Circulating Pump Motors Power Factors

[John.G]

I have noticed recently that all the older type (induction motors?) have apparently very high power factors, these include Grundfos and Wilo and my old Salmson.

For example, take a Wilo ST circ pump (~ 11 years old) powering my solar system, the PFs for the 3 speeds, starting at the lowest are, by my calculations, respectively, 0.93, 0.88 & 0.99. My A rated Wilo Yonos Pico CH circ pump motor ( a brushless DC Motor) gives a measured 0.53 which IMO is more to be expected but all the pump manufacturers were hardly posting incorrect numbers.

The attachment is a bit hazy so the numbers are, 230V/0.20A/43W, 230V/0.3A/61W & 230V/0.36A/82W which give the above calculated PFs of 0.93, 0.88 & 0.99.

Can anyone give a possible explanation for this?

 

[apprentice87]

What do you mean?? You WANT a high power factor, the higher the better..

john..

 

[revjames]

As John says, the higher the figure, the closer to a unity (ie voltage and current in phase) you get and the greater efficiency. Power in an AC circuit is VIs cos (havent got a symbol for 'fie' the greek symbol for it but the cos is the phase angle and the amount the current is lagging the voltage.

 

[Jean de Florette]

Back in the day, I remember power factor correction taking the form of small cabinets fitted with large electrolytics, the size of large baked beans tins, all with the intention of moving that VI lagging power factor somewhere closer to unity. The old pumping systems have gone to variable speed drives, and the beans tins have gone. Though, the savings in energy must still be an issue when the load on the pumps brings the drives up to speed. Life moves on in favour of 'green box' ticking.

 

[revjames]

most places have automatic PF correction in the form of 2 or 3 stages of capacitor banks that come in when the load/ PF requires it