3rd Iteratioal Coferece o Machiery, Materials ad Iformatio Techology Applicatios (ICMMITA 05) Desig of distributio trasformer loss meter cosiderig the harmoic loss based o oe side measuremet method HU Xi, a, ZENG Jiag,b, School of Electric Power, South Chia Uiversity of Techology, 50080 Guagzhou, Guagdog, Chia a 054497408@qq.com, b787793@qq.com Keywords: distributio trasformer; oe side measuremet; harmoic loss; Abstract. I power system, a large sum of harmoic produced by o-liear load will affect the loss of trasformers. I the meawhile, the traditioal methods to measure the loss do ot have eough adaptability. By aalyzig the priciple of oe side measuremet ad two sides measuremet methods, ad makig study o the harmoic copper loss ad harmoic iro loss, a progressed distributio trasformer loss meter cosiderig the harmoic loss is desiged i this paper. The meter with high precisio, strog adaptability ad operability has a wide applicatio prospect. Itroductio With the icrease of atioal ecoomy, the demad for eergy is beig expaded largely. As to be the mai equipmet of trasferrig voltage, curret ad power, trasformer which has a huge sum of quatity plays a importat role i power system, ad the quatity is beig icreased by the year[]. Despite of the little loss of each trasformer, cosiderig the large sum ad the log ruig time, the total loss of trasformers every year are surprisigly huge. I the meatime, old type trasformers are still used i some areas of which the loss are much higher tha the ew oes. As a result, it is ecessary to ehace the eergy efficiecy level ad lower the eergy loss by replacig old trasformers with ew oes[,3]. So accurate measuremet of trasformer s loss is eeded to provide basic data, i order to chage trasformers reasoably. So far, most commo way to measure trasformer loss is traditioal two sides measuremet method, which is to get the loss by measurig both sides of the trasformer. O oe side, high measuremet coditio is required i this kid of measuremet method. O the other side, with more ad more o-liear devices beig used i power system, large harmoics is produced[4], while traditioal ways do t cosider the loss caused by harmoics which leads to some errors. This article desiged a oe side trasformer loss meter cosiderig harmoic loss after aalyzig the differet loss of trasformer. Loss Calculatio Priciple of Distributio Trasformer Loss Costitutio of Trasformer. After the study of trasformer ruig priciple, it is foud that the loss of trasformer ca be divided ito four parts, of which the iro loss ad copper loss are the mai parts, almost accouts for 90 percet of the total loss. The rest are stray loss ad dielectric loss. Cosiderig the fact that the latter two kids of losses are very little compared with the former two losses, stray loss ad dielectric loss are usually eglected[5]. Magetic hysteresis loss is produced whe magetizig velocity of iro-core material is smaller tha the chagig velocity of exteral magetic field. Ad i the meawhile, the chagig iduced electromotive force will geerate the correspodig iduced curret, which make eergy loss by high temperature of iro-core material. This loss is called eddy-curret loss. Besides, there is still aother kid of loss called added loss[6]. Magetic hysteresis loss ad eddy-curret loss, which are called basic iro loss, costitute the mai part of iro loss. While added loss is small eough to be igored. So the formula of iro loss is show i Eq.. 05. The authors - Published by Atlatis Press 94
P = P P = K f B K fb. () Fe H + E H m + E m P H, P E are eddy-curret loss ad Magetic hysteresis loss, K H, K E are proportioality coefficiets of two losses, f is frequecy, B m is the max magetic flux desity. O the other side, eergy loss will produced whe there is curret flow through resistace, which is called copper loss. I trasformer, because of ski effect ad proximity effect, copper loss ca be divided ito added copper loss ad basic copper loss. Basic copper loss is regard as the eergy loss caused by the high temperature of coil widig whe curret flow through resistace. Ad added loss is the extra loss caused by the icrease of widig equivalet resistace[7]. The added loss has a small proportio i distributio trasformer, which also ca be igored. So the copper loss shall be expressed i Eq.. P = I R + I R. () Cu I, I are curret o both sides of trasformer, R, R are widig resistace of two sides of trasformer. While i practical applicatio, the iro loss ad copper loss is usually replaced with o-load loss ad load loss. Two sides measuremet method. I commo coditio, the curret ad voltage of high voltage ad low voltage sides will be measured to get the power of both sides, the trasformer loss ca be calculated by the differece of the two power value. As to the three-phase trasformer. P= UIcosϕ UI cosϕ. (3) ΔP is power loss of trasformer, U, I are voltage ad curret of primary side, ϕ is phase agle of primary side, U, I are voltage ad curret of secodary side, ϕ is phase agle of secodary side. Cosiderig the fact that high precisio measuremet devices are eeded i both sides of the trasformer whe usig this traditioal measuremet method, which highly raise the ecoomy costs, so a ew oe side measuremet method is proposed i this article. Oe side measuremet method. Accordig to the former aalysis, trasformer loss is made up by iro loss ad copper loss, which ca be replaced with o-load loss ad load loss i practical applicatio. So the iro loss is expressed through further derivatio. u P u PFe = = u = P. (4) R U U 0 0 Fe N N u is voltage, P 0 is rated o-load loss, U N is rated voltage. Similarly, copper loss ca be expressed as: P PU P = ir = i = i. (5) Cu k k N T IN SN i is curret, R T is widig resistor, P k is rated load loss, S N is rated capacity. Thus, the formula of trasformer loss i oe side measuremet method ca be got. u i P = PFe + PCu = P0 + P. (6) k UN IN Therefore, oly oe side of trasformer will be measuremet with oe side measuremet method based o the practical coditio. What s more, o the coditio of same precisio measuremet 95
devices, error of oe side method is smaller tha two sides method, ad oe side method is more reasoable whe put ito use. As a result, this article desiged a trasformer loss meter based o the oe side method priciple. Calculatio Priciple of Distributio Trasformer Harmoic Loss I recet years, with the applicatio of power electroic equipmet like SVG STATCON SVC, lots of harmoics produced correspodigly. Ad the harmoics lead to the icrease of iro ad copper losses. So the harmoic loss also ca be divided ito harmoic iro loss ad harmoic copper loss. It will be aalyzed below. Priciple of Harmoic Loss. Firstly, build up the t-type equivalet circuit of trasformer affected by the th harmoics. R() X() R() X() I() R(m) I() X(m) Fig.. T-type equivalet circuit of trasformer affected by the th harmoics R(), X() are harmoic resistace ad reactace of primary side, R(), X() are harmoic resistace ad reactace of secodary side, R(Fe), X(Fe) are excitatio resistace ad reactace, I(), I() are th harmoics of primary ad secodary sides. Uder the effect of harmoics, the RMS curret will icrease, leads to the elargemet of loss o coil widig. The icreased loss is harmoic copper loss. I order to gai the loss, superpositio priciple is applied which is to cosider every harmoics as idepedet power supply[8]. I the ed, the total harmoic copper loss ca be got. As to sigle phase trasformer, the expressio of harmoic copper loss is show below. Cu ( () () () ()) = P = I R + I R. (7) Similarly, magetic hysteresis loss ad eddy-curret loss will be bigger because of the harmoics, which make the icrease of iro loss. The icreased part ca be reflected by the loss o excitatio resistace. The harmoic iro loss is expressed as Eq. 8 accordigly. Fe ( ( ) ( )) = P = I Fe R Fe. (8) So the total harmoic loss is: ( () () () () ( ) ( )) = P = I R + I R + I Fe R Fe. (9) Calculatio of Harmoic Loss. It is easily foud from Eq. 9 that the harmoic ad harmoic parameters should be measured i order to get harmoic loss. Harmoic curret could be detected by special devices. While as to the harmoic parameters, scholar from Uiversity of Clmeso made repeated short-circuit test ad o-load test by cotrollig the order of harmoics, ad parametric polyomial is achieved through mathematical fittig[9]. R () / R () 0.9663608e 0.0685 =. (0) 96
3 = +. () X () / X () 0.9987983 0.5393 0 0.35955 0 R () / R () 0.9663608e 0.0685 =. () X () / X () 0.9987983 0.5393 0 0.35955 0 3 = +. (3) R ( Fe) / R ( Fe) 0.7060448503 0.4840685 0.6485 0 = +. (4) X ( Fe) / X ( Fe).077990695 0.066464 0.955 0 = +. (5) is the order of harmoics. 0.0685 Defie k() = k() = k = 0.9663608e. It s thus clear that harmoic resistace parameters is i direct proportio to fudametal harmoic resistace parameters. Therefore, the harmoic resistace whe calculatig copper loss ca be expressed as Eq. 6. R = kr. (6) T So the harmoic copper loss expressio is show below: PCu 3 I R = I = 3I R = I = 3I RT khri = = PCu khri = =. (7) I is fudametal harmoic curret, HRI is every order of harmoic curret. Also defie kfe = R ( Fe)/ R ( Fe). So the harmoic iro loss is deduced. P = Fe = U R = U U R ( Fe) = kfeu PFe HRU = kfe =. (8) U is fudametal harmoic voltage, HRU every order of harmoic voltage. Accordig to the aalysis, the total harmoic loss ca be expressed cosiderig the harmoic effect. 97
total = Cu (+ = P P k HRI ). (9) + PFe ( + HRU ) k = Fe Desig of Comprehesive Loss Meter of Distributio Trasformer Priciple of Loss Meter. O the basis of former aalysis, loss of fudametal harmoic parameter ad loss of differet harmoic parameter should be cosidered separately i order to get the total loss. Thus, firstly measure to get the oe side real time ruig data with PT ad CT. The obtai the fudametal harmoic ad harmoic compoet by calculatio. Accordig to the calculative process of copper loss ad iro loss, fudametal harmoic total loss by Eq. 6; ad the harmoic loss ca be got based o the harmoic copper loss ad harmoic iro loss of differet order. After that, the total harmoic loss is got through Eq. 9. At last, add the two parts of losses to gai the total loss of trasformer. The itegrated priciple of loss meter desiged i this article i show i Fig.. start Obtai data from PT,CT Calculate to get U,I,U,I Calculate the fudametal harmoic loss based o oe side method Calculate total harmoic loss Add to gai the total loss of trasformer ed Fig.. The itegrated priciple of loss meter Desig of Hardware Circuit. ) CT/PT. CT/PT is used to get the voltage ad curret data from trasformers. I order to make the meter has widely applicatio, the precisio demad of CT/PT is comparatively high. Cosiderig the commo three-phase trasformer, the three-phase voltage ad curret value ca be got through two CT/PT. Curret trasformer LA58-P ad voltage trasformer CLSM-0MA are used i this meter. ) Coditioig circuit. Operatioal amplifier costitute the voltage ad curret follower to coditio the origial voltage ad curret sigal I a, I b, U ba, U cb, make it adapt to the iput of ADC. 3) ADC. The four sigal after coditioig will be coverted to digital sigal by MAX34. The ADC module has multi-chael sigal, but 4 chael are used, the rest coected to groud. The output precisio is 4 bits. 4) DSP8.8 is the core module of the whole circuit, which is used to process ad operate the sigals to get the fial result. Firstly, the iput sigals based o I c = -(I a +I b ) ad U ca =U ba +U cb to obtai three-phase voltage ad curret value. The calculate the harmoics of differet orders by FFT. So the fudametal harmoic loss ad harmoic loss ca be got through Eq. 6 ad Eq. 9. I the same time, add to gai the total loss of trasformer. 98
5) Commuicatio module. Zigbee is applied to receive data from DSP, ad trasmit to the display scree ad database for observatio ad storage. The mai hardware circuits accordig to the precedig text aalysis are show below: Fig. 3. Samplig circuit Fig. 4. Sampled sigal coditioig circuit Fig. 5. ADC circuit Summary I power system, with the cotiuous appearace ad applicatio of o-liear load, lots of harmoics produced which leads to ifluece to trasformer ad higher the loss. The loss meter desiged i this article also cosider the loss caused by harmoics, ad ca get a comparatively precise result after appropriate simplificatio. Sice usig the oe side measuremet idea istead of two sides method, measuremet devices oly eed to be istalled o oe side of the trasformer, which highly exteds the applicatio rage, guaratee the precisio ad decrease risk of operatio. It has a good applicatio prospect i the developmet of eergy savig, cost reducig ad eergy efficiecy icrease. 99
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