Distribution Transformer Due to Non-linear Loads

Transcription

1 RESEARCH ARTICLE Derating of OPEN ACCESS Ditribution Tranformer Due to Non-linear Load Vihakha L. Mehram 1, Mr. S. V. Umredkar 2 Department of Electrical EngineeringShri Ramdeobaba College of Engineering and Management,Nagpur, India vihakhamehram.28@gmail.com ABSTRACT The tranformer are deigned and ued for different type load, at rated frequency and balanced upply voltage. Now a day energy efficiency of electrical load device increae with olid-tate electronic. But, due to the ue of non-linear load uch a computer, variable peed drive in heating ventilation and air conditioning ytem and electronic ballat of fluorecent lamp, harmonic ditortion i increaing in the commercial load and ervice. Becaue of thi reaon harmonic i injected into the power ytem. The ue of non-linear load on electrical power ytem caue different loe and aging problem of tranformer. To prevent thi problem rated capacity of tranformer upplying non-linear load mut be reduced. Tranformer derating i ued for minimizing harmonic ditortion in ditribution tranformer. In thi paper the imulation are performed uing Math work MATLAB on 50KVA ingle phae tranformer for derating purpoe. Keyword : Derating, Harmonic loe, non-linear load I. INTRODUCTION Power ytem operate at frequencie of 50Hz. However, certain type of load produce current and voltage with frequencie that are integer multiple of the fundamental frequency(50hz). Thee higher frequencie are a form of electrical pollution known a power ytem harmonic. Tranformer are the major component in power ytem and increaed harmonic ditortion can caue exceive winding loe and hence abnormal temperature rie. Temperature rie of tranformer due to noninuoidal load current wa dicued in IEEE Tranformer Committee in March 1980 [1].Rating ytem ha developed called K-factor, a deign which i capable of withtanding the effect of harmonic load current. An application of thi rating ytem to pecify a tranformer for a particular environment require knowledge of the fundamental & harmonic load current. Electrical inulation ued in ditribution tranformer get degraded when it i ubjected to the thermal, electrical, power quality problem like harmonic and variation in frequency are reponible for accelerated aging of it inulating material. A tranformer deigned without conidering all thee iue will reult into premature failure. Baically tranformer conit of ordinary parameter uch a leakage inductance and dc reitance, magnetizing inductance and core reitance that obtain from no-load tet, hort circuit tet and dc tet. In thi tray loe that conit of eddy current loe loe are proportional to frequency i more coniderable. II. HARMONIC DEFINITION A harmonic voltage or current frequency i integer multiple of the fundamental frequency. Thee harmonic ource have non-linear characteritic and thee harmonic ource reult in multiple of fundamental frequency or ytem frequency. The fundamental component i firt harmonic or rated frequency. Thi voltage and current harmonic are generated in power ytem by harmonic producing load. Switching equipment ued in indutrial production proce or electrical indutry caue harmonic [2]. III. TRANSFORMER LOSSES Tranformer loe conit of no-load or iron lo or core loe and load loe. A given in equation below. P T =P NL +P LL (1) Where, P NL i no-load loe, P LL i load loe, P T i total lo. No load lo i due to induced voltage in the core. Load loe conit of ohmic lo, eddy current lo, and other tray lo. in winding and other tray loe are not conidered. When tranformer upplying harmonic load thee PLL= PDC+ PEC+ POSL (2) 28 P a g e

2 Where, P DC i lo due to rated current and dc reitance of the winding, P EC i the winding eddy current lo; P OSL i other tray loe in clamp tank, etc. Winding eddy loe conit of eddy current loe and circulating current loe, which are conidered to be winding eddy current loe. Other tray loe are in tructure other than winding, uch a clamp, tank or encloure wall. And for high frequencie ( Hz) the reitance i In modern power ytem, the total harmonic voltage ditortion i normally below 5% and the magnitude of the voltage harmonic component are mall compared to fundamental component. Therefore voltage harmonic effect are neglected. The current harmonic are more ignificant. Thee harmonic load current component caue additional loe in the winding and other tructural part [1]. A. Eddy current loe in winding There are two effect that caue increae in winding eddy current loe, namely the kin effect and proximity effect. The winding eddy current lo in power frequency pectrum tend to proportional to the quare of the load current and quare of the frequency due to both kin effect and proximity effect [2]. IV. HARMONIC EFFECT ON LOAD LOSSES [5] EC I 2 x f 2 (3) A. Effect of harmonic on dc loe Type of Load K- factor Incandecent lighting Electric reitance heating, K-1 Motor, Control tranformer without olid tate controller. Electric dicharge lighting UPS, Induction heating K-4 equipment, Welder, PLC. Telecommunication Equipment, UPS without K-13 filtering, General health care and claroom of chool, Variou teting equipment. Mainframe computer load, Motor with VFD, K-20 Health care equipment in critical care area and operating room of hopital. Multi-wire receptacle circuit in indutrial K-30,medical, educational laboratorie etc. Load producing high order harmonic K-40 Other tray loe increae with power of 0.8 at low frequencie and decreae at high frequencie with power of 0.9. Hence other tray loe can be calculated a POSL = PTSL PEC (6) The other tray lo reitance for the primary and econdary ide in term of other tray lo at rated current 29 P a g e

3 Skin effect Skin effect i the trend of current to flow on the circumference of the wire o that the current denity i greater at the urface than at the core. High frequency noie in the range of 1kHz-1.5MHz increae the inductive reactance of the wire. Thi force the electrical charge toward the outer urface of the wire. Thi mean that the total available pace of the wire i not ued to carry the electrical power. Proximity effect [3] Thee loe will increae with quare of load current. A dc component of the load current will increae the tranformer core lo lightly due to bu bar connection, tructural part, tank are proportional to the quare of the load current and the harmonic frequency to the power of 0.8. Harmonic lo factor for other tray loe ) B. Effect of harmonic on eddy current loe: Winding eddy current lo (P EC ) in power frequency pectrum tend to proportional to quare of the load current and quare of frequency Along with kin effect, proximity effect i a common problem found in every electrical ytem. Proximity effect i defined a the jumping magnetic field from one conductor to another conductor nearby. The major caue of proximity effect are cloene of the wire, bend in the wire, kin effect and high frequency noie. B. Other tray loe in tranformer Fluxe in tranformer and inductor induce eddy current in metallic part over the urrounding e.g., encloure and clamp. The eddy current loe outide the winding are other tray loe a loe in core, clamp and tructural part will increae with quare of the load current but not proportional to the rate of frequency. The ac reitance of the other tray loe at low frequencie (0-360Hz) i equal to [3]: The harmonic lo factor for winding eddy current Effect of harmonic on other tray loe The heating due to other tray lo i not conidered for dry type tranformer but having effect on oil filled tranformer. Therefore loe DERATING OF TRANSFOREMR Derating i ued to reduce the tranformer KVA loading uch that total tranformer loe are limited to rated loe. The main method for etimating tranformer derating are: K-Factor, Harmonic Lo Factor, online harmonic lo meaurement and computed harmonic loe [4]. The IEEE tandard. C [5] introduced a term called the K-factor for rating a tranformer a per their capability to handle load current with ignificant harmonic content.it i an alternate technique for tranformer de-rating which conider load characteritic. It i a rating applied to a tranformer indicating it uitability for ue with load that draw non-inuoidal current. It i an index that determine the change in conventional tranformer mut undergo o that they can diipate heat due to additional iron and copper loe becaue of harmonic current at rated power. Hence the K-factor can be given a And the relation between K-factor and F HL i given a ( ) TABLE1 TRANSFORMER K-RATINGS [6] V. TRANSFORMER MODEL The total flux linking the primary coil in linear load i the um of magnetizing flux limited to the iron core and the primary leakage flux which link only primary coil. In non- linear load Φ1=Φl1+Φm+ Φec,1+ Φol,1 (17) 30 P a g e

4 Secondary current ha a negative polarity in repect of primary current. Therefore total flux in econdary winding i: Voltage V 1 can be further reduced to: V 1 V 2(V) I 1 (A) I 2(V) P 0 (W) P LL(W) P dc (W) (V) Φ2= -Φl2- Φm-Φec,2- Φol,2 (18) Where, Φ l2 =Secondary leakage flux, which link only econdary coil Φ m = Magnetizing flux confined to iron core Φ ec,2 = econdary winding flux which cut through econdary winding Φ ol,2 = Secondary other tructural part flux which cut through the tructural part or tank of the tranformer The upply voltage include reultant mutual flux, in the core that bring about magnetizing current. Thi can be expre a [7]: The total flux in primary and econdary coil i:the primary voltage V 1 and the econdary voltage V 2, at the terminal of the tranformer are given in term of Ohm and Faraday law:primary and econdary voltage can be expre in current by ubtitution of (20) into (22) and (21) into (30) TABLE 2 TRANSFORMER DATA TABLE 3 HARMONIC LOAD SPECIFICATION[6] Where, i equal to the induced emf in the primary coil. The voltage V 2 in the econdary coil i i equal to the induced emf in the econdary coil. h I h /I (I h /I) 2 h 2 (I h /I) 2 h 0.8 h 0.8 h 2 (I h /I) e^ e^ With the help of above equation the equivalent tranformer model i hown in fig (1) below. Fig how controlled voltage ource of V ec and V ol in erie with dc reitance and leakage inductance. 31 P a g e

5 (IL) Load current - V PQ International Journal of Engineering Reearch and Application (IJERA) ISSN: i1 i1 Linear Tranformer V V L l1 R dc1 Vec1 o l, 1 L l2 o l, R dc 2 Vec, 2 2 RMS + R MS 1 v V I Active & Reactive 1 P ower In1 -K Out1 In2 Ll1 Integrator RMS Subytem R MS i I Scope v VS 1 2 e1 e 2 V 1 LmRc V Fig. 2 Simulation model of tranformer Fig. 1 Equivalent tranformer model for harmonic tudie Harmonic ource VI. SIMULATION MODEL [8] Simulation model for 50KVA 2400/240V ingle phae tranformer imulated in MATLAB/Simulink hown in fig(2). Model how the harmonic load connected at the econdary of tranformer. The load conit of current ource in parallel with different frequencie and magnitude. The harmonic load pecification i given in Table 3 how harmonic order and per unit value. The current waveform for the harmonic load i hown in fig (3) v RMS - Dicrete, V1 R MS 4 = 5e i RMS R MS 2 powergui In1 1 Scope Ou t1 -K- In2 Ll2 Integrator1 Subytem1 - VS1 I2 + - Conn1 Fig. 3 Current waveform for non-linear load Total tray loe P TSL can be calculated a follow; P LL-R (pu)=1+ P EC-R (pu)+ P OSL-R (pu) (16) P LL-R (pu)= pu Time P TSL =P EC + P OSL = P LL -P dc = =144.56w The winding eddy current and other tray loe can be calculated a : P EC = =47.70w (0.33 for oil-filled tranformer) P OSL = =96.85w Hence, rated load loe when applied to linear load i I max(pu) = 0.826pu [ ] [ ] Equivalent KVA can be obtain a follow: Equivalent KVA= =41.316KVA VII. CONCLUSION The tudy of harmonic impact on ditribution tranformer i important becaue tranformer i important equipment in power ytem. The harmonic loe factor for eddy current winding and other tray loe ha been computed to evaluate the equivalent KVA of the tranformer and permiible current for upplying non-linear load calculated analytically. Derating i 32 P a g e

6 tudied in order to mitigate harmonic ditortion problem. VIII. ACKNOWLEDGMENT The author would like to thank department of electrical engineering of Shri. Ramdeobaba College of engineering and management, Nagpur REFERENCES [1] S. B. Sadati, H. Youufi, B. Darvihi, "Comparion of ditribution tranformer loe and capacity under linear and harmonic load," in nd IEEE Power and Energy. [2] O. C. Gedult, I. Hofajer, The impact of harmonic ditortion on power tranformer operating near thermal limit, Univerity of Johanneburg diertation oct2005 [3] D. Yeldirim, E. F. Fuche, Meaured tranformer derating and comparion with harmonic lo factor, IEEE Tranaction on power delivery, vol. 15, no. 1, january [4] M. A. S. Maoum, P. S. Moe, and S. Deilami, Student Member, Load Management in Smart Grid Conidering Harmonic Ditortion and Tranformer Derating, Innovative Smart Grid Technologie (ISGT), 2010 [5] IEEE Std C , IEEE Recommended practice for Etablihing Tranformer capability when upplying Non inuoidal Load Current. [6] S. S. Devkar, L. M. Waghmare, Analyi of ditribution tranformer performance under non-linear balance load condition and it remedial meaure, International Journal of Emerging Technology and Advanced Engineering Webite: (ISSN , Volume 1, Iue 2, December 2011). [7] S.V. Kulkarni, S.A. Khaparde, Tranformer Engineering Deign and Practice, Indian Intitute of Technology, Bombay Mumbai, India, 2004 [8] S. B. Sadati,A.Tahani, Derating of tranformer under non-inuoidal load,in 2008.OPTIM 11 th international conference. 33 P a g e