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Join Date: Mar 2016
Posts: 21

Replace MX321 AVR with R448 AVR

03/03/2017 11:16 AM

I have a Stamford 1000KVA alternator with an MX321 AVR. The sensing voltage of the MX321 AVR comes directly from the alternator's main output voltage via 3-phase safety isolating transformers (400VAC/50HZ ---> 200VAC/50HZ).

I would like to replace the MX321 AVR preferably with a Leroy Somer R448 that does NOT rely upon a separate isolating transformer to supply its input sensing voltage.

Is there someone out there who can give me some info about this.

John Meyer, Chevron, Niger Delta, Nigeria

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Join Date: Mar 2007
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#1

Re: Replace MX321 AVR with R448 AVR

03/03/2017 1:35 PM

Why would you want to do this?

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Active Contributor

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#2
In reply to #1

Re: Replace MX321 AVR with R448 AVR

03/04/2017 8:18 AM

Don't ask WHY!

Tell me HOW!

I need a solution, not someone that asks me WHY!

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#4
In reply to #2

Re: Replace MX321 AVR with R448 AVR

03/04/2017 12:46 PM
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Guru

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#3

Re: Replace MX321 AVR with R448 AVR

03/04/2017 12:06 PM

I think we went thro' this before with R448 vs R449.

I have the R448 manual with connection diagram, but MX321 AVR manual I got does not have connection diagram. If you give me Stamford generator type, I may be able to get from Cummins website.

Anyhow, critical value is auxiliary voltage you get from generator to give power input to AVR. MX321 has 170-220V (presumably line-line) 3 phase, 3 wire. R448 is single phase 100 to 140V. That means generator auxiliary volts is probably~ 200 and high for R448. But maybe a PMG with star winding with common brought out - might give you 120V line-star point?

I would expect rated DC field voltage to be related to AVR power input voltage.

Does this generator have Permanent Magnet Generator PMG or auxiliary winding to power AVR??

I appreciate you are in Nigeria, so it is "make it work with what is available and some risk!"

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Active Contributor

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#5
In reply to #3

Re: Replace MX321 AVR with R448 AVR

04/13/2017 6:43 AM

Thanks for your time! Much appreciated. It is now MX321 vs. R449 AVR.

The Stamford Alternator is Model HCI634J1 / 1100KVA / 400VAC/50Hz / Output U-V-W + N / MX321AVR

MX321AVR - PMG Voltage 170-220VAC; Sensing Voltage 170VAC - 250VAC (3-phase/3-wire through isolating step-down transformers connected to main output of alternator U-V-W); Reference voltage 230VAC (from output phase to neutral); Max Excitation Voltage 120VDC

R449AVR – PMG Voltage 150-180VAC; Sensing 170-260VAC; Max Excitation Voltage 140VDC (On R449 excitation ceiling can be dropped)

Can I take a chance to replace the MX321 with the R449? What do you think?

John Meyer / Niger Delta / Nigeria

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#6
In reply to #3

Re: Replace MX321 AVR with R448 AVR

04/13/2017 8:37 AM

OK,

Please disregard my other message above. This matter has now been resolved. There will be no swapping of AVR's.

Thank you

John

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Guru

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#7
In reply to #6

Re: Replace MX321 AVR with R448 AVR

04/14/2017 8:05 AM

Glad to hear it is fixed.

If I happened to have a 230V to 55-0-55V isolation transformer, with 10 amp rating on secondary [or anything similar], I would have tried that with half-secondary in series with and in opposition to available supply to reduce power input voltage to R448.

67model

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