Change of motor due to use of vsd

[ath1208jalanlor10]

Hi all

Need your help on this issue.
I was told by supplier that my motor needed to be upgraded to Div 1, Gp D, T3C if a vsd is to be installed.

My existing installation is motor with Div 2, Gp d, T3b.
Is there any resons why a new motor with different classification is needed for new vsd installation.

 

[Skogsgurra]

Yes, there are quite a few reasons for that.

The first reason is that the motor voltage no longer is a soft sinewave. Instead, you now have a stream of square wave pulses that are pulse-width modulated to simulate a sinewave. The edges of these pulses are harsh to the insulation system and older motors usually/always cannot withstand them for a very long time. Insulation failure within hours is not unusual.

The second reason is that a motor that is run with a reduced speed also gets a reduced cooling (not if cooled by a separate cooling system) since the shaft mounted fan also reduces its speed. That may dictate a motor with a higher insulation grade or a motor with a higher rated output.

There are also secondary effects like noise, bearing problems and others. But the insulation and cooling problems are the more important ones.

Google +PWM +motor +insulation for more data on this.

http://www.reliance.com/pdf_elements/d7722/d7722p1.pdf

is a good start.

Gunnar Englund

http://www.gke.org

 

[motorspert]

Sorry, I do not understand.
The area classification relates to the area the motor is to be situated in. If certain gases are present then equipment is specifed with for those gases. In this case the only difference is the surface temperature class which changes from T3B to T3C. This is a 5 degree C reduction in surface temperature. It looks like they are saying the motor will opperate 5degrees hotter so us a lower surface temp motor. I would expect the machine to be rated for the VS duty and certified as such.

 

[CJCPE]

The motor must be certified (UL listed) for VS duty in the specified hazardous location. To get the VS certification, I believe that you will need a new motor.

For the reasons mentioned by skogsgurra, winding insulation needs to withstand high voltage spikes. The design needs to be changed to reduce losses and/or allow the motor to cool itself more efficiently. A larger fan may be sufficient, but different laminations and other internal design ghanges may be needed.

It is difficult to protect an AS motor against overheating with a conventional current-monitoring overload relay. That means that a winding thermostat or thermister may be required to assure the T3b/c surface temperature is not exceeded. A thermostat switch in the motor may require the motor to be certified for Div 1.

The supplier may have offered T3c vs T3b simply because that is what they have a design for.

 

[Skogsgurra]

Sorry, I missed those finer points. Not used to the designations.

Gunnar Englund

http://www.gke.org

 

[johnnyw]

Could a sine wave filter be applied on the output of the drive instead of using a new motor? I would expect this to be less expensive provided this meets applicable regulations.

 

[Skogsgurra]

A sine wave filter or a sine wave inverter doesn't solve the cooling problem at lower speeds. How big is the motor?

Gunnar Englund

http://www.gke.org