3 Phase Delta-Wye or Delta-Delta Transformer

[kjjack]

I have a client that has a 2400V distribution voltage (fed from 3 phase, delta-delta, 3 wire transformers). I need to use this feed to feed a 480V motor, hence fed from a transformer. My question is, if the 2400V is delta, 3-wire, can I use a 2400V-480/277V delta-Wye or 2400V-480/240V delta-delta transformer?

 

[davidbeach]

Yes, you could use either. I wouldn't go with the 480V delta since that is much less commonly used than the wye, but there is nothing about the primary that would limit your choices on the secondary.

 

[fredpar]

I agree with davidbeach and want to ask: You think you may need 240V better than 277V for future single phase loads?

 

[rbulsara]

fredpar:

Obviously you are not in North America or USA. 480Y/277 is most common voltage for commercial and industrial facilities here. (600Y/347V in Canada, I beleive)

Industrial and commercial lighting is 277V or 347V here.

For the type of single phase loads you are refeering to (240V) which is common in Europe and Asia are served using 208Y/120V or 240/120V services obtained by stepping down 480V or 600V supply.

 

[waross]

If your motor load is less than 1/2 of the smallest readily available transformer, or transformer bank, consider open delta. It is often the most economical solution for small three phase loads.
respectfully

 

[davidbeach]

waross, there you go again assuming individual single-phase transformers. ;-) I almost always think of three-phase transformers for three phase applications. My guess is that given a three-phase transformer, a 2400V-480Y/277V transformer will be much more readily available than a 2400V-480/240V delta transformer. The amount of single phase from a three-phase 2400V-480/240V delta transformer would be severely limited (5-15% of nameplate max) where as if done using three single phase transformers in delta, it would be possible to have any amount of single-phase capacity relative to the three-phase capacity.

 

[waross]

Gosh David;
I didn't assume single transformers.

transformer, or transformer bank

From the original post, I did assume that the load may be only one motor.
I also suspected that the transformer had not yet been aquired.
For a small three phase motor load, I stand by my suggestion.
Open delta is often used for for small three phase loads economic reasons.
Respectfully

 

[dapotiti18]

Base on my experience it does not matter whether u use delta-delta or delta-star type of stepdown xformer but make sure ,either phase voltage or line voltage in both delta-star and delta-delta stepdown xformer respectively is thesame as operating voltage of electric motor.

 

[lakshmanan1974]

I do agree with Dapotiti18.Since the load is motor obviously you may not require neutral point supply...However, considering future single phase supply requirement such as lighting, you can go for 2400 (Delta) /480-277(Y)transformer.

 

[rbulsara]

Wye secondary also provide a convenient way of grouding the separately dervided source.

Plus there is no benefit of delta-delta. If anything it is uncommon setup and creates other grounding or non-grounding related issues. Unless there is a reason not to use Delta-wye, use it. It is the most common configuration in use, and it is for a reason.

 

[RalphChristie]

Agree with rbulsara.

Not sure where you are located, but a regulation in many countries state that every electrical systen rated at greater than 50V (UK, South Africa) shall be connected to earth. From a safety point of view this would indicate a delta-star transformer.

Regards
Ralph

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