1.Why be harmonic?

As a result of,the prime cause that in power system harmonic produces is nonlinear laden be caused by. When electric current sheds classics load, the tension that increases with place does not show linear concern, form blame sine electric current, there is harmonic generation in circuit namely. Overtone frequency is base the whole multiple of wave frequency, according to French mathematician teach establishs a part of a historical period (M. Fourier) analyses principle proof, any reduplicative weaveform can be decomposed to contain base wave frequency mixes a series of is base the sine wave heft of the harmonic of wave multiple. Harmonic is sine wave, every harmonic has different frequency, extent and photo corner. Harmonic can distinguish for occasionally second with strange second sex, the 3rd, 5, of 7 number to surprise second harmonic, and 2, 4, 6, 8 wait for occasionally second harmonic, be like base wave when be 50Hz, 2 times harmonic is 100Hz, 3 harmonic is 150Hz.

 

 

Will tell commonly, strange the harm that second harmonic causes is compared occasionally second harmonic more is bigger. In the three-phase system of the balance, because concern symmetrically, occasionally second harmonic had been eliminated, surprise only second harmonic exists. Laden to three-phase commutate, occurrence harmonic electric current is 6n±1 second harmonic, for example 5, 7, 11, 13, 17, 19 wait, transducer basically arises 5, 7 harmonic.

 

One word of “ harmonic ” traceable is acoustics. The several credit analyse of concerned harmonic is mixed in 18 centuries 19 centuries had laid good foundation. The harmonic that the person such as Fourier puts forward analyses a method to still be applied extensively up to now. The harmonic issue of power system is early the attention that in 20 centuries 20 time caused people with 30 time. Be in Germany at that time, because use convertor of dormant mercury arc and the distortion that created weaveform of voltage, electric current. The paper of the concerned convertor harmonic that J.C.Read published 1945 is inchoate the classical thesis that researchs about harmonic.

 

Arrived 50 time and 60 time, because high pressure sorts the development of transmit electricity technology continuously, published a large number of papers that pose problem of power system harmonic about converter. Since 70 time, as a result of the flying development of technology of electric power electron, device of all sorts of electric power electron reach a household in power system, industry, traffic medium application is increasingly wide, the harm that harmonic place causes is serious with each passing day also. World each country gives to harmonic problem mix adequately attention. The academic meeting of concerned harmonic problem was held for many times on international, many countries and international science organization made harmonic of limitative power system and the level that use electric equipment harmonic and provision.

 

2.Harmonic is restrained

Pollute a problem to solve the harmonic of device of electric power electron and other harmonic source, main train of thought has two: One is furnish harmonic compensates device to compensate harmonic, this is applicable to all sorts of harmonic sources; Another is to device of electric power electron itself undertakes transforming, make its do not produce harmonic, and power factor is controallable for 1, this applies to the device of electric power electron that regards main harmonic as the source only of course.

 

Furnish harmonic compensates the traditional method of device to use LC tuning filter namely. This kind of method can compensate harmonic already, can compensate again without result power, and the structure is simple, be used extensively all the time. The main drawback of this kind of method is to compensate character to suffer impedance of electrified wire netting and moving condition effect, mix easily systematic happening paralell connection is syntonic, bring about harmonic enlarge, make LC filter overload even burn down. In addition, it can compensate the harmonic of fixed frequency only, compensation effect is very not ideal also.

 

3.Without merit compensation

People is very easy to the understanding of power of have rendered great service, and wanting deep knowledge not to have result power is not easy to do however. In sine circuit, the concept that does not have result power is clear, and when containing harmonic, still do not have up to now obtain do not have result power definition acceptedly. But, to the significance that without result power this entirely misses, to having the understanding of merit compensation value, it is consistent however. Should include without merit compensation right base wave the compensation that be compensated without result power and does not have result power to harmonic.

 

Mix to power supply system without result power of bear moving is very important. The impedance of component of power system network basically is inductance sex. Accordingly, say roughly, to carry power of have rendered great service, the tension that be carried with respect to requirement power transmission and gets electric end has one phasic difference, this can come true inside quite wide range; And do not have result power to carry, ask two upright voltage have one amplitude difference, this can come true inside very narrow range only. Not only most network component is used up without result power, most load also needs to use up without result power. Must obtain of network component and laden place need from a certain place in the network without result power. Apparent, it is unreasonable that if want to be offerred by the dynamo and convey through Sunday run,these do not have result power, also be impossible normally. Reasonable method should be the local generation that does not have result power is used up not to have result power in need, this does not have merit compensation namely.

 

Basically have the following without result compensatory action:

(1) the power factor that rises to reach load for using electric system, reduce equipment size, reduce power loss.

(2) the voltage that stabilizes end getting report and electrified wire netting, improve power supply quality. Proper in line of Sunday run transmit electricity place installs trends not to have merit compensation device to still can improve the stability of transmit electricity system, increase transmit electricity capacity.

(3) the circumstance with three-phase lopsided load waits in electrification railroad, do not have work load through having result Lian appropriately to be able to balance the have rendered great service of three-phase to reach.

 

Harmonic arises with what do not have result power

 

In electric load is being used with the life in industry, block feeling load has very large proportion. Asynchronous electromotor, transformer, fluorescent lamp is typical block feeling load. Asynchronous electromotor does not have result power to be offerred in power system place with what transformer place uses up very high proportion is had in having result power. The reactor in power system and trolly wire also use up a few without result power. Feeling load must absorb block to work normally without result power ability, by its the nature place of itself decides this.

 

Device of electric power electron nonlinear device also should be used up without result power, especially all sorts of photographs charge unit. If accuse rectifier, photograph to accuse to communicate power to adjust circuit and Zhou Bo convertor, in lag of electric current of wave of working time base at voltage of electrified wire netting, should use up do not have result power in great quantities. Additional, these unit also can produce many harmonic electricity, harmonic source is to should use up those who do not have result power. Of diode commutate circuit base wave electric current is phasic with voltage of electrified wire netting phasic roughly identical, do not use up basically so base wave without result power. But it also produces many harmonic electricity, because this also is used up,do not have result power certainly.

 

Come nearly 30 years, the application of device of electric power electron is increasingly wide, also make device of electric power electron becomes the biggest harmonic source. In device of all sorts of electric power electron, the proportion that rectification plant institute holds is the largest. Current, commonly used rectification circuit uses brilliant brake canal to dominate rectification circuit or diode commutate circuit almost, it is with three-phase bridge-type and circuit of single-phase bridge-type commutate among them most. The harmonic pollution that the rectification circuit place of load of the feeling that take block produces and power factor lag already were people place to be familiar with. The diode commutate circuit that sheds side to use capacitance filter wave continuously also is the harmonic pollution source that punish severely. Of electric current of input of this kind of circuit base wave heft is phasic as phasic as power source voltage cardinal principle is same, consequently base wave power factor is adjacent 1. But the harmonic weight that its input electric current is very great however, cause serious pollution to electrified wire netting, also make total power factor very low. Additional, use the alternating current force that accuses means to adjust circuit and the device of electric power electron such as cycle convertor to also can be in the harmonic electric current with input side many generation.

 

3, the harm of the influence that does not have result power and harmonic

 

1. does not have the influence of result power

(1) the addition that does not have result power, can bring about report to flow to increase and be inspected increase in power, make electric equipment capacity and lead capacity increase etc of dynamo, transformer thereby. In the meantime, of power user start the size that reachs control equipment, measuring instrument table and norms to also want to increase.

(2) the addition that does not have result power, make total electric current increases, make the loss of equipment and circuitry increases consequently, this is clearly.

(3) the voltage drop that makes circuit reachs transformer increases, if be to pound a gender not to have result power load, still can make voltage produces acuteness wave motion, make power supply quality is reduced badly.

 

The harm of 2. harmonic

The voltage that place of good public electrified wire netting offers should be the voltage amplitude of onefold and fixed frequency and regulation. Of harmonic electric current and harmonic voltage appear, it is a kind of pollution to public electrified wire netting, the environment with located equipment of its use phone is exasperate, also apply extensively to the equipment of electron of ability electric power all round previously, people has had a few research to harmonic and its harm, have certain knowledge, but harmonic pollution has not caused enough attention in those days. Come nearly 339 years, the rapid development of device of all sorts of electric power electron makes the harmonic pollution of public electrified wire netting serious with each passing day, all sorts of trouble that cause by harmonic and accident also happen ceaselessly, the seriousness that harmonic endangers just causes the attention of people height. Harmonic has the following sides roughly to the harm of public electrified wire netting and other system.

(1) the component that harmonic makes public electrified wire netting medium arose additional harmonic loss, reduced generate electricity, transmit electricity and the efficiency of the equipment that use phone, the many meeting when 3 times harmonic has shed neuter line makes circuit overheat produces fire even.

(2) the regular job that harmonic affects all sorts of electric equipment. Harmonic is divided to the influence of electric machinery outside causing additional loss, still can produce mechanical vibration, noise and overvoltage, make transformer local and serious overheat. Harmonic makes ageing of the equipment overheat such as capacitor, cable, insulation, loss of life, down to attaint.

(3) harmonic can cause the local shunt-wound resonance in public electrified wire netting and series connection resonance, make harmonic magnifies thereby, this makes afore-mentioned (1) and (2) the harm increases greatly, cause casualty even.

(4) the misoperation that harmonic can bring about protection and automatic device, can make electric measuring instrument is expressed metric not accurate.

(5) harmonic will be right adjacent communication system generates interference, light person generation noise, reduce communication quality; The person that weigh brings about abode to lose, make communication system cannot work normally.