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

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.

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.

About Author //


Jignesh Parmar

jiguparmar - Jignesh Parmar has completed M.Tech (Power System Control) ,B.E(Electrical). He is member of Institution of Engineers (MIE),India. Membership No:M-1473586.He has more than 13 years experience in Transmission -Distribution-Electrical Energy theft detection-Electrical Maintenance-Electrical Projects (Planning-Designing-Technical Review-coordination -Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He has published numbers of Technical Articles in "Electrical Mirror", "Electrical India", "Lighting India", "Industrial Electrix"(Australian Power Publications) Magazines. He is Freelancer Programmer of Advance Excel and design useful Excel base Electrical Programs as per IS, NEC, IEC,IEEE codes. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & Knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.


  1. Sahfiq ur Rehman
    Dec 17, 2016


  2. Troy Blackburn
    Dec 12, 2016

    I didn’t know that power transformers’ average loads are only at about 75% of their full load capacity. Why is that? I’ve heard that certain kinds of transformers are more eco-friendly than others. Is this true? There’s been lots of construction in my neighborhood lately and I’ve noticed transformers being installed and now I’ll be able to have a better idea of what they are and what they do.

  3. Abdul Majid Nasir
    Aug 02, 2016

    Sir, I am a little confused, 420 kV is used in India and 500 kV generation system is used in Pakistan, whether they are same? Please clarify it.
    Abdul Majid Nasir

  4. U.M.Pattanshetti
    Jan 02, 2016

    I want t o know if I can use 132/11 KV Delta/Star Generator Transformer in place of 132/11 KV Star/Delta Generator Transformer what is happened? If I have no option & I want to use Delta/Star Transformer in place of Star/Delta Transformer what precautions I have to take?

    Aug 22, 2015


  6. ankur
    Jul 26, 2015

    Helloo every one
    I am new to power transformer

    Jul 14, 2015

    Dear sir,

    Existing consumer on 11kv/.4v ,1500kw transf.wants to upgrade with 2000kw load and 33/11kv tr. Plus existing infrastructure. Is it worth?please inform about losses,and tech advice ?

    With Regard
    Thank you

  8. venkata ramana
    Jul 14, 2015

    Sir I want to know why the generated voltage in India is restricted to certain level only???????

    • Shabir Ahmad Khan
      Jan 02, 2016

      the generated voltage in india and pakistain has been restricted to a maximum of 33kv, because of the size, maintenance and cost of generators. we can generate volatges more ten 33kv but it needs large size of generators. which cost more as compared to the present generators. its maintenance is difficult to handle. Also due to large size they are difficult to carry from one place to other, but its not a big issue. the main reason is its cost only.

  9. rakoo bhat
    May 15, 2015

    Well…I m interested in rcvg the newsletter.. Kindly send..thumbs up

  10. Jan Shair
    May 06, 2015

    Correction: In the main heading that says, Iron Losses and Copper Losses. In the second paragraph it would say “Distribution Transformers” instead of “Power Transformers”. Please correct it.


  11. Rajshekhar Rao
    Mar 25, 2015

    ours is a 8MW captive power plant with 10MVA distribution transformer 33KV /11KV with some synchronized with grid. The problem is that we ‘ve a disturbing power factor i.e. the of varies very frequently, is there any solution to keep it steady. Please provide a solution if any

    Thanking You.



    • Siddharth Davda
      Jul 31, 2015

      Hello sir,
      As per my knowledge pf is dependent on nonlinear load. There is one probability is that the capacitor banks are not working properly. I am not well known with the other probabilities.
      Thank you.
      Siddharth Davda

  12. Razdan masroor
    Feb 26, 2015

    sir .i want to known about power transformer .power transformer os a auto transformer ,or 200kv transformer is used to auto transformer

  13. Andrew Cottrell
    Feb 20, 2015

    Correction: Power transformers do not work at 100% efficiency, but rather are designed to work at maximum efficiency, at 100% load. Likewise, a distribution transformer is designed (generally), to work at maximum efficiency, at about 75% of full load. Both types of transformer have an excellent efficiency (>97%) – NEVER 50%, unless hardly loaded.

  14. T.Udaykumar reddy
    Jan 08, 2015

    Sir I am very interesting on electrical manufacturing field

  15. Mohan Y. Hundalekar
    Dec 31, 2014

    Please contact on 09881121484 for some important discussions.

  16. Rengamani vasudevan
    Nov 24, 2014

    Good article. However one Typo error observed. Under Iron and Copper Losses both Power and distribution transformers are given the same heading , viz, ‘Power Transformers’. Please correct when opportunity is available.
    Further an article on Selection of transformer Rating for machines with high starting (Pumps Compressors) will also be very informative.

  17. Ramya K R
    Oct 16, 2014

    Why Transformer rating is in MW and the induction motor rating is in MVA?

    • Prathap
      Feb 26, 2016

      You got it wrong. Transformers and Generators are rated in MVA, Motors are rated in MW and cap banks are rated in MVARs (or respective ‘kilo’ units). The reason why Xfmrs and gen are in MVA because, the type of load is not known. This basically means we don’t know how much MW or MVAR will be loaded on Xfmr or gen. However, a motor has a definite winding and definite power factor and is always inductive nature. Therefore it would be consuming a definite MW. Similarly, a cap bank has definite power factor and is always capacitive in nature. Therefore it would be consuming a definite MVAR. This is undefined for Xfmrs and gen as the load in unknown.

  18. Ramya K R
    Oct 16, 2014

    Hello Sir, Why Receiving End Voltage is more than the sending end voltage?
    Please send appropriate answer for this question….

    • Olanrewaju Adeniyi
      Mar 10, 2016

      Sir, receiving end voltage can never be more than sending end voltage.
      Sending End Voltage is always higher than Receiving End Voltage due to voltage lost.
      if 20 voltage is transmitted, only 18 voltage will get to Receiving End Voltage due to distance, heat, resistivity.

    • Salman Ali
      Jun 27, 2016

      What is advantages and disadvantages 11kv over 33kv? consider (invesment and benefits)?

  19. khanjari
    Sep 07, 2014

    hi sir – why transmission power transformers(such in powerplant) with same MVA and same condition are very larger than another in different manufacture like mitsubishi or abb ?

  20. N K SINGH
    Aug 22, 2014

    very good technical content. Recent Electrical Research paper can be shared on this.

  21. Hüseyin GÜZEL
    Aug 05, 2014

    very nice website and shares, thank you so much :)

  22. jithin raj r
    Jul 13, 2014

    its great.and fully loaded

  23. m imran khan
    Jun 21, 2014

    it is so much good website

  24. shubham
    Jun 14, 2014

    Very nice article indeed , very helpful to show the contrast in power transformer and distribution transformers.
    Here is another one i found pretty useful

  25. abhishek
    Aug 08, 2013

    Namesteh Jignesh Parmar sir,
    sir plz clear my querry.
    If i generate 1 volt ac and with help of a 1:240 transformer, i make it 240 volts then how much current can i take from output terminals. I mean can i glow a bulb of 100 watts with its rated intensity ? I know that some thing is going to be wrng, but i m not able to judge that WHAT ARE THE PARAMETERS, WHICH DONT LET THAT BULB GLOW, are they , the wires of what ? anyone please help

    Mar 31, 2013

    Great job, just to remind that the 2nd paragraph should begin with “Distribution transformers are used in Distribution Network so directly connected to the consumer ” instead of “Power Transformers are used in Distribution Network so directly connected to the consumer ” i guess…
    Thanks for the good job

  27. reply2amit1986
    May 02, 2012

    A good and informative article. I appreciate the writer.
    BTW, please correct the term Power Transformer in second para under the heading “Iron Losses and Copper Losses”.

  28. bernie
    Dec 30, 2011

    what is the peculiarity of 315 MVA, 220/132KV, which vector group is YNyno+d1 and YNaod1 power transformer..

    kindly send to my email the answer,

    Pls send your answer it is very much appreciated

  29. farooq
    Oct 11, 2011

    Could you please advise me on distribution class C2 pad mount transformer ? There general specs, feature and application. Can these be used for servicing commericail buildings ( 13.8kV primary, 1250kVA, 600V secondary- for an example).
    Thanking you.

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