Comment: Usually, the transformer data sheets are including the transformer test data.
The transformer tests are performed per industry standards, e.g. ANSI/IEEE Series C57. Visit
Comment: The transformer manufacturer provides transformer data sheets coming with product after testing. The transformer data sheets or tech data included in the transformer catalog are generic only since the manufactured transformer is somewhat off with its parameters, even though it is supposed be manufactured within some manufacturing tolerance, e.g. ±7% two winding transformer or ±10% three winding transformer.
I quite agree jb, If you are dealing with aspects relating to an existing installation, then it is clearly better to use actual test data from the manufacturers (I frequently deal with loadflow and short-circuit studies on industrial systems).
If you are preparing a design however, then generic data is all you can go on, however there are differences in transformer design which you need to consider eg, is it ONAN, AN, ANAF .....
Manufacturers data on web sites will give typical voltage impedance, power loss and noise levels etc, as well as dimensional data.
Comment on the previous posting: The engineering or conceptual stage of the Project uses the transformer impedances available in catalogs, software libraries and industry standards, which are often mandatory documents the Project adhere to or is committed to by contractual documents such as a bid or proposal. (Under an assumption that there no cowboy's business engineering ethics.)
The degree to which you can specify depends on the type of transformer and amount you wish to pay. For small dry-type transformers, you will pay a huge premium to get anything other than manufacturers' standard impedances. Each manufacturer has different impedances depending on the type specified. For mid-size transformers, ANSI specifies 5.75% as standard and many manufacturers stay close to that as a standard. For larger custom-built units, there is more lattitude to get what you want.
As far as UK projects are concerned, the transformer specification is generally defined in terms of the technical requirements and referenced to IEC 60076 standard.
This leaves the tender open to competitive tender unless there are reasons to specify a particular manufacturer / product range. The enquiry document is a contractual document.
The differences between typical quoted impedance values and final measured values on the test certificates are negligible.
NB - We do not undertake in 'wild west' tactics or corrupt tendering practices.
_______________________________________
Regards -
Colin J Flatters
Consulting Engineer & Project Manager
Comment: The transformer data sheets provided by the transformer manufacturer are used as a source of data to be imputed into software for the power distribution modeling to establish the voltage drops and short circuit current levels and to add appropriate options to the hardware, e.g. Transformer On Load Tab Changers (OLTCs).
There is very little it can be done about cowboy's bugs in the software, or corrupt files.