siemens ac motors classF utilised to classB 1

[mandarvs]

I have to use siemens make 1PQ8 & 1PQ4 series motors. Restriction on these motors is : ClassF insulation. Temp rise limited to classB for 100% loading.
How much pecentage more can i use these motors for classF insulation temp rise to classF? (i was told that we can use the same motors to 110% continuous if restiction is changed to insulation classF temp rise utilised to classF).

 

[edison123]

The motor ratings are based on ambient temperature of 40 deg C. If your ambient temp. is less, you can probably overload the motor (subject to cables, breaker etc can handle the increased current).

Caveat - Overloads reduce the life of the windings drastically.

If your load requires higher kw continuously, then you should use a matched motor.

Stick with the motor manufacturer's advice.



*Why make the same mistake twice when there so many new ones available*

 

[powerjunx]

mandarvs,
In your heading "siemens ac motors classF utilised to classB", it seems you're prefering to use classB as reference level for class F motor.
I suggest to disregards the class B insulation as your reference but rather use the temperature limit of class F for your definite application where 40 degrees celcius is the ambient.

 

[ozmosis]

mandarvs
Here's the advice from Siemens:

http://www.sea.siemens.com/motorsbu/product/Application Manual/section 5-6.pdf

 

[mandarvs]

thanks. the ambient temp to be used is 45 deg cel.
let me make myself clear.
I require following things :
converter fed operation / forced cooled. 45 deg C ambient temp. 115% continuous loading.
insulation class F utilisation limited to classB for 100% loading.
However, the siemens 1PQ8 / 1PQ4 catalogs donot make it clear the procedure for selection of these criteria.
at some places they mention that ambient of 45 deg C can be selected using options. At othe rplaces they mention that all siemens ac motors are constructed with insulation classF temp rise limited tpo classB. However, at other places, it is mentioned that this may not be applicable for forced cooled / converter fed motors. hence the confusion.

 

[edison123]

mandarvs

Your ambient is higher than the one specified in stds.

You mean inverter fed motors. These are different beasts using a special insulation technology different from that used in the std motors. So, Siemens is right in what they say about temp rise about these motors.

While this forum could offer you tips, this should not be used for final decisions.

Talk to Siemens about all your requirements/site conditions before you buy the motors

*Why make the same mistake twice when there so many new ones available*

 

[powerjunx]

mandarvs,
"converter fed operation / forced cooled. 45 deg C ambient temp. 115% continuous loading. insulation class F utilisation limited to classB for 100% loading."

Well, these things which you require are quite confusing but the real course is simply the insulation class F was derated only up to the limit of class B when using converter fed operation.
Upon hooking it up with such controller, the OEM directly derates their machine to withstand for the upcoming threats to the rated insulation class of motor itself. In fact, motor rating suitable for inverter duty uses inverter spike resistance conductor where the conductor (magnetic wire) were insulated or coated far more than the usual coating and more than class F specification.

 

[ozmosis]

All Siemens motors have Class F insulation. The term 'Utilised to Class B temp rise' provides the user with a degree of tolerance between F and B. If motor protection devices such as PTC thermistors or KTY80 temperature devices are fitted then the trip level will be at a Class F temperature level (155degC) and if you have thermistors fitted as well to provide a warning, this is typically 10 degrees C below the trip level.
Temperature classifications of Class B (130degC) and Class F(155degC) are maximum allowed and based on the average temperature of the conductors, not the hot-spot temperatures, so this is why when working at top limits you have to be careful and take all advice from the manf.
If using an inverter, then the Insulation class F will ensure you have adequate protection against the impact of the PWM waveform produced by your inverter as explained previously. However, you are now taking into consideration a higher ambient of 45DegC and this will require de-rating. The standard figure is 0.96. This needs to be qualified by your local Siemens supplier as it will depend largely on the frame size of you motor.
One other aspect not mentioned is the supply voltage. I've been assuming a 'nominal 400-460V' supply but if you are on a supply >500Vac then the impact of the PWM waveform will have a further impact on the motor insuilation. This again needs to be taken into consideration.