Does anybody knows where can i find information about diesel generators? ...
Try these two.
http://www.cumminspower.com/en/technical/application/t030/
http://www.cumminspower.com/en/technical/papers/
I'm not a fan of Cummins, but their website is pretty good. I would guess Caterpillar and others have similar stuff on their sites.
Also check the IEEE color book series. Here is a couple I recommend:
http://standards.ieee.org/colorbooks/sampler/redbook.html
http://standards.ieee.org/colorbooks/sampler/buffbook.html
http://standards.ieee.org/colorbooks/sampler/orangebook.html
... I mean if I have a non continuos load, I want to know how will the generator react? how do I control it?
the generator would be feeding a group of offices, wielding machines and illumination circuitry. ...
You have picked a difficult mix of loads to power. Office equipment does not get along well with production machinery such as welding machines. And as you noted, the loads are not continuous. If the loads are jumping around (fast changes) as little as 10% of the load, the frequency and voltage could be jumping around maybe as much as 2%.
So how do you control it? Well, if the load is all over the place, rapidly changing, not much you can do. Maybe put the office equipment on on-line UPS systems.
Generators this size don't tend to come with all of the equipment you will need for a system. There will be a separate cabinet(s) with the VR, frequency control to governor, circuit breaker control, protective relays, synchronizing control, load share, var share ... Sometimes the gen mfg will put together the system, and sometimes there is a separate system integrator. Either way you pay for that service extra.
yes all those questions, when the generator its already running...
How you will bring it on line? ...
If you are discussing a dead bus, as in the gen is islanded - not to be connected in parallel with a utility, then one just sets the voltage and frequency, opens all of the load cbs, then closes the gen main cb, then brings on the loads.
...I have been reading, and I found that usually the generator have to have a minimum continous load, 60 % - 50 % of full load, if it doesnt the machine will break in a short period of time. what have you heard of that?...
Yes, recip diesels have problems with being lightly loaded. Most I have worked with are okay at 50% load. But at say 30% there are issues with "wet stacking" (un-burned fuel passing through the engine). It is not good for them and will shorten the MTBF, but then so will running them at 100%.
From your description, it sounds like you are going to have trouble with low load at night when the production machinery is off-line, and near 100% when in full production.
Assuming you don't have a utility connection to fall back on, maybe consider two generators, operating in parallel during full production and shutting down one at night.
...what protections usually have this machines? ...
The engine will have several. Here are a few of the common ones;
low oil pressure
high oil temp
coolant over temp
intercooler high temp
overspeed
The generator will have another set, such as:
over current
over voltage
undervoltage
differential current
ground fault
loss of excititation
under freq
over freq
bearing over temp
...how do you supply the field? with batteries?
Current production generator normal set up is a Permanent Magnet Generator, controlled by a voltage regulator, supplying an exciter field, with the exciter output connected through diodes in the generator shaft to the generator field.
This way, a couple of amps of VR current can control the 250A of DC current to the Alternator (generator) rotating field. Also, there are no brushes required.
Here is a thread that tells how the generator governer/throttle controls frequency/load share and VR/DC field current controls voltage/var share.
http://forums.mikeholt.com/showthread.php?t=103971&highlight=generator
...I do remember something about Velocity Rulers... but its quite vague what I remember
I've never heard of a "Velocity Ruler" in connection with a generator. What is it?
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