HV motor size (?) for pump

[Anode]

Hi All,

Any help or assistance would be appreciated here thanks. We have a centrifugal pump that was originally driven by a steam turbine. The pump has been de-rated to deliver 1,800 cubic metres per hour. (Used to be 2,500) The drive is now to be by a two speed HV electric motor, 6.6kV, 50Hz, with a rating of 1200kW, 1500rpm or 360kW, 1000rpm. My question is whether the electric motor rating (1200/360Kw)is excessive for the required pump output?
Just as a side note,the motor weight is 8 tons.

Cheers and thanks in advance.

 

[BRIS]

need to know the pump head (h)and efficiency as well as the discharge (q) in order to calculate the power.

power = rho.q.g.h/efficiency.

 

[TD2K]

Just to include the units, BHP = Q * H * SG / (3960 * e)

BHP is the power required by your pump, Hp.
Q is the flow rate, gpm
H is the head, ft
SG is the specific gravity of the fluid.
e is the pump efficiency as a fraction.

You can get the pump efficiency off the pump curve. They will typically also have the Hp requirements shown there also which saves you the calculation. You might want to also consider the Hp requirements at the end of the curve, not just at your operating poing if that is a potential operating point to avoid possibly overloading the motor. Some companies require this as a practice, some consider it, etc.

 

[Anode]

Hi there, and thanks for the tips. I have managed to track down some of the pump data which was requested.

The original pumps specs were:
Capacity 2,500 cubic meters per hour (now de-rated to 1800.)
Total head is 125 meters
Suction head is -5 meters
Revolutions 1650 (now 1500 or 1000)
Bore Suct. x Delivery 450 x 400 mm
Single stage
The medium being pumped is crude oil (I am unaware of the SG at this stage)
Pump efficiency will be obtained shortly.

I hope the above can be of assistance. Thanks again

Cheers
Anode

 

[MortenA]

1200 kW seems over the top but it depends on your efficiency.

Q (m3/hr) * density (kg/m3) * g (9.81 m/s2) * head (m ) /3600 (sec/hr)/e = 1800*850*9.81*125/3600 = 521000/e kg m2 /s3=521 521/e kW

assuming a desity of 850 kg/m3

Talk to your pump vendor he can usually help you with correct motor sizeing. Its not only the operating duty to be considered but also when starting the pump etc.

Best regards

Morten