Hi. I have a problem in one part of designing generator,

[solidmechanica]

thread237-186654

I have short circuit torque and I do not know how it transfer to foundation in fact I want the torques on stator foundation. What is the relationship between them? The torque transmits with coeffiecient but what is it?

 

[7anoter4]

I don't think you need this since the generator is designed to withstand the maximum permitted torque. Major functions of a foundation are to:
Support the total weight of the generating set.
Isolate generator set vibration from surrounding structures.
To support the structural design, the civil engineer will need the following details:
-the plant's operating temperatures
-the overall dimensions of the proposed foundation mass.
-the mounting and fixing arrangements of the generator bed-frame.
The following formula may be used to calculate the minimum foundation depth:
t = k/(d x w x l)
t = thickness of foundation in m
k = net weight of set in kg
d = density of concrete (take 2403 kg/m2)
w = width of foundation in (m)
l = length of foundation in (m)

 

[electricpete]

I have short circuit torque and I do not know how it transfer to foundation in fact I want the torques on stator foundation. What is the relationship between them? The torque transmits with coeffiecient but what is it?

Here's my thought.
Every torque needs equal/opposite torque.
There are no acceleration torques since the stationary parts don't move.
Therefore the equal/opposite torque is seen on machine foundation. (coefficient = 1.0).


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(2B)+(2B)' ?

 

[waross]

I don't think you need this since the generator is designed to withstand the maximum permitted torque. Major functions of a foundation are to:
Support the total weight of the generating set.........
In addition the set must withstand the equal and opposite torque of the driving torque. Add to that the torque developed from the rotor and prime mover inertia when a severe fault causes an abrupt de-celeration. I remember an old motor-generator type welding machine with a problem which some internal connections. When the welder tried to strike an arc, the machine would try to stall the rotor and the whole machine would tip up on one skid. This was scary enough with a shop welder, I wouldn't want to see it happen with a Megawatt class machine.
As well, I seem to remember a thread some time ago concerning inspections for possible foundation damage when a large machine had been subjected to a severe fault.
I agree with electricpete with the following proviso; de-celeration torque is possible.
However if you have been supplied with the torque under short circuit conditions this should be included.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

My thoughts are:
Equal/opposite electromagnetic torques are applied to rotor and stator.
For a given electromagnetic torque, acceleration of the rotor affects torque transmitted to the load but it doesn't affect torque transmitted to the stator and ultimately to ground, that stator torque will be equal to the electromagnetic torque.


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(2B)+(2B)' ?

 

[waross]

I think we are in agreement Pete. My point is that under fault or short circuit conditions, the equal and opposite torque transmitted to the foundation may be aided by inertia and will be in excess of normal full load torque.
Another instance of short circuit torque was a 400 HP motor driving a fan. The contactor flashed over and the motor became an induction generator feeding a short circuit. The de-celeration was so abrupt that the coupling exploded, the motor shaft was bent and the fan shaft was bent. Whatever words we use to describe the torque and the origin of the torque, there is a large force load transmitted to the foundation under short circuit conditions.
Your friend Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[7anoter4]

I agree with electricpete and with waross. The short-circuit current will produce a very big torque. This torque at first will act on the frame bolts. This torque tries to spin the assembly motor-generator-foundation. But, usually, the motor-generator set mass in connection with foundation will provide a great inertia moment and also a counter-acting torque produce by Gravitation will be very big even in a few degrees of unbalance.
I said “usually” as 2 MW generator it seems to me a Diesel-Generator Set [heavy enough].

 

[ScottyUK]

Under short-circuit conditions the machine experiences an accelerating torque because the power output drops as terminal voltage collapses, but the fuel (or steam) which has passed the governor(s) is producing pre-fault power levels.

The worst fault torque will occur with an out-of-sync closure of the generator breaker. On a large machine the sensation is plain frightening as the whole machine and foundation shudders. Once felt it is not easily forgotten.