VFD For 2 Motors Driving Same Equipment - Continuation and Decision Arrived

"... the total power drawn by motor has never exceeded 37.5 KW (the motor capacity is 45 KW) ..."

Is it safe to assume that the new, larger (~doubled) load will consume twice this figure? Ie, 75 kW? If you use a smaller (60 kW) motor with a suitable gear box, what will be its load (<60 kW) and won't your machine's throughput be significantly less than twice the machine's previous throughput?

I still think the best option is the 90 KW drive and motor, less headache in the end.

Why do you type everything in bold, it's very distracting, and it's like you are shouting.

I am going to guess admin fixed the boldface, now we look like idiots.

Nah. If the reader isn't smart enough to deduce from our comments that his post had originally been posted in boldface, they probably won't have the wits to follow the conversation either. No worries

I don't know why I accidentally hit the reply button on top of your comment.

We call that condition: "Too broke to pay attention."

I agree with what you said about the misery of adding up the kW, and comparing production rates. Why don't they just add a complete pre-processing line, or whatever? Could it be this is not cane squeezing? Maybe it is a large coal-fired power plant, and they need to grind twice the coal, but cannot install another complete grinding line.

Either way, they will not enjoy the higher reliability of having so-called "lead-lag" production where one line can rest idle when not required, but is there for back-up, and also the heavy demand hours.

He said on his original thread that they were processing sugar cane.

<...we...>?

Think about it in terms of energy required: if it took X kW to process Y amount of sugar cane per hour, using less than 2X kW cannot process 2Y cane per same time interval. A smaller motor will necessarily have to be geared-down even more, slowing the process.

Taking this to the extreme, consider a scenario where you've a 1 kW motor and an outrageous gear ratio. You might get the required torque, but at the cost of throughput.

Doubling the machine's capacity without doubling the energy input results in a slower process. There's simply no way around it unless you use a different, more efficient process, but this isn't what you're doing. If it slows it enough, what is the point in using a scaled-up machine? Doubling the capacity will require at least 75 kW and you can't make it up by playing games with the gearing. Energy is energy and you need at least 75 kW for the job. Just bite the bullet and put your 90 kW motor/gearbox in there if you want to take advantage of your larger machine's capacity.

I might also add that you will pay for that larger motor whether or not you install it. You can either pay for a suitable motor up-front, or you will pay for it in lost productivity when compared with what you could have made had you used the larger motor. One way or another you will pay for it, so you might as well get the right motor for the job and be done with it.

I agree with you on both accounts, the management and your team need to see that they are about to step in "it" big time.

You engineer it right, and tell how the cow eats corn over there.

in lowercase, non-italics.

One hopes that the power supply and the cables are adequate for the bigger load, because it isn't obvious from this and the earlier thread.

No worries.

Now THAT is an extension cord!!!! Just loike 'eees knoife!

It looks as though the barrels on the left end of that thing could handle about 50x the amps of the cord on the right. What gives?

Your guess is as good as mine, but the connector itself is rated at 11 kV, 400 A (plus a bunch of other specs). A so-called 'wet mate' connector made by MacArtney of Scotland.

This whole thread is superfluous, anyway; it should have simply continued from the original thread.

Agreed.

Quite.

The responses in this forum constitute well-meant advice from anonymous strangers. It is a relief, because of it that none of them is liable in the event of a recommended course of action not working out.

It is the responsibility of the original poster to select and apply the chosen course of action on the basis of local Standards and best practice, for that individual's name will be on the solution. Engineers' reputations are built on getting things right.

<...member’s 1^st choice...> To rely on the votes, for want of a better word, of anonymous strangers to effect an installation in pursuit of business objectives is at best abstruse, ranging through various shades of immoral, towards the borderline of criminal. For those reasons: <unsubscribes>.

Can anyone tell what decision was actually made, other than ruling out the 60kW motor option?

"23 Members have responded with good suggestions and I am thankful for the members who responded. This response has been shown by me to the management as well as to my team."

So when do we split your consulting fee?

"Three weeks back I have posted a problem about VFD Motor and Gear Box and the link is http://cr4.globalspec.com/thread/111882#newcomments Please open this link and read so that you can re-call your memory for this topic, and read furthe below.

23 Members have responded with good suggestions and I am thankful for the members who responded. This response has been shown by me to the management as well as to my team.

It can be seen that member’s 1^st choice goes to single drive of 90 KW and 2^nd choice goes to identical capacity drive and motor to be installed on the other side of the present (which will be mirror image) and 3^rd choice goes to that of one common drive of 90 KW and connect to two 45 KW motors on either side.

Pl. remember that before expansion, the total power drawn by motor has never exceeded 37.5 KW (the motor capacity is 45 KW) for expanded capacity (Pl. open the link http://cr4.globalspec.com/thread/111882#newcomments and read my posting) 45 KW drive with motor suitable for VFD application.

But now one more suggestion has come up that replace the present drive with 60 KW motor with a suitable gear box – where the gear box out put hollow shaft will match to the existing driven shaft – since it is shrink disc type coupling and run the unit.

I am not agreeing for this, on two accounts.

1. For 60 KW the torque out put will increase, than the 45 KW and the hollow shaft thickness ( in order to accommodate shrink disc type fitting) will increase and the philosophy of shrink disc will be lost cannot be fitted.

2. The Service Factor of the gear box cannot be to our choice.

Further the 60 KW gear box weight will be more by 70 % to that of the existing gear box and over hanging bending moment will increase and deflection also will increase – perhaps more than the permissible level.

Therefore, it may not work out.

Now I request the members to share their views.

Thanks,

DHAYANANDHAN.S"

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How does this even remotely resemble a "Decision Arrived"???