his post edited for salient points
His words put into a diagram
the op agreed the diagram is accurate (it was previously posted) with minor comments
see post 4
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Recycling Power Through a Wye-Wye Transformer
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his post edited for salient points
His words put into a diagram
the op agreed the diagram is accurate (it was previously posted) with minor comments
see post 4
For the 900kW system I describe a few posts back the input and returned power had no isolation between them other than the Ddyn11 required for 12-pulse operation.
The transformer has a fixed turn ratio and there is no guarantee that the service taps and load-influenced changes will be compatible.
Basically the 480 and 240 need to be on different transformers. The converter can bridge from one to the other, but a direct grid connection may not make a suitable load for all tests. You still need a resistive or motor/brake load at some point.
mobile
Interesting project but there are several points of isolation
rectification to dc
elec-mech with the flywheel, replaced by dc-ac inversion
but the last step of isolation/transformation is not required in this case because the v is the original bus voltage, not a different v tied into the main bus xfmr primary
he would be better served by this method than his proposed
Rectification does not usually use or require isolation.
The flywheel drive motor acts a generator back into same common DC bus.
The mains commutated inverter dc to ac doesn't provide electrical isolation.
I hope that answers your points but I'd be happy to expand on any of them.
all imo all are forms of isolation
rectification negates any freq/phase or voltage discrepency, fresh slate when inverting back
the flywheel is major isolation elec-mech-elec
the field can be manipulated for control
gen windings act as isolation, basically a rotating xfmr
and you had a load: the motor/flywheel/load bank
then the motor/flywheel supplying the inverterh
he has no load, or energy storage
he is feeding 480 bus with 208, power can't flow (at least in the desired direction)
but the main point is that you put 400 vac synch'ed into a 400 bus
no need for a final isolation step
not 208 into a 480 xfmr via a common primary winding tap
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Not electrical isolation as a rule.
The flywheels are powered by inverter fed SCIMs. There is no seperate field to adjust. They are fed from the common 600Vdc link. These run in two quadrants. Motoring to run the flywheels up and generation to feed stored energy back into that same dc link. No isolatiion there.
A mains (line) commutated inverter actually ties it to line frequency. Even if it varies.
I hope that helps.
But I'd be happy to expand on any of the points.
you missed the key point
208 into a 480 xfmr primary via a direct tap
thought experiment
2000 A 505 vac supply >>> than test load(?)
100 A xfmr 480-480 with +/- 5% taps
a vfd input is 505 output controlled to 455
Configure as follows
the 505 is connected to the +5% 504 vac tap (sec is 504 also)
the sec is connected to the vfd supply
the vfd out/load of 455 vac is connected to the xfmr -5% (456 vac) tap
this is very similar, but not as extreme, as the op's proposal
what is the result?
Can i flow from the vfd 455 to the xfmr? What v is on the -5% tap?
what induces the vfd to produce/allow power to flow?
OK.
Power can't flow from the 'device' output to the 480 bus
3 ways to control power flow bus-bus
1 sending v > receiving v
2 line Z
3 power angle, ph delta v sending - v receiving
1 not the case, receiving > sending, if anything the 480 bus will flow power TO the device
2 ignore, short cables, low voltage
3 he stated the v's were in phase, no power can flow, but regardless could not be increased enough to overcome v delta
increasing power angle would make things worse, now the v's on the xfmr prim are out of phase
Imho the op needs to rethink this and consult his plant power ee
3 ways to control power flow bus-bus
1 sending v > receiving v
2 line Z
3 power angle, ph delta v sending - v receiving
1 not the case, receiving > sending, if anything the 480 bus will flow power TO the device
2 ignore, short cables, low voltage
3 he stated the v's were in phase, no power can flow, but regardless could not be increased enough to overcome v delta
increasing power angle would make things worse, now the v's on the xfmr prim are out of phase
Imho the op needs to rethink this and consult his plant power ee
That's what the system I designed did. At 400V 50Hz.
Four quad systems are fairly common in process industries. Call it recycling power or whatever.
It's an interesting area and one that have been involved with for a very long time.
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Not bickering, but respectful discussion
Your system has nothing in common with his
that is why yours worked and his will not
yours 400-400 (or minor differences to allow power flow) to a common xfmr tap
his 208-480 with 0 power angle into 2 different taps on a common winding/core
It is better to discuss now before he expends resources and damages equipment (depending on protective device trip times) or creates a hazardous condition for personnel
I also see it that way.
There are no differences. It's the exact same 400V common supply The mains commutated inverter doesn't worry about the exact voltage. Closed loop control would see to that. Ours had circuitry where the firing angle was directly compensated for voltage.
Essentially, like the system I've described, the output goes back into the same supply.
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the hugely significant difference being
yours 400-400 into a single tap xfmr
his 208-480 into a single winding/core with 2 disparate voltage taps
hence yours worked
his will not or worse
if your v magnitudes were identical then the v power angle must differ
otherwise no power transfer from your 400 vac inverter bus to the 400 vac power input bus
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why regenerated power of OP at 208V
can't be fed back through 208V tap of 480V transformer? I think it can. During such process, the net current taken by 480V transformer would be reduced.
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Being the same supply, they are identical.
Are you saying a 208 vac bus will flow power to a 480 vac bus?
if the ONLY load (or not) on the 208 bus is the 480 bus
what is the xfmr ratio?
Then no v or power angle delta = no power flow
#
Are you familiar with line commutated inverters?
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