CN114865585A - Control method for negative sequence current unbalance of three-phase power grid - Google Patents
Control method for negative sequence current unbalance of three-phase power grid Download PDFInfo
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- CN114865585A CN114865585A CN202210607691.6A CN202210607691A CN114865585A CN 114865585 A CN114865585 A CN 114865585A CN 202210607691 A CN202210607691 A CN 202210607691A CN 114865585 A CN114865585 A CN 114865585A
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- phase
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/16—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to fault current to earth, frame or mass
- H02H3/162—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to fault current to earth, frame or mass for ac systems
- H02H3/165—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to fault current to earth, frame or mass for ac systems for three-phase systems
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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
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks
Abstract
The invention relates to the field of power supply of a power grid, in particular to a control method for negative sequence current unbalance of a three-phase power grid. According to the invention, after positive and negative sequence current is sampled, the amplitude is realized in a frequency domain, and through multi-stage controllable gain or threshold value design, the protection grade, abnormal time and the like can be set according to the characteristics of a power grid.
Description
Technical Field
The invention relates to the field of power supply of a power grid, in particular to a control method for negative sequence current unbalance of a three-phase power grid.
Background
When a negative-sequence current three-phase power grid runs in an unbalanced mode, a large amount of negative-sequence and zero-sequence components are generated in the voltage of the power grid, and when the negative-sequence current components exist, alternating current with 2 omega (fundamental frequency of the power grid) frequency can be generated in a generator rotor through electromagnetic induction, so that the problems of generator set vibration, excessive rotor heating, reduction of the maximum running load of an asynchronous motor and the like are caused. These hazards cause the electric equipment not to work normally, even be damaged, and then cause normal production and living order not to go on, indirectly cause huge economic loss, and the asymmetric operation of electric power system can bring serious harm to transmission and distribution lines, electric equipment and users.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a control method for negative sequence current unbalance of a three-phase power grid. According to the invention, after positive and negative sequence current is sampled, the amplitude is realized in a frequency domain, and through multi-stage controllable gain or threshold value design, the protection grade, abnormal time and the like can be set according to the characteristics of a power grid.
The technical scheme of the invention is as follows: a control method for negative sequence current unbalance of a three-phase power grid is characterized by comprising the following steps: the method comprises the following steps:
step one, negative sequence current sampling; based on the sampling time of the phase A, the phase B is delayed by N1 sampling sample values relative to the phase A, the phase C is delayed by N2 sampling sample values relative to the phase A, and the calculation formulas of N1 and N2 are as follows:
f is three-phase electric frequency, and Fs is sampling frequency;
accumulating phase A, phase B and phase C currents, converting the phases into a frequency domain through a fast Fourier transform algorithm, extracting an amplitude in the frequency domain, and multiplying the extracted amplitude by a gain K1 to obtain a negative-sequence current weighing value I-;
step three, sampling positive sequence current; taking the sampling time of the phase A as a reference, delaying the phase B by N2 sampling sample values relative to the phase A, and delaying the phase C by N1 sampling sample values relative to the phase A;
step four, accumulating the currents of the phase A, the phase B and the phase C in the step three, performing Fast Fourier Transform (FFT) algorithm to convert the currents into a frequency domain, extracting an amplitude in the frequency domain, and multiplying the extracted amplitude by a gain K2 to obtain a positive sequence current weighing value I + ；
Step five, calculating a negative sequence ratio A which is equal to the negative sequence current weighing value I-divided by the positive sequence current weighing value I + ；
Step six, setting a ratio valve value B, calculating an abnormal value C according to the negative sequence ratio A and the ratio valve value B, and when B is larger than A, setting C to be 1; when B is less than a, C ═ 0;
and step seven, setting a trip value D, integrating the abnormal value C, supplying power to the three-phase power of the system when the integral value is smaller than the trip value D, and outputting a signal to cut off the power supply to the three-phase power when the integral value is larger than the trip value D.
The control method for the negative sequence current imbalance of the three-phase power grid is characterized by comprising the following steps: the three-phase power frequency is 50HZ, the sampling frequency is 10500Hz, N1 is 70, and N2 is 140.
The control method for the negative sequence current imbalance of the three-phase power grid is characterized by comprising the following steps: the gain K1 takes the value 1.
The control method for the negative sequence current imbalance of the three-phase power grid is characterized by comprising the following steps: the gain K2 takes the value 1.
The invention has the beneficial effects that: when the method is applied to different systems, different protection tripping time and tripping frequency can be realized only by modifying part of parameters on software, and the abnormal tripping times are reduced.
Drawings
Fig. 1 is a schematic circuit diagram of the present invention.
Detailed Description
The technical scheme of the invention is further explained by combining the attached drawings.
As shown in fig. 1, the method for controlling negative sequence current imbalance of a three-phase power grid of the present invention includes the following steps:
step one, negative sequence current sampling; based on the sampling time of the phase A, the phase B is delayed by N1 sampling sample values relative to the phase A, the phase C is delayed by N2 sampling sample values relative to the phase A, and the calculation formulas of N1 and N2 are as follows:
f is the three-phase frequency, 50HZ, Fs is the sampling frequency, for example 10500Hz, N1 is 70, and N2 is 140.
Accumulating the phase A, phase B and phase C currents, converting the phase A, phase B and phase C currents into a frequency domain by a Fast Fourier Transform (FFT) algorithm, extracting an amplitude in the frequency domain, and setting a gain K1 according to the extracted amplitude so as to realize a negative-sequence current weighing value I-;
step three, sampling positive sequence current; based on the sampling time of the A phase, the B phase is delayed by N2 sampling sample values relative to the A phase, and the C phase is delayed by N1 sampling sample values relative to the A phase.
Step four, accumulating the phase A, phase B and phase C currents in the step three, performing Fast Fourier Transform (FFT) algorithm to convert the phase A, the phase B and the phase C currents into a frequency domain, extracting an amplitude in the frequency domain, and setting a gain K2 according to the extracted amplitude, thereby realizing the positive sequence current weighing value I + (ii) a Through setting of K1 and K2, the level starting circuit can be automatically set according to the negative sequence current severity, so that different protection rules are adopted according to different power supply lines, if K1 and K2 are 1, the amplitude is a negative sequence current balance value I < - > or a positive sequence current balance value I < - >, and the protection rule is realized + 。
Step five, calculating the negative sequence ratio A, and dividing the negative sequence current weighing value I-by the positive sequence current weighing value I + ；
Step six, setting a ratio valve value B, calculating an abnormal value C according to the negative sequence ratio A and the ratio valve value B, and when B is larger than A, setting C to be 1; when B is less than a, C ═ 0; in the step, because the valve value B is smaller than the negative sequence ratio abnormal value and is reset to zero, the previous accumulated value can be cleared in the subsequent integration process, and the valve value B is ensured to be cleared only when the abnormal time reaches the set time.
And step seven, setting a trip value D, integrating the abnormal value C, supplying power to the three-phase power of the system when the integral value is smaller than the trip value D, and outputting a signal to cut off the power supply to the three-phase power when the integral value is larger than the trip value D. Therefore, the invention can design how much time the system is tripped each time by setting the magnitude of the tripping value D, thereby ensuring that abnormal tripping can not be caused when a part of high-power electrical appliances are started in the power supply process of the system.
In the experiment, the working time of a three-phase load A (the power is 5kW) is 0-20 s; the working time of a three-phase load B (the power is 3kW) is 2-10 s; the single-phase load (power is 4kW) has the working time of 6-20s, and when the unbalanced load is applied, the relay trips around 11 s; the unbalanced load is connected to the power grid in the 6 th s, the integrator starts integration, and when the integral value is larger than the threshold value, protection tripping is started; meanwhile, due to the introduction of a three-phase load and a single-phase unbalanced load in different time periods, the current of the circuit is obviously increased, and the current becomes 0 after the trip is performed at about 11 s; all loads do not work after tripping.
Claims (4)
1. A control method for negative sequence current unbalance of a three-phase power grid is characterized by comprising the following steps: the method comprises the following steps:
step one, negative sequence current sampling; based on the sampling time of the phase A, the phase B is delayed by N1 sampling sample values relative to the phase A, the phase C is delayed by N2 sampling sample values relative to the phase A, and the calculation formulas of N1 and N2 are as follows:
f is three-phase electric frequency, and Fs is sampling frequency;
accumulating phase A, phase B and phase C currents, converting the phases into a frequency domain through a fast Fourier transform algorithm, extracting an amplitude in the frequency domain, and multiplying the extracted amplitude by a gain K1 to obtain a negative-sequence current weighing value I-;
step three, sampling positive sequence current; taking the sampling time of the phase A as a reference, delaying the phase B by N2 sampling sample values relative to the phase A, and delaying the phase C by N1 sampling sample values relative to the phase A;
step four, accumulating the phase A, phase B and phase C currents in the step three, performing Fast Fourier Transform (FFT) algorithm to convert the phase A, the phase B and the phase C currents into a frequency domain, extracting an amplitude in the frequency domain, and multiplying the extracted amplitude by a gain K2 to obtain a positive-sequence current weighing value I + ；
Step five, calculating a negative sequence ratio A which is equal to the negative sequence current weighing value I-divided by the positive sequence current weighing value I + ；
Step six, setting a ratio valve value B, calculating an abnormal value C according to the negative sequence ratio A and the ratio valve value B, and when B is larger than A, setting C to be 1; when B is less than a, C ═ 0;
and step seven, setting a trip value D, integrating the abnormal value C, supplying power to the three-phase power of the system when the integral value is smaller than the trip value D, and outputting a signal to cut off the power supply to the three-phase power when the integral value is larger than the trip value D.
2. The method for controlling negative sequence current imbalance of the three-phase power grid according to claim 1, wherein: the three-phase power frequency is 50HZ, the sampling frequency is 10500Hz, N1 is 70, and N2 is 140.
3. A method of controlling a negative sequence current imbalance in a three phase grid according to claim 1 or 2, wherein: the gain K1 takes the value 1.
4. A method of controlling a negative-sequence current imbalance of a three-phase grid according to claim 1 or 2, characterised in that: the gain K2 takes the value 1.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210607691.6A CN114865585A (en) | 2022-05-31 | 2022-05-31 | Control method for negative sequence current unbalance of three-phase power grid |
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| CN202210607691.6A CN114865585A (en) | 2022-05-31 | 2022-05-31 | Control method for negative sequence current unbalance of three-phase power grid |
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| CN114865585A true CN114865585A (en) | 2022-08-05 |
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| CN202210607691.6A Pending CN114865585A (en) | 2022-05-31 | 2022-05-31 | Control method for negative sequence current unbalance of three-phase power grid |
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- 2022-05-31 CN CN202210607691.6A patent/CN114865585A/en active Pending
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