Results of a novel algorithm for the calculation of the characteristic temperatures in power oil transformers

Radaković, Zoran; Kalić, Dj.

doi:10.1007/bf01235716

Cited by 24 publications

(27 citation statements)

References 6 publications

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“…The most realistic case is that only measurements of top oil are available (no special measurements during heat run test such as described in [2] nor fiber optics measurements of winding temperature). In this case, the thermal capacity of oil, core, and tank ( C OCC ) can be determined accurately and the thermal capacitance of the windings approximately (Eqs.…”

Section: Determination Of Parameters Of Thermal Networkmentioning

confidence: 99%

“…If data about the change of top oil temperature during a transient thermal process are available, thermal capacitances can be determined using a numerical estimation method [2,12]. The most realistic case is that only measurements of top oil are available (no special measurements during heat run test such as described in [2] nor fiber optics measurements of winding temperature).…”

Section: Determination Of Parameters Of Thermal Networkmentioning

confidence: 99%

“…(1)- (3)) are determined using results of software for thermal calculations based on the detailed THNM for the above specified loads of 60%, 70%, 80%, 85%, 90%, 95%, and 100% of rated load. Since there are two parameters in function (1)- (3) for each of the thermal conductances, these two parameters can theoretically be determined from the values of the losses and calculated temperature differences in two steady states ( (1) and (2)) as (example for K to and n to ): (2) ln (ϑto−ϑa) (1) (ϑto−ϑa) (2) − 1 (8)…”

Section: Determination Of Parameters Of Thermal Networkmentioning

confidence: 99%

“…As explained in [2], it can be done from the recording of the average winding temperature during transient thermal processes, applying a numerical method for parameter estimation.…”

Section: Determination Of Parameters Of Thermal Networkmentioning

confidence: 99%

“…These data can be: a) results of calculation in the design phase, based on detailed construction, b) factory heat run tests results, and c) measurements during operation of the transformer. An example of parameterization of a thermal model based on data measured in heat run tests is presented in [2]. Reference [3] describes a model oriented to top oil temperature, requiring no data from the design stage and no data from heat run tests.…”

Section: Introductionmentioning

confidence: 99%

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Thermal model of oil power transformers with a tap changer

Radaković¹,

Tenbohlen²

2016

Turk J Elec Eng & Comp Sci

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Abstract:The paper presents a new method for on-line temperature calculation taking into account change in the tap changer position. The method introduces accurate calculation of the losses, depending on the current, average temperature of the winding, and tap changer position (it affects both Joules (DC) losses and stray losses). The thermal model itself is the common three-body model (for a transformer with two windings per phase), with temperature dependent thermal conductances. Elements of the model describing steady-state characteristics are determined based on detailed construction and calculation of distribution of losses in the windings using the finite-elements method (FEM) and calculation of distribution of temperatures using the detailed thermal-hydraulic network model (THNM). Detailed calculation of the losses and temperatures enables the determination of the hot-spot factor ( H = Q S) ; factor Q describes the nonuniform losses and factor S describes nonuniform cooling. The paper shows how these factors depend on tap changer position and the load.

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Section: Determination Of Parameters Of Thermal Networkmentioning

confidence: 99%

Section: Determination Of Parameters Of Thermal Networkmentioning

confidence: 99%

Section: Determination Of Parameters Of Thermal Networkmentioning

confidence: 99%

“…As explained in [2], it can be done from the recording of the average winding temperature during transient thermal processes, applying a numerical method for parameter estimation.…”

Section: Determination Of Parameters Of Thermal Networkmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermal model of oil power transformers with a tap changer

Radaković¹,

Tenbohlen²

2016

Turk J Elec Eng & Comp Sci

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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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Loading of transformers in conditions of controlled cooling system

Radaković

Jacic

Lukić

et al. 2012

Int. Trans. Electr. Energ. Syst.

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SUMMARY The paper deals with thermal modelling of transformers with automatic control of the cooling system. The case study was done on 725 MVA transformer with OFAF cooling, having eight compact coolers, each of them with their own pump and hysteresis control: four coolers, when top oil temperature drops below 30 °C, and six coolers, when top oil temperature rises above 45 °C. The consequence of operation with different number of coolers is change of thermal characteristics of the transformer. Additional phenomenon causing change of thermal characteristics is fouling of the coolers. These variable thermal characteristics are included in mathematical models used for the calculation of top oil and hot‐spot temperatures in all applications of such calculation algorithms: protection, monitoring, estimation of overload capability, calculation of thermal ageing, etc. Copyright © 2012 John Wiley & Sons, Ltd.

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Results of a novel algorithm for the calculation of the characteristic temperatures in power oil transformers

Cited by 24 publications

References 6 publications

Thermal model of oil power transformers with a tap changer

Thermal model of oil power transformers with a tap changer

IEC 60076-7 loading guide thermal model constants estimation

Loading of transformers in conditions of controlled cooling system

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