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VFD Flexibility?


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#1 plainjs

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Posted 16 July 2003 - 04:33 PM

I recently inherited and maintain 3 HVAC units equiped with VFD's (Square D "Altivar" series)
2 @ 15 hp
1 @ 20 hp
In order to maintain some redundancy with the minimum spares, I was wondering......

Question 1;
Can I use a 20 hp motor in a 15 hp drive application, how would I set up the drive?

Question 2;
Can I set up a 20 hp drive to control a 15 hp motor, how to set up drive?

This would e a temporary measure while a correct motor (1 day) or Drive (7-10 days?) could be located and installed.

..john
"It isn't f..... up until you can't fix it"
;)

#2 GGOSS

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Posted 28 July 2003 - 05:40 AM

Hello plainjs,

Re your quetion 1; I am lead to believe that it is possible but have not had direct experience myself. Therefore its probably best to see what others have to say here.

Re your question 2; This is generally not a problem. Drive set-up will be dependant upon drive model/features. If the drive has in-built motor protection its normally a case of setting the FLC either by actual value or as a percentage of drive rating. If you are able to advice Altivar model number or series, I may be able to guide you further.

Regards,
GGOSS

#3 plainjs

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Posted 28 July 2003 - 03:44 PM

Drives in question are both ALTIVAR 66 type;

15Hp = ATV66D16N4

20Hp = ATV66D23N4

Motor protection is (as I understand it) computed by the drive based on FLA (full load amps).

Logically I could run the drive manually to determine the actual RLA (run load amps) approaching nameplate FLA rating, then set the Maximum Hz. accordingly?
Too simplistic?

Cheers, John

Cheers, John.

#4 GGOSS

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Posted 29 July 2003 - 12:24 AM

Hello plainjs,

Run with FLA, not RLA. The reason I am suggesting this because it will allow for greater utilisation of the motor and minimise nuisance overload & over-current tripping. Needless to say, I am assuming the motor is not continually run in an overloaded state, that is, actual RLA is less than the motor nameplate FLA (FLC).

Hopefully another member or visitor will be able to contribute to the first question in your post of 17/7/03.

Regards,
GGOSS

#5 gogo

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Posted 30 July 2003 - 10:26 PM

according to square d site the continuous output current is 21 amps for ATV66D16N4. What is the FLA of the motor?

#6 grobert

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Posted 20 October 2003 - 07:27 PM

John I would not recommend operating a 20 HP motor on a 15 HP drive. Typical maximum overload setting in a VFD is 115% of drive rated amps. I do not believe this will be enough to allow the larger motor to run consistantly and not trip not to mention the fact that you are placing a larger load than drive is rated to supply. Why take the chance of damaging the larger and more exspensive drive? Keep a 20HP as backup. It is no problem to use a smaller motor than VFD rating.
As pointed out you will need to set electronic thermal over load protection to protect the smaller motor. Most drives have an address that you can go straight to that perimeter and set value as needed.




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