{HEAD ~ The individual sources} are responsive to {TAIL ~ an error signal} representing the difference between a component of power common to the sources or frequency, if the power sources are AC generators, and a reference and to individual signals representing a variable power component 
{ HEAD ~ The individual sources } are responsive to { TAIL ~ an error signal } representing the difference between a component of power common to the sources or frequency , if the power sources are AC generators , and a reference and to individual signals representing a variable power component
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH