Frequency conversion

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Besoeker

Senior Member
Location
UK
AFAIK, when your speed changes in a fan/pump, the afffinity laws are:
1) Volume output/discharge: Q1/Q2 = N1/N2, in this case : Q2 =5/6 x Q1 = 83%Q1 (17% decrease)
2) Change in head/pressure: p1/p2 = (N1/N2)^2: p1 = 25/36 x p1 = 69%p1 (31% decrease)
Lastly:
3) Power drawn: kW1/kW2 = (N1/N2)^3; kW2 = 58%kW1 (42% decrease)
Or, more simply, (50/60)^3
 

Open Neutral

Senior Member
Location
Inside the Beltway
Occupation
Engineer
You might look at Amtrak for frequency conversion experience; they have to turn 60 Hz to 25 for the WAS-NYC NEC. (And generate 25 Hz directly.)

You can use rotary converters, static inverters, and cycloconverters. The downside of the last, and advantage of the first soon became apparent....harmonics. Their rotary inverters are needed to eat the crap generated by the new kids.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
You might look at Amtrak for frequency conversion experience; they have to turn 60 Hz to 25 for the WAS-NYC NEC. (And generate 25 Hz directly.)

You can use rotary converters, static inverters, and cycloconverters. The downside of the last, and advantage of the first soon became apparent....harmonics. Their rotary inverters are needed to eat the crap generated by the new kids.


I once read that engineers wanted to convert 25 to 30 cycles in that at 60Hz a good ratio could be established, in fact a direct connection could be made just reducing the number of poles in the generator potion of the motor generator set.
 

Open Neutral

Senior Member
Location
Inside the Beltway
Occupation
Engineer
I once read that engineers wanted to convert 25 to 30 cycles in that at 60Hz a good ratio could be established, in fact a direct connection could be made just reducing the number of poles in the generator potion of the motor generator set.

I suspect harmonics issues would not encourage that. The NEC used to use 100Hz for signaling and control [i.e. motor driven (RR track) switches], but the harmonics of the 25Hz/12KV caused grief. So they moved to 91.333 Hz.
 
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