The magnitude of a power component common to all the power sources or frequency, if {HEAD ~ the power sources} are AC generators driven by constant speed drives, is compared to a reference to provide {TAIL ~ an error signal} 
The magnitude of a power component common to all the power sources or frequency , if { HEAD ~ the power sources } are AC generators driven by constant speed drives , is compared to a reference to provide { TAIL ~ an error signal }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL