Short Notes series SCORE ACADEMY
for, KPSC, SSC, RRB, KSEB
This note is for theoretical topics only. Refer class sessions for numerical & application-level topics
Cooling in Transformers
➢ Cooling of Transformer is the process by which heat generated in the transformer is
dissipated or treated to the safe value. The major factor for the generation of heat in the
transformer is the various losses like Core losses (hysteresis, eddy current, iron) and Page |
1
Copper loss. Among all the various losses the major contributor of the heat generation is the
Copper loss or I2R loss.
➢ The core loss occurs in the core of transformer and copper loss occurs in the winding of the
transformer. These losses appear in the form of thermal energy and increase the temperature
of the transformer.
➢ If the temperature of the transformer continues to increase rapidly, it will result in the
degradation of the insulation used in the transformer resulting in the damaging of the various
parts and hence the failure of the transformer. Thus, proper removal or treatment of heat is
necessary for the efficient working, longer life and higher efficiency of the transformer.
Methods of removing this heat can depend on the application, the size of the unit, and the amount
of heat that needs to be dissipated. Basically, there are two types of transformers one is the Dry
type, and another one is Oil-immersed type
Factors that determine the life expectancy of solid insulation,
1. Temperature,
2. Moisture
3. Oxidation
The temperature of solid insulation is the primary factor in transformer aging if moisture in
the insulation is at a normal level (≤ 0.5 %)
For the cooling of transformers, the following cooling methods listed below are used
The various cooling arrangements of a transformer are
For Dry Type Transformer:
1. Natural Air Cooling (AN)
2. Forced Air Cooling (Air Blast)
SCORE ACADEMY TRIVANDRUM Contact: 9895975777
Telegram link: t.me/scoreacademy facebook.com/score.tvm
,Short Notes series SCORE ACADEMY
for, KPSC, SSC, RRB, KSEB
This note is for theoretical topics only. Refer class sessions for numerical & application-level topics
For Oil Immersed Transformer:
Download our APP here:
1. Oil Natural Air Natural (ONAN)
SCORE E3 Learning APP
2. Oil Natural Air Forced (ONAF)
https://bit.ly/3mZ3qT7
3. Oil Forced Air Forced (OFAF) Page |
2
4. Oil Natural Water Forced (ONWF)
5. Oil Forced Water Forced (OFWF)
Method of Cooling in Dry-type Transformers:
Cooling In Dry Type
Air Natural (AN) Air Forced (AF)
1. Natural Air Cooling (AN)
➢ By Air Natural method the generated heat in the transformer is cooled by the circulation
of natural air. When the temperature of the transformer becomes higher as compared to
the temperature of the surrounding air, by the process of natural convection, heated air
is replaced by the cool air. This method is also known as a self-cooled method.
➢ In this method, only natural circulation of air without using any fan, blower etc is
used for cooling.
➢ The surface area of the core and transformer winding is increased to dissipate the heat
generated. Fins are made on the body of transformer similar to that in an engine to
increase its surface exposure area.
➢ This cooling is used for small transformer up-to voltage rating of 10 to 15 kV, and
rating upto 3 MVA
SCORE ACADEMY TRIVANDRUM Contact: 9895975777
Telegram link: t.me/scoreacademy facebook.com/score.tvm
, Short Notes series SCORE ACADEMY
for, KPSC, SSC, RRB, KSEB
This note is for theoretical topics only. Refer class sessions for numerical & application-level topics
Page |
3
Fig (a): Natural air-cooling Transformer where fins are provided on the main tank of
Transformer to increase its surface exposure
The advantages of this method of cooling are:
1. Freedom from dust
2. It is pollution-free
3. Low Side clearance
4. Capacity is high to support overloads
2. Air Forced (AF) or Air Blast
➢ We can say that it is the type of artificial cooling because the forced air is used for cooling
purposes.
➢ With the help of fans and blowers, high velocity of air is forced on the core and the
windings of the transformer.
➢ As the temperature inside the transformer goes beyond the standard safe level, an alarm
is activated, and the fans and blowers are switched ON automatically.
➢ This method is used for transformer rating from 3MVA to upto 15MVA
SCORE ACADEMY TRIVANDRUM Contact: 9895975777
Telegram link: t.me/scoreacademy facebook.com/score.tvm
for, KPSC, SSC, RRB, KSEB
This note is for theoretical topics only. Refer class sessions for numerical & application-level topics
Cooling in Transformers
➢ Cooling of Transformer is the process by which heat generated in the transformer is
dissipated or treated to the safe value. The major factor for the generation of heat in the
transformer is the various losses like Core losses (hysteresis, eddy current, iron) and Page |
1
Copper loss. Among all the various losses the major contributor of the heat generation is the
Copper loss or I2R loss.
➢ The core loss occurs in the core of transformer and copper loss occurs in the winding of the
transformer. These losses appear in the form of thermal energy and increase the temperature
of the transformer.
➢ If the temperature of the transformer continues to increase rapidly, it will result in the
degradation of the insulation used in the transformer resulting in the damaging of the various
parts and hence the failure of the transformer. Thus, proper removal or treatment of heat is
necessary for the efficient working, longer life and higher efficiency of the transformer.
Methods of removing this heat can depend on the application, the size of the unit, and the amount
of heat that needs to be dissipated. Basically, there are two types of transformers one is the Dry
type, and another one is Oil-immersed type
Factors that determine the life expectancy of solid insulation,
1. Temperature,
2. Moisture
3. Oxidation
The temperature of solid insulation is the primary factor in transformer aging if moisture in
the insulation is at a normal level (≤ 0.5 %)
For the cooling of transformers, the following cooling methods listed below are used
The various cooling arrangements of a transformer are
For Dry Type Transformer:
1. Natural Air Cooling (AN)
2. Forced Air Cooling (Air Blast)
SCORE ACADEMY TRIVANDRUM Contact: 9895975777
Telegram link: t.me/scoreacademy facebook.com/score.tvm
,Short Notes series SCORE ACADEMY
for, KPSC, SSC, RRB, KSEB
This note is for theoretical topics only. Refer class sessions for numerical & application-level topics
For Oil Immersed Transformer:
Download our APP here:
1. Oil Natural Air Natural (ONAN)
SCORE E3 Learning APP
2. Oil Natural Air Forced (ONAF)
https://bit.ly/3mZ3qT7
3. Oil Forced Air Forced (OFAF) Page |
2
4. Oil Natural Water Forced (ONWF)
5. Oil Forced Water Forced (OFWF)
Method of Cooling in Dry-type Transformers:
Cooling In Dry Type
Air Natural (AN) Air Forced (AF)
1. Natural Air Cooling (AN)
➢ By Air Natural method the generated heat in the transformer is cooled by the circulation
of natural air. When the temperature of the transformer becomes higher as compared to
the temperature of the surrounding air, by the process of natural convection, heated air
is replaced by the cool air. This method is also known as a self-cooled method.
➢ In this method, only natural circulation of air without using any fan, blower etc is
used for cooling.
➢ The surface area of the core and transformer winding is increased to dissipate the heat
generated. Fins are made on the body of transformer similar to that in an engine to
increase its surface exposure area.
➢ This cooling is used for small transformer up-to voltage rating of 10 to 15 kV, and
rating upto 3 MVA
SCORE ACADEMY TRIVANDRUM Contact: 9895975777
Telegram link: t.me/scoreacademy facebook.com/score.tvm
, Short Notes series SCORE ACADEMY
for, KPSC, SSC, RRB, KSEB
This note is for theoretical topics only. Refer class sessions for numerical & application-level topics
Page |
3
Fig (a): Natural air-cooling Transformer where fins are provided on the main tank of
Transformer to increase its surface exposure
The advantages of this method of cooling are:
1. Freedom from dust
2. It is pollution-free
3. Low Side clearance
4. Capacity is high to support overloads
2. Air Forced (AF) or Air Blast
➢ We can say that it is the type of artificial cooling because the forced air is used for cooling
purposes.
➢ With the help of fans and blowers, high velocity of air is forced on the core and the
windings of the transformer.
➢ As the temperature inside the transformer goes beyond the standard safe level, an alarm
is activated, and the fans and blowers are switched ON automatically.
➢ This method is used for transformer rating from 3MVA to upto 15MVA
SCORE ACADEMY TRIVANDRUM Contact: 9895975777
Telegram link: t.me/scoreacademy facebook.com/score.tvm
