Below is a list of 3 Phase Transformer manufacturers from Covina, California. 3 phase transformers are important components in 3 phase electric power transmission. 3 phase transmission is among the most common power transmission methods worldwide. It is one of several polyphase current transmission methods utilized by electric power companies and utility operators; the main advantage of polyphase transmission over single phase transmission is the increased electrical transmission capacity despite a lower requirement for transmission wires.