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