What is the difference.....

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Mr Ron
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Location: Vancleave, Mississippi

What is the difference.....

Post by Mr Ron » Thu Feb 06, 2020 12:49 pm

between a rotary phase converter and a motor generator (M/G) set.
Mr.Ron from South Mississippi

John Hasler
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Re: What is the difference.....

Post by John Hasler » Thu Feb 06, 2020 1:05 pm

A rotary phase converter uses a three-phase motor connected via capacitors so that it runs on single phase but generates three phase. The phase voltages on the output side are somewhat unequal but good enough to run three phase motors. Two of the output phases are also directly connected to the input.

In a motor-generator set a single phase motor drives a completely seperate three phase generator.

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tornitore45
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Re: What is the difference.....

Post by tornitore45 » Thu Feb 06, 2020 1:07 pm

The question is not clear, if I guess correctly
A rotary phase converter is an oversized 3 phase motor powered with one phase. It will not self start like any induction motor missing the starting winding will not start. It will buzz undecided whether to spin CW on CCW because of inherent simmetry.
On the other hand, like any induction motor it will run once started.
A 3P motor running single phase will generate (poorly) the 3rd leg.
Now you can connect the 3PM you want to use to L1 L2 and the third leg generated by the RPC.

A motor generator is just that an single phase induction motor turning a 3P generator.

Lot's of info on line.
Mauro Gaetano
in Austin TX

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tornitore45
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Re: What is the difference.....

Post by tornitore45 » Thu Feb 06, 2020 1:08 pm

John Hasler type faster than I.
Mauro Gaetano
in Austin TX

rrnut-2
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Re: What is the difference.....

Post by rrnut-2 » Thu Feb 06, 2020 1:11 pm

A motor-generator is a electric Motor driving a generator. Such as Harolds MG melter, the motor end is 240vac 3 phase, turning a generator that is putting out 3000 VAC at 3kHz, Harold correct me if I am wrong. This is quite often all as one unit. However, I have one here that is 480VAC, 60Hz, 3 phase motor connected to a Generator putting out 380 VAC, 50Hz, 3 Phase. These are more common now a days. And no, the motor connected to the generator does not have to be single phase.

A rotary phase convertor is a motor and only a motor. Feed 240VAC into L1 and L3 and then connect the 3 phase load to L1, L2, and L3, The motor must be running to get 3 Phase out and it is not true 3 phase unless more is done with capacitors.

Jim B

Mr Ron
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Re: What is the difference.....

Post by Mr Ron » Thu Feb 06, 2020 1:29 pm

Thanks for clearing that up. I was familiar with M/G sets onboard navy ships which were motors coupled to generators on a single base plate; monsters weighing half a ton. A motor would operate at 220/3ph/60hz coupled to a generator generating 400hz; Very loud.
Mr.Ron from South Mississippi

John Hasler
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Re: What is the difference.....

Post by John Hasler » Thu Feb 06, 2020 1:56 pm

tornitore45 wrote:
Thu Feb 06, 2020 1:07 pm
The question is not clear, if I guess correctly
A rotary phase converter is an oversized 3 phase motor powered with one phase. It will not self start like any induction motor missing the starting winding will not start. It will buzz undecided whether to spin CW on CCW because of inherent simmetry.
On the other hand, like any induction motor it will run once started.
A 3P motor running single phase will generate (poorly) the 3rd leg.
Now you can connect the 3PM you want to use to L1 L2 and the third leg generated by the RPC.

A motor generator is just that an single phase induction motor turning a 3P generator.

Lot's of info on line.
A rotatary converter can be started with a starting capacitor and relay just as a single phase motor is. Decent motor generators use synchronous motors so that the output frequency is correct.

whateg0
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Re: What is the difference.....

Post by whateg0 » Thu Feb 06, 2020 5:34 pm

rrnut-2 wrote:
Thu Feb 06, 2020 1:11 pm
A motor-generator is a electric Motor driving a generator. Such as Harolds MG melter, the motor end is 240vac 3 phase, turning a generator that is putting out 3000 VAC at 3kHz, Harold correct me if I am wrong. This is quite often all as one unit. However, I have one here that is 480VAC, 60Hz, 3 phase motor connected to a Generator putting out 380 VAC, 50Hz, 3 Phase. These are more common now a days. And no, the motor connected to the generator does not have to be single phase.

A rotary phase convertor is a motor and only a motor. Feed 240VAC into L1 and L3 and then connect the 3 phase load to L1, L2, and L3, The motor must be running to get 3 Phase out and it is not true 3 phase unless more is done with capacitors.

Jim B
The old DC Monarch 10ee were built with a 300VDC spindle motor. In the other end of the machine resides a 3ph motor/generator. A single shaft goes from the air raid siren on one end to a pulley at the other end which drove, IIRC, a separate field voltage generator. One end of the main shaft had the armature for the 3ph motor and the other end of the shaft had the armature for the 300VDC generator. I'll see if I have a pic of mine sitting by the house. It's a bit of a beast to move.

Dave

whateg0
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Re: What is the difference.....

Post by whateg0 » Thu Feb 06, 2020 5:36 pm

Mr Ron wrote:
Thu Feb 06, 2020 1:29 pm
Thanks for clearing that up. I was familiar with M/G sets onboard navy ships which were motors coupled to generators on a single base plate; monsters weighing half a ton. A motor would operate at 220/3ph/60hz coupled to a generator generating 400hz; Very loud.
Reminds me of EM2 (SS) Locee in BEE telling us to just remember Motor (rotates hand CCW)/Generator (rotates hand CW), repeat. Completely different application, though, as he was teaching us the electric plant on submarines.

Dave

Harold_V
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Re: What is the difference.....

Post by Harold_V » Fri Feb 07, 2020 4:43 am

rrnut-2 wrote:
Thu Feb 06, 2020 1:11 pm
A motor-generator is a electric Motor driving a generator. Such as Harolds MG melter, the motor end is 240vac 3 phase, turning a generator that is putting out 3000 VAC at 3kHz, Harold correct me if I am wrong.

Slight correction. The motor/generator is powered by 240 three phase, and outputs 3kHz as you said, but at 400 volts, single phase.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

rrnut-2
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Location: New Hampshire

Re: What is the difference.....

Post by rrnut-2 » Fri Feb 07, 2020 6:18 am

When I started at the foundry, we had 5 mg sets for melting. Two of which I hated to work on, one was a 300kw, and the other 200kw Brown Boveris, 4160vac, 60Hz in and 3000vac out at 1500Hz, both water cooled. Did I mention that one of them leaked water? Shortly after I had started, the 300Kw unit had a piece of lamination break off in the generator end and got jammed for a split second between the rotor and stator. It twisted the 4" diameter shaft about 180 degrees. It vibrated bad after that. The 200kw control unit caught fire and had to be wired to "get by" so after that the normal practice was for the melter to kick the field relay in with his shoe. Scary!
Both got replaced with a couple of used solid state inverters that was built in '69, but that wasn't a whole hell of a lot better. I quickly found out why they needed to hire an electronic technician, me.

Jim B

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NP317
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Re: What is the difference.....

Post by NP317 » Fri Feb 07, 2020 11:55 am

The two Seattle Center Monorail trains had BIG Motor-Generator sets (MG) to convert from 600 Vdc to 110 ac for the interior lighting. They vibrated noticeably and we were never able to correct that despite our best efforts. When the lights were turned on you could hear and feel the MG sets turning below the passenger deck.

Built in 1960 by ALWEG Corp. in Germany, their electrical drive systems were basically NY Subway car systems. While I was Maintenance Manager for the Seattle Center Monorail System (~2008 - 2013), we restored both trains back to near-original operation for their 50th anniversary in 2012. Improvements were made including removing miles of signal wires from each train and replacing them with 2-wire communication pairs for multiple local computers, 2/car. New air brake systems and Driver controls were engineered too. Some serious stories there.

Of note, we also replaced the old MG sets (one per 4-car train) with solid state converters, of 1/8th the physical size. A huge improvement!
With all of that work and improvements Train operational reliability returned to nearly 99% ! Really good for half-century-old transportation systems operated 14 hours/day!!
And still going strong today.

So I am definitely a fan of the solid state converter systems.
RussN
RedTrain at McGrawPlaza2011.jpg
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