1000 kVA diesel generator

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Mayimbe

Senior Member
Location
Horsham, UK
Hello everybody,

Does anybody knows where can i find information about diesel generators? im worry about the control of it, 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.

My concern is about the control of the diesel generator. Does anybody know something about it??

f=60 Hz
V=480
S=1000kVA

I do remember something about Velocity Rulers... but its quite vague what I remember
 

brian john

Senior Member
Location
Leesburg, VA
I/we need a more detailed explanation of what you mean.

How it will respond to load changes?

How you will bring it on line?

Typically with a generator this size it should be all automatic, when properly installed, commissioned and with regular maintenance it should be worry free.
 

Mayimbe

Senior Member
Location
Horsham, UK
yes all those questions, when the generator its already running

How it will respond to load changes?

How you will bring it on line?

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?

what protections usually have this machines?

how do you supply the field? with batteries?
 

Rick Christopherson

Senior Member
How it will respond to load changes?
Most modern generators have electronic governors that will maintain very close tolerance on engine RPM as the load varies. As long as no single load is large enough to overwhelm the diesel engine as that load comes on or off line, then it will maintain its set speed within a fraction of a Hertz.

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?
Running a diesel engine without a load can result in carbon buildup in the cylinders. This is why most standby generators are connected to a loadbank for their periodic testing. This is mainly a problem for generators that are operated without any load during their monthly test, but it shouldn't be too much of a problem for a loaded generator. It is not an instantaneous problem, but takes prolonged time of running at no load or light load.

how do you supply the field? with batteries?
The voltage to the field windings is controlled by the voltage regulator to ensure that your output voltage remains steady at varying load. Modern voltage regulators are advanced enough that this is not something to be too concerned about. At worst, all you will need to do is periodically inspect your output voltage.
 

Cold Fusion

Senior Member
Location
way north
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?

cf
 

Mayimbe

Senior Member
Location
Horsham, UK
Thank you very very much Cold Fusion, I have no further questions, you have said everything that I needed to know. :D

By "Velocity Ruler" I meant your governor. Bad traslation.
 

Besoeker

Senior Member
Location
UK
how do you supply the field? with batteries?
We have retrofitted a number of fairly large generators (5MW to 30MW range) with new static exciters over the last few years.
These have been essentially controlled three-phase rectifiers using SCRs and diodes. For some, there has been an available three-phase source without the generator running. For others, there is no supply until the generator is up and running. This is sometimes referred to as a "black start". My experience with those is that a battery is used to provide initial excitation - field flashing - and, when there is sufficient voltage, the static exciter comes on line.
 

Besoeker

Senior Member
Location
UK
Thank you very very much Cold Fusion, I have no further questions, you have said everything that I needed to know. :D

By "Velocity Ruler" I meant your governor. Bad traslation.
I understood your meaning (governor and ruler) and assumed it to be to do with translation. It did make me smile, though. No offense intended.
Where are you from Mayimbe and what's your first language if you don't mind saying?
 

Mayimbe

Senior Member
Location
Horsham, UK
No offense taken. I did smile too. Im from Venezuela (South America). My first language is spanish. The funny thing is that in spanish we say "Gobernador de Velocidad", so you can easily think that Gobernador = Governor, which its true. I dont know why I said "Ruler". Languages are a very serious matter :D

Thanks by the way for the previous post.
 

Mayimbe

Senior Member
Location
Horsham, UK
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.


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


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.

Hello again,

Im designing the electric protections for this generator I've been talking.
I got a few doubts about this matter.

Vbase = 480 V
Sbase = 1138 kVA

1) when I assume a 3 phase short circuit right on the outputs of the generator, I find two ways of model it:
a) Assume that Xq'' doesnt matter, and in the circuit analisys put Xd'' in serie with the Ef (V output of the machine).
b) I found this equation of the armature current in function of time:
ia(t)=sqrt(2)*Ef*((-1/Xd')*(COS(w*t+t0))+0.5*((1/Xd')-(1/Xq))*COS(2*w*t+t0)+0.5*((1/Xd')+(1/Xq))*COS(t0))

where
ia = armature current of the machine.
Ef = electro magnetic force induced, 1 p.u assumed
Xd' = direct transitory reactance, 0.28777 p.u
Xq = quadrature reactance, 1.19904 p.u
w = machine velocity, 30 rad/sec
t = time, sec
t0 = angle between the rotor position and the magnetic field. 15? assumed

In a) i got a failure current of 4.55461 p.u, (Ef = 1 p.u, and an armature resistance of 0.01417 p.u, Xd'' = 0.2191 p.u)

In b) I ploted this expression and got a peak of the failure current of 9 p.u

Which one would you choose when you need to design the protections?

In other hand, when I tried to find the single phase short circuit analisys, assuming the secuences connected in serie. I found that the failure current was 5.20319 p.u (Xneg = 0.31448 and X0 = 0.04142 p.u)

Any thougts?

the values on the table anexed are in p.u on the bases published on that table
 

Cold Fusion

Senior Member
Location
way north
...Any thougts?...

Yes - but first a disclaimer: I'm not a designer - I'm a field dog. Designers design it, ECs put it in, I go make it run like the customer wants. I don't have anything against designers. They have made me plenty of money. However, any good designer could help you out more than I could on this.

So, one ususlly looks at the available short circuit current to size the withstand ratings of the equipment. Using either model, your short circuit current is under 10kA. That is pretty low, so you won't have any issues with equipment.

Next, the selection and settings of protective relays is to get the gen shut off, or disconnected inside of the gen damage curve. A secondary concern is to keep the system reliable - generator on-line and providing power. Most times this means the protective relays are set right out against the damage curve.

A place you might start is with, Protective Relaying: Principles and Applications, by J Lewis Blackburn. It is not a new book, and has a lot of references to mechanical relays, but the principles apply to modern microprocessor relays.

cf
 

Mayimbe

Senior Member
Location
Horsham, UK
A place you might start is with, Protective Relaying: Principles and Applications, by J Lewis Blackburn. It is not a new book, and has a lot of references to mechanical relays, but the principles apply to modern microprocessor relays.

You've been more than helpfull, Thank you very much. I will put my eye on that book, I found it already. Seems VERY interesting
 
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