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kssschsekhar (Electrical)
15 Sep 08 0:14
What is the meaning of 6 starts per hour for High voltage motors?
Is there any relation with 3 cold start and 2 hot start with 6 number of starts?
Can I get any informative weblinks in the internet?
Example : 740 Kw, 993 rpm, 50HZ motor, 11kv
rotman (Electrical)
15 Sep 08 7:13
'X starts per hour' means - unless additional data are specified - X starts equally spaced within 1 hour (first start when the motor is cold); in case 6 starts = each next after 10 min. Generally, the same applies to LV, MV or HV machines.
There is do direct relation between number of starts defined as 'X per hour' and 'Y consecutive starts' (eg. 3 from cold state (the first when motor is at ambient temp.) OR 2 from hot state (=first 'hot' start when motor is at rated thermal condition). Starting capabilities of particular type o motor shall be defined by the manufacturer.
LionelHutz (Electrical)
15 Sep 08 8:17
I don't believe that 6 starts per hour means they have to be evenly spaced out. Just that when the first start occurs that you can only start 5 more times within an hour after that start.

It's actually a little work to track because you need to retain the 6 start times so that you can add-in another start as an hour passes after each of the 6 starts then record that next start as the 6th start and drop the one that has already passed the hour.
 
electricpete (Electrical)
15 Sep 08 8:22
I don't think it is well defined.  Certainly you can't do 6 starts in the row, then wait an hour and repeat.  In the face of ambiguity (no minimum time between starts specified), I personally would be inclined toward the conservative interpretation (equally spaced starts).

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aolalde (Electrical)
15 Sep 08 8:55
For "High Voltage Motors" the manufacturer designs the number of starts that the motor can endure before thermal damage is developed.
They comply the standard of manufacture or the customer requests.
The number of starts is close linked to the load inertia since the starting time and the heat developed during each start are proportional to the load inertia.
A constant of inertia like Wk2(Lb*Ft2) or GD2( kgm2) maximum limit, as well as the allowed number of starts are provided in a nameplate attached to the motor.
By the way, 6 starts per hour is far away from normal motors capacity, that should be an extremely light load inertia, other way the rotor or stator windings will be roasted.
 
waross (Electrical)
15 Sep 08 11:03
Search this site. This issue has been discussed several times.

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

LionelHutz (Electrical)
15 Sep 08 15:55
I forgot, I don't see any co-relation between 3-cold starts/2-hots starts and 6 starts per hour.

3 cold starts is illogical. Once the first start is performed the motor is no longer at ambient or "cold".

 
kssschsekhar (Electrical)
18 Sep 08 3:54
Can any body tell me Thread number or site. I did find in eng-Tips.com site
Helpful Member!  dpc (Electrical)
18 Sep 08 10:31
kssschsekhar (Electrical)
21 Sep 08 0:49
Thank you very much "dpc".

 
electricpete (Electrical)
23 Sep 08 11:18
I just found this link which provides a pretty darned good discussion of considerations for repetitive starting, including large motors:
http://findarticles.com/p/articles/mi_qa3726/is_200806/ai_n27900075/pg_1?tag=artBody;col1

I get the hardcopy of the magazine which includes figures, but somehow I missed this article this past June.. can't find my hardcopy ;-(

I have added this link to the FAQ on repetitive motor starting.

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kssschsekhar (Electrical)
24 Sep 08 2:17
Thank you Very much Mr. Electricpete

The information provided is useful for furthur study of individual interest. However Article not concluded our topic only answered.

Final conclusion to this topic is Motor (High voltage, High rating motors)number starts will be depends on the requirement of end user. The end user requirements can be fulfilled by the manufactuer.

However interested people can read for exact information from NEMA MG 1/MG 100 standard.






 

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