BS IEC 61378-3:2015 pdf download-Converter transformers Part 3: Application guide.
When industrial transformer units are provided with transductors (saturable reactors) in their tank, transductor cores make the test challenging because of the distortion of current and voltage wave shapes they cause. An agreement on the test modalities needs to be reached between the supplier and the purchaser before signing of the contract. No method has been commonly accepted. Some are presented in Annex G of IEC 61 378-1 :201 1 . Guaranteed temperature rise values are relevant for a specific loading condition as defined by agreement between purchaser and manufacturer. As a converter transformer is exposed to a current with a certain harmonic content, the actual losses will deviate from the losses developed with a true sinusoidal current. In general, harmonics in the current will give rise to an enhancement in load losses as compared to operation with true sinusoidal current. From the aspect of transformer design, it is important to distinguish between – applications with essentially sinusoidal voltage across the transformer line winding, and – applications with non-sinusoidal voltage where the transformer primary winding is energized from a converter circuit for a.c. power control or variable frequency conversion. Information about the converter application should be supplied in the transformer specification. The no-load loss guaranteed value is defined by the rated sinusoidal voltage. The actual load loss in converter operation is estimated with sufficient accuracy by the calculation procedure presented in IEC 61 378-1 :201 1 , 6.2 and in IEC 61 378-2. From this set of formulae the corresponding test current for establishing the corresponding temperature rise can be deduced (see IEC 61 378-1 :201 1 , 7.6 or IEC 61 378-2:2001 , 1 0.5). It should also be noted that the actual load current in operation may be higher than the rated current, when measured by an instrument reading r.m.s. values of current, since the rated current on the nameplate refers to the fundamental component of the load current.