Small Power Transformers
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Small Power Transformers
Bringing the energy safely to the consumer: A basic requirement applicable to all Power Transformers. However, every single one is unique – designed according to individual factors such as voltage, power, climate, system topography, sound level and many more. Siemens is your partner, who picks up these requirements converting them into convincing solutions with maximum quality. Power Transformers that render their service reliably at site. Cost-efficient and safe throughout decades.
The precision of core manufacture is a decisive factor for the later efficiency of the transformer. Siemens Power Transformers are manufactured as coretypes, with the limbs arranged at the same level and interconnected via yokes.
We are using high-grade cold-rolled laminates of transformer steel. Depending on the requirement also lasertreated ones.
When cutting the laminates, we rely on most modern numerical control systems, enabling the so-called step-lap-technique, with the consequence of an especially appropriate flow of characteristic within the core of a Power Transformer.
For high electrical and mechanical stress windings in Power Transformer are made of disc coils; for low voltages the use of layer windings has proven successful.
To adjust the ratio safely and easily to system conditions, Siemens Power Transformers have tapped winding. In this way the ratio of Power Transformer can be changed gradually - either in no-load condition via off-load tap-changers or under load by means of on-load tap-changers.
Another main component besides the core and the winding is the tank of a Power Transformer: It accomodates the active part and the oil filling.
The core, windings, pressed parts, tap-changer and connecting cables make up the active part of the Power Transformer.
The drying of the active part is done according to the vapor phase procedure.
After that the active part is installed in the tank and filled with high-grade insulating oil under vacuum. The transformer is now ready for testing.
Why Mean Time Between Failures (MTBF) is something to consider
The business success of the energy intensive industry is heavily reliant on a reliable power supply. Attaining a reliable electric service requires a broad understanding of reactive, ex post interventions, and the development of a portfolio of strategies which embraces proactive, ex ante risk management measures. Strategies to manage uncertainties with negative consequences, i.e. a single point failure such as power transformer outage, typically include avoiding the threat, reducing the negative effect or probability of a threat, transferring all or part of the threat to another party, and other methods of risk management. To be specific, a full risk description comprises a measure of the uncertainty, often but not necessarily in the form of probability, of the events and consequences. The mean time between failures may be one key performance indicator.
As every transformer supplier will always stress the reliability of his products, a careful assessment is necessary. For example, every reputable manufacturer may be asked to report a so-called “Failure Rate” (FRe), respectively a list of the “Mean Time Between Failures” (MTBF) of his units. The calculation of reliability indices is generally given in standards. However, as previously stated, it is important to consider the incorporation of the reliability indices in a congruent risk management framework, and it is important to consider the limitations of risk indices. Furthermore, calculating reliability indices and metrics is most useful when there is a target level of performance to be met. Targets cannot be selected based on a “one-size-fits all” strategy, but should be tailored to specific needs. Finally, the average failure rate of a transformer may change several times over its lifetime. Even slight deviations can make a big difference – maybe not during the first years of service, but in the later lifetime.
Small Power Transformers are distribution transformers from 5 to 40 MVA with a maximum service voltage of 145 kV. They are used as network transformers in distribution networks. This type of transformer is normally a 3-phase application and designed according to national and international standards. The low-voltage windings should be designed as foil or layer windings. The high-voltage windings should use layer or disc execution, including transposed conductors. Normally, the cooling type of Small Power Transformers is ONAN (oil-natural, air-natural) or ONAF (oilnatural, air-forced). The tapping can be designed with no-load or on-load tap changers (NLTC or OLTC).
The Power Engineering Guide is the comprehensive manual for transmission and distribution of electrical energy.