Early in the development of electrical transmission systems it was found that cost was lowest if the bulk power was transferred at very high voltages, up to 440kV in the UK.  This results in lower currents and power losses and reduces cable dimensions.   It follows that voltages have to be increased as power leaves generators and then reduced from the transmission voltage down to distribution loads.  These voltage steps are provided by transformers.  The key requirements of transformers is that they are efficient and reliable.  Power transformers are remarkably successful in meeting these requirements; there are transformers in use that were installed in the 19??s and modern transformers can be up to ??% efficient.   Almost all newly manufactured network transformers are now required to meet the EcoDesign Tier 1 efficiency targets and from 2021 they must meet even more stringent Tier 2 requirements.  BEAMA Networks members offer high quality transformers from the smallest to largest power levels.