50 / 60 Hz electrical motors

[lpb]

My firm operates in a 50 Hz area, but I've just received a 50/60 Hz electrical motor to be used on a submersible pump. The performance curves of the pump are however based on a 60 Hz supply. How can I determine the available head etc. of the pump at this frequency.

 

[electricpete]

The pump will operate at approximately 5/6 of the speed upon which the 60hz curves are based.

The pump affinity laws tell us that for a given system (with system characteric head-loss curve hd~gpm^2), the flow rate will vary in proportion to speed (5/6) and the head will vary in proportion to speed^2 (5/6)^2.

So here's how you create the curve: Pick a few points (x60,y60)=(gpm60,hd60) on the old 60hz pump curve. For each point of these points you can compute a point on the new curve (x50,y50)=(gpm60*5/6,hd60*25/36). Then connect the dots.

 

[electricpete]

The above procedure assumes that the curve you're starting with gives differential head vs flow rate... since differential head is the quantity that varies with speed^2. If you happen to have a curve with a different vertical axis (discharge head or some other related quantity), then you have to make appropriate corrections

 

[electricpete]

By "differential head", I meant the differential pressure (discharge minus suction) divided by the density.

Maybe there's a better term.