This list is being updated on regular basis so please check it again if you do not find your question here or simply send us an email and we will include your questions in our next scheduled update.

 

To protect the privacy of our clients and manufacturers, we avoid specific references. Most questions address mega-power customized power converters or transformers/reactors and may not be applicable to smaller standard off-the-shelf-products.

 

  • How a transformer, that is not properly designed, could hurt a business?

Custom transformers and reactors are designed in short order using cookie-cutter tools and procedures to minimize the engineering costs. Typical design time allowance can range from 2 hours to 8 hours depending on the complexity and size of the unit and the type of design tools and procedures. To make up for design uncertainties, the designers may use fudge factors that could result in an overrated or underrated design with inadequate safety margin for worst case operating conditions. In general, an overrated design could be larger with higher capital cost and energy (core) loss whereas an underrated transformer will have higher load loss, shorter life and higher chance of failure under worst case operating conditions. In either case, the user is spending more on operating energy expenses and could also be at risk of a catastrophic failure.

 

  • Will a properly rated and optimized design be more expensive than a non-optimized transformer?

Not necessarily. In some applications, we have been able to reduce (from 10% to 30%) the size and cost of a given design after optimization. The first and foremost factor in our design is to ensure the safety margins are maintained particularly in regard to the temperature rise which is the most illusive and yet important factor in the design. Since we have tools that allow us to estimate temperature rise more accurately with confidence, we do not use fudge factors to oversize and overprice a design. In applications with harmonics, our design tools calculate the harmonic losses properly under skin and proximity effects thereby selecting just the right size and shape of conductor. Last but not the least, our one-of-a-kind cooling design tool allows implementation of creative ways to dissipate the heat losses economically.

 

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    Why is the calculation of temperature rise so important and yet illusive in a transformer or reactor design?

The reliability and life of transformers and reactors have historically been related to insulation and its degradation with temperature. But the accurate value of the highest temperature in a transformer or reactor cannot easily be calculated due to complexity in loss distribution in windings, core and structure as well as thermodynamics of air or oil flow.  Designers may estimate temperature rise based on charts, past designs, heuristic approaches and other approximate tools during the quotation phase. This issue becomes more severe in the presence of harmonics and complex oil or air flow channels. More accurate approaches are based on FEA methods requiring substantially higher time and manpower that cannot be accommodated during initial quotation phase.

 

  • What sets apart Power Magnetronics Solutions ™ in transformer or reactor optimization and how to compare with FEA methods?

Power Magnetronics Solutions™ uses a proprietary Mathcad program for design of transformers and reactors in order to increase the accuracy of average temperature rise and other performance factors. Our design tool calculates harmonic losses under skin and proximity effects for each winding layer based on a recursive iterative method to minimize errors in calculation. Such an approach is uncommon in routine transformer design (including FEA tools without CFD). By eliminating the uncertainties in calculation, we are then able to optimize the cost/performance criteria in a timely manner even during the quotation phase.

 

FEA tools can provide variation of temperature, losses or other variables of a given design over the transformer profile in graphical forms. However, good accuracy (under 10%) is achieved if millions of nodes are triangulated in a Multiphysics platform (including CFD) meaning that substantial amount of time and resources are needed for modeling and calculation. For comparing multiple transformer designs with different core, winding and coil duct profile, the FEA design cost and time can become prohibitive in routine industrial quotations.

 

  • What are the most important factors in procurement of a mega-sized custom DC power supply?

From the perspective of compliance to application needs and reliability of the product, we believe proper specifications for the product and outlining the worst-case operating conditions are the most important factors. In most cases, the specifications of the product become part of the legal tender between the client and manufacturer, and should there be any dispute, it is important the contingency terms for compliance (or deviation thereof) be clearly defined and remain consistent throughout the documents. Along with such efforts, the specifications must cover necessary steps to ensure the manufacturer complies with the defined requirements either during the production or post-production in the field application through witness test plans or verification by third parties.

 

  • Is the "warranty period" adequate in protecting clients against product defects, poor design or workmanship?

Traditionally, during the warranty period, the client is covered for infant mortality field issues as well as operating non-compliance of the product or some other types of failure. However, it is possible that the worst-case operating conditions would not happen during the warranty period thus leaving the client unprotected should there be a catastrophic failure in the product after the warranty period has ended.  Therefore, implementation of additional factory or field tests similar to HAST or other worst-case testing is essential. Whereas in smaller systems such tests may be feasible, for large DC power supplies of 10 MVA or higher, the testing becomes unwieldy due to extensive logistical cost and difficulty in replicating the exact load and environmental conditions. The more substantial the investment and the critically of the application, the more important it is for the client to dedicate enough resources for this purpose. Such efforts are comparable to short circuit testing of large power transformers that by itself could be destructive and cost upwards of hundreds of thousands of dollars.

 

  • How do I know if a manufacturer is a reliable source?

The reputation is the most common indicator of a company with a recognizable name. But some large reputable companies also experience their fair share of customer complaints and flops. In our experience, such complaints may stem from underestimating the complexity of a custom product and its associated test requirements. Rare events such as short-circuits, transient hot spots or even GMD may cause failure modes unaccounted for during a design and development process. Our clients experience that multi-billion dollar manufacturers are less flexible and less accessible whereas smaller manufacturer lack the clout to tackle complex manufacturing and test issues expediently.  On the other hand, a client receives more attention when its contract with a small manufacturer makes up a major part of the manufacturer's annual sales. Although, the clients can check on references, we also recommend investigating the litigation history, employee turnover and financial stability of a manufacturer through a third party.

 

  • How do typical clients find a manufacturer for their mega-sized power supply needs?

In general, the end-user may not have in-house expertise in directly developing specifications, searching for and evaluating a manufacturer for their factory process' power conversion equipment. Commonly, the clients resort to multi-national large consulting corporations. Since such consulting companies employ hundreds of expert engineers in different fields, it is not uncommon for them to need substantial efforts to coordinate and fully understand the application needs of a given client. The process of going through such consulting companies can often delay the product definition phase and qualification of a manufacturer leading to significant increase in client's expenses.

 

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