What's the impact on pump and motor when power system changes to 50Hz

[mtsnerdi]

The same fluid system requirements and just the driven power system converts from 60Hz to 50Hz, which means the driven motor's(4 poles) synchronous speed will change from 1800rpm to 1500rpm. What's the impact on pump and driven motor for this change? Regardless of the pump's different efficiency, the same fluid system requirements will lead the same pump required power? Will the lower rotating speed just increase the impeller radius to meet the same fludi system requirements? will it cause the larger pump size and motor size? Thanks!

 

[BigInch]

Basically it just follows the affinity laws.

Thus the 50 Hz motor will deliver lower head, and have a lower flowrate and, consequently will require lesser power at its new 50Hz BEP.

Pump "Size" <per say> is generally considered to be a measure of flowrate, so I'll say that won't change, if you want to keep the same flowrate.

Head is related to impeller size. At lower rpm, to generate the same head, you will need a larger impeller.

You will need a larger diameter volute to deliver the same flowrate at the lower 50 Hz RPM.

Hydraulic power to deliver the same flow at the same head should not change too much, IF the pump with the larger diameter impeller and larger volute has more or less the same hydraulic efficiency as the 60 Hz unit.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

Fan law time. 1500/1800 = .833
New Capacity Q = old Capacity Q * .83333
New Head h = old head h * .8333^2
new HP = old HP * .833^3

The motor may have some cooling capacity on the cooling fan. The amps will drop significantly (almost in 1/2) so that shouldn't be a problem.

 

[Artisi]

The expect the pump to give the same hydraulic performance at 50Hz may not be possible. It will depend on the impeller diameter being used now at 60Hz, if it is full diameter to generate the current head/flow when you will not be able to achieve the same flow / head at 50Hz. However, if the current impeller diameter is less than full diamter and depending on the difference between reduced / full dia. it maybe possible with a change of impeller to a larger diameter to generate the head/flow you need.
You also need to check with the motor supplier to establish if the motor can run at 50Hz - the theory say's it is possible the the physical design may exclude it.

Why not ask the pump manufacturer - who better to give you the correct advice.

Phitsanulok
Thailand

 

[mtsnerdi]

Thank you guys for your fast and helpful responses.That makes sense to me.

 

[MortenA]

Remember to check if the motor cooling is designed for a lower frequency. A motor designed for VFD will have an externally powered fan - but many motors not designed for VFD will just just share the shaft of the motor itself. This means that the fan speed also changes and the new fan speed may provide insufficient cooling - even tough the power consumption of the motor also drops.

Best regards

Morten