how to calculate the foundation for a 2 MW generator 2

[181273]

I´m trying to define the foundation for a 2 MW syncronous generator, and I don´t know how to calculate the next things maybe someone of you could help me....
How can I calculate the short circuit torque and how to use it for the calculation of the foundation... this is a horizontal hydro unit with francis runner....
What is the best option: double T asembly or a piece of metal mechanized with the holes for the bolts of the generator??
sorry for my badly english and I hope to get some help from you... I´m just trying to know how to know how to do it

thanks in advance

 

[sreid]

We would need the speed of the generator (or the number of poles) and is it 50 or 60 Hz

 

[181273]

ohhh, sorry.. yes I imagine you will need speed...
1000 rpm....
when I write it, I was thinking in get some formula .... or explanation...
I hope someone could help me... I´m new on this mechanical things

 

[181273]

and the frequency is 50 hzm, this is Europe (Spain)

 

[sreid]

2 MW = 1.47x10^6 lb-ft/sec

1000 RPM = 105 Rad/sec

T=P/w = 1.47x10^6/105 = 14,000 lb-ft of torque

 

[hec64]

You need to get a structural engineer to do this for you.

 

[181273]

yes, I´d contacted with a structural engineer but I want to know something about it... to discuss with him or understand what he explain me...
other question, does somebody knows how to translate lb-ft to kg-metre.
Ah, other question, Sreid, how you get the numbers for the formula
2 MW = 1.47x10^6 lb-ft/sec
why you say 2 MW that valium

thanks in advance to all of you

 

[sreid]

Power (lb-ft/sec) = Watts/(746 Watts/HP)X 550 lb-ft/sec/HP

I hate Kg-m as a torque unit. How about Newton-Meter?

 

[electricpete]

I don't know much about foundations. For smaller machinery a thumbrule is 5 times the mass of the machine.

Note that the torque calculated above was the full load torque. You asked about short circuit torque... I'm not sure how one would calculate that.

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[181273]

yes, normally the shrot circuit torque is 6 times the full load torque... or as long I remember...

thank to everybody for the attention

and thank sreid for your help, why you hate kg m??

 

[davidbeach]

Torque is power times angular velocity, and since the power goes way down during a short circuit, there is no way that short circuit torque could be 6 times full load torque. The problem you're going to have during a fault is that the generator is going to overspeed and your foundation will have to deal with that.

 

[sreid]

181273,

Kilogram is properly a mass unit but torque is a force x length unit. I know that Kg Force is a legitament unit of force but I think it creates confusion and leads to mistakes.

 

[motorspert]

The short circuit torque can be calculted apprximately from the generator reactances, if you have x"d and X2. i have seen short cct torques as high as 10-12 times flt.

You also need the distance between the holding down bolt holes. ie width across the feet.

Regards

 

[electricpete]

Good point. cct = critical clearing time?

I'm remembering that case we are talking about a transient where the generator swings against the system. The power is
P= E1*E2*sin(delta)/X

The max possible torque would be where delta approaches 90. I can imagine that would be many times full load torque. Protective relaying should disconnect the generator before it gets there.

Out of phase closing might create torques close to that same maximum.

In the specific case of short circuit, there are large forces on the conductors but as David says I don't think necessarily large torques.

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[motorspert]

Pete
cct = circuit, sorry for the confusion.

The short circuit does cause a large torque, albeit only for a few cycles.

Typically:
3 phase short circuit 2 - 5 x FLT
Line to Line short circuit 5 - 9 x FLT
An out of phase synchronism, 180 degrees out, up to 12xFLT.

An out of phase synch is unlikely, so designers ignore that possibility and normally quote the line to line as the worst case.

My little black book gives an approximation to the fault torque as:
1+ (3/2 x (sqrt3)x V^2/(x"d+x2))

So for x"d of 0.18pu and x2 of .2 gives 7.8 x FLT at 100% line volts.

Hope i havent confused you further!
richard

 

[davidbeach]

motorspert, could you kindly explain how torque could go up during a short circuit when power goes down dramatically and speed doesn't change much?

 

[itsmoked]

Is not the biggest hit the accidental way-out-of-phase paralleling? Isn't that when the rotor lands out in the parking lot?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[davidbeach]

Keith, yep, bad paralleling is going to produce the highest possible torques, so high that mountings are not generally designed to withstand them.

 

[181273]

hi, and thanks for the reply to everybody.... specially motorspert... I got a little question...
"So for x"d of 0.18pu and x2 of .2 " you talk of two reactances...what´s is the name of this reactances???

thanks in advance

 

[davidbeach]

x''d is the subtransient reactance and x2 is the negative sequence reactance, often very close in value to x''d.