A new method for the calculation of the hot-spot temperature in power transformers with onan cooling

Radaković, Zoran; Feser, K.

doi:10.1109/tpwrd.2003.817740

Cited by 109 publications

(28 citation statements)

References 4 publications

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“…By analysing measured results from tested power transformers, it has been noticed that the hot‐spot temperature rise over top‐oil temperature following load changes is a function depending on time as well as the transformer loading (overshoot time‐dependent function), Figure . Similar results were obtained for distribution transformers with external cooling, . The maximum values and shapes of this function (represented in terms of the overshoot factor Bp ) for different transformers with external cooling, different loadings, different oil circulation modes in the windings (zigzag and axial), and different cooling modes are given in .…”

Section: Introductionsupporting

confidence: 70%

“…Pierce's method is also presented as a more complex dynamic hot‐spot temperature calculation procedure in the IEEE Loading Guide Annex G in . As already stated above, Radakovic performed thermal tests on distribution transformers with external cooling, , where he observed the same phenomenon and suggested a calculation procedure based on the bottom‐oil temperature and application of the lumped capacitance theory. Also, Susa focuses specifically on further refinement in the definition of the nonlinear thermal resistances (by considering specific design differences between the transformer windings and vertical plates, and consequently, the fluid flow around their surfaces) and the relevant thermal models.…”

Section: Introductionmentioning

confidence: 60%

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IEC 60076-7 loading guide thermal model constants estimation

Susa

Nordman

2012

Int. Trans. Electr. Energ. Syst.

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When fiber optic probes were taken into use to record local hot-spots in windings and oil ducts, it was noticed that the hot-spot temperature rise over top-oil temperature due to load changes is a function depending on time as well as the transformer loading (overshoot time dependent function). This results in winding hottest spot temperatures higher than those predicted by the old loading guide during transient states after the load current increases, before the corresponding steady states have been reached.The new loading guide, (IEC 60076-7), takes into account these findings by introducing two thermal models. The first one, which is given as an exponential equation solution, is suitable for a load variation according to a step function. This method is particularly suited to determination of the heat transfer parameters by test, especially by manufacturers. The second one, which is given as a differential equations solution, is suitable for arbitrarily time-varying load factor K and time-varying ambient temperature θa. This method is particularly applicable for on-line monitoring. This method is a mathematical variation of the exponential model. A significant advantage of the suggested thermal models is that they are tied to measured parameters that are readily available (i.e., data obtained from a non-truncated heat run test performed by the transformer manufacturer).However, it has been reported recently by many users that this new approach causes a lot of technical hitches. It is unclear when and why the exponential method should be used instead of or the differential method and vice versa. Also, is there any difference between the recommended models, especially in their output? How the new thermal constants, (k 11 , k 21 , and k 22 ) , should be applied and how they could be derived? Answers to these questions and more are given in the text below.

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Section: Introductionsupporting

confidence: 70%

Section: Introductionmentioning

confidence: 60%

IEC 60076-7 loading guide thermal model constants estimation

Susa

Nordman

2012

Int. Trans. Electr. Energ. Syst.

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“…Thermal models of a power transformer based on the principles of heat exchange and electric circuit law have been developed by some authors [3–6]. Not only assumptions need to be made but the location and temperature of the hottest spot might also change in versatile cooling systems used by different OFT transformer constructions [7,8].…”

Section: Introductionmentioning

confidence: 99%

A study on hot spot detection possibility in simulated oil‐filled‐type transformer tank by using ultrasonic methods

Chen¹,

Zhi-cheng²

2011

IEEJ Transactions Elec Engng

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Failure of oil-filled-type (OFT) power transformers usually results in very big losses comprising the loss of the transformer itself as well as production loss in industry. Most of the energy lost in OFT transformers, induced by faults, will become heat at a location close to the fault, which then becomes a hot spot. The detection of hot spots in OFT transformers can be an effective way for transformer fault location and diagnosis. As the OFT transformer enclosure is completely sealed and is opaque, to date there is no effective way to find out hot spots in them. It is known that ultrasonic energy can be transmitted into the sealed transformer enclosure which is filled with the fluid, and ultrasonic waves can be affected by the temperature of the materials they propagate through; so the ultrasonic method can be a possible method for hot spot detection. In this paper, we describe a study on the possibility of developing a method to detect hot spots in an environment filled with a fluid, simulating a transformer. Trails using a different times-of-flight (TOFs) evaluation techniques and attenuation measurement of the ultrasonic energy propagated were carried out, which showed encouraging results for locating the hot spot as well as measuring the hot spot temperature in fluids; we also discuss the possibility of applying these results to the diagnosis of OFT transformers eventually. 

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“…In the steady-state condition, transferred thermal energy is equal to zero [5], but in transient condition, transferred thermal energy to the unit appears as an increase in total energy of the unit. In this case, unit behaves as an integrated capacitor and equation (2) can be rewritten as shown in (3) [7].…”

Section: Introductionmentioning

confidence: 99%

A dynamic thermal based reliability model of cast-resin dry-type transformers

Azizian

Bigdeli

Fotuhi-Firuzabad

2010

2010 International Conference on Power System Technology

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In this paper, some models have been introduced for dynamic thermal modeling of cast-resin transformers which are based on genetic algorithm. A typical 400kV A cast-resin transformer has been selected and the model parameters are estimated and validated with the help of experimental data extracted from different load cycles. The estimated models are used to generate a reliability model for cast-resin dry-type transformers and the effects of variation in load, ambient temperature and atmosphere conditions on the reliability of cast resin transformer are illustrated.As it will be shown in this paper, the effects of working conditions on the life-time of insulation in dry-type transformers is very considerable and because of highest temperature range (in comparison with oil-immersed transformer), reliability is more sensitive to variation of load, ambient temperature and atmosphere conditions.

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A new method for the calculation of the hot-spot temperature in power transformers with onan cooling

Cited by 109 publications

References 4 publications

IEC 60076-7 loading guide thermal model constants estimation

IEC 60076-7 loading guide thermal model constants estimation

A study on hot spot detection possibility in simulated oil‐filled‐type transformer tank by using ultrasonic methods

A dynamic thermal based reliability model of cast-resin dry-type transformers

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