ISSN 2319-8885
Vol.03,Issue.17
August-2014,
Pages:3500-3504
www.semargroup.org,
www.ijsetr.com
Design of Cast Resin Dry Type Transformer
AYE AYE PYONE1, MYO THET TUN2
1
Dept of Electrical Power Engineering, Mandalay Technological University, Mandalay, Myanmar,
E-mail: ayepyone57@gmail.com.
2
Dept of Electrical Power Engineering, Mandalay Technological University, Mandalay, Myanmar,
E-mail: myothettun7@gmail.com.
Abstract: This paper is a research based on the upcoming type if transformer which is a dry type transformer or commonly
known as Cast resin transformer. The study focuses on the manufacturing process of producing transformer as well as the
design and temperature control relay. Moreover the advantages using dry type transformer over the other types will be
analyzed. The transformer is also widely used its load for maximum power transfer, isolating one circuit from another, or
isolating direct current while maintaining ac continuity between two circuit. In this paper, the design of 315 kVA, 11/0.4kV dry
type distribution transformer is discussed. Rectangular wire is used in low voltage winding as well as round wire is used in high
voltage winding in this transformer design. Dry-type are normally cooled by natural circulation of air and also the type of epoxy
material that is used on the windings help minimize the heat dissipated by the copper when the transformer is loaded.
Keywords: Transformer Design, Temperature Control Relay, Cooling System, Dry Type, Round And Rectangular Wires.
I. INTRODUCTION
Transformers are electric equipment that changes the
voltage and the current of electricity to facilitate its efficient
transmission and distribution. Transformers are commonly
use at power generation facilities to increase voltage and to
decrease current in order to transport electric energy across
transmission lines. When the electricity reaches the end user,
transformers are used to reduce voltage and to increase
current to make the electricity suitable for general use. The
process of transforming voltage results in energy loss that is
released in the form of heat and therefore transformers must
contain effective cooling systems. Dry type transformers
dissipate heat directly into the ambient air. Liquid cooled
transformers dissipate heat into liquid mediums. Dry type
transformers require little or no maintenance through their
service life other than assuring that connections remain clean
and tight, that the loading on the transformer remains within
design limits, and that air flow through the transformer is not
impeded by extraneous materials or dust.
Dry-type transformers are therefore the primary choice for
indoor locations, and can be used anywhere a transformer is
required. Dry-type transformers are replacing liquidimmersed transformers in many commercial and industrial
applications including power plants, hospitals, schools, multistory buildings, paper and steel mills, mining, chemical
plants and subway systems. There are many types of dry type
transformer. Some of dry-type transformers are
 Cast resin dry type transformer
 Gas-filled dry type transformer



Epoxy coated dry type transformer
RESIBLOC epoxy cast type transformer
Vacuum pressure impregnated conventional dry
type transformer and so on.
II. CAST RESIN DRY-TYPE DISTRIBUTION
TRANSFORMERS
Cast resin dry type transformer is a transformer which one
of the dry type transformers as shown in Fig.1. A cast resin
dry-type indoor 3phase, 315kVA, 11/0.4 KV, Dyn11,
distribution transformer has been developed. This
transformer is of IP00 protection degreeThis transformer is
the most suitable transformer for distribution of electricity in
high degree of safety. They do not propagate fire. They are
self-extinguishing and in the event of a break down, there is
no risk of leakage of inflammable or contaminating
substances such as oil. The thickness insulation pouring with
transformer, with thick insulation transformer is filter casting
resin encapsulation winding transformer, cast resin plus
quartz powder as casting, quartz powder 60%, only 40% of
resin and pigment of the product. Thickness of epoxy resin
before casting in general 6~12 mm, now 3~ 5 mm, thick
insulation pouring it said transformer. Flame-retardant, selfextinguishing, good, high mechanical strength.
In a two winding transformer two windings would be
present. The one which is connected to a voltage source and
creates the flux is called as a primary winding. The secondary
winding where the voltage is induced by induction is called a
secondary. If the secondary voltage is less than that of the
primary the transformer is called a step down transformer. If
Copyright @ 2014 SEMAR GROUPS TECHNICAL SOCIETY. All rights reserved.
AYE AYE PYONE, MYO THET TUN
the secondary voltage is more than it is a step up transformer.
b) High And Low Voltage Windings
A step down transformer can be made a step up transformer
High voltage windings are made in layer or section-layer
by making the low voltage winding its primary. Hence it may
form with the series connection of sections forms. Low
be more appropriate to designate the windings as High
voltage winding are made in foil or layer form.
Voltage (HV) and Low Voltage (LV) windings. The high
HV and LV winding is made of insulated wire on high
voltage and low voltage coils are wound of either copper or
accuracy
coil-processing machines. Vacuum resin filling of
aluminium conductor which are suitable for class F and class
windings is carried out during a completely automated
H insulation systems. The coils are completely impregnated
process. Epoxy compound includes a number of components
and cast under vacuum in fiberglass reinforced epoxy resin
providing a good heat emission, and also a high
into the moulds. The casting process produces an insulation
thermostability.
system of uniform fiberglass-epoxy laminate. The final
product is a composite of highest electrical and mechanical
c) Transformer Windings
quality. The windings are embedded into the first class
Windings form another important part of transformers.
lamina
The windings of the transformer are normally arranged in the
following two ways:
 Concentrically in relation to one another (used for
core type) and called concentric winding.
 In group of LV, HV coils stacked alternately one
over the other, along the height of the limb (used for
shell type) and known as interleaved winding or
sandwich winding.
Most commonly used types of winding in transformers are
the following:
 Cross over winding
 Continuous disc coil type winding
 Disc type section winding
 Helical winding
 Sandwich winding (for shell type transformer)
 Dry type/ Cast resin [1]
Fig.1. Cast resin dry type transformer [3].
A. Basic Parts of Cast Resin Dry-type Transformer
a) Core
Fig.2 presents the core is made of cold-rolled electrotechnical sheet steel with a heat-proof coating. Stacking
technology and step-lap cutting provide low level of no-load
losses. Cutting of lector-technical steel is carried out on the
automatic cutting line with the high cut accuracy.
d) Transformer Housing
Transformer housing provides necessary protection degree
of the active part. It is made of steel construction with walls,
a bottom and a roof. The walls and the bottom havevent
holes, providing a normalized cooling level of the
transformer. Wide walls have access panels for access to
adjusting taps. Al walls are deta chabled that assures visual
inspection and maintenance service on a schedule date.
Transformers can be manufactured of the following design
versions:
 Lеft: HV winding inputs are on the left regarding
the front;
 Right: HV winding inputs are on the right regarding
the front;
 Up: inputs of the LV and HV windings are on the
transformer upper cover.
Other design versions are up to the customer request
(Fig.3). Transformers can have any protection class up to
IP54 included.
Fig.2. Stacking core.
e) Temperature control relay
The temperature, as standard is provided with a thermal
protection device as shown in Fig.4. The thermal sensors are
located in the low voltage winding of each phase and they are
removable in the event of damage/failure.PT100 device shall
be supplied as a sensor for this purpose. The PT100, a single
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.17, August-2014, Pages: 3500-3504
Design of Cast Resin Dry Type Transformer
PT100 sensor in each low voltage winding, provides the
(Fig.5). Cooling fans are installed on both sides of
same function but provides the additional benefit of local
transformer, the fans are automatically switched on and off
temperature indication. The alarm and trip setting can be
by means of sensor [3].
independently adjusted by the user. Should the transformer
be provided with fans for forced ventilation, their control will
be achieved via the relevant panel supplied with the unit. The
circuit diagram will be located in the panel. The relevant
control settings for fans on/ off are illustrated in the table [3].
Fig.5. Fan used in dry type transformer [3].
Fig.3. IP 00 transformer housing.
III. DESIGN CONSIDERATION
The design of the dry-type transformer is to obtain main
dimensions of the magnetic circuit (core, yoke and window),
low voltage and high voltage windings, performance
characteristic as shown in Fig.6.
TABLE I: Relevant Control Setting For Fans On/Off
Fig.6. Main dimensions of magnetic frame.
V1
V2

N1
N2

I1
(1)
I2
The e.m.f per turn,
Et  K
Fig.4. Temperature relay.
f) Cooling System
Cooling method of dry-type transformer is divided into
the natural air cooling (AN) and forced air cooling (AF).
Natural air cooling, the transformer at rated capacity under
long-termed continuous operation. Forced air cooling,
transformer output capacity can be increased by 50%. To
increase the capacity of the transformer as much as 40%, the
cast resin transformers are equipped with cooling fans
kVA
phase
(2)
For 5 stepped core, K=0.6365
The e.m.f per turn,
(3)
Where,
Bm= maximum value of flux density in the core, Tesla
f = frequency of supply, Hz
Ai = net cross sectional area of the core, m2
Cross sectional area of the core,
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.17, August-2014, Pages: 3500-3504
(4)
AYE AYE PYONE, MYO THET TUN
Output of transformer for three-phase,
(24)
(5)
Where, δ=average value of current density, A/mm2
Window space factor,
(6)
The window space factor depends upon the voltage rating
of the windings, mainly the highest voltage and KVA rating
of the transformer.
Window area,
(7)
Width of the window,
(8)
Overall length of the yoke,
(9)
(25)
Number of turn per phase in low voltage winding,
V
(26)
T2  2
Et
The r.m.s value of magnetizing current per phase in terms
of l.v,
Total Ampereturn s per phase
(27)
Im 
2  Number of turns in l.v winding
The r.m.s value of active compoment of no load current in
terms of l.v,
Total iron losses per phase
Iw 
(28)
Phase voltage of l.v winding
Gross core section,
Ac 
Ai
Iron Factor
(10)
Gross yoke area,
No load current,
Io  I m  I w
2
2
(29)
Cross sectional area,
(11)
a
Width of the yoke,
(12)
I
δ
Outer diameter of insulating cylinder,
Height of the yoke,
hy 
Ay
by
(30)
(31)
(13)
(14)
Inner diameter of l.v winding,
(32)
Outer diameter of l.v winding,
(33)
(15)
(16)
Mean diameter of l.v winding,
D m2 
(17)
Di2  D o2
2
(34)
Mean length of l.v turn,
(18)
(35)
Flux density of the yoke,
B y  1.5
Ac
Ay
(19)
Resistance per phase of l.v winding,
ρL T
r2  mt 2
a2
(20)
(21)
(36)
(37)
Number of turn per phase in high voltage winding,
Total ampere turns for three cores,
(38)
(22)
Total ampere turns for two yokes,
(23)
Total ampere turns for cores and yokes,
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.17, August-2014, Pages: 3500-3504
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(40)
Design of Cast Resin Dry Type Transformer
IV. TRANSFORMER SPECIFICATION
TABLE VI: Calculation Results of Dry Type
To calculate the transformer design, first step is based on
Transformer for losses and efficiency
the main data and the properly assumed values. The design of
the distribution transformer is to obtain main dimensions of
the magnetic circuit (core), yoke and window, low voltage
and high voltage windings, performance characteristics and
the cooling tank [2].
TABLE II: Specifications of Dry Type Transformer
Design
TABLE III: Calculation results Of Dry Type
Transformer for Magnetic Frame Design
TABLE IV: Calculation results Of Dry Type
Transformer for H.V Winding Design
TABLE V: Calculation Results of Dry Type Transformer
for L.V Winding Design
V. CONCLUSION
In this paper, 315 KVA, 11/0.4 KV, 50 Hz, three phase dry
type distribution transformer is discussed. The connection of
transformer is delta/star and core type transformer is
designed. The design is carried out based on the given
specification by using available material economically and
achieving better operating performance. This transformer is
used to step down the transmission voltage to the low voltage
for the power distribution requirement with minimize losses
and cost, and increase the distribution capacity of the lines.
Dry type transformer is widely used in factories,
constructions, buildings, mails, etc. By using dry type
transformer, core losses and winding losses can be reduced
than other types of transformer. Therefore, dry type
transformer is needed to study as one of the important role in
electrical engineering field.
VI. ACKNOWLEDGEMENT
Firstly, the author especially thanks to her supervisor, Dr.
Myo Thet Tun, Associate Professor, Electrical power
Engineering Department of Mandalay Technological
University, for his guidelines for this paper. The author is
deeply indebted to her Co-supervisor, Dr. Soe Win Naing,
Associate Professor, Department of Electrical Power
Engineering, Mandalay Technological University. Then Dr.
Khin Thuzar Soe, Associate Professor and Head, Department
of Electrical Power Engineering, Mandalay Technological
University also thanks. The author greatly express thanks to
all persons whom will concern to support in preparing this
paper.
VII. REFERENCES
[1]Dr. Mittle, V.N and Arvind Mittle., 1996. Design of
Electrical Machine 5th Edition, Standard Publishers
Distributiors.
[2]Transfor S.A (Switzerland) and the Transformer is locally
assembled by Charoenchai Transformer co.Ltd.
[3] www.besttransformer.com
[4]Zhejiang Leren Transformer Co.,Ltd, 2010.
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.17, August-2014, Pages: 3500-3504