| 1. |
- Arifianto, I., et al.
(författare)
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Investigation of transformer top-oil temperature considering external factors
- 2012
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Ingår i: Condition Monitoring and Diagnosis (CMD), 2012 International Conference on. - : IEEE. - 9781467310208 ; , s. 198-201
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Konferensbidrag (refereegranskat)abstract
- Standard estimation of top-oil temperature uses a thermal model related to load changes and variation of ambient temperature. Attempts have been done to improve the accuracy of top-oil temperature calculations by introducing internal properties into the model i.e. oil viscosity and winding resistance. The interest of this paper is to investigate the effect of external factors on top-oil temperature by looking into the weather, i.e. wind velocity. The results are compared with measurements on a 63MVA-ONAF 55/140 kV transformer unit, which is operated in ONAN cooling mode. The unit is located in subarctic climate, and it is equipped with a monitoring system and a weather station.
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| 2. |
- Edström, Fredrik, et al.
(författare)
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Influence of Ambient Temperature on Transformer Overloading During Cold Load Pickup
- 2013
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Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 28:1, s. 153-161
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a method to investigate the socioeconomical aspects of transformer overloading during a cold load pickup (CLPU) in residential areas. The method uses customer damage functions to estimate the cost for their power interruption and a deterioration model to estimate the cost for transformer wear due to the CLPU. A thermodynamic model is implemented to estimate the peak and the duration of cold residential load. A stochastic differential equation is used to capture the volatility of the load and to estimate the probability for transformer overloading. In a numerical example, an optimal cold load pickup for a two-area system is demonstrated where transformer overloading is allowed. In this example, an ambient temperature threshold is identified, where transformer overloading is socioeconomically beneficial.
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| 3. |
- Edström, Fredrik, et al.
(författare)
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Modeling Impact of Cold Load Pickup on Transformer Aging Using Ornstein-Uhlenbeck Process
- 2012
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Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 27:2, s. 590-595
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Tidskriftsartikel (refereegranskat)abstract
- Thermostatically controlled devices, such as air conditioners, heaters, and heat pumps may cause cold load pickup (CLPU) problems after a prolonged blackout. This causes an increased load on the power components in the electrical grid. The result is unpredictable aging and increased risk of failure. Quantifying this risk is crucial for efficient asset management for cost-intensive components such as the transformer. This paper presents a new approach to model the loading profile of a CLPU using stochastic differential equations. The realization of the loading profile is used to determine the aging of a transformer. Two models for the deterioration of transformer solid insulation represent the loss of life due to the CLPU. A comparison between two models for the aging of the solid insulation in the transformer is made in a case study. Due to the stochastic behavior of the load, there is a probability for loading the transformer above the recommended ratings, and this probability is estimated with Monte Carlo simulations.
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| 4. |
- Grahn, Pia, et al.
(författare)
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A method for evaluating the impact of electric vehicle charging on transformer hotspot temperature
- 2011
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Ingår i: 2011 2nd IEEE PES International Conference and Exhibition on Innovative Smart Grid Technologies (ISGT Europe). - : IEEE.
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Konferensbidrag (refereegranskat)abstract
- The expected increasing market share of electric vehicles is a response to the combination of new technological developments, governmental financial control, and an attitude shift of residents to a more environmentally friendly lifestyle. The expected capacity required for charging, imposes changes in the load to the already existing components in the electric power grid. In order to continue managing these existing assets efficiently during this load change, it is important to evaluate the impact imposed by the battery charging.
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| 5. |
- Hilber, Patrik, et al.
(författare)
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Benefits of Reliability Centred Asset Management
- 2013
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Ingår i: 22nd International Conference and Exhibition on Electricity Distribution (CIRED 2013). - : Institution of Engineering and Technology. - 9781849197328 ; , s. 0668-
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Konferensbidrag (refereegranskat)abstract
- This paper provides an overview of risk and reliability assessment techniques, some which are available for distribution system operators, and others that are in the process of development. The main contribution of this paper is showing the possibilities and benefits of detailed risk and reliability analysis. Six samples of findings from research developed over the last decade within the RCAM group (Reliability Centred Asset Management) at the Royal Institute of Technology, Stockholm Sweden, are presented. The research is directly associated with risk and asset management applied to power systems. The first three examples are within developed research, followed by three areas where great potential is seen: 1) The value of accurate thermal models of transformers; 2) The impact of tariff regulation on asset management decisions; 3) Detailed interruption studies; 4) Dynamic rating; 5) Combined risk and reliability analysis of primary equipment and control equipment; 6) Systematic diagnostic measures for asset management.
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| 6. |
- Hilber, Patrik, et al.
(författare)
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Risk analysis for power systems : overview and potential benefits
- 2010
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Konferensbidrag (refereegranskat)abstract
- This paper provides a mapping and sample of recently developed risk assessment techniques that are available for the distribution system operator. Three estimates on the value of more detailed risk analysis are desccribed. I.e. component reliability importance indices can be used to divversify the maintenance efforts, gaining better expected system performance at no cost. Furthermore, components that are assumed to be relatively harmless (based on average values) are identified as critical for longer interruptions. Finally it is shown that losses in a transformer are critical in the decision on transformer lifetime.
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| 7. |
- Josue, Fretz, et al.
(författare)
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Transformer hot-spot temperature estimation for short-time dynamic loading
- 2012
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Ingår i: Proceedings of 2012 IEEE International Conference on Condition Monitoring and Diagnosis, CMD 2012. - : IEEE. - 9781467310208 ; , s. 217-220
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Konferensbidrag (refereegranskat)abstract
- On the transformer, the effect of thermal stress is aging of the solid insulation. Excessive thermal stress could damage the solid insulation. To avoid this, transformer condition monitoring systems could use thermal models to forecast the operating temperatures during dynamic loading. There are several thermal models of varying complexity, including the thermal models stipulated by the IEC and IEEE standards. In this paper, the thermal model which is referred to by IEC Std. 60076-7 as the differential method, is modified, so it accounts for the oil viscosity dependence on temperature. The model is validated using hot-spot temperature measurements from a 40-MVA transformer, OFAF-cooled, 21/115 kV which is located in the subarctic climate region.
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| 8. |
- Rosenlind, Johanna, 1985-, et al.
(författare)
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Frequency Response Analysis (FRA) in the Service of Reliability Analysis of Power Transformers
- 2011
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Konferensbidrag (refereegranskat)abstract
- This paper aims to improve condition monitoring of power transformers by concerning thermal modeling. The common loss of life estimate could be used as a condition estimate during condition monitoring but for this estimate to be reliable, an accurate thermal model for the hotspot temperature calculations is absolutely essential to develop.Studies have shown a significant deviation between measured and calculated hotspot values. This deviation is particularly pronounced during transient load at severe environments. Temperature modeling during transient load conditions puts high requirements on the dynamic part of the model; hence focus has been given to this particular load type in this paper. Moreover, the Nordic climate have winters with temperatures as low as -20C. In order to apply these models in these settings, this paper is discussing this as well. As possible thermal model improvements, this paper identifies the ambient temperature, loss variation with temperature, and oil viscosity changes with temperature as features which need to be utilized in the thermal model. This paper describes the current research within these areas.Furthermore, presented in a concluding discussion, the appropriate approach for these models are seen to be either the thermal-electrical analogy or the soft modeling techniques.
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| 9. |
- Rosenlind, Johanna, 1985-
(författare)
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Lifetime modeling and management of transformers
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work have studied and developed lifetime estimation methods for the power transformer and how these could be used for asset management purposes. It is researchperformed in the intersection of the fields of reliability theory, statistical analysis, and stochastic process theory applied to lifetime estimations and management of transformers.The chosen approaches are the following. The thesis assess the effect of thermal stresses on the lifetime of the transformer. The effect of hotspot temperature is assessed with a loss of life measure. Within this study, improvements to the thermal model have been made.The thesis moves on to an alternative method for lifetime estimation in which diagnostic measurements are forecasted using a stochastic process and iterative realizations of this stochastic process is used to estimate a probability distribution for the transformer.The thesis moves on to study the loss of life measure from a system perspective by calculating the loss of life estimate from the load profiles of cold load pickup, increased electric vehicle penetration, and normal operation. These are applied in such a way that they can be used for asset management purposes.Then, the thesis uses estimates of failure times with the aim to reach a probabilistic, dynamic capacity rating selection method which use a failure rate which is conditioned on the time-dependent load level.
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| 10. |
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