accompanying drawings, wherein:
Figure 1 illustrates a current vector diagram of a three-phase line operating in an incomplete phase regime ~' (with phase "a" wire deenergized), Figure 2 shows a transformation diagram of zero sequence currents through a three-phase transformer with a unity transformation ratio' Figure 3 is the same as Figure 2 for first sequence currents, Figure 4 illustrates the vector diagram of phase currents on the transformer side, the transformer windings being delta-connected, Figure 5 shows the schematic diagram of a three- ;~
phase line operating in the incomplete phase regime, wherein one of the ends of the deenergized wire is earthed, according to the invention, A ~:
~ .. . .
. . .. .. , ~ . . . .. ~ ~ . .
;34~
Figure 6 same as Figure 5, when the deenergized wire is connected to the neutral of the transformer windings electrically connected to the line operating in the incomplete phase regime, according to the invention, Figure 7 illustrates the schematic diagram of a three-phase line operating in the incomplete phase regime and a trans-mission sub-station, for the case when a single-phase trans-former is used as said voltage source and a deenergized wire of the line, earthed at the receiving sub-station is used as said wire;
Figure 8 same as Figure 7, for the case when a lightning protection wire rope is used as said wire and a stand-by three-phase transformer is used as said voltage source;
Figure 9 illustrates the diagram for connecting a de-energized line wire to the transformer neutral, Figure 10 illustrates the aiagram for connecting a lightning protection wire rope to the transformer neutral.
Referring now to the Figures, Figure 1 illustrates a current vector diagram in the wires of a three-phase line operating in the incomplete phase regime. Since any one of the three wires can be damaged and thus deenergized and the phenomena occurring in the line will be the same irrespective of which of the wires is deenergized, the processes occurring in the line operating in the incomplete phase regime will be explained here-inunder for the case when phase A is deenergized.
~. .
~)44~Z~ ~
The symbol ib in Figure 1 indicates the current in phase "B" of the line, whereas 9ymbol iC indicates the current in phase "C" of the line.
A system of two currents can be represented as a sum of currents of two systems of symmetric components. Let us -define one system as zero sequence currents and the other - as first sequence currents. The zero sequence currents are equal to half the sum of the phase "B" and "C" currents each. For phase "B" the first sequence currents are equal to half the difference between the phase "s" and "C" currents, whereas for phase "~" they are equal to half the difference between phase ~ -C and B currents.
Denote the zero sequence currents by symbols iob for phase "B" and ioC for phase "C", whereas the first sequence currents will be denoted by symbols iib and iiC respectively.
Since the transformer windings (Figure 2) are connected in series with the line, they carry currents iob, ioC, and iic, which currents are transformed by the transformer. The currents in the second winding of the transformer are denoted as Iob, Ioc~ Iib' Iic-The zero sequence currents as well as the first sequence currents are transformed through a star-delta-connected trans-former in a different way.
Figures 2 and 3 illustrate the transformation of zero and first sequence currents through a transformer with a ;~
~43,~
unity transformation ratio, and connected to star with an earthed neutral and delta.
When phase "A" (Figure 2) is disconnected from the line coupled to the star-connected windings of the transformer, the resistance of delta-connected winding of the transformer between phases "A" and "C" is very high, therefoxe all the current IOb which this winding carries will flow in the reverse direction in phase "A" of the load, whereas the current I
oc in phase "C" flows without changing its direction in phase "C"
of the load.
The first sequence currents are transformed in a diff-erent manner. Referring to Figure 3, consider that since for the first sequence currents, as well as for the zero sequence currents, the resistance of phase "A" winding connected to the delta circuit of the transformer is by two orders higher than the resistance of the other delta windings, the current in phase "A" winding is practically zero. Therefore the first sequence current in phase "B", Iib flows in the reverse direction in the phase "A"
load. The "C" phase current, IiC, flows without changing its direction in the phase "C" load, whereas the "B" phase current of the load is equal to the sum of phase "B" current, Iib and phase "C" current, IiC, taken with a reverse sign, that is the phase "B" current, Iib of the load is equal to double current ib ,' ', ~: ' .:
-14- ~
326;~
The sum of first and zero sequence currents of the load are true currents flowing in the load phases. They are illustrated in Figure 4.
Symbol Ia denotes phase "A" current of the load, symbol Ib is phase "B" current of the load, and symbol Ic is phase ,~
"C" current of the load.
Current Ib of phase "B" equals to double first sequence current. Current Ic of phase C is equal to current ic of -~
phase "C". Current Ia of phase "A" is equal to the value of current ib and is opposite to it.
As seen from Figure 4, current unbalance can be reduced by increasing current IOb to I'ob and current IoC to current I'oC, without changing the first sequence currents. The line -~
currents IOb and IoC are equal to currents iob and ioC, respect-' ively.
In other words, if we increase zero sequence currents iob and ioC in the line, without changing the first sequence currents iib and iiC, the current unbalance will be decreased.
Current unbalance is known to decrease until the angle of 20 currents iib and iiC in the line operating in the incomplete phase regime, reaches 60. Further, the unbalance tends to increase with the angle decreasing.
Thus in summary it may be said that in operating a line in the incomplete phase regime we can reduce current unbalance by increasing zero sequence currents io~ and ioC in the line phases. ~-:': " ..
: : . . . . ., . . .: - . .
~344;~0 Figures 5 and 6 schematically represent power trans-mission lines operating in the incomplete phase regime using the ~ethod according to the present invention.
In these Figures, 1 indicates a three-phase line operating in the incomplete phase regime, with a deenergized wire 2 of phase "An. The line 1 is supplied by a generator system 3, with a transformer 4 connected to the opposite end of the line.
A voltage source 5 is connected to the deenergized wire 2 from the side of the generator system 3, said voltage source being synchronously coupled with the generator system 3. The wire 2 is earthed from the other end thereof with earthing 6. :~
In Figure 6 the neutral of transformer 4 is disconnected from earth by means of a disconnector 7, whereas the wire 2 is connected to the neutral of transformer 4.
As seen from Figure 5, the voltage source 5 connected -to the deenergized wire 2 of line 1 operating in the incomplete pha~e regime, offers an additional electrical closed loop for the zero sequence currents iob and ioC to flow in the line 1.
Current i2 in the wire 2, impressed by the voltage f ~ ~ ~
source 5 will partially flow through the neutral of transformer ~. :
4, the line 1 and the neutral of the generator system 3. -:
In this case it is necessary for the direction of `
voltage from the said source to be such that the zero sequence currents in the energized wires of line 1, determined by the voltage ;'' :
' _~ ~Lo9~3~ 0 source 5, have the same direction as the zero sequence currents iob and ioC in this line when operating in the conventional incomplete phase regime.
Such connection of the voltage source 5 enables us to increase the zero sequence currents in the line 1, since the zero sequence currents, determined by the generator system 3 and the voltage source 5 are summed up with one and the same direction. Accordingly, an increase of zero sequence currents in the line 1 results in reduced current unbalance in the generating system 3 and in the load p~ases.
Zero sequence currents in the line can be increased by connecting the deenergized wire 2 (Figure 6) to the neutral of transformer 4, which is disconnected from earth by means of the disconnector 7, and connecting to the other end of the wire 2 a voltage source 5.
Here all the zero sequence current flows along the path made up by the generator system 3, the wire of the i.n-complete phase regime line 1, the transformer 4 winding, the wire 2, the voltage source 5 and earth. In this case the current in the deenergized wire 2 will be equal to the sum of zero sequence currents iob and ioC in the line 1. -~ :
Such connection of the deenergized wire 2 to the neutral of the transformer 4 disconnected from earth is feasible, provided the insulation of the transformer neutral is rated at ~4~Z~) a voltage which is bound to appear in it after the voltage source
In this case it is necessary for the direction of `
voltage from the said source to be such that the zero sequence currents in the energized wires of line 1, determined by the voltage ;'' :
' _~ ~Lo9~3~ 0 source 5, have the same direction as the zero sequence currents iob and ioC in this line when operating in the conventional incomplete phase regime.
Such connection of the voltage source 5 enables us to increase the zero sequence currents in the line 1, since the zero sequence currents, determined by the generator system 3 and the voltage source 5 are summed up with one and the same direction. Accordingly, an increase of zero sequence currents in the line 1 results in reduced current unbalance in the generating system 3 and in the load p~ases.
Zero sequence currents in the line can be increased by connecting the deenergized wire 2 (Figure 6) to the neutral of transformer 4, which is disconnected from earth by means of the disconnector 7, and connecting to the other end of the wire 2 a voltage source 5.
Here all the zero sequence current flows along the path made up by the generator system 3, the wire of the i.n-complete phase regime line 1, the transformer 4 winding, the wire 2, the voltage source 5 and earth. In this case the current in the deenergized wire 2 will be equal to the sum of zero sequence currents iob and ioC in the line 1. -~ :
Such connection of the deenergized wire 2 to the neutral of the transformer 4 disconnected from earth is feasible, provided the insulation of the transformer neutral is rated at ~4~Z~) a voltage which is bound to appear in it after the voltage source
5 is connected to the deenergized wire 2.
Consider some examples of embodying the present invention. Referring to the circuit illustrated in Figure 7 showing-a 220 kV line operating in the incomplete phase regi~e with a deenergized wire 2. One end of the line 1 is connected to buses 8 t220 kV) of the transmission sub-station, the other end thereof being connected to buses 9 (220 kV) of the receiving sub-station.
It is understood that in addition to said line, other lines not shown in Figure 7 can be easily connected to the buses 8, 9 (220 kV) of the both sub-stations as well.
The transmitting sub-station houses two three-winding three-phase transformers 10 and 10` with windings rated at 220, 110 and 35 kV, which windings are connected via three-phase : :
circuit breakers 11, 12, 13 and 11', 12' and 13' respectively, -the buses 8 (220kV), buses 14 (llOkV) and buses 15(35kV).
The windings (35kV) of the transformer 10 are delta connected. :
, In order to simplify the drawing, the three-phase con-nections of transformers 10 and 10' with circuit breakers 11, 12, ; : ~:~
13 and 11', 12', 13' respectively, are shown as single lines.
A single-phase three-winding transformer 16 is also provided at ~
the transmitting sub-station to be used as a stand-by trans- ~::
former to back up any phase of the three-phase transformers 10 14~Z~
or 10' for repairs. The single-phase transformer 16 can be connected via single-phase switches 17 or 18 to any bus system 8 or 14, respectively.
In case of a fault in the wire 2 of the line 1, which didl not result in its breakage, while the insulation at the point of fault is able to sustain a voltage of 35 kV, the present invention can be embodied as follows.
The deenergized wire 2 is earthed at the receiving sub-station 9 with the earthing 6. At the transmitting sub-station,, one of the lead-outs of the 35 kV windin3 of the single-phase transformer 16 is earthed, whereas the other leadout of said winding is connected via a circuit breaker 19 to the disconnected wire 2. The single-phase transformer 16 is connected to the respective phase of bus 8 (220 kV) or 14 (110 kV), and voltage is fed to the disconnected wire 2 by means of the switch 17 or ~-18, respectively.
If for some reason a single-phase transformer cannot ~ -be used while the power supplied by one of the three-phase trans-formers 10 or 10' is sufficient to supply the consumers connected to the buses 15 (35 kV), one of the transformers 10 or 10' must be disconnected from the buses 15 (35 kV) in order to supply - voltage to the disconnected wire. In order to ~upply voltage to the disconnected wire 2, after th~ transformer 10 or 10~ is disconnected from the buses 15 (35 kV) one of its 4~3Z~
35 kV winding leadouts must be earthed and the other leadout of the winding (35 kV) must be connected to the disconnected wire 2 of the line 1.
Consider the diagram illustrated in Figure 8. As a result of a short circuit in the wire 2, the power transmission line 1 i5 operated in the incomplete phase regime mode. The failure resulted in a broken wire 2. A lightning protection wire rope 20 is provided on the line 1, being earthed at the receiving ~ub-station 21, its insulation along the entire length ~ .
thereof being capable of sustaining 10 kV voltage.
The power transmission line 1 connects buses 21 (110 kV) of the receiving sub-statïon and buses 22 (110 kV) of ~ ~ .
: the transmitting sub-station. Connected to the buses ;
; 22 (110 kV) via circuit breakers 23 and 24 two three-phase two-winding transformers 25 and 26 respectively, the rated vol-tage of their windings being 110 kV and 10 kV, one of the trans-formers being used for supplying power consumers connected across ~.
buses 2!7 (10 kV). Generally, taking into consideration the value of permissible overload, the power delivered by one of the trans-formers 25 or 26 is sufficient to supply all consumers connected .
across buses 27 (10 kV). These buses are coupled to the trans~
former 25 via circuit breaker 28. Figure 8 illustrates the . :~
coupling of only one transformer (25) since the other transformer :
.(26).. is disconnected from the buses 28 (10 kV), ~
`
.: ,' .~
' ' -20- `
o while one of the leadouts of the 10 kV winding of the latter transformer is earthed and the other leadout of the 10 kV
winding is connected to the lightning protection wire rope 20.
Figure 9 illustrates a 110 kV line 1 with a disconnected wire 2. The sub-station diagram is the same as in the preceding example. The transformer 4 is connected to the line at the receiving sub-station. Figure 9 shows only 110 kV winding of the transformer, which is disconnected from earth by the dis-connector 7. At the transmitting sub-station the disconnected wire is connected to one of the leadouts of the 10 kV winding of the transformer 26. Other operations at the transmitting `
sub-station are the same as in the previous example.
In case the disconnected wire 2 is broken as a result of the fault, use can be made of the lightning protection wire rope.
Referring to Figure 10, illustrated is the line 1 with the disconnected wire 2. The diagram of receiving and trans-mitting sub-stations is the same as in the previous example.
The line 1 is provided with a lightning protection wire rope 20 which is insulated relative to earth. On the receiving sub-station side the wire rope is earthed by a dis-connector 29. In order to switch the line to operate in the in-complete phase regime, the disconnector 29 is switched off, the wlre rope '~' ;~ ' ~ ' -21- ~
.. .... ~ .. . .. ...... ... . .. . .... .. . .
32~
20 is connected to the neutral of the transformer 4 and the neutral is disconnected from earth by means of the disconnector 7. At the transmitting sub-station, the wire rope 20 is con-nected to one of the leadouts (10 kV) of the transformer 26.
Other operations at the transmitting sub-station are the same as in the previous example.
Thus, a method is proposed for reducing current un-balance when operating the electrical system of a three-phase A.C. power transmission line in an incomplete phase regime by using the wires of the line involved and transformers electric-; ally coupled thereto, the method permitting the power trans-mitted over a line operating in the incomplete phase regime to be increased 1.4 to 1.6 times with only negligible expenses involved, with a simultaneous reduction of zero sequence currents.
Consider two calculated examples of increasing the transmitted power in the incomplete phase regime of the line.
Example 1 A 150 km long 220 kV line is operating in the incomplete phase regime. From the transmitting sub-station side the line is connected to a 1400 MWt power station. Operating in the receiving system are generators having a total output of 400 MWt.
.' ,. ' ' .
,'.~ ' ' .'':
: ,, ~ .
-22- ~
3Z'O
Owing to current unbalance in the generator windings the power transmitted over the line operating in the conventional incomplete phase regime does not exceed 62 MWt.
If the deenergized wire of the line earthed at the receiving sub-station is connected from the transmitting sub- -station side to a voltage source of 35 kV, the power trans-mitted over the line can be increased to 108 MWt, the current ~ -unbalance in the generator windings being equal.
Example 2 A 40 km long 110 kV line is supplying through a trans-former located at a 1~ MWt receiving sub-station a region which consumes 10 MWt. Current unbalance of electric receivers is limited to 20%. In the conventional incomplete phase regime the power transmitted is limited by current unbalance to 3.2 MWt.
If the disconnected wire of the line is connected to the disconnected from the earth neutral of the transformer of the receiving sub-station, while a voltage of 10 kV is impressed at the other end of said disconnected wire, the power transmitted 20 in the incomplete phase regime of the line and with the above-mentioned current unbalance can be increased to 7.4 MWt.
Consider some examples of embodying the present invention. Referring to the circuit illustrated in Figure 7 showing-a 220 kV line operating in the incomplete phase regi~e with a deenergized wire 2. One end of the line 1 is connected to buses 8 t220 kV) of the transmission sub-station, the other end thereof being connected to buses 9 (220 kV) of the receiving sub-station.
It is understood that in addition to said line, other lines not shown in Figure 7 can be easily connected to the buses 8, 9 (220 kV) of the both sub-stations as well.
The transmitting sub-station houses two three-winding three-phase transformers 10 and 10` with windings rated at 220, 110 and 35 kV, which windings are connected via three-phase : :
circuit breakers 11, 12, 13 and 11', 12' and 13' respectively, -the buses 8 (220kV), buses 14 (llOkV) and buses 15(35kV).
The windings (35kV) of the transformer 10 are delta connected. :
, In order to simplify the drawing, the three-phase con-nections of transformers 10 and 10' with circuit breakers 11, 12, ; : ~:~
13 and 11', 12', 13' respectively, are shown as single lines.
A single-phase three-winding transformer 16 is also provided at ~
the transmitting sub-station to be used as a stand-by trans- ~::
former to back up any phase of the three-phase transformers 10 14~Z~
or 10' for repairs. The single-phase transformer 16 can be connected via single-phase switches 17 or 18 to any bus system 8 or 14, respectively.
In case of a fault in the wire 2 of the line 1, which didl not result in its breakage, while the insulation at the point of fault is able to sustain a voltage of 35 kV, the present invention can be embodied as follows.
The deenergized wire 2 is earthed at the receiving sub-station 9 with the earthing 6. At the transmitting sub-station,, one of the lead-outs of the 35 kV windin3 of the single-phase transformer 16 is earthed, whereas the other leadout of said winding is connected via a circuit breaker 19 to the disconnected wire 2. The single-phase transformer 16 is connected to the respective phase of bus 8 (220 kV) or 14 (110 kV), and voltage is fed to the disconnected wire 2 by means of the switch 17 or ~-18, respectively.
If for some reason a single-phase transformer cannot ~ -be used while the power supplied by one of the three-phase trans-formers 10 or 10' is sufficient to supply the consumers connected to the buses 15 (35 kV), one of the transformers 10 or 10' must be disconnected from the buses 15 (35 kV) in order to supply - voltage to the disconnected wire. In order to ~upply voltage to the disconnected wire 2, after th~ transformer 10 or 10~ is disconnected from the buses 15 (35 kV) one of its 4~3Z~
35 kV winding leadouts must be earthed and the other leadout of the winding (35 kV) must be connected to the disconnected wire 2 of the line 1.
Consider the diagram illustrated in Figure 8. As a result of a short circuit in the wire 2, the power transmission line 1 i5 operated in the incomplete phase regime mode. The failure resulted in a broken wire 2. A lightning protection wire rope 20 is provided on the line 1, being earthed at the receiving ~ub-station 21, its insulation along the entire length ~ .
thereof being capable of sustaining 10 kV voltage.
The power transmission line 1 connects buses 21 (110 kV) of the receiving sub-statïon and buses 22 (110 kV) of ~ ~ .
: the transmitting sub-station. Connected to the buses ;
; 22 (110 kV) via circuit breakers 23 and 24 two three-phase two-winding transformers 25 and 26 respectively, the rated vol-tage of their windings being 110 kV and 10 kV, one of the trans-formers being used for supplying power consumers connected across ~.
buses 2!7 (10 kV). Generally, taking into consideration the value of permissible overload, the power delivered by one of the trans-formers 25 or 26 is sufficient to supply all consumers connected .
across buses 27 (10 kV). These buses are coupled to the trans~
former 25 via circuit breaker 28. Figure 8 illustrates the . :~
coupling of only one transformer (25) since the other transformer :
.(26).. is disconnected from the buses 28 (10 kV), ~
`
.: ,' .~
' ' -20- `
o while one of the leadouts of the 10 kV winding of the latter transformer is earthed and the other leadout of the 10 kV
winding is connected to the lightning protection wire rope 20.
Figure 9 illustrates a 110 kV line 1 with a disconnected wire 2. The sub-station diagram is the same as in the preceding example. The transformer 4 is connected to the line at the receiving sub-station. Figure 9 shows only 110 kV winding of the transformer, which is disconnected from earth by the dis-connector 7. At the transmitting sub-station the disconnected wire is connected to one of the leadouts of the 10 kV winding of the transformer 26. Other operations at the transmitting `
sub-station are the same as in the previous example.
In case the disconnected wire 2 is broken as a result of the fault, use can be made of the lightning protection wire rope.
Referring to Figure 10, illustrated is the line 1 with the disconnected wire 2. The diagram of receiving and trans-mitting sub-stations is the same as in the previous example.
The line 1 is provided with a lightning protection wire rope 20 which is insulated relative to earth. On the receiving sub-station side the wire rope is earthed by a dis-connector 29. In order to switch the line to operate in the in-complete phase regime, the disconnector 29 is switched off, the wlre rope '~' ;~ ' ~ ' -21- ~
.. .... ~ .. . .. ...... ... . .. . .... .. . .
32~
20 is connected to the neutral of the transformer 4 and the neutral is disconnected from earth by means of the disconnector 7. At the transmitting sub-station, the wire rope 20 is con-nected to one of the leadouts (10 kV) of the transformer 26.
Other operations at the transmitting sub-station are the same as in the previous example.
Thus, a method is proposed for reducing current un-balance when operating the electrical system of a three-phase A.C. power transmission line in an incomplete phase regime by using the wires of the line involved and transformers electric-; ally coupled thereto, the method permitting the power trans-mitted over a line operating in the incomplete phase regime to be increased 1.4 to 1.6 times with only negligible expenses involved, with a simultaneous reduction of zero sequence currents.
Consider two calculated examples of increasing the transmitted power in the incomplete phase regime of the line.
Example 1 A 150 km long 220 kV line is operating in the incomplete phase regime. From the transmitting sub-station side the line is connected to a 1400 MWt power station. Operating in the receiving system are generators having a total output of 400 MWt.
.' ,. ' ' .
,'.~ ' ' .'':
: ,, ~ .
-22- ~
3Z'O
Owing to current unbalance in the generator windings the power transmitted over the line operating in the conventional incomplete phase regime does not exceed 62 MWt.
If the deenergized wire of the line earthed at the receiving sub-station is connected from the transmitting sub- -station side to a voltage source of 35 kV, the power trans-mitted over the line can be increased to 108 MWt, the current ~ -unbalance in the generator windings being equal.
Example 2 A 40 km long 110 kV line is supplying through a trans-former located at a 1~ MWt receiving sub-station a region which consumes 10 MWt. Current unbalance of electric receivers is limited to 20%. In the conventional incomplete phase regime the power transmitted is limited by current unbalance to 3.2 MWt.
If the disconnected wire of the line is connected to the disconnected from the earth neutral of the transformer of the receiving sub-station, while a voltage of 10 kV is impressed at the other end of said disconnected wire, the power transmitted 20 in the incomplete phase regime of the line and with the above-mentioned current unbalance can be increased to 7.4 MWt.
Claims (5)
1. A method for reducing current unbalance in the electric system of a three-phase A.C. power transmission line operating in an incomplete phase regime using the wires of the line and transformers electrically coupled thereto, com-prising the following steps:
providing an electric closed loop circuit comprising the line operating in the incomplete phase regime, a wire insulated from earth and disposed parallel to said line along the whole length thereof, and the neutral terminals of said transformers, connecting into the provided electric closed loop circuit a source of alternating voltage in step with the electric system to which said line is connected, selecting the corresponding phase and value of voltage of said source to obtain an increase of currents flowing through the neutrals of said transformers, resulting in decreased current unbalance in the electric system.
providing an electric closed loop circuit comprising the line operating in the incomplete phase regime, a wire insulated from earth and disposed parallel to said line along the whole length thereof, and the neutral terminals of said transformers, connecting into the provided electric closed loop circuit a source of alternating voltage in step with the electric system to which said line is connected, selecting the corresponding phase and value of voltage of said source to obtain an increase of currents flowing through the neutrals of said transformers, resulting in decreased current unbalance in the electric system.
2. A method as claimed in claim 1, wherein the wire which is insulated relative to earth and disposed parallel to the line along the whole length thereof is a dis-connected wire of said line, earthed at one of the ends thereof, and said alternating voltage source is a trans-former located at the opposite end of said earthed end of said disconnected wire, one of the windings of said transformer being connected between the disco-nnected wire and earth, the other winding of said transformer being connected to the phase or line voltage of the electric system to which said line is connected.
3. A method as claimed in claim 1, wherein the wire insulated relative to the earth and disposed in parallel to the power transmission line along the entire length thereof, said line operating in the incomplete phase regime, is the lightning protection wire rope of said line, insulated relative to earth along the entire length thereof and earthed at one of the ends thereof, and said alternating voltage source is a transformer located at the opposite, non-earthed end of said wire rope, one of the windings of said transformer being connected between earth and the wire rope while the other winding of said trans-former is connected to the phase or line voltage of the electric system to which said line is connected.
4. A method as claimed in claim 1, wherein said closed loop circuit is provided by directly connecting one of the ends of the disconnected wire of the line operating in the incomplete phase regime to the neutral of at least one of the transformers electrically coupled with said line, the neutral of said trans-former being disconnected from earth; the source of said al-ternating voltage is a transformer located at the opposite end of said disconnected wire, one of the windings of said trans-former being connected between the disconnected wire and earth and the other winding being connected to the phase or line voltage of the electric system to which said line is connected.
5. A method as claimed in claim 1, wherein said closed loop circuit is obtained by directly connecting one of the ends of the lightning protection wire rope of said line, electrically insulated relative to earth along the entire length thereof, to the neutral of at least one of the transformers electrically coupled to said line, the neutral of said transformer being disconnected from earth; the source of said alternating voltage being a trans-former located at the opposite end of said wire rope, one of the windings of said transformer being connected between the lightning protection wire rope and earth, while the other winding is connected to the phase or line voltage of the electric system to which said line is connected.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA225,315A CA1044320A (en) | 1975-04-23 | 1975-04-23 | Method of reducing current unbalance in a three-phase power transmission line operating with one faulty phase |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA225,315A CA1044320A (en) | 1975-04-23 | 1975-04-23 | Method of reducing current unbalance in a three-phase power transmission line operating with one faulty phase |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1044320A true CA1044320A (en) | 1978-12-12 |
Family
ID=4102892
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA225,315A Expired CA1044320A (en) | 1975-04-23 | 1975-04-23 | Method of reducing current unbalance in a three-phase power transmission line operating with one faulty phase |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1044320A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112881782A (en) * | 2020-12-30 | 2021-06-01 | 广东电网有限责任公司电力科学研究院 | Single-phase short-circuit current online monitoring method and device for power system |
-
1975
- 1975-04-23 CA CA225,315A patent/CA1044320A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112881782A (en) * | 2020-12-30 | 2021-06-01 | 广东电网有限责任公司电力科学研究院 | Single-phase short-circuit current online monitoring method and device for power system |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Beeman et al. | Industrial power systems handbook | |
| de Metz-Noblat et al. | Calculation of short-circuit currents | |
| Neumann | Superconducting fault current limiter (SFCL) in the medium and high voltage grid | |
| Pillai et al. | Grounding and ground fault protection of multiple generator installations on medium-voltage industrial and commercial power systems II. Grounding methods | |
| Owen | The historical development of neutral grounding practices | |
| US4004191A (en) | Method of reducing current unbalance in a three-phase power transmission line operating with one faulty phase | |
| CA1044320A (en) | Method of reducing current unbalance in a three-phase power transmission line operating with one faulty phase | |
| El-Sherif et al. | A design guide to neutral grounding of industrial power systems: The pros and cons of various methods | |
| CN111224384B (en) | Method for comparing line voltage vector difference on two sides of line and protecting line breakage by adopting loop closing and opening operation | |
| KOUIDRI et al. | Distribution Grid Protection | |
| Crary et al. | Analysis of the application of high-speed reclosing breakers to transmission systems | |
| DSouza et al. | Power System Design for a Large, Dynamic Natural Gas Field: Improving the Field Production Profile | |
| JPH03132436A (en) | Different power supply mixed-contact detecting system and device therefor | |
| Dewey | General considerations in grounding the neutral of power systems | |
| EP4339988A1 (en) | Passive fault protection arrangement for a measuring voltage transformer or a power voltage transformer for use in high voltage applications | |
| US2327190A (en) | Protective arrangement for high voltage systems | |
| Andrei et al. | Neutral point treatment in the medium voltage distribution networks | |
| Holm | Direct-current power transmission [includes discussion] | |
| Wedmore | Automatic protective switchgear for alternating-current systems | |
| Torchio | Relays for high-tension lines | |
| Moghbelli et al. | A design project to evaluate the protective device settings for an industrial plant | |
| Basu et al. | Maintenance of Three-phase Load Voltage during Single Phase Auto Reclosing in Medium Voltage Radial Distribution Lines | |
| US1919077A (en) | Protective system | |
| Hickok | Expansion of a Power System using Existing Switchgear | |
| Fielding et al. | Industrial feeder protection |