High pole count motors and VFDs. 4

[itsmoked]

Elsewhere I'm working on a 10 pole motor:
thread237-469957

I'm about to spec a VFD for this 25Hp 10pole motor. I was thinking about keeping options open and using a drive with sensorless vector mode. Of course, vector mode can provide a fixed speed unavailable with scalar mode and the motor's slip.

So questions.
1) Do higher pole counts cause issues with vector modes?

2) Does an output reactor muddle the off-phase read-back measurements required for successful FOC (Field Oriented Control) used in vector modes?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

1) No performance issues in SVC or FOC that I have ever experienced. The only issue with high pole counts is it means higher amps, so make sure to buy the VFD based on motor nameplate FLA, not "HP". Been burned by that one...

2) Muddle? Not if the output reactor is there when you tune the drive. In fact when you have a higher pole count (i.e. >6), a load reactor is often a requirement because the higher the pole count, the lower the inductance in the motor. So you may NEED that inductor to keep the drive from going into current limit on you.


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

 

[itsmoked]

oOoohhh. Nice tips Jeff. Thanks!

No name plates on these motors.. They're in-house motors made by the machine company. They do state 25hp in several places.

The entire machine is plated "220V 65kVA" But this entails the '25HP' motor and a large geared rotating table the 25hp works against. I think it's 5hp.

The motor is stated as:
WESTFRAME W445
or
GE FRAME 446

It's served by 480V 30A and has an associated step down 220V transformer.

Ugh. 66kVA @ 220V 3Ø represents 173A!
A typical 5hp represents about 16A
Another 10A for nill controls.

173A - 26A = 147A Good grief!

That calls for a 50 to 60HP drive!

The machine is only plumbed with a 25kVA circuit (480V 30A) and has never tripped the breaker in 25 years.

That alludes to using 113A @ 220V - 26A = 87A into the motor. Which is about a 30HP drive.

Do you think that provides any relief in VFD sizing?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

I can't find a 446 Frame motor.
A 445 Frame will be about 100 HP at 900 RPM. (As much as 250 HP at 3500 RPM)
I am guessing that the wrong nameplate may be fitted.

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

 

[itsmoked]

NO nameplate is fitted.

This is in the manual.

Thanks for checking!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

I meant this plate, Keith.

The entire machine is plated "220V 65kVA"

How about a WAG?
If speed is critical they may have specially wound a grossly oversized frame to get the lowest slip possible.
eg: A 1760 rpm, 100 HP motor will be running at approximately 1790 RPM with a 25 HP load. (Example only. I am not familiar with common speeds for 720 RPM motors.)
If so I would expect a much higher than normal magnetizing or no load current.

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

 

[edison123]

fwiw, the machines we did had stator core of 250 mm long and 900 mm OD and were rated for 415 V, 150 HP, 210 A, 50 Hz, 300 RPM, 20 poles.

Unable to upload the image into the post or as a link.

Muthu

http://www.edison.co.in

 

[itsmoked]

I was wondering about that Bill. I was assuming BIGGER more MASSIVE more stable.. But I bet your example is more on target.

edison; Thank you very much for that info. I was actually thinking "Muthu might have an idea about Blanchard motor currents".

That is a monster compared to this one. 6x the horsepower! Definitely metal grinding.

One of the problems with grinding ceramics is that the grinding wheel doesn't carry away the heat but the metal work pieces easily do it. But when you switch to ceramic it doesn't carry the heat so the grinding stone overheats which overheats the matrix which releases the diamonds. Hence the need to slow down.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Sounds to me as though you have had to learn a lot more about grinding than you probably ever thought you would as an EE...

That’s actually one of the things I like about what we do; we get exposed to and involved in lots of other industries sooner or later.

Thank you Nikola Tesla for being the virtual father of the electrical world by facilitating its spread to every corner and every industry... (because it’s Fathers Day today)


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

 

[waross]

That’s actually one of the things I like about what we do; we get exposed to and involved in lots of other industries sooner or later.

Amen to that!

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

 

[itsmoked]

Well yah!

Besides being interested in dang near everything helps. Primarily designing control systems means I often have to learn considerably more about something than the people who are asking me to control something. They want, "all the eggs to come out of the carrier and go into the flats" they know nothing about acceleration, torque, power, jerk, kinetic energy, duty cycles, fatigue, boundary conditions, and all the ramifications of E-stopping, but we have to.

And, happy father's day you two!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Keith - Yup, machining ceramics is a different ball game. Since my client found the original 300 RPM was too fast, cutting the life of costly diamond tool tips drastically, I did the Dahlander conversion. With some of the ceramics, even 150 RPM was found to be too high. So, the client later on went VFD route, altivar drives, IIRR.

Here is the pic of the motor with original stator winding.

Muthu

http://www.edison.co.in

 

[itsmoked]

What a monster! Square wire and all. Thanks for hunting down that picture. Altivar; Noted.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

A monster alright.

Muthu

http://www.edison.co.in

 

[edison123]

jeff

the higher the pole count, the lower the inductance in the motor

In ac motors, for a given frame, the higher the poles, higher is the no. of turns per phase as per EMF equation, which would imply higher inductance, no?

Muthu

http://www.edison.co.in