Generator excitation


#1

How common are generators(alternators) that don’t have permanent magnet generators? I haven’t seen any personally but was browsing the CFRs and it doesn’t specifically say for main generators. Although 111.12-3 does mention something about e-gen excitation.


#2

Very common. Either with an external exciter or onboard the main rotor as brushless arrangment or with the static exciters. Just about any AC generator of size on ships will have this arrangement.


#3

I’ve never seen a permanent magnet setup in service generators. The generators rely on residual magnetism in the field windings for start-up. On occasion, if the genset has been dormant for months, or new installations, an external flash excitation may be required.


#4

I wasn’t very accurate in my OP. What I meant was permanent magnet generators (PMG) to power the AVR which in turn powers the exciter field for the exciter armature and rotating rectifier assy powering the actual field(maybe done with brushes on older gens?). All the generators I’ve personally been around have been Kato between 2000-2500 with PMGs mounted on the end of the rotor.

Just curious if it’s common to power the AVR via auxiliary winding or shunt both of which aren’t the greatest for marine use as far as losing residual magnetism and reflashing issues as injunear said


#5

what types of vessels are these on? do many of these gensets have built in flashing circuits or do you use batteries typically?


#6

I must have misread your OP or inverted something in my reading of it. I thought you were saying have you ever seen a non PMG generator.

Not sure I’ve seen a true PMG in that application but as mentioned above. residual magnetism does play a part in starting with even an engine driven DC exciter.


#7

In the old days it was common to have a separate DC generator (sometime called PMG or rotating exciter) that was connected to the main generator (technically, an alternator). This things are just like DC motors (and look like them) with all the PITA in maintenance, and most have been shit-canned. This is likely what the CFR is referring to.


#8

I’ve never seen a built in flashing circuit but that doesn’t mean they’re not in use.

Depending on the layout, I’d normally flash off the starting battery. Air or hydraulic start units, if no battery banks or DC buss in reach, I’ve used portable battery charger. I once used a 6 volt gel cell emergency light battery to flash a 50 KW gen.


#9

https://power.cummins.com/system/files/literature/brochures/GLPT-6008-EN.pdf

Ok this explains what I’m talking about better, more specifically PMGs which don’t rely on residual magnetism in the in the rotor to begin building up voltage. Basically powering the AVR which powers the field.