Rotary Convertors in parralel and phase matching

How do I assure that 2 Rotary convertors ran in parralel have all phases matched?

Not knowing the particulars, I would try the following.

Connect only the 2 single phase leads of each RPC.
Connect a 3 phase motor to one RPC and note the direction of rotation.
Move just the third phase lead of the motor to the second RPC and note the direction of rotation.
If it turns the same way, you can connect both third phase leads.
If the rotation is opposite, swap both single phase leads of the second RPC and recheck.

Bill

Thanks Bill. Makes sence. Easy to comprehend as well.

Phase-A-Matic has a voltmeter test for the third leg when doing a parallel set of Rotarys that checks vlotage.


Phase-A-Matic, Inc. Rotary Phase Converter Installation Instructions Unit Installation Illustration


Your explanation is far easier to understand for me since I don't get what they mean by:" Test run the individual units before connecting the T-3 lines together. Carefully measure the voltages between the different T-3 lines. It should not read more than 60V for the R......etc. "

This is an interesting question and I don't really have a full answer. However there are a couple of points that might be worth considering:

The advice from hitandmiss is fine, but it only covers the possibility that you have the two RPC rotating in opposite directions. This would definitely be a serious problem, but I don't think that this is a sufficient check.

I think that there could be a difference in phase angle caused by one RPC running slightly slower than the other, i.e. a slightly different amount of slip between the two motors. This could show up as a small voltage difference between the output phases of the two RPCs. I think that this is what Phase a matic is referring to in their guidance. I have a suspicion that any variation of slip would be likely to change as the RPCs were loaded, but I am unsure about the interaction between the two RPCs which might possibly cause the two to try to pull back into synchronicity???

If you need more power than one can generate, add a second idler motor, started by the first after it is running. My system is like that. Two 15hp idler motors. I can run either one or both. The extra capacitance needed to balance out the second motor is wired with the second motor.

I'm gonna agree with Cougar here...

Running two RPCs in parallel isn't such a good idea... and there's no reason to... better to build a large RPC control system, and use a small idler, for the 'base' loads, then just connect in a larger idler to cover the larger loads.

If you need two RPCs, the other way to do it, is to have the shop feeders split... put half the machines on one, and half on the other.

Having two RPCs both trying to generate a third phase, is somewhat of an Invitation of Electrical Disaster. (IED).

I'm with Cougar and DaveKamp : My system is set up like that. A 10 horse phase converter with a 7 1/2 hp pony motor to boost the third leg and stabilize the voltage's . Good luck.

JH

DaveKamp said:

...Having two RPCs both trying to generate a third phase, is somewhat of an Invitation of Electrical Disaster. (IED).

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Once or assuming the second rotary phase converter is running what is the difference in connecting it in parallel to the first converter as compared to adding another idler motor?
As I see it the second rotary converter is simply another idler although with it's own starting system; which once running would then be out of the picture.

I agree that if you have one rotary converter then the the "starting system" on the second rotary converter, idler if you will, is unnecessary but I don't see how it hurts anything?
Adding a plain idler motor is simpler.

Grigg

Grigg said:

Once or assuming the second rotary phase converter is running what is the difference in connecting it in parallel to the first converter as compared to adding another idler motor?
As I see it the second rotary converter is simply another idler although with it's own starting system; which once running would then be out of the picture.

Click to expand...

Because the second rotary converter is developing it's own 'generated' leg which is not necessarily going to have the same phase displacement of another unit. Remember- the rotary converter does not create a phase relationship that is 'stable'... the displacement varies with load, and is a function of the motor's impedance and slip.

Since you have TWO sources of incoming power, you'll have two rotary converters, and where the phases don't match, you'll have current flow to TRY to make the voltages equal. The end result, is that one converter is trying to push the voltage/current in one direction, while the other is pulling it backwards.

Its like having two synchronous generators, where one of the legs of each, are improperly phased, so they're perpetually fighting.

Using a second idler, with the first idler's contactors all capable of powering the second idler, means the second HAS to follow the first in a BENEFICIAL state.. it WANTS to help support the first's phase angle, not fight it.

An excellent demonstration of this, is to put a set of voltmeters on each leg, then start one converter, then start a machine that has a good-sized motor... and just let that machine spin (don't put it to work). Just idling, it'll help 'stiffen up' that generated leg's output. you can start and stop more machines, because the idling machine is CONTRIBUTING to the stability of the primary idler.

DaveKamp said:

Because the second rotary converter is developing it's own 'generated' leg which is not necessarily going to have the same phase displacement of another unit...

Since you have TWO sources of incoming power, you'll have two rotary converters, and where the phases don't match, you'll have current flow to TRY to make the voltages equal.

Click to expand...

If the converters are in parallel they would/should be fed from the same source of power, if this the case are the troubles you mention still an issue? In what situation/shop and for what reason could you have 2 converters fed from different sources and still be in parallel, excluding the use of a generator?

Perhaps we're talking about different sorts of converters?
I'm thinking about a rotary converter and assuming basic capacitor start but just as well could be pony motor start. So with a basic converter once it is started it's nothing more than a 3 phase motor running on single phase, no problem turning on a machine and letting it idle, or adding another dedicated idler to increase the apparent size of the "converter".
I think the question of running 2 converters in parallel fed from same source would be the same result as above; adding the second converter is no more than another idler. Sure if it is actually a "converter" it'll have a method of starting it's self, which would be redundant and once running not affect how the motor runs in parallel with the first converter.

Grigg

My lathe is a 7 1/2 HP clutch start lathe. No hard load to start motor.
I have a 7 1/2 HP Anderson RPC and a spare 5 HP 3 phase motor. Is it simple enough to just wire the 5 HP motor as an idler that is started by the 7 1/2 HP RPC and then run the lathe off of this set up?

Yep, sounds like a good simple plan.
You may find the lathe starts fine on the 7.5HP RPC,
If not then adding the 5HP idler with it's own on off switch is a great idea and the combo should easily start the lathe. You'd first start the converter, start the 5HP idler, start the lathe, and if you wanted to then turn off the 5hp idler, or leave it running.

Grigg said:

Yep, sounds like a good simple plan.
You may find the lathe starts fine on the 7.5HP RPC,
If not then adding the 5HP idler with it's own on off switch is a great idea and the combo should easily start the lathe. You'd first start the converter, start the 5HP idler, start the lathe, and if you wanted to then turn off the 5hp idler, or leave it running.

Click to expand...

Does the addition of the idler motor add any benefit other than starting the machine motor? ie: under a heavy load would it be better with the additional 5 HP idler or realy no difference?

Correct, under heavy load it helps. Most folks have a hard time putting an engine lathe under heavy load outside of a production shop or very often.

Thanks for this info Grigg. It sure simplifys grasping what I need to know.

I have ran 3 phase machinery for close to 45 years and until recently never had to get involved with what it actualy was. The way I understand single phase now is that it is like a 2 cyl. engine and 3 phase is like a 3 cyl. engine. Kind of.

No problem, and I think as you get more into it you'll see it's not that complicated to figure out any wiring you'd need in your shop.

2cyl and 3cyl is a good analogy, I hadn't quite thought of that. A little confusing that "single phase" has 2 lines/wires and 3 phase has 3 but once you get past that it's simple enough... Well the more confusing part is there is/was 2 phase power... is that 4 wires, I forget.

Grigg

Grigg said:

If the converters are in parallel they would/should be fed from the same source of power, if this the case are the troubles you mention still an issue? In what situation/shop and for what reason could you have 2 converters fed from different sources and still be in parallel, excluding the use of a generator?

Click to expand...

By the converters being in parallel, I take it that each one COULD be run as-is, on it's own... meaning that you have two line feeders going to two separate contactors, feeding two idlers with their corresponding start and balance capacitors, and then after that, the two are merged together to feed a common 3-phase bus.

The reason why this results in a problem, is because the rotary converter's output, while yielding true three-phase power, does so in an assymetrical fashion, and is naturally displaced from L0 (your single-phase neutral). The reason for balancing capacitors, is to try to 'push' the generated leg's phasing to be equidistant between the two driven corners. It seems simple from the outset, but because the capacitor's effect is caused by altering the load impedance, any OTHER exterior load, including simple drag on the idler's shaft... will cause the generated's phase angle to change as well.

Having two converters in parallel makes for a very troubling situation... This is because the two actively driven phases are being 'reacted' into the third phase, and the response of that reaction varies based on output load.
one idler motor's combination of inductive and capacitive reactance, will inherently be different from another... and this constitutes an incongruence in generated phase angle. The end result, is that the imbalance that exists between each of the generated legs results in current flow BETWEEN the converters which could be close enough to be insignificant, OR, could be anywhere form incredible to catastrophic, based on the changing state of power loads. A comparable, but simplified scenario would be connecting a 240v breaker to a pair of wires, go to a receptacle, and then come off the receptacle back into the panel, to another 240v breaker. As long as the breakers are arranged so that the input phases MATCH, it'll run... but if you overloald anything, neither breaker will trip, and if you shut off one breaker, the other will still be live...

If you simply parallel on a second idler, it'll just latch on and help stiffen the generated leg, with a whole lot less complexity and danger... you'll have a whole lot less investment in controls, and doing so, you'll not need a second starting system.

Sounds like adding the idler motor is pretty simple. Another question comes to mind in this set up. Is there any concern regarding motor direction of rotation between the idler and the end user, the machine motor?

None.
The converter can run either way it wants as well, which should then be the same way all the time. Finally wire your tools to run the direction you want, switching any 2 of the 3 wires feeding the tool will change rotation direction.

If you have any magnetic motor starters or possibly 2 overloads in a starter and not 3 I always use the 2 real legs for the controls and feeding 2 of 3 overloads, try not to use the fake leg for anything it's not necessary for.
http://www.practicalmachinist.com/v.../dumb-rpc-question-find-generated-leg-284519/

That's correct- direction of the idler is irrelevant, so long as you don't swap the run vs start capacitor bank connections around, it'll always start in the same direction, hence, your phase sequence at your load machines won't change.

Don't put MOL's on the idler motor... they won't serve a valid purpose because the idler motor isn't under a mechanical load... the only change in the idler's action, will be demand placed on the generated leg, and that will not be respective of any overload condition.

Motor overloads on your tools, should be just as they would in any other circumstance, but Grigg's suggestion is correct- if your MOL only reads two of the three, make your connections for the MOL match the 240v feed phases.

When I build rotary converters, I always use the same practice- the 240v feeders are red and black, the GENERATED leg is ALWAYS BLUE. That way, if I'm working with a machine that has some issue regarding generated leg, I can easily identify it at the connection point.

Also, when I install a receptacle on the wall, I identify the generated leg's connection point, so that when I'm working with a connected machine, I just trace the wire going to that pin on the receptacle, and mark it in the machine's connection box accordingly.