Absolute most compact motor technology 125kW Motor 8000rpm

[jmspeedfreak]

Hi,

I'm trying to find out what constitutes absolute minimum volume and mass for a 125kW motor to drive a propulsion propellor at 8000rpm. Maximum torque of 750Nm at 1500rpm or so.

Preference is for minimum frontal area ie. motor diameter with length less an issue:

<350mm ideal
<450mm acceptable/fine
<550mm ok

Many thanks - I appreciate cost is always important, but not so critical for this app.

John

 

[Skogsgurra]

Complex question, this.

Do you have a load torque peak at 1500 RPM? Your 750 Nm at 1500 RPM is equivalent to around 125 kW. What torque do you have at 8000 RPM?

Anyhow, a slender PM synchronuous motor is probably your best bet. There is a balance between area and length and critical speed which needs to be found. I cannot give any hard numbers, but I think that it should be possible to meet your requirements with such a motor.

Going up in speed (50 000 - 100 000 RPM) and using a planet gear would probably also be a solution. At some efficiency penalty.

I imagine that cooling is good when this motor develops its peak power. How good?

Also, is this for continuous duty or intermittent? What kind of duty? It all influences the copper and iron masses needed.

Gunnar Englund

http://www.gke.org

 

[jmspeedfreak]

Thanks Gunnar,

The motor would be constant power from 1500rpm out to 8000.
Hence torque at 8000rpm is 150Nm.

I tend to agree on the PM solution yep.

The performance target for power (125kW) is certainly continuous at 8000rpm. In reality the 1500rpm torque would probably have to be sustained for minutes (vehicle drive application).

Cooling is almost certainly required - liquid cooled I presume?

 

[motorspert]

Does a propellor load not require increased torque with load? is the peak torque an accelerating torque or short time?

From the work done for the naval propulsion systems I would assume that superconducting gives the best energy density asthere are serious ampunts of money being spent on the developments - but theses are at ratings 5000-20,000kW. At 125kW an established technology such as PM or induction would be the best bet.

 

[DickDV]

Check out Reliance Electric's RPM-AC line of motors. These are non-NEMA motors and are exceptionally compact for induction motors.

They are not suitable for across-the-line starting--must use inverter for power source.

This is about as compact as induction motor technology gets.

 

[tgmcg]

Calnetix is another supplier of high-speed PM motors and generators...on magnetic bearings too, if you need them.

 

[ScottyUK]

Depending on how serious you are in your pursuit of 'absolute' smallest possible size, consider some of the cooling methods employed in large HV generators where heat removal is a much tougher task because of the square/cube relationship between surface area and volume: liquid cooled stator windings, hydrogen cooled rotors.

Both bring additional complexity and require auxiliary subsystems with problems of their own, but that depends on how much you want to minimise the size of the motor.

----------------------------------

I don't suffer from insanity. I enjoy it...

 

[UKpete]

I would also go for PM synchronous, they have the highest power density of them all.

At 125kW your spec is at the high end of automotive traction motor specs, PM water cooled versions of these are appearing although unfortunately these are often "in-house" developments. Some independent suppliers do exist, for example try UQM:

http://www.uqm.com/

 

[MikeHalloran]

Does it _have_ to be an _electric_ motor?

Other options exist.



Mike Halloran
Pembroke Pines, FL, USA

 

[UKpete]

Hello Mike
There are other options, possibly more compact at the point of application (e.g. hydraulic motor) and there are also issues such as:
controlability
reliability
total system mass
total system efficiency

I think that an electric drive scores highly on all of these, though in this forum we probably don't know much about the alternatives.

 

[waross]

If you need the full 125 kw at 1500 rpm, I would suggest looking for a 1500 rpm, 125 kw motor that can be bought off the shelf and will stand the forces at 8000 rpm. I did a little surfing and found a 75kw Baldor motor at 1500 with a diameter of 524 mm. Two of these in tandem would give you your required power.
You will probably save a large percentage of your budget if you can go with off the shelf motors. You would probably want to get the balance checked before spinning them at 8000 rpm.
If you look around you will probably find even smaller 75 kw motors. You may be able to use a three in line "Tridem" arrangement for an even smaller diameter. Start googling motor manufacturers and checking out the spec. sheets
yours

 

[itsmoked]

Waross makes a good point.

Is this for an Azipod? Hence the diameter concerns?

Keith Cress
Flamin Systems, Inc.- <

http://www.flaminsystems.com>

 

[MikeHalloran]

It sounds like a torpedo drive.



Mike Halloran
Pembroke Pines, FL, USA

 

[waross]

Hello jmspeedfreak
Your speeds seem extremely high for a propulsion propellor. If you are using a reduction gear system you may want to consider a two speed planetary system. If you use a greater reduction ratio for slower speeds, you can use a higher motor speed with the resulting reduction in motor size. The two speed planetary gearbox was used by Henry Ford in the Model "T", and later was also used by Buick in the early 50's behind a V-8. It's not rocket science.
That is if you constrain your speed ratio to 3000/8000 instead of 1500/8000, you can cut the physical size of the motor considerably.
yours

 

[jmspeedfreak]

Thanks Waross,

I tend to agree, the torque target is more probably more sensibly met by gearing.

I would have no problem using a two speed epicylic.

Whats the gist if I use 3000/8000 instead then?

Also, Mike H - what other options are you thinking of?

 

[ozmosis]

The following link is to a company in the UK. I cannot say that I have used them myself but have always contemplated them on high speed test rigs, especially where space is of a premium.

http://www.compactorbitalgears.com/

 

[waross]

Hello jmspeedfreak
I am not familiar with the permanent magnet synchronous motors but it may be well for you to investigate them.
Re. the change in speed ratio. It may not cut the physical size exactly in half, but it will double the power of your chosen motor. A 62.5Kw 1500 RPM motor is typically the same frame as a 125 Kw 3000 RPM motor.