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iguparmar 

Difference between Power Transfor mer and Distribution

Transformer 

Difference between power and distribution transformer (Large distributive transformer by 'Powertech Transformers' on pic)

Power transformers are used in transmission network of higher voltages for step-up and step down applicatio

(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.

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The distribution transformer  is used for the distribution of electrical energy at low voltage as less than 33KV

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, soload 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

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

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. th

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 o

distribution demand. Whereas power transformer is designed for maximum efficiency at 100% load as it alway

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 voltag

is almost always the voltage delivered to the end consumer. Because of voltage drop limitations, it is usually no

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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 suppo

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 

iguparmar  - Jignesh Parmar has completed his B.E(Electrical) from Gujarat

University. He is member of Institution of Engineers (MIE),India. Membership No:M-

1473586.He has more than 12 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 Assistant 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.

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31 Comments

1.

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.

(reply)

2.

Practical Considerations When Selecting Mineral Oil-Filled Distribution Transformer | EEP 

Nov 19, 2014

[…] you already know, this is the most common type of distribution transformer. It is one of the most

important part and can be found on electrical supply systems in every […]

8/10/2019 Difference Between Power Transformer and Distribution Transformer _ EEP

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12/16/2014 Difference between Power Transformer and Distr ibution Transformer | EEP

http://electr ical-engineering-portal.com/difference-between-power-transformer-and-distr ibution-transformer

(reply)

3.

Ramya K R 

Oct 16, 2014

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

(reply)

4.

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….

(reply)

5.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 ?

(reply)

6.

Maintenance Management Of Electrical Equipment (Condition Monitoring Based) – Part 4 | EEP 

Sep 05, 2014

[…] Power transformers, power generators and large sized HV motors are well known examples of on-

line monitoring system. CDM systems used on these equipment have been providing useful data of 

operating parameters for assessing the condition of the equipment, though some vital parts of the

equipment have not been covered under CDM due to limitations of technology available at that time. […]

(reply)

7.

N K SINGH 

 Aug 22, 2014

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

(reply)

8.

Hüseyin GÜZEL

 Aug 05, 2014

8/10/2019 Difference Between Power Transformer and Distribution Transformer _ EEP

http://slidepdf.com/reader/full/difference-between-power-transformer-and-distribution-transformer-eep 5/5

12/16/2014 Difference between Power Transformer and Distr ibution Transformer | EEP

http://electr ical-engineering-portal.com/difference-between-power-transformer-and-distr ibution-transformer

very nice website and shares, thank you so much

(reply)

9.

 jithin raj r 

Jul 13, 2014

its great.and fully loaded

(reply)

10.

m imran khan

Jun 21, 2014

it is so much good website

(reply)

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