1、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 sciences and
2、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 power supply syst
3、em 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 life, to dis
4、turb 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 battles , therefore
5、, 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 the harmonic c
6、ancellation, 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 kinds: in 1, syst
7、ems 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 is the electr
8、ical 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 power system
9、, 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 source. 2, t
10、he 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 controlling elemen
11、t, 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 these equipmen
12、ts 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. The generator w
13、ill 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 impedance. T
14、herefore 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: Agrees wave
15、 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 electrical netwo
16、rk 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 determination harmo
17、nic 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 must act accord
18、ing 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 overtone impedance:
19、(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 electric potenti
20、al 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, the positive se
21、quence 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 transformer and
22、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 computation high
23、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, as soon as t
24、ransformers 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 transformers res
25、istance 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 circuit, on i
26、ts 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 overtone impedan
27、ce , 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 change positi
28、onss 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)/(Znshrnl) ZN an
29、d 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 tidal curren
30、t 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 resistance value
31、 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 generally, thus
32、 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 plan overtone f
33、unction 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 overtone source, b
34、ut 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 carries on th
35、e 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 joint resonan
36、ce, 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 current and the
37、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 calculate accor
38、ding 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 according to
39、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 tidal curren
40、t 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 matrix, and calcul
41、ates 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 measurement leave
42、s, 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 power, therefo
43、re 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 various, moreover
44、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 fundamental wave the v
45、oltage, 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 supply system po
46、ssesses 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 the base freq
47、uency, 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 electric potential
48、 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 effect. When
49、 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 oneself seriously, m
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