Transformer connection

[Markdegracia0370]

Good day;

Our system tripped when we connected the distribution transformer Y-Δ, to our main transformer Δ-Δ.

Is there a problem if i connect Δ-Δ to Y-Δ? or its better to connect transformer in Δ-Y to Y-Δ?


Please Advise

 

[electrofelon]

I don't follow what is going on. Is the "distribution transformer" the utility's? Is the system ungrounded or corner grounded? Nothing should trip. Only thing you don't want to do is connect the primary neutral to a wye-delta.

 

[Markdegracia0370]

I don't follow what is going on. Is the "distribution transformer" the utility's? Is the system ungrounded or corner grounded? Nothing should trip. Only thing you don't want to do is connect the primary neutral to a wye-delta.

Hi;

Yes sir, our distribution transformer is the utility wye-delta, connected to main substation delta-delta that is ungrounded.

What did you mean sir about connecting the primary neutral to a wye-delta? Is the "primary neutral" is the neutral of the primary delta-delta of our main substation? What is the effect of this sir?

 

[electrofelon]

Hi;

Yes sir, our distribution transformer is the utility wye-delta, connected to main substation delta-delta that is ungrounded.

What did you mean sir about connecting the primary neutral to a wye-delta? Is the "primary neutral" is the neutral of the primary delta-delta of our main substation? What is the effect of this sir?

If you have a wye delta, you would leave the primary wye point unconnected, otherwise large circulating currents can occur. This doesn't apply to you as you have a delta.

What tripped? An ocpd or do you mean the ground fault sensor is indicating a fault?

 

[wirenut1980]

Hi;

Yes sir, our distribution transformer is the utility wye-delta, connected to main substation delta-delta that is ungrounded.

What did you mean sir about connecting the primary neutral to a wye-delta? Is the "primary neutral" is the neutral of the primary delta-delta of our main substation? What is the effect of this sir?

Can you post a single line diagram? Even a hand drawn one would help clarify. Are the two transformers connected in parallel? Or is the delta-delta transformer connected downstream of the wye-delta?

 

[Markdegracia0370]

Can you post a single line diagram? Even a hand drawn one would help clarify. Are the two transformers connected in parallel? Or is the delta-delta transformer connected downstream of the wye-delta?

Hi sir

Please see attached file. the 2.5 Δ-Δ is our existing main substation, and we have a new proposal to change it to Δ-Y. Can this transition affects the downstream loads?

2.5MVA is already installed when we took over the company and its very old but its still functional. The 5MVA transformer is the only available unit so we used it temporarily.
I already installed a power system that all our transformer is connected Δ(ungrounded) - Y(grounded) but this is my first time that i connected to Δ-Δ (both ungrounded). Can this be the possible reason of frequent tripping to our fault protection. All our metering in our substation are grounded.

View attachment ISRI_BAGUIO ONE LINE DIAGRAM_ 12292015_attachement for ISRI Report-Layout1.pdf

 

[Markdegracia0370]

If you have a wye delta, you would leave the primary wye point unconnected, otherwise large circulating currents can occur. This doesn't apply to you as you have a delta.

What tripped? An ocpd or do you mean the ground fault sensor is indicating a fault?

I think its Ground fault sensor due to abrupt tripping of the system.

Thanks for the advise.

 

[NewtonLaw]

Good day;

Our system tripped when we connected the distribution transformer Y-Δ, to our main transformer Δ-Δ.

Is there a problem if i connect Δ-Δ to Y-Δ? or its better to connect transformer in Δ-Y to Y-Δ?


Please Advise

When you connect two three phase transformer banks in parallel you must consider the phase relationship between the two transformer banks. Connecting Y-Y or D-D causes zero degree or 180 degree phase shifting depending on the connections made. In the case of a Y-D or D-Y connection you may have a 30 degree or 210 degree phase shift and this must be accounted for. Last placing a Y-D in parallel with D-D you force a 30 phase shift between the two that can not be ignored and it will cause short circuit current to flow.

Hope this helps.

 

[Ingenieur]

you connect a wye sec in parallel with a delta sec?

 

[electrofelon]

When you connect two three phase transformer banks in parallel you must consider the phase relationship between the two transformer banks. Connecting Y-Y or D-D causes zero degree or 180 degree phase shifting depending on the connections made. In the case of a Y-D or D-Y connection you may have a 30 degree or 210 degree phase shift and this must be accounted for. Last placing a Y-D in parallel with D-D you force a 30 phase shift between the two that can not be ignored and it will cause short circuit current to flow.

Hope this helps.

I didn't see any mention of using transformers in parallel.

 

[Ingenieur]

I didn't see any mention of using transformers in parallel.

the drawing shows a 2.5 mva d-d in parallel with a 5 mva d-y
whether they will both be energized is not clear

 

[Markdegracia0370]

you connect a wye sec in parallel with a delta sec?

No sir we will replaced the existing 2.5MVA Δ-Δ, by 5MVA Δ-Y transformer. DOes this have an effect to the loads

 

[Markdegracia0370]

When you connect two three phase transformer banks in parallel you must consider the phase relationship between the two transformer banks. Connecting Y-Y or D-D causes zero degree or 180 degree phase shifting depending on the connections made. In the case of a Y-D or D-Y connection you may have a 30 degree or 210 degree phase shift and this must be accounted for. Last placing a Y-D in parallel with D-D you force a 30 phase shift between the two that can not be ignored and it will cause short circuit current to flow.

Hope this helps.

No sir, We didn't bank it parallel, we will replaced the existing 2.5MVA Δ-Δ, by 5MVA Δ-Y transformer. Does this have an effect to the loads

 

[Markdegracia0370]

the drawing shows a 2.5 mva d-d in parallel with a 5 mva d-y
whether they will both be energized is not clear

No sir, We didn't bank it in parallel, we will plan to replace the existing 2.5MVA Δ-Δ, by 5MVA Δ-Y transformer. Does this have an effect to the loads

 

[mh06670]

The breaker is coordinated with the transformer inrush, correct?


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