ECN Forum Forums General Topics of the Trade General Discussion Area Two phase motors

There are a few ways of going at this, depending on what level of complexity you intend to apply.
i.e.:
* some complexity is OK,
* whatever we can do to run the Motor the best way possible, is the only approach we will take,
* basically having it run is OK,
* no one really knows how to address this one.

If the Motor is a 2Ø 3 Wire Motor, it might be something that could simply be directly connected to an appropriately rated (Voltage wise) 3Ø Power System, without the need of any "Phase Alteration" techniques.

If the Motor is a 2Ø 4 Wire type, &/or the Machine needs to be driven from an actual 2 Phase System, then choose one of the following Transformer Options described below:



Fig. 1: 3 Phase 3 Wire "Closed" Delta Primary to 2 Phase 4 Wire "Taylor" Secondary.

This arrangement would be classified "Higher Complexity", as there are 3 Transformers, and some "non-standard" tap points (86.6% taps).

It does offer the best stability and load balancing options, and is very much a "Steadier 2 Phase Output" from a 3 Phase Supply.

Actual Phase Offset - in degrees, may "Creep" around, resulting in something that might be 105 degrees in one case, 82 degrees in another, or set precicely at 90 degrees all the time.

I am not sure of any issues of how well this connection scheme performs, in regards to the two individual Phases being exactly at, or remaining steadilly at, 90 degree offset.
(btw, the "two individual Phases" are the separate 1 Phase 2 Wire "Sets", represented as "...'A' & 'B' ... Phase 1..." and "...'A' & 'B' ... Phase 2..."



Fig. 2: 3 Phase 3 Wire Open Delta "Tee" Primary to 2 Phase 4 Wire Open Delta "Tee" Secondary.

Here is a simpler approach to the issue, yet still involves a "non-standard" Transformer (the 86.6% tap again!).
The configuration is much simpler to install, but has some balancing issues, which lead to some level of instability.

It nonetheless is still a 2 Phase 4 Wire SDS, derived from a 3 Phase supply - and the degree of offset may be more "easier" to keep at 90 degrees in this arrangement.

Again, I am unaware of any issues regarding Phase offset in these 2 Phase configurations.



Fig. 2: 3 Phase 3 Wire Open Delta "Tee" Primary to 2 Phase 3 Wire Open Delta "Tee" Secondary.

This one is somewhat similar to the one shown above in "Figure 2" - only there is a "Common" Conductor derived from two coil ends, and results in a 3 Wire output.

Additional options may include Motor-Generator setups, VFDs with 2 Phase output design intentions, or a stand-alone Diesel Prime Mover driven Generator.

Something to mention:
Many low power polyphase dry-type transformers (upto 15 KVA), with a Secondary rated as 208Y/120V 3 Phase 4 Wire, are in fact an Open Delta Tee configuration.
This is only a mention, but something to ponder...

Many options available, others may have much better examples to choose from; your results may vary

Scott35

*** REFERENCES ***

Links to 2 Phase pages at ECN:

2 Phase Transformer Schematics

Information relating to the posted images in this reply.

2 Phase Motor Drawings

Some Schematics of 2 Phase Motors.

S.E.T.

p.s.


Could you expand on this a bit, such as:

* How was it hooked up before,

* Was it connected to a 3 Phase system _DIRECTLY_ or _INDIRECTLY_,

* The Code Issues encountered on the existing installation.

TIA (Thanks In Advance)