CN112865045A - Impedance differential-based power transmission line protection method with tuning half-wavelength - Google Patents
Impedance differential-based power transmission line protection method with tuning half-wavelength Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
- H02H7/263—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of measured values
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
Abstract
The invention relates to a method for protecting a power transmission line containing a tuned half-wavelength based on impedance differential, and belongs to the technical field of relay protection of power systems. The invention firstly obtains the fault voltage and the fault current power frequency component measured by the measuring end, and then calculates the ratio of the fault voltage component and the current component at the two sides of the circuit
The ratio is the measured impedance of the measuring end; then, the measured impedances obtained by the two ends in the last step are summed to obtain a differential impedance ZcdWhen the differential impedance satisfies-180 DEG < argZcd< 0 ° and | Im (Z)set)|＜|Im(Zcd) If yes, judging the fault is an internal fault, otherwise, judging the fault is an external fault. The invention realizes the identification of the faults inside and outside the area by using the magnitude of the imaginary part of the differential impedance and the differential angle, and can realize the identification of the faults inside and outside the area at any position, any fault angle and transition of the whole lineAnd effectively identifying faults inside and outside the area under the condition of resistance.
Description
Technical Field
The invention relates to a method for protecting a power transmission line containing a tuned half-wavelength based on impedance differential, and belongs to the technical field of relay protection of power systems.
Background
The half-wavelength alternating current transmission technology is an ultra-long distance alternating current transmission technology with the transmission electrical distance close to a power frequency half-wave (about 3000km under the condition of 50 Hz), and is firstly proposed by Su Union experts in the 40 th century in the 20 th century. With the reduction of energy reserves in the middle area of China and the increasing of electricity utilization scale in economically developed areas such as the east, the extra-high voltage half-wavelength alternating current transmission technology can be used as one of future transmission modes in China. In addition, the alternating-current half-wavelength line can transmit power beyond the conventional safe economic range, the line length of the alternating-current half-wavelength line reaches the electrical characteristic of half wavelength, but the transmission distance of the actual line is difficult to meet the half wavelength of a power frequency, and the half-wavelength transmission line containing the tuning compensation technology becomes an effective method for solving the problem of the half-wavelength transmission distance.
In the aspect of relay protection of a half-wavelength line, the half-wavelength transmission line is extremely long, and the electrical characteristics are complex, so that the traditional alternating current relay protection method cannot meet the requirement of the half-wavelength transmission line. The power direction element based on the steady-state power frequency quantity, the fault sudden change quantity and the fault traveling wave quantity can still represent the fault direction of the half-wavelength line after the fault by using the back side impedance characteristic. However, when the directional element is used for longitudinal directional protection of a half-wavelength line, the communication time of relay protection locking or tripping signals on two sides of the line is obviously longer than the protection action time of the existing line, and the refraction and reflection time of the wave process of the half-wavelength transmission line is very long during reverse fault, so that the conventional directional element cannot accurately identify the reverse fault after protection starting.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a power transmission line protection method containing a tuned half-wavelength based on impedance differential, which is used for solving the problem.
The technical scheme of the invention is as follows: a method for protecting the power transmission line containing tuned half-wavelength based on impedance differential includes such steps as measuring the power frequency components of fault voltage and current, and calculating the ratio between the voltage and current components of both sides of said line
The ratio is the measured impedance of the measuring end; then, the measured impedances obtained by the two ends in the last step are summed to obtain a differential impedance ZcdWhen the differential impedance satisfies-180 DEG < arg Zcd< 0 ° and | Im (Z)set)|＜|Im(Zcd) If yes, judging the fault is an internal fault, otherwise, judging the fault is an external fault.
The method comprises the following specific steps:
step 1: when the power transmission system with the tuned half-wavelength is protected and started, the fault voltage u of one period at the side is collected at a measuring pointmAnd fault current imAnd delaying the acquisition of the fault voltage u of one period at the opposite side by 10msnAnd fault current inSeparately calculate the fault component Δ um、Δim、Δun、Δin；
Step 2: calculate out
Summing to obtain a differential impedance Zcd；
Wherein, in case of a failure in the area,
reflecting the negative M-terminal back side system impedance,
is a negative N-terminal back side system impedance, and the differential impedance is the sum of the negative two-side system impedance, namely Zcd＝-(Zm+Zn)；
According to the equation of the uniform transmission line, the relation between the voltage and the current at the first end and the last end of the half-wavelength is obtained as follows:
when an external fault occurs, l in the formula (1) is the line length, the corresponding rl is equal to j pi, and for a nearly lossless half-wavelength line, the voltage effective values at two ends are the same, and the phases are opposite; the effective values of the currents are the same, and the phases are the same.
Namely, the differential impedance satisfies:
step 3: differential impedance angle arg Z using differential impedancecdAnd the absolute value | Im (Z) of the imaginary part of the differential impedancecd) Forming a fault identification criterion:
in order to prevent the sensitivity of the one-side protection device from being insufficient and the protection from being refused to be moved, Z is arrangedset＝min(Zm，Zn) When the differential impedance satisfies the formula (3), judging that the fault is an internal fault and performing protection action;
otherwise, judging the fault as an out-of-area fault, and protecting and locking.
The sampling rate in the invention is 100 kHz.
The invention has the beneficial effects that: because the system impedance is approximately constant in a short time, the invention does not need to strictly synchronize the data at two ends of the line, and only needs the information of the voltage and the current at each side to be respectively synchronized. When the fault happens outside the area, the differential impedance is not influenced by the reverse fault wave process, and the action speed is high.
Drawings
Fig. 1 is a block diagram of an ac transmission system including tuned half wavelengths in accordance with the present invention;
fig. 2 is an additional state diagram of the forward fault component of the ac transmission system with tuned half-wavelength of the present invention;
fig. 3 is an additional state diagram of the reverse fault component of the ac transmission system with tuned half-wavelength of the present invention;
FIG. 4 is a graph showing a comparison of the internal and external differential impedance angles in the single-phase metallic grounding time zone in the line according to example 1 of the present invention;
FIG. 5 is a comparison graph of the absolute values of the imaginary parts of the differential impedances inside and outside the time zone along the single-phase metallic grounding in accordance with example 1 of the present invention;
FIG. 6 is a graph comparing the internal and external differential impedance angles in the two-phase short-circuit grounding time zone along the line in embodiment 1 of the present invention;
FIG. 7 is a comparison graph of absolute values of imaginary parts of internal and external differential impedances along a two-phase short-circuit grounding time zone in embodiment 1 of the present invention;
FIG. 8 is a comparison graph of the internal and external differential impedance angles in the three-phase short-circuit grounding time zone along the line in embodiment 1 of the present invention;
FIG. 9 is a comparison graph of absolute values of imaginary parts of internal and external differential impedances in a three-phase short-circuit grounding time zone along the line in embodiment 1 of the present invention;
FIG. 10 is a diagram showing the result of the protection operation at a single-phase metallic grounding state at different fault angles in embodiment 2 of the present invention;
fig. 11 is a diagram showing the protection operation result when two phases of different transition resistances are short-circuited and grounded in embodiment 3 of the present invention;
fig. 12 is a diagram showing the protection operation results when three phases of different transition resistors are short-circuited and grounded in embodiment 3 of the present invention;
Detailed Description
The invention is further described with reference to the following drawings and detailed description.
As shown in figures 1-3, a method for protecting a transmission line containing a tuned half-wavelength based on impedance differential comprises the steps of firstly obtaining a fault voltage and a fault current power frequency component measured by a measuring end, and secondly calculating the ratio of the fault voltage component and the current component at two sides of the line
The ratio is the measured impedance of the measuring end; then, the measured impedances obtained by the two ends in the last step are summed to obtain a differential impedance ZcdWhen the differential impedance satisfies-180 DEG < arg Zcd< 0 ° and | Im (Z)set)|＜|Im(Zcd) If yes, judging the fault is an internal fault, otherwise, judging the fault is an external fault.
The method comprises the following specific steps:
step 1: when the power transmission system with the tuned half-wavelength is protected and started, the fault voltage u of one period at the side is collected at a measuring pointmAnd fault current imAnd delaying the acquisition by 10ms for the opposite side onePeriodic fault voltage unAnd fault current inSeparately calculate the fault component Δ um、Δim、Δun、Δin；
Step 2: calculate out
Summing to obtain a differential impedance Zcd；
Step 3: differential impedance angle arg Z using differential impedancecdAnd the absolute value | Im (Z) of the imaginary part of the differential impedancecd) Forming a fault identification criterion:
when the differential impedance meets the formula (1), judging that the fault is in the area, and performing protection action; otherwise, judging the fault as an out-of-area fault, and protecting and locking.
In the event of an in-zone fault,
reflecting the negative M-terminal back side system impedance,
is a negative N-terminal back side system impedance, and the differential impedance is the sum of the negative two-side system impedance, namely Zcd＝-(Zm+Zn) The differential impedance is positioned in the third quadrant, the impedance angle is a negative value, and the absolute value of an imaginary part is the sum of imaginary parts of the negative two-side system impedance.
When the fault occurs outside the area, the voltage and current relationship of the first end and the last end of the half-wavelength is obtained according to the equation of the uniform transmission line as follows:
when an external fault occurs, l in the formula (2) is the line length, the corresponding rl is equal to j pi, and for a nearly lossless half-wavelength line, the voltage effective values at two ends are the same, and the phases are opposite; the effective values of the currents are the same, and the phases are the same, namely, the differential impedance satisfies the following conditions:
the imaginary part of the differential impedance is ideally zero, which is much smaller than the absolute value of the imaginary part of the differential impedance at the time of the in-zone fault.
In order to prevent the protection from refusing to operate due to the insufficient sensitivity of the one-side protection device, Z is arrangedset＝min(Zm，Zn)。
An alternating-current transmission system with the tuning half-wavelength as shown in the attached figure 1 is established as a simulation model, and the total length of a line is 2540 km. The tuning network PI10 is arranged at two ends of the circuit, the total compensation length is 450km, and the two ends tune each compensation for 225 km. According to the invention, a tuned half-wavelength power transmission line model is built by temporarily adopting the line parameters and line models of triangular arrangement of 1000kV ultra-high voltage test demonstration engineering which is put into operation, and the power transmission line is uniformly transposed. The simulation system parameters are as follows: at 50Hz power frequency, positive sequence inductance L1＝8.404×10-7H/m, positive sequence resistance R1＝1.032×10-5Omega/m, positive sequence capacitance C1＝1.375×10-11F/m, zero sequence inductance L0＝2.692×10-6H/m, zero sequence resistance R0＝2.513×10-4Omega/m, zero sequence capacitance C0＝8.804×10-12F/m，Em＝1.05∠0°，Rm＝0.8，Lm1＝0.1254H，En＝1.00∠150°，Rn1＝0.84Ω，Ln1＝0.1432H。
Example 1, as shown in fig. 4-9:
(1) fault location: f1、F2、F3、F4、F5、F6、F7Single-phase, two-phase and three-phase metallic earth faults occur, and the initial fault phase angle is 0 degree; the sampling frequency was 100 kHz.
(2) According to the first step in the specification, the fault voltage and the fault current of the same side in one period are collected at a measuring point, and the fault components are calculated respectively.
(3) According to the second step in the specification, the impedance calculation is respectively carried out on the fault components of the voltage and the current at two sides, and the differential impedance Z is obtained by summingcd。
(4) Differential impedance Z obtained according to the third step of the descriptioncdAnd forming a fault identification criterion.
(5) According to the protection criterion, the absolute values of the differential impedance angle and the imaginary part of the differential impedance satisfy-180 DEG < arg Zcd< 0 ° and | Im (Z)set)|＜|Im(Zcd) If yes, the fault is judged to be an internal fault. In this example, the differential impedance angle arg Z is the angle of the differential impedance under different types of ground faults at the time of an in-zone faultcdApproximately-94 °, absolute value of imaginary part of differential impedance | Im (Z)cd) L is approximately equal to 103 omega, and is approximately equal to the negative value of the capacitive reactance sum of the systems on the two sides; differential impedance angle arg Z in case of external faultcd≈-9°，|Im(Zcd) The value of | ≈ 1.8 Ω is a very small value, and the division with the fault time zone in the zone is very large, so that the out-of-zone fault cannot be surpassed.
Example 2:
(1) fault location: f1、F2、F3、F4、F5、F6、F7Single-phase metallic earth faults occur, and the initial fault phase angles are respectively 30 degrees, 60 degrees and 90 degrees; the sampling frequency was 100 kHz.
(2) According to the first step in the specification, the fault voltage and the fault current of the same side in one period are collected at a measuring point, and the fault components are calculated respectively.
(3) According to the second step in the specification, the impedance calculation is respectively carried out on the fault components of the voltage and the current at two sides, and the differential impedance Z is obtained by summingcd。
(4) Differential impedance Z obtained according to the third step of the descriptioncdAnd forming a fault identification criterion.
(5) According to the protection criterion, the absolute values of the differential impedance angle and the imaginary part of the differential impedance satisfy-180 DEG < arg Zcd< 0 ° and | Im (Z)set)|＜|Im(Zcd) If yes, the fault is judged to be an internal fault. In this example, the differential impedance angles at the time of the in-zone fault are all at-94 ° at different initial fault anglesLower ripple, absolute value of imaginary part of differential impedance | Im (Z)cd) L is approximately equal to 105 Ω; differential impedance angle arg Z in case of an out-of-range faultcd≈-9°，|Im(Zcd) I ≈ 1.8 Ω. As shown in fig. 10, the results of this example show that the protection method is effective under the operating conditions of different fault distances and initial fault angles.
Example 3:
(1) fault location: at F1、F2、F3、F4、F5、F6、F7Two-phase and three-phase short circuit earth faults with different transition resistances of 50ohm, 100ohm and 150ohm occur, and the initial fault phase angle is 30 degrees; the sampling frequency was 100 kHz.
(2) According to the first step in the specification, the fault voltage and the fault current of the same side in one period are collected at a measuring point, and the fault components are calculated respectively.
(3) According to the second step in the specification, the impedance calculation is respectively carried out on the fault components of the voltage and the current at two sides, and the differential impedance Z is obtained by summingcd。
(4) Differential impedance Z obtained according to the third step of the descriptioncdForming fault identification criteria
(5) According to the protection criterion, the absolute values of the differential impedance angle and the imaginary part of the differential impedance satisfy-180 DEG < arg Zcd< 0 ° and | Im (Z)set)|＜|Im(Zcd) If yes, the fault is judged to be an internal fault.
It can be seen from the test results of fig. 11 and 12 that the calculated value of the differential impedance in the method is independent of the type of the fault and the magnitude of the transition resistance, the protection can operate reliably regardless of the area or the outside fault, and the imaginary absolute value of the differential impedance under the outside fault condition of the circuit is greatly divided from the inside fault time zone, so that the protection can operate reliably.
While the present invention has been described in detail with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, and various changes can be made without departing from the spirit and scope of the present invention.
Claims (4)
1. A method for protecting a power transmission line containing a tuned half-wavelength based on impedance differential is characterized by comprising the following steps: firstly, obtaining the fault voltage and fault current power frequency component measured by measuring end, then obtaining the ratio of fault voltage component and current component of two sides of circuit
The ratio is the measured impedance of the measuring end; then, the measured impedances obtained by the two ends in the last step are summed to obtain a differential impedance ZcdWhen the differential impedance satisfies-180 DEG < arg Zcd< 0 ° and | Im (Z)set)|＜|Im(Zcd) If yes, judging the fault is an internal fault, otherwise, judging the fault is an external fault.
2. The impedance differential based power transmission line protection method with the tuned half-wavelength according to claim 1, characterized by comprising the following specific steps:
step 1: when the power transmission system with the tuned half-wavelength is protected and started, the fault voltage u of one period at the side is collected at a measuring pointmAnd fault current imAnd delaying the acquisition of the fault voltage u of one period at the opposite side by 10msnAnd fault current inSeparately calculate the fault component Δ um、Δim、Δun、Δin；
Step 2: calculate out
Summing to obtain a differential impedance Zcd；
Step 3: differential impedance angle arg Z using differential impedancecdAnd the absolute value | Im (Z) of the imaginary part of the differential impedancecd) Forming a fault identification criterion:
when the differential impedance meets the formula (1), judging that the fault is in the area, and performing protection action; otherwise, judging the fault as an out-of-area fault, and protecting and locking.
3. The impedance differential based transmission line protection method with the tuned half-wavelength according to claim 2, characterized in that: when the fault occurs in the area, the fault occurs,
reflecting the negative M-terminal back side system impedance,
is a negative N-terminal back side system impedance, and the differential impedance is the sum of the negative two-side system impedance, namely Zcd＝-(Zm+Zn) The differential impedance is positioned in the third quadrant, the impedance angle is a negative value, and the absolute value of an imaginary part is the sum of imaginary parts of the negative two-side system impedance.
4. The impedance differential based transmission line protection method with the tuned half-wavelength according to claim 2, characterized in that: when the fault occurs outside the area, the voltage and current relationship of the first end and the last end of the half-wavelength is obtained according to the equation of the uniform transmission line as follows:
when an external fault occurs, l in the formula (2) is the line length, the corresponding rl is equal to j pi, and for a nearly lossless half-wavelength line, the voltage effective values at two ends are the same, and the phases are opposite; the effective values of the currents are the same, and the phases are the same, namely, the differential impedance satisfies the following conditions:
the imaginary part of the differential impedance is ideally zero, which is much smaller than the absolute value of the imaginary part of the differential impedance at the time of the in-zone fault.
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