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Distributed Energy Resources (DERs): Impact of Reverse Power Flow on Transformer

Dr. Amal Khashab's picture
Expert Independent Consultant ,Electric Power Systems Engineering Free lancer

Summary Full Academic Qualification by obtaining B.Sc. (1971), M.Sc. (1980) and Ph.D. (1991) of Electric Power Engineering. Active continuous education by participating in long periods of...

  • Member since 2019
  • 510 items added with 64,960 views
  • Jan 29, 2021

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In the Utility Connected Microgrid, Does the Reverse Power flow from DEG affect the interconnection Transformer?

There is a rising trend of generating energy locally at distribution voltage level by using small-scale, low-carbon, non-conventional and/or renewable energy sources, like wind power, solar photovoltaic, fuel cells and their integration into the utility distribution network. This is termed as dispersed or distributed generation (DG) and the generators are termed as distributed energy resources (DERs) or micro-sources.

It is possible to interconnect DERs in the form of Microgrids, which can be connected to the utility as grid-connected operations helping in generation augmentation, thereby improving overall power quality and reliability as shown in figure below.

Two important questions, have been raised:

(i) does reverse power flow impact the performance of existing transformers in the grid?

(ii) does It make sense to replace interface transformer using a customized design to minimize restrictions on reverse power flow.

The analysis of this companion paper answer to both questions with “YES”, with the reasons and operating limits given.

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Thank Dr. Amal for the Post!
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Matt Chester's picture
Matt Chester on Jan 29, 2021

Really interesting-- especially the impact of power flow on transformers. Not something that the utility industry was likely anticipating needing to answer not too long ago, but now the paradigm shift is making new equipment questions relevant. Eager to see how the sector responds! Thanks for sharing

Bob Meinetz's picture
Bob Meinetz on Jan 29, 2021

From the paper:

"6. Conclusions

1. The phenomena of reverse power flow impact[s] the performance of the interconnect transformers.
2. The transformer losses (core and harmonic) {are significantly increase[d] even at 15% higher excitations.
3. For any design, reverse active and reactive power flow condition[s] (Q3) observes maximum core losses for any load conditions.
4. If the reverse power flow is not restricted, the interconnect transformer loses its life by 25%."

Utility transmission was designed to carry electrical energy one way. Why should these questions be ones the utility industry needs to answer (or for which ratepayers without solar panels need to pay)?

Dr. Amal Khashab's picture
Dr. Amal Khashab on Feb 1, 2021

Because , sooner or later utility will recognize the bidirectional power flow , and Regulators will permit. Then , The excess losses and shorten life time of transformers will need assessment . will consumers pay for utilities losses for ever?

Tripp Tucker's picture
Tripp Tucker on Feb 4, 2021

Thank you Dr. Khashab. This article and report sheds more light on the importance of upf and being mindful of your P's and Q's.

Dr. Amal Khashab's picture
Dr. Amal Khashab on Feb 13, 2021

Thanks for you kindness.


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