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leblar1
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25 Hz Input 60 Hz Output

04/16/2021 4:55 PM

Good day,

Just as a VFD will change the input frequency from say 60hz to output of a varying degree. Does anybody know of a VFD or controller or way to convert 25hz to 60hz to run about 125kw of equipment.

Thanks
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redfred
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#1

Re: 25hz input 60Hz output

04/16/2021 6:23 PM

Please explain the 25hz source capable of driving a 150kw load. I am assuming the VFD can consume 25kw of power in the conversion.

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leblar1
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#12
In reply to #1

Re: 25hz input 60Hz output

04/19/2021 11:10 AM

The generator is powering old pumps that are 25hz. The engines are EMD 645-20 cyl turning an oversized generator at a speed to produce the 25hz. The controls of he engine are 60hz, cooling fans are 60hz. In the event of Main utility loss to the facility they have separate standby generators to provide the 60hz. The customer claims they have s small VFD that they are able to input 25hz and get out 60hz which they use for testing. This is not verified.
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SolarEagle
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#2

Re: 25hz input 60Hz output

04/16/2021 7:11 PM

..."Rotary Frequency Converters are machines that convert power from one frequency to another. This is achieved by coupling a motor to a generator, which is mechanically coupled and electrically isolated. The coupling method can be direct or via belts & sheaves. However, there are a few with a gear box connection and in this case, they are not electrically isolated. In other words, this is completed by either changing the rotational speed of the generator (in the versions with belts & sheaves) or the gear box. The motors and generators may or may not have the same number of poles, depending upon the output frequency. The result is operating to achieve the same result of producing the desired output frequency. A rotary frequency converter is also capable of producing a different voltage at the same time. If you are operating at another voltage other than 208V, you will need to change the voltage.

Power Systems & Controls’ Series RFC's are Rotary Frequency Converters designed to convert utility power into many other frequencies. For instance, the standard frequencies are 25Hz, 50Hz, 60Hz, 100Hz, and 400Hz power. The rotary frequency converter will provide the rated kVA requirements at the output needed. In addition, a motor and synchronous generator will provide the required frequency and voltage. PS&C’s Rotary Frequency Converters are built with 2 bearing and 4 bearing solutions, as well as, vertical or horizontal configurations. A precision voltage regulator integrated within the system maintains the output voltage at (+/- .5%) far better than the industry standard."....

https://pscpower.com/25hz-frequency-converter/

https://pscpower.com/rotary-frequency-converter/

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SolarEagle
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#3
In reply to #2

Re: 25hz input 60Hz output

04/16/2021 7:28 PM

https://pscpower.com/frequency-converters/

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Rixter
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#4

Re: 25hz input 60Hz output

04/16/2021 8:00 PM

There are solid-state units in that power range. I don't know how they compare price-wise with Motor Generator Sets.

https://novaelectric.com/product/10-450-kva-frequency-converter-jupiter-series/
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Stef
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#5

Re: 25hz input 60Hz output

04/16/2021 10:54 PM

Have done a similar conversion but from 60Hz to 50Hz on a drill rig anly there the demand was 100KW. Used a 150KW motor and a 150kw self excited generator.

Had a 10" triple C pulley on the motor and a 12" triple C on the generator, should have been 12.1" to allow for slip frequency loss.

So in your application the pulley ratio would be 2.4:1 with the larger pulley on the 25HZ motor.

Easy to do just make sure the MG set is properly guarded and the motor and generator have suitable protection for stall, OC, OV, UV, EF.

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rwilliams
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#6

Re: 25hz input 60Hz output

04/17/2021 6:18 PM

I’m not sure, but I imagine that in a 150kW inverter PWM drive, you probably have the software adjustments to allow you to supply the incoming rectifiers for the dc bus with 25Hz power. Not sure that an SCR firing circuit or a straight rectifier would know the difference. You don’t mention incoming voltage, that voltage control might be a stopper...
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SolarEagle
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#7
In reply to #6

Re: 25hz input 60Hz output

04/17/2021 8:16 PM

Yeah... voltage, single phase or three?

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redfred
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#9
In reply to #7

Re: 25hz input 60Hz output

04/17/2021 10:49 PM

The IEEE had a nice article on the old 25 HZ power produced at Niagara for traction motors (trains) and The Pittsburgh Reduction company and later Alcoa. This low frequency was useful at the time to more easily convert to DC for ore reduction at the time. Niagara no longer produces 25 HZ power.

I'm certain there are still some legacy 25 HZ power systems out there, most likely railroad related. Today, this is a very atypical power distribution frequency. The available power to move a train is quite large and with dynamic braking and starting currents the voltages are likely to not be very stable.

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leblar1
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#14
In reply to #9

Re: 25hz input 60Hz output

04/19/2021 11:13 AM

Exactly, this is a legacy system.
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redfred
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#10
In reply to #7

Re: 25hz input 60Hz output

04/17/2021 10:51 PM

Oops, my post was intended as a reply to the OP, not you SE.

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leblar1
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#13
In reply to #6

Re: 25hz input 60Hz output

04/19/2021 11:13 AM

Incoming voltage is 480VAC
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jmueller
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#8

Re: 25hz input 60Hz output

04/17/2021 10:25 PM

Friend,

Typical industrial VFD's have an input section that rectifies the incoming AC to DC, then a DC section with filter capacitors to smooth the ripple of this rectified power into a steady DC voltage, then an inverter section to chop this DC using pulse-width-modulation to synthesize a new AC output at the desired voltage and frequency.

So, the input section doesn't really care if it is 25Hz, 50Hz, 60Hz, etc. The output section doesn't care either. However, the DC bus section may have some problems with the filtering of the ripple because of the greater time between peaks in the waveform.

I suggest you contact a VFD manufacturer to see their suggestions.

Others have suggested a suitable motor-generator set to do the conversion. This is a proven and very effective method.

Do answer the questions you were asked by others. I am curious about where this 25Hz source is located, because it is disappearing from normal usage. My memory of one place was the Alcatraz Island prison in the middle of San Francisco Bay, but I recall reading many years ago that they finally changed to a land-based 60Hz system.

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leblar1
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#15
In reply to #8

Re: 25hz input 60Hz output

04/19/2021 11:15 AM

This is for multiple pumping stations and legacy equipment.
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JRaef
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#16
In reply to #8

Re: 25hz input 60Hz output

04/19/2021 4:03 PM

Per this excellent response:

To reinforce the concept of "ask before assuming":

SOME VFDs use an AC power supply connected to the line side terminals to derive control power for the electronics, those likely would have a problem with the 25Hz input. Others derive their internal control power from the DC bus with a DC to DC converter, so they would not have a problem with 25Hz. In addition, some VFDs in some size ranges use an SCR based line rectifier (to control capacitor inrush on power up) and the gate firing circuit for the SCRs might be incompatible with 25Hz.

All of that said, I once helped work on specifying VFDs on 25Hz systems in New Orleans for the older pumps used for flood water mitigation. If you recall the Katrina disaster, one of the many many problems there was that some of the old pump stations were still 25Hz and were run from generators. The generators flooded and although they could clean and fix the pumps quickly, they had no source of 25Hz power to run them without the generators, and of course getting 25Hz generators was not something you could call up a rental yard for. So for some of them, they (later) retrofitted 60Hz motors, but for a few of the smaller ones, they put in VFDs that would accept 25Hz input or 60Hz input so that they could be run from any generator, I got to help work on specifying those VFDs. We over sized the VFDs by 50% to handle the added DC bus ripple. But again, we had to make sure of the other issues as well. That was a fun and interesting project.

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leblar1
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#18
In reply to #16

Re: 25hz input 60Hz output

04/20/2021 4:59 PM

You don't happen to remember the brand drives?
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JRaef
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#19
In reply to #18

Re: 25hz input 60Hz output

04/21/2021 8:48 PM

Rockwell PowerFlex 700. Their documentation said something like 47-63Hz input frequency tolerance, but that's apparently because it depends on the size; some of them used SCRs on the rectifier and those are sensitive to the incoming frequency. I think it was 60HP to maybe 150HP? I can't remember. We asked their engineering team at the time because ours were 200-300HP, they came back and said it wasn't a problem. They have now changed to the PF755 for that size, I don't know if it's still true, you'd have to ask them to be sure. When we did it the front-line guys initially said no, I had to get to an engineer at the factory to get confirmation.

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#11

Re: 25hz input 60Hz output

04/18/2021 4:43 PM

No luck with Google, then?

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leblar1
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#17
In reply to #11

Re: 25hz input 60Hz output

04/20/2021 4:39 PM

Not anything good. I found some stuff.

I appreciate everybody's input.
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