Resistive Load Safety
Resistive Load Safety
(OP)
Another design theory question here...
My application is going to rectify 480vac 3phase to 648VDC and send it into a dummy load. The load is 13Ohms, with 50Adc load, 32.5kW dissipation.
I'm designing the control now, that the user will interface with. I suppose my question is theory, is it safe/what are the effects of just using a heavy duty contactor for the 3 phase AC input...and as soon as we are ready to test...just close the contacts with full load attached.
Will slamming a large load with that much voltage/current cause problems? There is nothing reactive...no caps that need to slowly charge up etc. I don't see any problem with my green eyes...but this is a learning project I don't want to create any hazards.
My application is going to rectify 480vac 3phase to 648VDC and send it into a dummy load. The load is 13Ohms, with 50Adc load, 32.5kW dissipation.
I'm designing the control now, that the user will interface with. I suppose my question is theory, is it safe/what are the effects of just using a heavy duty contactor for the 3 phase AC input...and as soon as we are ready to test...just close the contacts with full load attached.
Will slamming a large load with that much voltage/current cause problems? There is nothing reactive...no caps that need to slowly charge up etc. I don't see any problem with my green eyes...but this is a learning project I don't want to create any hazards.






RE: Resistive Load Safety
On the subject of your original question, is this a controlled rectifier or just a 3-phase plain bridge? A controlled bridge would allow you gently ramp up the voltage. If you just switch on a big load like that consider what effect it may have on other users fed from the same bus.
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I don't have an attitude problem. You have a perception problem...
RE: Resistive Load Safety
As it wasn't meant to be rude, no need to be defensive on my end.
(Personally I would have reserved that portion for a private message as a professional courtesy though.)
To alleviate some concern, I will be passing the design by another engineer before implementing of course. Even if I was an expert in this field, I would do the same as its always possible to overlook something. With such a potential safety risk on this particular project, I would certainly hope any engineer would do the same.
As I said its a learning experience, and I do appreciate any and all comments, off-topic, or just helpful one's that may be useful down the road for any post of mine. As a general rule of thumb in my field, I love when questions are asked...to me its a complement via the confidence they have in asking me.
RE: Resistive Load Safety
Could you please answer Scotty's questions?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Resistive Load Safety
1 What does this kind of load do to the mains?
2 What cable area do you need?
3 Fusing, temperature cut out.
4 An emergency stop button with tested function and that everyone knows where it is and why.
5 Getting rid of the heat. This is like having at least 30 radiators turned on.
6 How long will this be activated? What will the end temperature be?
7 A lot of code issues have to be addressed. Are you really aware of what the national code says?
If that other engineer is a practising electrical engineer with power background (all EE:s are not power EE:s) I think that things might work out. But, personally, I would turn to a company that is doing these things for their living. They know about these things, they have the right materials available, tooling and know-how. It is not something I would build myself. And I have a power electronics background with 40+ years of experience.
It may seem simple ("It's nothing more than Ohm's law") and that may be so. But power engineering is a little bit more than Ohm's law.
Finally. In many countries, a PE is supposed to supervise and approve power circuits. Where are you situated?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...