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Home / Technical Articles / Difference between Power Transformer and Distribution Transformer

Main Differences

Power transformers are used in transmission network of higher voltages for step-up and step down application (400 kV, 200 kV, 110 kV, 66 kV, 33kV) and are generally rated above 200MVA.

Difference between Power Transformer and Distribution Transformer
Difference between Power Transformer and Distribution Transformer (photo credit:

Distribution transformers are used for lower voltage distribution networks as a means to end user connectivity. (11kV, 6.6 kV, 3.3 kV, 440V, 230V) and are generally rated less than 200 MVA.

Transformer Size / Insulation Level:

Power transformer is used for the transmission purpose at heavy load, high voltage greater than 33 KV & 100% efficiency. It also having a big in size as compare to distribution transformer, it used in generating station and Transmission substation .high insulation level.

The distribution transformer is used for the distribution of electrical energy at low voltage as less than 33KV in industrial purpose and 440v-220v in domestic purpose. It work at low efficiency at 50-70%, small size, easy in installation, having low magnetic losses & it is not always fully loaded.

Iron Losses and Copper Losses

Power Transformers are used in Transmission network so they do not directly connect to the consumers, so load fluctuations are very less. These are loaded fully during 24 hr’s a day, so Cu losses & Fe losses takes place throughout day the specific weight i.e. (iron weight)/(cu weight) is very less.

The average loads are nearer to full loaded or full load and these are designed in such a way that maximum efficiency at full load condition. These are independent of time so in calculating the efficiency only power basis is enough.

Power Transformers are used in Distribution Network so directly connected to the consumer so load fluctuations are very high. these are not loaded fully at all time so iron losses takes place 24hr a day and cu losses takes place based on load cycle. the specific weight is more i.e. (iron weight)/(cu weight).average loads are about only 75% of full load and these are designed in such a way that max efficiency occurs at 75% of full load.

As these are time dependent the all day efficiency is defined in order to calculate the efficiency.

Power transformers are used for transmission as a step up devices so that the I2r loss can be minimized for a given power flow. These transformers are designed to utilize the core to maximum and will operate very much near to the knee point of B-H curve (slightly above the knee point value).This brings down the mass of the core enormously.

Naturally these transformers have the matched iron losses and copper losses at peak load (i.e. the maximum efficiency point where both the losses match).

Distribution transformers obviously cannot be designed like this. Hence the all-day-efficiency comes into picture while designing it. It depends on the typical load cycle for which it has to supply. Definitely Core design will be done to take care of peak load and as well as all-day-efficiency. It is a bargain between these two points.

Power transformer generally operated at full load. Hence, it is designed such that copper losses are minimal. However, a distribution transformer is always online and operated at loads less than full load for most of time. Hence, it is designed such that core losses are minimal.

In Power Transformer the flux density is higher than the distribution transformer.

Maximum Efficiency

The main difference between power and distribution transformer is distribution transformer is designed for maximum efficiency at 60% to 70% load as normally doesn’t operate at full load all the time. Its load depends on distribution demand. Whereas power transformer is designed for maximum efficiency at 100% load as it always runs at 100% load being near to generating station.

Distribution Transformer is used at the distribution level where voltages tend to be lower .The secondary voltage is almost always the voltage delivered to the end consumer. Because of voltage drop limitations, it is usually not possible to deliver that secondary voltage over great distances.

As a result, most distribution systems tend to involve many ‘clusters’ of loads fed from distribution transformers, and this in turn means that the thermal rating of distribution transformers doesn’t have to be very high to support the loads that they have to serve.

All day efficiency = (Output in KWhr) / (Input in KWhr) in 24 hrs which is always less than power efficiency.

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More Information

Jignesh Parmar

Jignesh Parmar has completed M.Tech (Power System Control), B.E (Electrical). He is member of Institution of Engineers (MIE), India. He has more than 20 years experience in transmission & distribution-energy theft detection and maintenance electrical projects.


  1. Antonio Pisaniello
    Jan 07, 2020

    Receiving EEP news letter

  2. Saleem
    Jul 27, 2019

    In industries it is common to use transformers redundant for reliability. transformers are normally loaded 50%. Only for the duration of PM or CM, transformers are fully loaded. This is the case with Power transformers for step down in the range of 100MVA as well as distribution transformers of the range of 2MVA. Whats the best way this condition to be conveyed in Requisition for safe, reliable and optimized solution.

  3. Akash Yadav
    Jul 24, 2019

    At one place in above explanation you have mentioned Power transformer in place of Distribution transformer. So make the correction of it.

    • Tanveer
      Jan 04, 2021

      Can you tell me about correction as well, where it is? I have to make a project cuz :(

  4. mostafa
    May 01, 2019

    hello Jignesh Parmar
    i have adistrubution transformer 3250 kva step down 22kv to 575 volt two secondary
    what is the required if i have input only 11 kv ,
    i have same output
    transformer company (madhya pradesh )

      Mar 05, 2020

      if you give the 11kv to the primary of transformer than output will become 287.5kv.
      because output depends upon the primary and secondary number of turns of the transformer.

  5. John Vincent dela Torre
    Mar 20, 2019

    Hi. I have a question about the correct connection of transformer going to load. We’re using the separate utility transformer which is 44kVA direct to control panel of pump controller and we’re using VFD’s to control the pumps. The question is can I direct connect the secondary line of transfer to main CB(200A) of my control panel or there should be a Breaker before to my Main CB of the control?

    Really appreciate of your answer. Thank you.

    • P C Kalra
      Jun 07, 2020

      You can directly feed your Pump Control Panel from Transformer Output provided the distance between the two is less than 15-20 Mtrs.

      If the two are located in different rooms you certainly need to add breaker on transformer output..
      If the two rooms are adjacent to each other and easily commutable you would not need Breaker on Transformer output Terminals but 15-20 meters limit still stands.

      PC Kalra
      This is normally the code requirement for safety reasons

  6. S Patel
    Feb 23, 2019

    For delivering power at 11 Kv ,55 MVA with single run (1cx630, 2d spacing,buried) as space of @1 mtr.trench was available.Now in advance stage power demand increase to 75 MVA and available space for cable route becomes 0.5 mtr width buried cable route(means only trefoil configuration is possible with 1cx 630 sqmm.cable) what to do?

  7. S Patel
    Feb 23, 2019

    For 132/11 kv transformer what is allowed maximum capacity(KVA) as per latest Indian standard? What are the factor which governs the maximum rating of this transformer?

  8. kasyap
    Dec 27, 2018

    i feel the corresponding headings are wrongly matched. that is in the place of distribution transformer it was written power transformer. pls check them.

  9. k r suri
    Aug 27, 2018

    what is practical technical and commercial difference between a DYn11 and YNzn1 for a 220/11kv 25mva transformer.

  10. Dan Stark
    May 20, 2018

    Why is an electrical jacket cable with multiple insulated conductors inside it,have a twist configuration [not a lot as in data cable, because I know about Near End Cross Talk (NEXT) but still a twist where the insulated conductors are spiralling around the center of the cable under the jacket sheath. Should one undue the spiral where the jacket/sheath is removed and terminate these insulated conductors (straight runs) when attaching them to a bus bar inside a main grid switch gear. Like in the type of switch gear in very large 200ton vessel. Will noise be a result, if these runs are 5ft long (1.5 meters) spiralled.? I wish to know the electrical reason behind this engineering construction configuration method? Thanks.

  11. Daniel Chuma
    May 02, 2018

    Educative paper. Has exhausted the topic relevant to both beginners and advanced engineers.

    Editor needs to check the language before releasing the paper. In most instances I had to assume what the writer is trying to convey. This is an international platform. Or is it released unedited, on as is basis? Please take note of that. Otherwise I love the platform.

    • jiguparmar
      May 02, 2018

      Dear Daniel,

      If you understand what the author said means There is no any Language issue.
      This is electrical knowledge sharing Site not for testing of language proficiency.
      All authors are sharing their knowledge in the cost of their precious time.
      Authors are not professional writers and there is no any post of EDITOR.
      If you are confident that you are tooooo good in language than try to give your valuable service at any English learning site as a Editor.

  12. Rajan kumar
    Apr 23, 2018

    Dear sir can you please and please tell me the minimum prize of stepdown transformer far single home electric line of 10000v is pass near my home.I want to get electricity of 210 v fram that line.there is no electricity in my home.can you give me your mobile number sir please

  13. Fatoro
    Apr 08, 2018

    For three-phase transformers with 3 coils made entirely of copper (Cu), the power losses in the whole system will be much lower if the coil is added with iron (Fe).
    You can refer to my article Thank you for the article

  14. Anil Yadav
    Feb 21, 2018

    If a power transformer and distribution transformer are of same duty than whose size is bigger
    Which transformer has greater
    iron to copper ratio

      Mar 05, 2020

      a power transformer is bigger in size as the rating of power transformer is more than distribution transformer

  15. rommel
    Dec 09, 2017

    Dear sir.

    good day, can you give me the simple diagram of a 3ph diesel generator connected to 3ph power transformer, and mention the safety device and equipment which are going to used. I hope you can give me the possible solution.

    thanks and best regards!

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