1、Analysis of power system overtone and overtone tidal current to calculate First, 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 sys
3、tem 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 di
4、sturb 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 , therefor
5、e, 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
6、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 kinds: in 1, sys
7、tems 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 elect
8、rical 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 syste
9、m, 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,
10、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 controlling eleme
11、nt, 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 equipme
12、nts 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
13、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 impedance.
14、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: Agrees wa
15、ve 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 net
16、work 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 har
17、monic 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 acco
18、rding 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 poten
20、tial 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
21、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 transformer an
22、d 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 hig
23、h 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
24、 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 transformers r
25、esistance 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
26、 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 overtone imped
27、ance , 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 posi
28、tionss 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
29、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 tidal curr
30、ent 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 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,
