460 volt or 600 volt supply 5

[CharlesFaller]

I am a new Maintenance Engineer in our company. My boss suddenly gave me an assignment to research about the advantages and disadvantages if he changed the supply of a motor control system from 460 volts to 600 volts, but I'm really not familiar with the system. Can you please help me on this? He specifically asked me about the effect of this to its wirings, motors and codes. Thank you.

 

[waross]

Change for the sake of change is expensive.
The first choice for voltage is the standard voltage of the utility in your area.
The second choice is equipment voltage when there is a large amount of legacy equipment involved.
If the utility voltage is 480 V then most of the motors and equipment available locally will be 460 V rated. If you go to a 600 V system, you may often find that the 575 V motor that you need in an emergency is not available in local stock.
As for losses, the 600 V system may have a little less loss in the feeders. I am sure that if you take one of your motors as an example, (not the largest, not the smallest, medium sized and medium length of feeders) and calculate the feeder losses at both 480 V and 600 V, versus the cost of changing, you will find the payback period ridiculously long.
One of our customers had a plant with a mix of 460 V motors and 575 V motors. They had a 480 V MCC and a 600 V MCC. Almost every time they re-arranged the machinery or the plant in the east sent a piece of equipment, it was the wrong voltage. We made a lot of money installing buck-boost transformers to correct the voltage.
If you consider changing or mixing voltages, look into the open delta auto-transformer scheme. This is the cheapest, to buy and to instal. It is quite user friendly.
Wiring and codes for 480V and 600 V are generally the same but arc flash issue may differ.
Wiring is the same except that you may often be one wire size smaller with the slightly lower current at 600 V.

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

 

[X49]

Are you talking about changing an entire MCC from 480V to 600V? Chances are that if you are in a location where 600V is a common voltage (Canada), the switchgear itself would already be rated for 600V use, but you may have to get the manufacturer to relabel the equipment as such. Changing the voltage to 600V will increase the amount of load you can connect to your bus by approx. 25% (in terms of power).

Motor starters could be retained, but overload heaters must be changed and MCP's would need to be changed if outside of their adjustment range.

If you have VFD's or soft starts, chances are that the current 480V equipment will not be rated for a 600V system (generally 690V max operating voltage). They would have to be replaced at high expense.

Cables could be retained since they will almost certainly have 600V insulation. The advantage here would be reduced losses and voltage drop.

Of course your motors would also have to be replaced with 600V motors. 600V motors are not fundamentally cheaper or more efficient than 480V motors so you won't really see any benefits other than reduced losses and voltage drop from the cables. It seems like a lot of work for very little gain. However, if starting from scratch, I would most often use a 600V system.

 

[jraef]

Excellent answers from both of the above members (as usual). I'll only chime in another vote for Bill's comment on the availability of equipment. If you are anywhere other than Canada, your chances of getting 600V motors, transformers etc. off the shelf are slim to none. The meager energy savings from lower cable losses could be wiped out by one single air freight charge in an emergency, let alone the cost of additional down time.

If your boss is thinking along the lines of "higher voltage = lower current = lower energy bills", then you need to educate him (/her). Energy is energy, i.e. the watts stay the same and the utility bills you for watts, not amps.


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[CharlesFaller]

I'm very grateful to all of you. This is a very big help for me. I hope I can also impart my knowledge and ideas soon.
Thanks again guys!

 

[ozmosis]

CharlesFaller
Nothing much to add to what the previous posters have added but it did remind me of a small cartoon I remember I'd seen in an old text book about Project Management. Maybe you could show it to your boss...if he has a sense of humour!