Power To Tower Crane

Hi All

Have any of you got any experience of connecting up tower cranes on a large construction site. What is the configuration like?

I have been given the task of arranging the power supply for the crane and the site compound. This will entail submitting an application to UKPN. It is estimated that the site will need approx 230kVA.

Before doing so is there anything that I may be asked by UKPN or need to know regarding the power for the crane?  All that I have at the moment is that the crane requires a 150kVA 3 phase supply.

I have the preferred location for the incoming and a site layout plan etc.

Does the outfit that hired out/supplied the crane not have anyone to do it?

I would have thought that this would be part of the hire/contractual agreement.

I am sure that they will make the final connections.

I have been asked to arrange the supply to site and hence would like to gain an understanding of the configuration etc in order to be able to put an application to UKPN and avoid getting things wrong or UKPN keep coming back asking for more info.

Does anyone have any experience of connecting up tower cranes?

I did a couple about 5 years ago. Cant remember exactly but I know we surprised on how light the load was, I suppose its geared up. Are you sure you have spec correct ?

The info that I have been told is that the crane requires 150kVA, has a 60m boom radius and is capable of lifting 2.5 tonnes at 60m.

I won't be making the connection but would like to know how it would be connected in order to arrange incoming position, any switchgear housing etc.

And the motors , hoist, traverse etc  are not continuous rated . Probably use more power for floodlights and cab heater.

Are you sure those KVA ratings are correct?

Evans Electric said:

And the motors , hoist, traverse etc  are not continuous rated . Probably use more power for floodlights and cab heater.

Are you sure those KVA ratings are correct?

Click to expand...

Like i say above that is what I have been told. I have done a bit of research around it and a found a few other cranes with similar power requirements. To be honest I was shocked when i was told it needed that much too.

Well thats a 400A supply  to the site and 200A to the crane   ....could be wrong ...often am..... seems a lot .

Can't you connect it to the nearest street light :innocent

Yes thats correct. The remaining 200A is only used for floodlights, power for site cabins. Its for a temporary site connection during the construction phase.

A large printing works runs on a 400A supply ...

Just saying .

Just pointing out ,  as I'm sure Canoey is  already aware of ,   many machine suppliers/makers  state a much higher power than is necessary .

Printing presses are notorious for asking for much bigger feeds than necessary but if you don't follow manufacturer's instructions they could absolve their guarantees after commisioning .

I've known firms have to upgrade their incomming supply when it was not necessary , just to comply.

Just rabbiting.

Thing is with Servo drives on CNC machines, and some printing presses they can run @ 400% overload for a few seconds, and would expect the supply to be stiff enough to cope, especially with a big say 4 tower press with a folder then re-webbing it because the power tripped off under a minor (machine wise) overload could force the print run to be moved to another press or missed completely.

With CNC machines it is the instantaneous current from the jerk generated when axes have high accelerations programmed, as I say this can be up to 400% above full load nominal current for the drive/motor combination.

An example I am working on now, on equipment from a previous employer.

Take a motor with a rated current of 32.5A, this would have a 25mm sq power cable between the motor & drive.

Peak operating current to be expected 163A.

These are per phase values.

Hence why the manufacturers ask for such large supplies, taking a CNC machine in a dedicated manufacturing plant, think say Ford, where it makes the same thing day in day out for its whole life, then you can easily size the supply down with use of a power analyser.

IF you have a jobbing shop machine then it may only do a batch of on part once in its life.

I was working on a Cincinnati machine a few weeks back, there was an alignment error, it had a fault that we were identifying, it ended up taking a 30mm deep cut, it should only have been 10mm, the tooling and machine were easily capable of taking the forces, the drives and motors just stepped up to the mark and the necessary current was supplied.

Yes this was a fault condition, but, the machine was more than capable of the forces & power required.

You could feel the floor shaking!!!

One of the highest peak power requirements is High Speed Machining where it is all G0 stuff, as the reverse jerk is immense and the peak motor power requirements often hit maximum values.

Whilst this is only for very short times, there can be MANY of these per minute.

Hence the overall duty cycle can be quite high.

Printing is quite different, but, the inertial loads are generally huge in comparison to the motors, the reflected inertial values are almost orders of magnitude, so the accelerations are quite low, but, the initial jerk can again be quite high, and often all drives ramp up simultaneously as they are all synchronised. 

One thing I discovered from at least 4 different firms was they never run them at full speed  and ipso facto the IR driers never went over 80% .

These were for 6 colour .