How to prepare an enquiry for a power transformer: Design and tendering tips

Nothing is more crucial during the early phase of a transformer inquiry than a complete and explicit listing of all requirements that must be met from both the manufacturer’s and the user’s perspectives. The IEC standards include detailed requirements that affect the design and manufacture of transformers depending upon their rating, voltage and application.

Often, however, there are other additional local or regional technical requirements that need to be included in a specification, as well as requirements which arise from the purchaser’s previous experience. Therefore, the purchaser should state any technical requirements different from or not contained in the IEC standards or other listed standards.

Any additional technical information that will assist a manufacturer to optimize the design and manufacture of the transformer should also be provided by the purchaser.

A technical specification has three most important objectives:

1^st OBJECTIVE – To give the manufacturer, or tenderer, all the technical details he needs to implement his design and which will differ from unit to unit, such as rating, voltage ratio, cooling type, etc.

2^nd OBJECTIVE – To inform the manufacturer or tenderer of the strategic significance of the transformer and the importance that should be given to dependability, maintainability, and long service life.

3^rd OBJECTIVE – To give the tenderer, or manufacturer, information that will guarantee the transformer will satisfactorily interface with its aforementioned plant and equipment and that installation and commissioning will go smoothly and without undue delays.

The first two objectives must be accomplished by the inquiry paper for the manufacturer to be able to create his tender, and it is obvious that they will have a considerable impact on the transformer’s price. The third will have a lot of elements that will have little to no impact on total cost and that may be resolved during contract engineering.

It is important to remember that the purpose of a specification is not solely to describe what is wanted but also, to state what is not wanted. The latter often result from the purchasers’ previous experience.

When Whatsapp, Facebook, or Gmail is down, it’s manageable, but if transformers fail, the entire business comes to a standstill. No-power-no-business transformers, as the heart of every substation, impact industries and affect the country’s economy and have social and political ramifications. Any malfunction in this expensive machinery can be the leading cause for a complete outage of the network failures.

Solar activity can cause Geomagnetic Induced Currents (GIC) to flow in the earth and these currents can find their way onto the power system usually via the earthed neutral points of transformers. The occurrence of GIC’s in electrical grids is linked to position on the earths’ surface and to the orientation and length of overhead line circuits connected.

Higher latitudes are generally more affected, being closer to the magnetic poles. Purchasers should determine whether the transformer being specified will be located at a site which may be subjected to GIC events from time to time.

The temperature rise experienced in any object is depending on:

1. Details of the design
2. Constructional details
3. Intensity of the GIC in duration and magnitude
4. Loading condition of the transformer
5. Heat transfer capacity of the affected structures.