Motor Swap 3

[itsmoked]

I've got a 15HP 575V motor that's lost it's country finding itself wandering in 460V land.

I want to replace it with a 460V unit.

I see that it's a Chassis/Frame 254T.
I'm not all that clued-in to exactly what 254T relates to in detail.

What else should I be watching out for?
Shaft length?
Shaft diameter?
Foot pattern?
Or, are those covered by the 254T?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[RedSnake]

This might be something.

https://www.baldor.com/Shared/pdf/nema_chart_04.pdf

This is not the actual motor but maybe can be to some help.

https://www.usarollerchain.com/Automatic-254T-Frame-Motor-Base-p/621-automatic-base-254.htm

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[Gr8blu]

itsmoked: Other than geometry, there are a few rating things you need to watch for as well.
1) Note the KVA code (G): this means inrush is supposed to be limited to something between 5.6and 6.3x rated current. More importantly, that translates to an actual AMP range (85-96 A). You might need to verify the replacement 460 design also meets that maximum current limitation (which should mean a lower allowed "per unit" inrush, since the 460 design will draw more current at rated condition).
2) Also note that the 575 nameplate gives a 1.25 SF - this means it could run at 25% above nameplate (or roughly 19 HP) continuously: if the process still requires this capability, make sure the replacement machine is capable of it.
3) In a similar vein, if the process is actually speed-dependent, verify the running speed of the new design. Chances are you'll be close to the listed 1770 of the original ... but it pays to check before you get to the "fire it up" stage.
4) Lastly - check the power factor of the replacement machine. Your PF correction might not be correct for the 460 design if it's much different than the listed 0.82 PU.
5) NEMA (and IEC, come to think of it) both use "standard" frame sizes in the smaller power ranges: 254T is one such for NEMA. In general, this standardization governs the exterior geometry of the design (shaft height, foot bolt location, length between bearing centers, overall height/width, shaft extension diameter and usable length, shaft key geometry, and distance from end-of-shaft to first hold-down bolt). It does not necessarily limit you to foot- or face-mount designs ... there's usually something buried in the manufacturer's "smart" model number that tells you which it is (if you can't physically see the thing for yourself).

Converting energy to motion for more than half a century

 

[waross]

Design B;

Motor design letters
The National Electrical Manufacturer’s Association (NEMA)
has defined four standard motor designs using the letters
A, B, C and D. These letters refer to the shape of the motors’
torque and inrush current vs. speed curves. Design B is the
most popular motor. It has a relatively high starting torque
with reasonable starting currents. The other designs are only
used on fairly specialized applications. Design A is frequently
used on injection molding machines that require high pullout
torques. Design C is a high starting torque motor that is
usually confined to hard to start loads, such as conveyors that
are going to operate under difficult conditions.
Design D is a so-called high slip motor and is normally limited
to applications such as cranes, hoists, and low speed punch
presses where high starting torque with low starting current
is desirable. Design B motors do very well on most HVAC

You need 18 Amps and an extra 120 Volts. That's 2.16 KVA.
Add 25% per code and we have 2.7 KVA.
A pair of 480:120V, 3 KVA or larger lighting transformers should do the job.
We used to mount the transformers adjacent to the motors and trim the overload settings in the ratio of 5/6 or 6/5 as needed.

In addition to the standard numbering system for frames,
there are some variations that will appear. These are itemized
below along with an explanation of what the various letters
represent.
C Designates a “C” face (flange) mounted motor. This
is the most popular type of face mounted motor and
has a specific bolt pattern on the shaft end to allow
mounting. The critical items on “C” face motors are
the “bolt circle” (AJ dimension), register (also called
rabbet) diameter (AK dimension) and the shaft size
(U dimension). C flange motors always have threaded
mounting holes in the face of the motor.
D The “D” flange has a special type of mounting flange
installed on the shaft end. In the case of the “D” flange,
the flange diameter is larger than the body of the
motor and it has clearance holes suitable for mounting
bolts to pass through from the back of the motor into
threaded holes in the mating part. “D” flange motors
are not as popular as “C” flange motors.
H Used on some 56 frame motors, “H” indicates that the
base is suitable for mounting in either 56, 143T, or 145T
mounting dimensions.
J This designation is used with 56 frame motors and
indicates that the motor is made for “jet pump” service
with a threaded stainless steel shaft and standard 56C
face.
JM The letters “JM” designate a special pump shaft
originally designed for a “mechanical seal”. This motor
also has a C face.
JP Similar to the JM style of motor having a special shaft,
the JP motor was originally designed for a “packing”
type of seal. The motor also has a C face.
S The use of the letter “S” in a motor frame designates
that the motor has a “short shaft”. Short shaft motors
have shaft dimensions that are smaller than the shafts
associated with the normal frame size. Short shaft
motors are designed to be directly coupled to a load
through a flexible coupling. They are not supposed to
be used on applications where belts are used to drive
the load.
T A “T” at the end of the frame size indicates that the
motor is of the 1964 and later “T” frame vintage.
U A “U” at the end of the frame size indicates that the
motor falls into the “U” frame size assignment (1952 to
1964) era.
Y When a “Y” appears as a part of the frame size it means
that the motor has a special mounting configuration.
It is impossible to tell exactly what the special
configuration is but it does denote that there is a
special non-standard mounting.
Z Indicates the existence of a special shaft which could
be longer, larger, or have special features such as
threads, holes, etc. “Z” indicates only that the shaft is
special in some undefined way

I have mentioned before, a customer we used to service.
The business was cutting and bending re-bar.
The original plant was based on 480 Volts.
The company was associated with a plant in Ontario where 575 Volts had been the standard voltage for decades.
The plant was moved to a new location and BC had gone from 480 Volts to 600 Volts as the standard voltage.
The new plant featured an integrated service with a 600 Volt MCC and underground conduits to the locations of 600 Volt machines.
The next section was an auto-transformer stepping 600 Volts down to 480 Volts.
Finally there was a 480 Volt MCC with underground conduits to the 480 volt machines.
There was no easy way to run from the 600 Volt section to the 480 Volt section.
Then they brought a 575V (600V) machine in from the eastern plant to replace a 460V (480V) machine.
A pair of small transformers connected in open delta solved that.
Then a 575V motor failed and was replaced with a 460V motor from spares.
A pair of small transformers connected in open delta solved that.
After a few years, we had open delta auto-transformers all over the plant.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[dArsonval]

This motor could be a collector's item Ha Ha ; )

I can't resist. That's a U.S. Motor that was actually made in the United States!
(Have not seen one of those in a long time ; )

For a decade or longer... most of their name plates have been stamped,
"U.S. Motors- Made in Mexico"

Not a useful contribution I know... just an observation.

John

 

[RedSnake]

On that note the young mechanics are so concerned over the old motors wanting to send them of for maintenance repare for no good reason.
I try to tell them as long as you lubricates the ball bearings accordingly it will be fine, a good quality motor, dimensioned and set up properly, it is like a iron lever, you can't wear it out. ;-)
At least not as long as the ball bearings are fine and you don't overheat it.
Hade more problems with the ones they sent off then the ones they haven't touched.

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[itsmoked]

Thanks much Red, Gr8blu, and Bill!

Your responses were very helpful. Bill you have me reconsidering.. I can buy 2 transformers for less than an Ebay motor with a questionable pedigree and this would bypass all the motor gotchas too.


Thought I responded yesterday! Since I didn't I'll add that I did go with the open delta. I went to my favorite site and was greeted with every last "lighting" transformer being out-of-stock except they had two 3kVA units.

That is some serious omenage so I proceeded down that path.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

On an open delta, the secondary windings have to carry the motor rated current. It is a single connection, not a combination of two phases as a full delta,so there is no worry about phase angles or the resultant of currents at two different phase angles.
Current in equals current out equals motor phase current.

For a 120 Volt secondary, (480V + 120V = 600V) the rated transformer current at 3000 VA = 25 Amps.
Service factor Amps = 19 Amps.
19 Amps x 1.25 (code) = 23.75 Amps capacity required. Good to go.
We used to hook them up directly to the motor and tweak the overload relay for the current at the supply voltage.

For future sizing, when stepping down with an open delta auto-transformer, the secondary carries the motor current plus the transformer primary current. It adds a step or two to the arithmetic but it is still a simple calculation.



--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[itsmoked]

You have it Bill. You forced me to figure it all out a couple of years ago.

What I don't have figured out is that doing this we've raised two of the three phases to 600V but where's that leave the third phase?


Re: For this "Collector's Item" motor I'm going to megger it and if it's low saddle it with a bunch of heat lamps for a couple of days while the rest of the controls come together. Make sense? What should I consider a too low reading?

Keith Cress
kcress -

http://www.flaminsystems.com