Hi, It's not quite clear on the transformer issue, are you scourcing a transformer in UK or America, or are the customers in China scourcing transformer? The VFD doesnt care if the input is 50 or 60 Hz, the transfomer will be rated for 50Hz if from UK, and also China. So there wont be any problems with heating. Here is a link I use for industrial transformers, both auto wound and isolating single and 3 phase. https://airlinktransformers.com