0.18 kW motor - single phase 230V or three phase 400 V? 3

[krisys]

We are procuring a small chemical injection skid which has a chemical injection pump. The motor rating of the pump is 0.18 kW. The skid supplier has offered the motor having single phase. My client wants a three phase motor. He says that it is the industry standard.

In my opinion, such a low rating motor (0.18 kW) will be more economical at single phase rather than three phase. So providing a single phase 230 V motor is justified.

Any one has a different view?
Can you just give me few points for arguing my case.

 

[edison123]

What is the speed since a 3-ph motor has speed limits?

At that low rating, the price differential cannot be much. A 3-ph motor is more efficient, has lesser components to fail and has a smoother torque curve. Only cost driver could be running 3 wires, instead of 2 for the supply.

Muthu

http://www.edison.co.in

 

[krisys]

It is a 1500 rpm motor.

 

[waross]

I agree with you. A 230 Volt motor can easily be connected. A 400 Volt motor will possibly need some expensive supply gear.
There is more to consider than just the cost of the motor itself.
Also, you can easily derive 230 Volts single phase from 400 Volts three phase, but you can't run a 400 Volt three phase motor on 230 Volts single phase.
But, the customer may not always be right but he is always the customer.
Try to get a memo (You may write it yourself and submit it for him to sign off on.) requesting a three phase motor and give him what he wants.

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

 

[Skogsgurra]

"Industry standard" - what does that mean? Is this customer one of those guys that "has heard" that three phase is the industry standard? Or is it really the industry standard? Even at these extremely low power levels?

I agree totally with Bill. A single 230 V outlet is all you need to make the device run. Easy to set up, easy to move, easy to maintain or replace if needed.

Industry standard? Yes, when you are getting above a few HP. But I wouldn't say that FHP motors in general are three-phase. Rather the opposite. Some are even DC motors or steppers.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[waross]

There may be an exception.
If there is a three phase, 400 Volt MCC or PDC with 400 Volt three phase readily available, and this is permanent part of a skid and will not be moved, I would not resist using a three phase motor. If the plant standard is 400 Volts three phase, then a neutral to derive 230 Volts may not be readily available.
Too close to call.

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

 

[Skogsgurra]

On this side of the pool, 220 or 230 V outlets are available "almost" everywhere. But, we don't know from where the OP is (although the early posting hours seem to indicate 50 Hz land). So, it all depends. As always.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

The premise that 3phase are simpler and cost less is incorrect - with regard to sub-HP motors. I generally prefer them as they are more dependable and VFDable but I have never found one to ever be less expensive than a single phase motor of the same HP. Probably, because there are 5,000 single phase sub-HP motors made for every three phase one.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Agreed. 1/4HP (186W) is the smallest 3 phase motor I’ve ever seen, but I have NEVER seen one readily available off the shelf anywhere. Single phase motors that size however are available almost everywhere. So depending on the use, any (incorrectly) perceived savings or “standardization” they may hope to get will be wiped out by down time costs the first time they must replace this motor and have to wait a week or even a few days to get it.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[RRaghunath]

In power plant, I have seen 3-phase motors of such small rating.
There, it is a standard to specify 3-phase motors even in sub-kW range.
Three phase motors do not need start/run capacitors and thus more reliable and long lasting especially under harsh industrial environment, I suppose.

Rompicherla Raghunath

 

[itsmoked]

Absolutely more dependable, better even in all ways. Except. They need 4 wires instead of three and as discussed harder to get and more expensive.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Well this is part of an equipment skid.
The skid manufacturer offers two motor options, single phase and three phase.
I imagine that the skid manufacturer has both single phase and three phase replacements available.
Barring special circumstances, both single phase and three phase motors are very dependable.
The customer wants three phase.
Despite the discussion as to the relative merits of three phase motors versus single phase motors, give the customer what he wants.
As for feed conductors, three conductor plus ground cable is common in industrial settings.
As well as the grounding conductor included in the cable, it is common in petro-chemical plants here to add an external ground conductor with an ampacity many times the code minimum.

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

 

[Skogsgurra]

Bill has some very sensible comments.
Still, it has been a valuable "ventilation" of different views. Good thread.
But I do not understan the four wire thing. If the fourth wire isn't PE.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

I agree also. Maybe educate the customer a little, then get them what the they want.

Yes, the fourth wire is the PE.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[krisys]

I thank the Eng-tips fraternity for the overwhelming response.

The location is in the middle east region, at one of the offshore oil platforms. It is certainly an industrial environment and 3-phase would not have been a problem. Frequency is 50 Hz and following IEC standards.
No doubt that the environment is also extremely harsh.

I was really impressed by Raghunath’s

It did not strike to me that there is a capacitor (and may be a cut off switch also) in the single phase motor. Certainly it is a weak spot.

Had it been a new proposal, I would have certainly insisted for the three phase induction motor. But now it is too late because the motor (part of a chemical injection skid) is already delivered to site and commissioning is going on. During the commissioning someone has raised this issue.

At this stage it is too painful to replace the motor. It is not only replacing the motor, but also to identify the motor starter in the 415 V MCC and laying a cable etc. Presently the power supply to the chemical injection skid control panel is given from small power distribution board (small power DB).

The consequences of a decision to replace the 1-phase motor with 3-phase motor is the delay in commissioning, increased cost and an impaired reputation. Inconvenience is also there.

Now my effort is towards convincing my internal client to accept the installed equipment without dragging it further.

The customers own standard for the motors states that the motors 0.18 kW and above shall be 3-phase design.

But this motor is part of a package equipment. So whether I can make my case to get some concession?
Can anyone suggest any additional inputs to argue the case in my favor?
eg: the reliability record of 1-phase motors, or part of the package unit etc?

 

[itsmoked]

From what you describe definitely stick with the installed 1Ø motor. It'll last 5 to 8 years anyway. A three phase might've lasted +2 more but things change pretty fast on oil platforms anyway.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Lots of single phase motors last twenty years or more.
The small fan motors on air conditioners often outlive the air conditioner.
I/4 HP fan motors on residential furnaces last for years, often until the furnace is scrapped because the heat exchanger has failed.
The design of the centrifugal switch in a single phase motor is such that there are no sliding or wearing parts once the motor is up to speed. The life expectancy of the starting circuit is more a factor of the number of starts than of the years of service.
If the skid will ever be shut down, serviced and recommissioned that is a good opportunity to change out the motor for a three phase motor.
I expect that a single phase motor will easily last until the next scheduled shutdown.

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

 

[krisys]

Thanks Waross.

Once our end user accepts the installation, the motor will not be replaced. It will continue to be in service with the same motor.