The BASIC requirements are a) voltmeters on busbar and incoming generator which can measure voltage to match to within 1%: b) Manual AVR (voltage regulator) voltage adjust lower and raise switch c) Circuit breaker and manual close switch which can connect generator within 0.2s of your pressing close button d) Governor and speed lower and raise switch which can adjust frequency to within 0.05 Hz or better of busbar frequency e) Synchronising Lamps to indicate when incoming and running gensets are in phase. All the switches/buttons and indicators need to be close together for the effectiveness of the operator. But if you have 500 and 500 kVA, you can wreck the 500 kVA if you get it all wrong and connect 180 degrees out of phase and I would suggest a CHECK SYNC relay which has a contact in the closing circuit which is closed only while the phase angle is acceptable. There are also Synchroscopes and phase meters which indicate the phase error and automatic synchronisers, but these are not basic