Generating sets in parallel

http://en.wikipedia.org/wiki/Alternator_synchronization

Yes, You can very much parallel generating sets of different ratings provided:

i) Voltages are equal

ii) Frequencies are equal

iii) Phase Rotation is equal

iv) The lowest capacity generator rating is not less than 1/3rd of the largest capacity generator rating (to be cross checked by verifying the reactances of the generators)

However, it is advisable to go for load sharing relays (one each for active loadsharing and for reactive load sharing - so that the available load is shared by the generators in proportion to their rated capacities. Otherwise, the biggest generator would try to "swallow" all the available load and might trip leading to cascade tripping of all the generators.

Thank so much,

A literature on this topic will be very helpfull.