Created by Santosh Kumar Yadav

1. A Presentation On
“Economic Loading Of Distribution Transformer”
Department of Electrical Engineering
School of Engineering
Gautam Buddha University
Gautam Budh Nagar UP, India
By:
Santosh Kumar Yadav
15/IEE/043

2. Introduction of Distribution Transformer
 In general distribution transformers are used to reduce primary system
voltages (2.4-34.5kV) to utilization voltages (120- 600V).
 IEC (International electrotechnical comission) standards do not distinguish
between distribution transformers and power transformer.
 They are all power transformers in the sense that their purpose is to transmit
power from one voltage level to another.
 Traditionally, transformers that transform the voltage down to the domestic
consumer voltage (usually 400V or less) are called distribution transformers.

3. Types of Distribution Transformer
On the basis of size there are two types of distribution transformer:
 Large Distribution Transformers:
Used for receiving the energy from higher voltage levels.
Transform and distribute the energy to lower voltage level substation or
directly to large industrial consumers.
The core is constructed of grain oriented steel laminations.
The windings are made of paper insulated rectangular wire in the form of
multi-layer disc or helical windings.
The conductor material are either copper or aluminum.
The tanks typically have radiators.

4. Small Distribution Transformers
Used to step down three-phase high voltage to low voltage for energy
distribution. Mainly in the countryside or low-density populated areas.
They are three phase oil immersed hermetically (air tight) sealed, adaptable for
pole mounting.
On customer request, the transformer can be equipped with an oil conservator.
Hot dip zinc coating is often the preferred surface treatment for outdoor
applications.

5. ECONOMIC STUDY
Various parameters for the economic loading of distribution transformer-
Life of equipment
Sensitivity studies
Annual cost to own
Operating efficiency

6. Life of equipment
Distribution transformers are one of the main components of electric distribution
systems and have an average expected lifetime of 35 years.
By PV integration we can extend the lifetime of distribution transformers.
The lifetime of a distribution transformer is mainly determined by insulation life.
Insulation, itself is affected by the transformer loading including magnitude and
quality, ambient temperature, the moisture and the oxygen content of the oil.
The load profile of a feeder is the main factor to choose the distribution
transformer and to manage its lifetime.

7. Sensitive Studies
These are conducted to determine the effects of changing-
The initial cost of the transformer
Power factor of the load
Annual fixed cost rate(cost of land, installation, equipment, etc.)
The annual load factor(average load/peak load) on the transformer
The amount of the voltage sensitive load

8. Annul Cost to Own
The annual cost to own a transformer is the summation of
The cost of energy losses (no-load loss and a load loss).
A demand charge based on the kilowatt of loss
An annual fixed cost associated with the initial cost of the transformer
A reduction in revenue to the voltage spread in the transformer
The cost of supplying the exciting VAR to the transformer

9. Operating Efficiency
Economic based solution, the concept of all day efficiency of distribution
transformer came into the picture.
All day efficiency is determined as, the ratio of total kWh at the secondary to
the total kWh at the primary of the transformer for a long specific time period
preferably 24 hrs.
All day efficiency=
𝑂𝑢𝑡𝑝𝑢𝑡 𝑖𝑛 𝑘𝑊ℎ
𝑖𝑛𝑝𝑢𝑡 𝑖𝑛 𝑘𝑊ℎ

10. References
[1] H. Pender and W. A. Del Mar, Eds., Electrical Engineers Handbook,
Electric Power, Fourth Edition. New York: Wiley, 1967.
[2] H. W. Book, "Loading of distribution transformers," CP-57-
1169,AJEE Farm Electrification Conference, Minneapolis, MN, Oct.
1957.
[3] Electric Utility Engineering Reference Book, Vol. 3, Distribution
System, Westinghouse Electric Corporation, East Pittsburgh, PA, 1965.
[4] Allen R. Spangler, member of IEE “The Economical Loading of
Distribution Transformers” IEEE transaction on industry applications,
Vol. IA-I 3, no. 2,april 1977

11. Thank You