Maximum Number of Motor Starts/Hour

[Nick82]

I am working with some 50+ year old GE 100HP Squirrel-Cage motors used as an oil pump for a large generator. The info I've gathered from them include: 3-phase, 4000V, 18.2 FLA, 700RPM, 60Hz, Frame 6334Y, Type K, 10-pole, Nema Class B, Model 5K6334PL1. My question is how many times per hour can these motors be started safely?

NEMA MG-1 has some general specifications, but points to the manufacturer for more specific recommendations.

 

[jraef]

Only GE can answer that question for you. MV motors of that sort are generally built one-off and often specifically to an application, where the duty cycle requirements were part of the design criteria. So without knowing that, there is no telling. I have run into motors designed for one cold start plus one hot start PER DAY with a minimum of 4 hours between the two. That an extreme example just to point out that it really boils down to what the original purpose was and how much that original user was willing to pay.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[ashtree]

If GE don't know and if possible start off with something really conservative and measure the temperature rise on the motor. Even just using a infrared non contact thermometer will give you an idea on how things are going. Whilst the number of starts is important its also going to depend on how you are starting the motor, how long it takes to get up to speed the amount of load at start , how long the motor is stopped and the percentage of the load when its running.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[waross]

Some general comments:
In the 50s NEMA frame motors were common.
When they re-rated the NEMA frames to "U" frames in 1952* they produced about 41% more power out of the same size frame.
For normal applications of large "U" frame motors, three starts per hour was generally safe and conservative.
A lot of large motors used compensator starters back in those days for hard to start loads. (Auto-Transformer starters)
DOL plugging stops and DOL plugging reversal was common with NEMA frame and "U" frame motors in the integral HP sizes.
Then came the "T" frame re-rate in 1964*. Another 41% HP out of the same size frame.
See if you can find the frame designator. That is "U" frame or "T" frame. What was normal service on many "U" frame motors would be abuse of a "T" frame motor.
If there is any indication that these were compensator start, you may want to consider retaining the compensator.
With no "U" or "T" in the frame size they may be NEMA frames. Rugged as a sledge hammer and cool running.

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.

*- Cowern Papers;

http://www.baldor.com/Shared/manuals/PR2525.pdf

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

 

[dpc]

If they are 50 years old, they don't owe you much. I'd start thinking about replacements. I'm struggling to come up with a scenario that would require generator oil pumps to be started multiple times per hour.

 

[electricpete]

4kv 100hp - that's a weird beast.

=====================================
(2B)+(2B)' ?

 

[dpc]

And an expensive beast.

 

[ashtree]

I agree. Unless 4kv is absolutely the only power supply option, for the amount of grief a 50 yr old motor might give you when you are uncertain about some of its operating parameters , why not just fit something more modern. Motors of this size in standard voltage would be cheap compared to the hassle the failure of an oil pump would give you on a big genset.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[LionelHutz]

Is the number needed to setup a relay or because you actually want to start the motors multiple times per hour?

Overall, considering they are GE motors and 50 years old, the starts per hour capability of the motors are probably better than what your application requires. So, for setting a relay pick a fairly safe number like 2 starts per hour and see what happens.

 

[Nick82]

Thank you everyone for the responses. The motors are going to be yanked out, refurbished (customer requested this as the only option), and put back into service. In normal operation, the starts per hour should not be a problem, however, for commissioning the new system we will need to start the motors multiple times to fully test the new control scheme. There are 42 of these beasts altogether, so limiting to only a couple starts per hour will stretch the process out quite a bit.

 

[waross]

Some comments and suggestions.
I spent some time looking for starting frequency information on a couple of manufacturers sites with no joy.
I remember setting up the controls for a 125 HP, U frame motor driving an air compressor.
I still remember that there was a note on the name plate limiting starts to 3 starts per hour.
You have some advantages.
1> A NEMA frame is tougher than a "U" frame motor.
2> After the rewind, I expect that the windings will be rated for a higher temperature than originally.
3> Your oil pumps probably have lower inertia than the air compressor and will be easier to start.
Suggestion; See if you can get the rewind shop to specify a number of starts per hour and sign off on it.
I would be confident with three starts per hour and may go to four starts per hour while monitoring the temperature build-up on the first few motors to be started at 15 minute intervals.
But, the best and safest number will be supplied by the re-winders. I am sure that with modern magnet wire the motor will safely take more starts per hour than it would with the original wire and insulation.
If you can get guidance from the re-winders, please share it with us.
Yours

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