IN SYNCHRONOUS machines the rotor turns in synchronism with the e.m.f. developed or the alternating voltage applied. A synchronous machine can function either as a motor or as a generator and sometimes does both, as in the 1.8GW pumped-storage scheme at Dinorwig in N Wales, which uses six, 300MVA, reversible pump-generators. Virtually all the electrical power we use is generated by synchronous generators, some of which are among the largest of all electrical machines. They are large, not only because we need vast quantities of electricity, but also because large generators are cheaper per MW to construct and to operate, and are more efficient than small generators. A synchronous generator rated at 1000 MVA should turn more than 98% of the mechanical power input into electrical power.
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