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Permissible no.of starts per hour for MV Sync and Ind motors

Permissible no.of starts per hour for MV Sync and Ind motors

Permissible no.of starts per hour for MV Sync and Ind motors

(OP)
I did find some interesting Q & A sessions on this subject in this forum and I thank all contributors but none addressing large Medium Voltage motors except stating that ask manufacturer of motors to provide data on number of starts per hour and start inhibit time settings between starts for COLD or HOT starts per MG-1.

I have questions about 3 different motors in our plant that are some 25+ years old but were idle for 15 years. We just had them rewound and in process of putting in service. We also don't have data on these motors can you help me with the number of start per hour.

1) 1500 HP, 3 Phase, 2400V, 1800 RPM TEFC High efficiency Induction motor used in Pumping application.

2) 8000 HP, 3 Phase, 4160V, 900 RPM Induction motor used for reciporacting compressor application.

3) 5500HP, 3 Phase, 4160V, 327 RPM (22 Pole) Synchronous motors also used for reciprocating compressor application.

All are full voltage starting. Synchronous motor is Brushless motor with Amortisseur winding which after 10 seconds starting time switches over to brusless exciter powered rotor field.

Can anybody give me some idea on permissible number of starts per hour and inhibit time between starts cold and at rated running temperatures for motors of these ratings and differences between Synchronous and Induction motors.

 

RE: Permissible no.of starts per hour for MV Sync and Ind motors

There is no difference between a synch motor starting on amortisseur winding or a cage induction motor since the amortisseur winding is really a cage winding used dor starting. So, the no. of starts for a cage induction motor should also apply to a synch motor also.  

Muthu
www.edison.co.in

RE: Permissible no.of starts per hour for MV Sync and Ind motors

There are major differences in the rotor construction which would cause differences in iron losses during start, and an amortisseur's primary function is to act as damper winding so it probably isn't as heavily built as a squirrel cage on a similarly rated induction machine. Which brings us back to "Ask the manufacturer". smile
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Permissible no.of starts per hour for MV Sync and Ind motors

Does somebody can tell me if the rotor mass of the 449T and 449TS frame on reliance motor are exactly equals?  

RE: Permissible no.of starts per hour for MV Sync and Ind motors

The reason I always say "ask the manufacturer" is because I have seen similar looking large motors that have SPH ratings of 3/Hr, 1/Hr, and even 1/day! There is no generalization that can be made IMHO.


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RE: Permissible no.of starts per hour for MV Sync and Ind motors

I agree with jraef.  You have the NEMA 1 start hot and 2 start cold driving some specified load inertia that the motor is "designed for" (which inertia isn't specified in the standard, but is part of the starting limit).

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Permissible no.of starts per hour for MV Sync and Ind motors

Beyond the NEMA limit, in absence of manufacturer data, it's a matter of how lucky do ya feel?

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Permissible no.of starts per hour for MV Sync and Ind motors

Yup, there is no fixed number for these motor sizes.

I could guess and say the 1500hp would be the safest to push say 2/hr assuming the pump starts closed valve to remove much of the load.

That 8000hp could have been sized specifically to that compressor. I doubt there would be plans to start/stop a compressor of that size multiple times per hour so it could be very limited - even up to one start per shift or day.

I'd also guess that the synchronous motor is the most limited. The rotor is not the same as an induction motor and will not handle the same starting duty as an equivalent induction motor. Above that, I'm betting that the motor current will stay in the 250% of FLA region until the field is applied which will cause more motor heating compared to an induction motor. So, the one start per shift or day limit could easily apply here too. It would help the motor if you can install controls to energize the field as soon as full speed is reached. At the very least, monitor the start and reduce the timer if 10 seconds is much longer than necessary.

 

RE: Permissible no.of starts per hour for MV Sync and Ind motors

"Does somebody can tell me if the rotor mass of the 449T and 449TS frame on reliance motor are exactly equals?"

Rotor is the same.  The difference btwn the 449T and 449TS is shaft length.  You can contact any Baldor District Office to get a dimensional dwg and if you have the Reliance model number, they can provide you with performance data...

Hope this helps...in fact, if you get me a spec number, I might be able to come up with it for you...

RE: Permissible no.of starts per hour for MV Sync and Ind motors

Welcome to Eng-Tips terod228.
Enjoy!

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

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