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1、精选优质文档-倾情为你奉上Analysis of power system overtone and overtone tidal current to calculateFirst, introduction an ideal electrical power system is by the sole constant frequency and the stipulation peak-to-peak value regulated voltage power supply. But in fact, as a result of the recent years along with
2、sciences and technologys unceasing development, the high efficiency traded the class equipment and the modulator use, high in the electrical power system presses the nonlinear element which the direct current transmission the application, the massive misalignment loads appearance as well as the powe
3、r supply system itself existed and so on to cause in the systems voltage waveform distortion to be getting more and more serious, has caused the very big harm to the electrical power system, for example: Causes in the power supply system the part to lose increases, reduces current collectors service
4、 life, to disturb the communication system and so on. Serious when even can also cause equipment the damage, automatic control malfunction, relay protection misoperation, thus creates the power cut accident and so on and other questions. So-called the friend knows other, is undefeated in many battle
5、s , therefore, must realize to the electrical network overtone comprehensive program of public order, must make clear the overtone origin and the electrical network in under the each different movement way the overtone tidal current distributed situation, adopts the corresponding measure limit and t
6、he harmonic cancellation, thus changes the friendly power supply system power supply quality and guarantees systems security economy movement. Second, electrical power system overtones origin in the electrical power system the overtone source is many and varied. Mainly has the following several kind
7、s: in 1, systems each kind of misalignment current collector for example: Trades the class equipment, the modulator, the electrification railroad, the arc furnace, fluorescence the lamp, the domestic electric appliances as well as each kind of electronic energy conservation control device and so on
8、is the electrical power system overtone important source. Even if these equipment supplies its ideal sine wave voltage, it uses the electric current is also non-linear, namely has the harmonic current existence. And these the equipment produces the harmonic current will also pour into the electrical
9、 power system, will cause system each place voltage to have the harmonic component. These equipments harmony the wave content decided that in its characteristic and the working condition, basically has nothing to do with the electrical power system parameter, may regard as overtone constant flow the
10、 source. 2, the power supply system itself exists the nonlinear element is overtone another origin. These nonlinear element mainly has the transformer to stir up the capacitor which, the reactor group the magnetism leg, the alternating and direct convertor stations silicon-controlled rectifier contr
11、olling element, the silicon-controlled rectifier control and so on. 3rd, like the fluorescent lamp, the domestic electric appliances and so on single capacity is not big, but quantity and spreads very greatly in each place, electric power department with difficulty management current collector. If t
12、hese equipments current harmonics content is oversized, will then have the serious influence to the electrical power system, to this kind of equipments current harmonics content, when manufacture namely should limit in certain quantity scope. 4, the generator send out overtone electric potential. Th
13、e generator will send out the overtone electric potential at the same time also to have the overtone electric potential production, its overtone electricity the potential will be decided by generators structure and the working condition, basically will have nothing to do with the external connection
14、 impedance. Therefore may regard as overtone constant pressure source , but its value is very small.the three, electrical power system overtone tidal current calculates the so-called electrical power system overtone tidal current computation, is through solution network equation In=YnUn (n=3,5,7 . n
15、: Agrees wave number the number. In is the overtone source load pours into electrical networks n subharmonic electric current row vector. Yn is electrical networks n subharmonic conductance. Un is in the electrical network a various nodes bus bar n subharmonic voltage row vector). Obtains in the ele
16、ctrical network various nodes (bus bar) the harmonic voltage, enters to obtain in various legs harmonic current. When in the electrical power system the existence has the overtone source, this time in the system the contact voltage and the branch current will have the higher harmonic. For the determ
17、ination harmonic voltage and harmonic currents in power supply system distribution, needed to carry on to the overtone impedance constitution equivalent circuit the tidal current computation, when simultaneously in the rectifier unit power supply system possessed forbearance the part existed, but mu
18、st act according to various legs overtone impedance the nature and the size, whether there is examined the resonant situation. carries on the overtone tidal current computation, must first determine the electrical network parts overtone impedance. (3.1), electrical network each kind of parts overton
19、e impedance: (1), synchronous generators overtone impedance the qualified generators electric potential is the pure sine, does not include the higher harmonic, its generator electric potential only exists in the fundamental wave network. in higher harmonic network, because the generator overtone ele
20、ctric potential is very small, this time the visible generator overtone electric potential is zero. Therefore its and so on the value electric circuit is the junctor end and neutral point overtone reactance . And XGn=nXG1-(1) in the formula XG1 is when a fundamental wave generators zero foreword, th
21、e positive sequence or the negative sequence reactance, has this subharmonic foreword characteristic to decide , if needs to take into account the network to lose, regarding the generator, may its impedance angle according to 85 degrees estimates, regarding the transmission line, parts and so on tra
22、nsformer and load equivalent generators, may its impedance angle according to 75 degrees estimates. . (2), transformers overtone impedance the electrical power system overtones peak-to-peak value often is elevates along with the frequency weakens, therefore in the fundamental wave tidal current comp
23、utation high tension line , often neglects transformers initiation leg and the capacitance between turns particularly. When calculates the harmonic current, only considers transformers leakage reactance, and thought that recognizes the frequency with the harmonic order to be proportional. Generally,
24、 as soon as transformers equivalent circuit simplifies for links to meet the original vice-mid-side node overtone reactance * * is the transformer fundamental wave leakage reactance. under higher harmonics function, the winding internal kelvin effect and approaches the effect to increase, by now tra
25、nsformers resistance harmonic orders square was proportional approximately with the , this times transformer overtone impedance is: Zn=sqrt(n)RT1+jnXT1-(3) And RT1 is the fundamental wave time-variable depressors resistance. regarding the three-phase winding transformer, may use the star equivalent
26、circuit, on its overtone impedance computation side Fathom. when the overtone source pours into when higher harmonic current three-phase not symmetry, then must figures out the three-phase overtone impedance according to transformers wiring way and various forewords impedance meter . 3) reactors ove
27、rtone impedance , when only takes into account the reactor induction reactance, to the n subharmonic frequency is: XLn=Nxl*UN/sqrt(3)IN 4), transmission lines overtone impedance the transmission line has the uniform distribution parameter electric circuit, passes through the transmission line which
28、change positionss completely to be possible to regard as is three-phase symmetrical. in tidal current computation, usually by lumped parameter PI equivalent circuit expression. Following chart: in takes into account in the distribution characteristic situation, then: ZLn=Znsh(rnl) Yln/2=(chrnl-1)/(Z
29、nshrnl) ZN and RN respectively be regarding in this subharmonic when lines wave impedance and propagation constant. Zn=sqrt(Z0n/Y0n) Rn=sqrt(Z0nYon) Z0N and Y0N respectively be this subharmonic when transmission line unit length impedance and conductance five), load overtone impedance .When overtone
30、 tidal current computation, the fundamental wave part may pour into power regarding according to the node, but regards as in the overtone network it is the constant impedance, may think that approximately the synthesis load is an equivalent electric motor. Its synthesis loads overtone equivalent res
31、istance value is: ZN=SQRT (N) R1+JNX1 R1, X1 is the fundamental wave equivalent electric motors negative sequence resistance, the reactance, its value may by this node fundamental wave voltage, power the value obtain after the conversion. the zero foreword electric current will not enter the load ge
32、nerally, thus in zero forewords higher harmonic network, may neglect shoulders the leg. when after has determined in the electric circuit various electrical elements overtone impedance, may constitute an overtone function equivalent circuit, with the aim of carrying on the computation, under when pl
33、an overtone function equivalent circuit should pay attention to the following several characteristics: (1), the overtone functions equivalent circuit, should take the rectifier unit as a center, according to actual wiring constitution, therefore the rectification installs to set regards as the overt
34、one source, but electrical power systems generator is not appears by the energy, but as overtone source loaded impedance part. (2), the circuit element impedance may use the famous value to carry on the computation, may also use the sign Yao value to carry on the computation. When uses famous value
35、carries on the computation, the complete electric circuit should convert to some voltage reference, is advantageous for the analysis and the application. (3) in the general computation, parts all resistances may neglect, but when system some part occurs either close parallel or strings together the
36、joint resonance, this times resistance influence actually cannot neglect. (4), in harmonic current approximate calculation, what determined is the rectifier unit side total harmonic current, according to and so on overtone function the effect electric circuit, can determine various legs harmonic cur
37、rent and the voltage distribution. the 3.2nd, overtone tidal current calculates (3.2.1), not to allow the part network overtone tidal current to calculate (1), symmetrical systems overtone tidal current to calculate in the symmetrical system the three-phase situation to be the same, therefore may ca
38、lculate according to a situation. when has determined the rectifier unit, no matter what after one side total harmonic current, the union overtone equivalent circuit, may determine in the system network, no matter what a legs harmonic current distribution. Then again pours into the harmonic current
39、according to the node harmonic voltage and the node relational I=YU (in its , Y is overtone conductance), might determine each place node harmonic voltage. Then may extract the tidal current power. It counts to calculate that the step is as follows: , the basis give the operating condition, by usual
40、 tidal current computational method solution fundamental wave tidal current. , according to the overtone source working condition, determined other related parameters and need to calculate harmonic order. , calculates various parts overtone parameter, forms various subharmonics node admittance matri
41、x, and calculates the corresponding overtone net to pour into the electric current. , by type IN=YNUN determined that various nodes the harmonic voltage, and calculates various legs harmonic power. in which, should pay attention has the overtone injection current which the overtone instrumental meas
42、urement leaves, its phase angle is opposite in the fundamental current phase angle. Therefore after extracting the fundamental current, must carry on the overtone injection current phase angle the revision. Similarly, the system nodes power is the fundamental wave power with agrees sum of the wave p
43、ower, therefore the fundamental wave pours into the power also to carry on the revision. But the linear loads place fundamental wave pours into the power not to need to revise. (2), the symmetrical system overtone tidal current calculates in the symmetrical system, the three-phase situation is vario
44、us, moreover mutual influence, must therefore simultaneously carry on three-phase systems idea to calculate. the symmetrical net tidal currents computation may divide into the network various subharmonics network, calculates the fundamental wave network first, after obtaining various nodes fundament
45、al wave the voltage, calculates various overtones tidal current according to it each injection current, then presses this overtone injection current to resolve various subharmonics net to wind the equation, extracts various nodes various subharmonics voltage. (3.2.2), in the rectifier unit power sup
46、ply system possesses forbearance the part has when the overtone tidal current to calculate , when in the rectifier unit power supply system possesses forbearance the part exists, the capacitor to rectifier units phase change process and voltage current wave the shape is influential. Generally under
47、the base frequency, the induction reactance and the capacitance legs parameter differs really in a big way in the value, does not send produces the resonance effect, but a rectifier units non-sinusoidal return route, may regard as is several different frequencies and oscillation amplitude sine elect
48、ric potential the comprehensive result which affects separately in the return route, because the induction reactance frequency characteristic and the capacitance frequency characteristic are just opposite, have the possibility subharmonic both value to be close in some under the , have the resonance
49、 effect. When besides carries on the normal overtone tidal current computation, but also wants to act according to various legs overtone impedance the nature and the size, whether there is examines the resonance.four, summarize in the electrical power systems overtone appearance, regarding the electrical power system movement is one kind the pollution . They reduced systemic voltage the unreliable profile quality, not only has affected electrical power system one