[query] 3 phase converter monitoring setup
willray
Greetings all,
I'm working on balancing my rotary converter and need
a sanity check.
(Basic statistics for the record. 1125RPM 15HP idler.
Feeds off a 125A breaker in the shop panel, through
a 100A fused disconnect. L1 and L2 from the disconnect
feed L1 and L2 in a 3p panel on the rails (I might pull
single-phase 220 from this subpanel for other uses in
the shop). The idler and start circuit feed out, and
back in through the 3P panel's original 100A Main breaker.
Starting is the standard push-and-hold auto starting setup,
with a Grainger voltage-sensing relay to cut out the
starter switch when L3 comes up. I've forgotten how
much starting capacitance I have in the box, but it
spins the (kinda chunky) 15HP idler up in less than 2
seconds. When running, it'll currently spin up a 5HP
high-pressure blower (Invincible vacuum), in about 5
seconds, pulling about 45A on L1 and L2, and 23A on
L3. Once spinning, it pulls about 25A on L1, 19A on L2,
and 5A on L3. I don't currently have voltages on it.)
Just for gits and shiggles, rather than just tweaking
the balancing caps with an amp-clamp and DVM, I thought
I'd build a full-blown current and voltage monitoring
system for it.
For current monitoring, I've stuffed 3x 100:5 current
transformers into the 3P subpanel, and brought them out
to current-sensing resistors.
For voltage monitoring I need voltage in the range -1V -- 1V
to match my scope inputs, so I need to build a voltage-divider.
This would be no big deal, except I just tossed myself a puzzler
when getting ready to solder the bits together.
One could build 3 bridges (say 2MOhm and 2KOhm roughly,
just to make the numbers reasonably neat), and bridge
L1->L2, L2->L3, and L3->L1, thereby being able to measure
the between-leg voltages. Alternatively one could bridge
L1->C, L2->C, L3->C (and possibly tie C to ground/N). I've
doodled an ASCII version of this below. Hopefully it survives
being posted. L1, L2, and L3 are as traditional. L1->a is 2MOhms,
a->d is 2KOhms. The other legs are symmetric.
L1 L2
. .
_ _
| |
_ _
| |
_ _
. a b .
| |
_ _
| |
_ _
. d
\
/
\
. c
\
/
\
/
\
/
.
L3
This setup appears allows metering of both the between leg
voltages by metering across both middle .1% resistors on
a leg pair ( ie, a to b, b to c, c to a) and the
Leg->Neutral voltages if the d is tied to ground/N.
I hadn't originally thought of using the "Wye connected" meter
setup, but I can't currently think of a downside. I'm
wondering if anyone who does this stuff more regularly might
know some reason not to do this, that I haven't thought of.
Hmm - while I'm at it, another question -- Is there any reason
that I can't tie together one leg of each current-sensing
resistor for the current monitor part, and use this as a
"common", for metering purposes? I'm suspicious that my
scope inputs don't have isolated grounds.
Many thanks for your time,
William Ray
DoN. Nichols
>
> Greetings all,
>
> I'm working on balancing my rotary converter and need
> a sanity check.
>
> (Basic statistics for the record. 1125RPM 15HP idler.
> Feeds off a 125A breaker in the shop panel, through
[ ... ]
> Just for gits and shiggles, rather than just tweaking
> the balancing caps with an amp-clamp and DVM, I thought
> I'd build a full-blown current and voltage monitoring
> system for it.
>
> For current monitoring, I've stuffed 3x 100:5 current
> transformers into the 3P subpanel, and brought them out
> to current-sensing resistors.
Good -- that gives you isolation.
Yes -- one very good reason -- have you tried measuring the
voltage from ground to the center point? I'll bet that it is a nasty
range above ground, since you have no isolation between the incoming
power line and the rotary converter.
Get three identical filament transformers with input voltage
appropriate to the leg-to-leg voltage. You can then tie one side of
each secondary to ground and safely measure voltages (taking into
account the ratio of the transformer, of course.
>
> Hmm - while I'm at it, another question -- Is there any reason
> that I can't tie together one leg of each current-sensing
> resistor for the current monitor part, and use this as a
> "common", for metering purposes?
Yes -- since the current transformers give you isolation.
> I'm suspicious that my
> scope inputs don't have isolated grounds.
Most don't. The probe ground is connected to the safety ground
pin on the power cord.
You want the isolation that the current transformers give you,
and similar isolation on the voltage side with the filament
transformers. (Those used to be cheap enough and common enough so you
should be able to pick up three identical ones.
Good Luck,
DoN.
--
Email: <dnic...@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Steve Lusardi
I don't wish to rain on your parade, but if you value your time at all, you
will find you can replace your entire setup with a new solid state
sinusoidal VFD that will easily handle your loads. These are available both
monitored and unmonitored at prices around $500 not made in China on eBay.
These VFDs are far more balanced than your rotary converter with far better
power factors. If you consider the money realized from the sale of your
existing kit and the cost of your time, the VFD would be virtually free.
Steve
"willray" <wil...@mac.com> wrote in message
news:66c049b8-e2ac-49c9...@m4g2000vbp.googlegroups.com...
pent...@yahoo.com
<dnic...@d-and-d.com> wrote:
>On 2009-01-11, willray <wil...@mac.com> wrote:
>>
>> Greetings all,
>>
>> I'm working on balancing my rotary converter and need
>> a sanity check.
>>
>> (Basic statistics for the record. 1125RPM 15HP idler.
>> Feeds off a 125A breaker in the shop panel, through
>
> [ ... ]
>
>> Just for gits and shiggles, rather than just tweaking
>> the balancing caps with an amp-clamp and DVM, I thought
>> I'd build a full-blown current and voltage monitoring
>> system for it.
>>
>> For current monitoring, I've stuffed 3x 100:5 current
>> transformers into the 3P subpanel, and brought them out
>> to current-sensing resistors.
>
> Good -- that gives you isolation.
>
>> For voltage monitoring I need voltage in the range -1V -- 1V
>> to match my scope inputs, so I need to build a voltage-divider.
>> This would be no big deal, except I just tossed myself a puzzler
>> when getting ready to solder the bits together.
>>
>> One could build 3 bridges (say 2MOhm and 2KOhm roughly,
>> just to make the numbers reasonably neat), and bridge
>> L1->L2, L2->L3, and L3->L1, thereby being able to measure
>> the between-leg voltages. ?Alternatively one could bridge
>> setup, but I can't currently think of a downside. ?I'm
I see you're aiming for the luxury of both current and
voltage measurement.
When there is significant unbalance, the apparent 3 phase
balance of the current set and the voltage set can be very
different.
With both sets of figures available you may be tempted to
aim for a rough average betweeen voltage and current balance.
Because motors are essentially current driven devices
this is not the way. Balanced current should be your aim even if
this results in larger voltage unbalance.
Jim
Jim Wilkins
What do you think of displaying the current transformer output on the
scope to watch the phase angle? A vectorscope would be really nice but
I don't know how to show 3 phases on an X-Y display.
jw
willray
> William,
> I don't wish to rain on your parade, but if you value your time at all, you
> will find you can replace your entire setup with a new solid state
> sinusoidal VFD that will easily handle your loads. These are available both
> monitored and unmonitored at prices around $500 not made in China on eBay.
> These VFDs are far more balanced than your rotary converter with far better
> power factors. If you consider the money realized from the sale of your
> existing kit and the cost of your time, the VFD would be virtually free.
> Steve
Unless things have changed rather significantly in the VFD world
recently,
I think I'd either need something ridiculous in the VFD world, or a
rather complex and extensive switching and control system to route
power
and control around the shop.
The current setup will replace Mains power for 8 to 10 machines,
including
hopefully allowing me to run a step-up transformer to power a 440V 5HP
subsystem. To simulate Mains power with a VFD (as opposed to using
either
a separate VFD for the switching/control system of each machine, or
one
VFD that can be cut over to each of many machines), I believe the
consensus
has been that it required a monstrously oversized VFD.
Are there inexpensive VFDs out there now that can provide "Mains
Service like"
(capable of handling load-local switching, plug reversing etc)
power to a subpanel for distribution?
(of course, half the reason I'm doing this at all, is for the
amusement
of it, so entirely reasonable suggestions along the lines of "do it
the
smart way", will end up deprecated in favor of suggestions for
byzantine
but functional :-)
Thanks!
Will
Will
willray
> On 2009-01-11, willray <will...@mac.com> wrote:
>
>
>
> > Greetings all,
>
> > I'm working on balancing my rotary converter and need
> > a sanity check.
>
> > to match my scope inputs, so I need to build a voltage-divider.
> > This would be no big deal, except I just tossed myself a puzzler
> > when getting ready to solder the bits together.
>
> > One could build 3 bridges (say 2MOhm and 2KOhm roughly,
> > just to make the numbers reasonably neat), and bridge
> > L1->L2, L2->L3, and L3->L1, thereby being able to measure
> > the between-leg voltages. Alternatively one could bridge
> > L1->C, L2->C, L3->C (and possibly tie C to ground/N). I've
> > doodled an ASCII version of this below. Hopefully it survives
> > being posted. L1, L2, and L3 are as traditional. L1->a is 2MOhms,
> > a->d is 2KOhms. The other legs are symmetric.
>
> > I hadn't originally thought of using the "Wye connected" meter
> > setup, but I can't currently think of a downside. I'm
> > wondering if anyone who does this stuff more regularly might
> > know some reason not to do this, that I haven't thought of.
>
> Yes -- one very good reason -- have you tried measuring the
> voltage from ground to the center point? I'll bet that it is a nasty
> range above ground, since you have no isolation between the incoming
> power line and the rotary converter.
>
Hi DoN - always nice to see familiar knowledgeable faces when I have
time
to drop in!
I haven't measured the center point, but I'm assuming it's off center.
The "Wye Connected" bridge network was my solution to let me monitor
the center - but of course you're right - if it's off center, that
screws up the leg-leg measures.
Filament transformers it is. I probably have enough identical ones
in a box somewhere here to put that together from spare parts.
Finding
that box, could take a while, so maybe I'll order some more...
> > I'm suspicious that my
> > scope inputs don't have isolated grounds.
>
> Most don't. The probe ground is connected to the safety ground
> pin on the power cord.
I let the smoke out of the first scope I discovered that on... I
"manually float" most scopes that cross my path now. I'm pretty sure
my Tek. scopemeter has completely isolated inputs, but I don't
trust that "pretty sure" enough to bet the magic smoke on it, and
I'm less-sure about the 4-channel Tek that I'm planning to use for
monitoring the 3P converter.
Ok. Back to the barn to search for transformers...
Thanks much!
Will Ray
>
You want the isolation that the current transformers give
you,
> and similar isolation on the voltage side with the filament
> transformers. (Those used to be cheap enough and common enough so you
> should be able to pick up three identical ones.
>
> Good Luck,
> DoN.
>
> --
> Email: <dnich...@d-and-d.com> | Voice (all times): (703) 938-4564
Robert Swinney
"(of course, half the reason I'm doing this at all, is for the
amusement
of it, so entirely reasonable suggestions along the lines of "do it
the
smart way", will end up deprecated in favor of suggestions for
byzantine
but functional :-)"
Depricate as you will . . . but the method of voltage balancing rotary phase converters as outlined
in RCM over the years is probably the best way to go. See articles in www.metalwebnews.com which
describe the voltage balance method in detail.
Bob Swinney
DoN. Nichols
> On 11 Jan 2009 07:03:37 GMT, "DoN. Nichols"
><dnic...@d-and-d.com> wrote:
>
>>On 2009-01-11, willray <wil...@mac.com> wrote:
[ ... ]
>>> For current monitoring, I've stuffed 3x 100:5 current
>>> transformers into the 3P subpanel, and brought them out
>>> to current-sensing resistors.
>>
>> Good -- that gives you isolation.
>>
>>> For voltage monitoring I need voltage in the range -1V -- 1V
>>> to match my scope inputs, so I need to build a voltage-divider.
>>> This would be no big deal, except I just tossed myself a puzzler
>>> when getting ready to solder the bits together.
[ ... ]
[ ... ]
> I see you're aiming for the luxury of both current and
> voltage measurement.
>
> When there is significant unbalance, the apparent 3 phase
> balance of the current set and the voltage set can be very
> different.
>
> With both sets of figures available you may be tempted to
> aim for a rough average betweeen voltage and current balance.
>
> Because motors are essentially current driven devices
> this is not the way. Balanced current should be your aim even if
> this results in larger voltage unbalance.
That depends. Yes, if a motor is the only load. But if it is
also powering something like a Bridgeport BOSS-3 through BOSS-6, a
voltage imbalance will pop stepper driver power transistors like
popocorn on the opening night of a big movie. :-)
The transistors used in these systems were just barely high
enough voltage rating to handle what was being applied. (Of course,
really high voltage power transistors were very rare and very expensive
when the system was designed. I think that the BOSS-3 hit the streets
about 1977. :-)
If you're using such a machine, it might be good to use two
rotary converters -- one tuned for current balance for the spindle
motor, and one tuned for voltage balance for the electronics boxes.
Enjoy,
Ignoramus8841
on ebay. I have one and am going to install it on my phase converter
"one day". My phase converter already does a fine job, so I keep
postponing it in favor of more fun things.
i
willray
This isn't the first rotary I've built or balanced - just the first
that I decided to incorporate a full monitoring package into, so that
it can draw pretty pictures on my 4-channel scope. The availability
of 4 channels provides some visualization and monitoring capabilities
that aren't typically taken advantage of by the RCM techniques.
Fitch and Jim R. seem to be the people who have done spent the most
time staring at scopemeters hooked up to their converters, but they
were stuck with the Fluke's dual-sweep inputs, and weren't really
working for designing an available-full-time monitoring system.
In the end, it'll end up balanced just as normal, but it'll be more
fun doing it, and it'll draw pretty, and moderately meaningful
pictures for me :-)
Will
Don Young
Thanks much!
Will Ray
Don't worry too much about the transformers being identical. It is easy
enough to scale the outputs to be equal when the primaries are all connected
in parallel to the same source. Any non-linearities will be insignificant if
the primary voltages are within ratings.
Don Young
Robert Swinney
winding core of a 12:120 Vac transformer and read the voltage scaled current waveform on either the
primary or secondary of the transformer. The resulting waveform can be displayed on 1 channel of
the scope at some conveint size determined by the scope's calibrated vertical amplifier. Place a
voltage divider across the leg under measurement and display it on channel 2, with the two waveforms
dispalyed in the same "size". View both waveforms on a common timebase and read phase displacement
between the traces. Make sure the scope is powered through an isolation transformer.
Bob Swinney
"willray" <wil...@mac.com> wrote in message
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