Circuits and switching groups
The Transformatorenwerk Breimer-Roth GmbH identifies its three-phase transformers in line with the more common and user-friendly approach as follows:
The first capital letter describes the primary input winding and the second lower case letter – the secondary output winding.
If no other order details are formulated with more precise position assignment of upper and lower tension, the above-mentioned type of marking is selected! Three-phase transformers are preferably manufactured in Dyn5, if no information is available.
Load capacity of the neutral conductor (star point)
In the star-star circuit (Yy), the neutral point may only be loaded with the full rated current if the neutral of the supplying mains is connected to the primary-side transformer neutral point. If this is not the case, then the neutral point can only be loaded with approx. 10% of the outer conductor current.
For three-phase auto transformers designed in star-economy mode (YNa0), the same rule applies. If a fully loadable star point is desired, but this is not available on the line side, the double zigzag connection (ZZan0) must be selected.