DG Set Generator Design:- One Bearing or Two Bearing?

I don't yet know what the deal is in the meaning of a single bearing. I have on order as of yesterday 4 500KW diesel generators and paralleling switchgear. The generators all have a single bearing. This seems to be tooted as the latest technology for gensets. I am still trying to get my head around this. I've been rebuilding motors for years of all sizes and there is 4, 5, 6, 7, 8 main bearings and journals involved. So this single bearing is one that I am seeking answers from CAT on. The only thing I can picture is, from the shaft of the motor, you have the ARM and at the end is 1 bearing for the gen section relying on the Motor bearings to support the ARM if directly coupled. Kinda like a lathe and live center. Still waiting on an answer from CAT though.

Surely having a single bearing is primarily intended to be cheaper to build and simpler to design? I would also accept that it is also physically stronger and more stable.....

But has the negative side that really it must be either on a single, long fixed shaft or something special in a shaft U. joint (that I personally have never seen) to keep things stable....!!

Saving a bearing or two and usually a U.J. as well probably saves quite a bit of money.....

Thats my personal take.....

If I understand the question correctly:

The Generator and Motor are mounted on separate skids. Each skid has a in-line bearing, to support the protruding shaft. At the end of each shaft is a coupling half. Between the skids, a drive shaft is installed with a coupling half on each end. The theory is that the "floating" drive shaft will compensate for "minor" misalignment between the skids.

I don't know, and you don't specify, what the configuration is of the MGen "set." Even one-piece foundations will "work" and the two units will go out of alignment.

NOTE: The coupling-halves are matched sets with eccentricity marks on the coupling. Make sure the marks are aligned and the couplings are "matched." More high-tech couplings have a unique identification on them to identify the coupling-halves. Good Luck in the contest.

I forgot to add that the aligned-couplings will operate as a solid unit. As the coupled units go out of alignmkent, the coupling will begin to "work" and generate heat, which is the bane of couplings and bearings. A calibrated sensor array, with audible and visual alrms, to monitor the the bearing, and coupling, temperature is desireable. Perhaps, even an automatic, threshhold-tiggered, shut down can be employed.

The next best solution s close-periodic monitoring of the elements. A temperature probe is not recommended to be used around rotating elements.

Single Bearing means that the alternator is supported with one bearing only, at the far open end. The coupling end will rely on the engine end bearing.

Usually, the alternator housing is bolted on the engine side with the coupling, and this should be properly located to minimise any misallignement between the engine shaft and the alternator shaft.

The single bearing concept is better for allignement and reduces the extra bearing friction losses and failure risk etc. ...

But the bearing of engine shall be supporting its equipment weight and also generator rotor, making it vulnerable to failure.

My opinion, two bearing design is better.

Engine end bearings are designed to take the loads of the driven equipment, even when loaded sideways. But in the case of an alternator coupled in line, the Inertia of the rotor and its proper balancing contribute to alleviate any side loads and even the vertical load on the bearing.

The extra load inconvenience is amply compensated by the other factors already mentioned. Of course, a badly designed engine end bearing is not an excuse.

If you are talking about "under sized" bearings, you are right! But how about "correctly or even OVER sized" bearings? What do you say to that?

Not having a a middle, difficult to access maybe, bearing, may make the whole machine actually better......

Another advantage of a machine with two bearing is the air gap between stator and rotor of generator shall be uniform all the time and not a function of alignment. As uneven air gap affect electrical performance of alternator which is more likely in single bearing alternator of DG set.

The concept of single bearing is appealing for mechanical machines like blower, where uneven air gap between fixed and moving member is not much affecting mechanical performance of equipment.

Since you asked the question in the 1st place, and seem to know the answers and the reason for the manufacturer to economise (as you tend to believe), why bother to ask and even to waste our time?

On the other hand, If you thought that there might be a better and REAL reason for using One Bearing then I can Understand your question, but then try to reason with us instead of accusing the manufacturers of short fitting One bearing ....AND HAVE MORE TROUBLE TRYING TO MACHINE AND FIT THE ALTERNATOR HOUSING MORE PRECISELY (Capital for emphasis...not shouting!).

Why don't you ask the manufacturer?

Manufacturer always advocate for product they produce.