Short circuit forces used for structural design of the gantry structure

[brTCP]

Dear all, I am a structural engineer, and the electrical engineer gave me the short circuit forces to be applied to the gantry structure. The trouble is that I can't seem to find any reference in the European norms about the consideration of these loads for my strucutral design. Do I consider them as "accidental"? Do I apply a dynamic amplification factor, since the force will be acting during a very short time period? What is the common practice here?

 

[che12345]

"... I am a structural engineer, and the electrical engineer gave me the short circuit forces to be applied to the gantry structure. The trouble is that I can't seem to find any reference in the European norms about the consideration of these loads for my strucutral design...".
1. I am not clear what the electrical engineer "short circuit forces to be applied to the gantry structure" Could it be a misunderstanding/miscommunication, as electrical and structure are of different field of engineering.
2. Could it be the electrical engineer means the "short-circuit (kA) current rating/protection ..."? If this is the case, it is relevant to the electrical design engineer to handle. It has nothing to do with the mechanical structural design.
3. Info. Electrical short-circuit current in kA usually <1s duration does stress the busbars and busbar holders/insulators mechanically, but that force can easily handle by mechanical fittings without damaging the mechanical structure.
Che Kuan Yau (Singapore)

 

[brTCP]

Thank you for your reply! It is possible it is a miscommunication, but according to the electrical engineer, these are forces imposed on the structure, and the structure must be calculated to support these forces. EN 50341 does mention these forces, but leaves it to the National Annex to determine. In my case, the National Annex has no info. It is a substation, and these forces seem to be relevant.

 

[Gr8blu]

brTCP : A motor's torque and weight are supported by the foundation (in your case, gantry) via the motor's housing and feet or flange. In view of this, the foundation's dimensions must be based on the maximum possible levels of torque. These are generally the transient torques generated when the machine is switched on. As these occur in the form of oscillating torques, both compression and tensile forces are generated at the mounting points. All mounting elements and the equipment used to anchor them to the foundation must be dimensioned for these forces, and for any additional forces created by the belt drive or other elements capable of transferring force. Steel base frames should be designed in such a way that these loads are unable to generate impermissible levels of deformation or resonance.

As well as the weight forces, the foundation has to bear all the forces and torques generated when energy is transferred from the motor to the driven machine and pass these onto the subsurface. This also applies to any additional factors which may arise, such as axial thrust and vibrations. In view of this, the foundation must be appropriately designed and adequately dimensioned. The type of subsurface can have a significant influence on the nature of the foundation.

Special care is required when planning steel-framed foundations which are capable of vibration. These are often used in the raw materials or chemicals industries or for harbor cranes.

DIN 4024 must be taken into account when designing the machine foundation as regards the natural frequencies of the foundation (natural frequencies of the foundation after installation of the machine set).

The foundation must be designed in such a way that vibrations cannot be transferred from/to adjacent units.





Converting energy to motion for more than half a century

 

[che12345]

1. I am still not clear what is issue. Need further clarification. It must not be confused between the short-circuit current force and the motor starting torque.
2. En 50341-1 title " overhead electrical lines exceeding AC 1kV..." is unlikely to be applicable, as the gantry is unlikely to be involved with voltage > AC 1 kV. Usually the loads are likely to be within say < 50kW. The power supply is likely to be 400/230Vac say < 100A.
3. Any motor say < 10kW starting torque mechanical stress and running vibration can easily be managed by simple mechanical reinforcement. Generally no big issue to the mechanical structure or to the footing foundation. The weight of the gantry structure would be >>> exceed the torque produced/weight of any motor therein.
Che Kuan Yau (Singapore)

 

[davidbeach]

How did motor torques enter a discussion about short circuit forces?

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

 

[bacon4life]

In the USA, IEEE Standard 605 provides guidance on designing substation structures for short circuit forces. I am not sure what the equivalent European standard number is.

I suspect their might be confusion over the term 'gantry', since I typically heard it as part of the term 'gantry crane'. Maybe the OP just means a bus support structure.

In general the short circuit forces are only relevant to a structure (or portions of a structure) carrying a single phase. The short circuit forces on the wires act in opposite directions, so the overall forces cancel out for portions of the structure carrying all three phases.

 

[oldrunner]

When the electrical engineer designs the transformer coil windings assembly, the physical design is for the wind assembly not to fly apart when a fault goes through the system. For axial loadings of the assembly, he provides a force value that the tie rods must resist - say 300,000 lbs. This load is for a short time. Therefore your electrical engineer should provide a real force that you can use to size whatever you have.