Transformers In Parallel
Transformers are placed in parallel by electric utilities when they want to provide a ‘stronger’ voltage source and will result in higher available fault current that can be delivered downstream. Usually the utility transformer can serve its own load but two are put together to achieve with a ties primary and secondary bus to ‘stiffen’ the voltage to ride through system load changes.
Yes the utilities have to worry about automatic load tap changers that could hunt forever.
Some industrial customers try this method to serve a load that is too large for a single transformer. This arrangement has to be done carefully or you can damage one or both of the transformers. You need an exactly matched pair of transformers or transformers of different manufacturers with identical characteristics or circulating currents can build up in the parallel connection that consumes energy and does not pass to the load. Routine maintenance of the parallel connected transformers in the non-utility world is nixed because neither transformer is big enough to serve the load on its own. This would mean extended outages to the load during maintenance of either transformer. Parallel connections of transformers in the industrial world are usually not attempted because the lack of maintenance makes for a less reliable installation. Transformers come in various sizes and the best or optimum transformer size is one that can adequately handle its load all by itself.