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The National Engineering University
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College of Engineering
EE 422
Laboratory Report
Transformer Parts and
Functions
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I.
Introduction
The following report discusses different types of electrical transformers: step-up
and step-down transformers, single-phase and three-phase transformers, power
transformers, distribution transformers, current transformers, and potential
transformers.
II.
Objectives
The objective of this report is to define the parts, and functions of the different types
of transformers mentioned above.
III.
Background
Electrical transformers are machines that transfer electricity from one circuit to
another with changing voltage levels but no frequency change. Because they are
designed to use alternating current, changes in supply voltage are influenced by
changes in supply current. They either increase or decrease voltage levels, ensuring a
safe and efficient power system in both industrial and residential areas. (Industrial
Quick Search, n.d.)
IV.
Discussion
The following discusses the types of electrical transformers.
a. Step-up Transformer and Step-down Transformer
Definition:
A step-up transformer is a transformer that increases the voltage from
primary to secondary by having more secondary winding turns than primary
winding turns. Moreover, its primary current is greater than its secondary current.
The primary winding of the transformer is the LV winding, and the secondary
winding is the HV winding. In most cases, a step-up transformer is used for power
transmission and its example is the one found in a power plant. (Kuphaldt &
Haughery, 2020)
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On the other hand, a step-down transformer is designed to do just the
opposite. It has a primary voltage greater than the secondary voltage. On the other
hand, the HV winding of the transformer is the primary, and the LV winding is
secondary. Also, the number of turns in the primary winding is more than in the
secondary winding. The secondary current is more than the primary current. A stepdown transformer is used in power distribution. One of its examples is the
transformer in a residential colony. (Kuphaldt & Haughery, 2020)
Parts:
The step-up transformer and step-down transformer both have 2 parts: (Linquip
Team, 2021)
• Core
A high permeability substance can be used to mimic the core of the
transformer. Its core material enables magnetic current to flow more efficiently.
When compared to the air, the core material has a high permeability. As a result,
the magnetic flux lines passing through the core material will be limited by this
core substance. As a result, decreasing transformer waste can enhance
transformer efficiency.
• Windings
The step-up transformer's windings will aid in the transfer of the current
generated by the transformer. These windings are generally designed to keep the
transformer cool during operation and testing.
The windings include primary and secondary windings. The primary part of
the coil has a high density but fewer turns. Similarly, the coil density in the
second part is thin but contains a large number of turns. This can be modeled by
assuming that the major part contains less energy than the secondary side.
b. Single-phase Transformer
Definition:
A single-phase transformer is an electrical device that converts alternating
current (AC) from one voltage level to another. It is a static (or stationary) electric
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machine with two or more windings, and transformers are classified according to
the number of windings they have. Transformers are used in electric power
applications to increase or decrease alternating voltages. Single-phase transformers
are the most common type of transformer. Single-phase transformers are used in a
wide range of applications, including power distribution, electronic equipment, and
lighting. (Sorting Hat Technologies Pvt Ltd, n.d.)
Parts:
The single-phase transformer parts work together to provide a safe and efficient
way to transfer electrical energy. The single-phase transformer have 3 parts:
(Sorting Hat Technologies Pvt Ltd, n.d.)
• Core
The core of the transformer is made of iron or steel. It provides a path for
the magnetic flux.
• Winding
The winding is a coil of wire that is wound around the transformer core. It
carries the current that flows through the transformer. The primary winding is
winding on the transformer's side that is connected to the alternating current
power source. When an alternating current voltage is applied to the primary
winding, it generates a magnetic field. The winding on the side of the transformer
connected to the load is known as secondary winding. When an alternating
current voltage is applied to the primary winding, a voltage is induced in the
secondary winding.
• Isolation
Isolation is necessary to protect the transformer winding from the core. It is
done by using an insulation material such as glass, mica, varnish, etc.
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c. Three-phase Transformer
Definition:
A three-phase transformer, also known as a 3-phase or 3-transformer, is
made up of three primary coils and three secondary coils. A three-phase system can
be built using three identical single-phase transformers, and this type of three-phase
transformer is known as a bank of three transformers. The three-phase transformer,
on the other hand, can be built on a single core. A transformer's windings can be
connected in either a delta or a wye configuration. The operation of a three-phase
system is similar to that of a single-phase transformer, and they are commonly used
in power plants. (Elprocus, 2020)
Parts:
The most important parts used in the three-phase transformer are windings and core.
• Laminated Steel Core
Silicon steel is used in the construction of three-phase transformer cores. Its
high permeability, low magnetic reluctance, and low hysteresis loss make it
useful. The core is made up of stacks of laminated thin steel sheets that are
electrically insulated from one another thanks to a thin coat of varnish. To reduce
eddy current loss, the core is laminated.
• Windings
The cylindrical coils (windings) are arranged concentrically around the
same limb, with the low-voltage winding inside and the high-voltage winding
outside. Because it is easy to insulate a low voltage winding from the core, it is
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placed close to the core. Both windings are properly insulated from one another
and from the core. Three high-voltage and three low-voltage windings are used
in the construction of a three-phase transformer.
• Transformer Oil
Transformer oil is a mineral oil obtained by fractional distillation of crude
petroleum that is used in transformers. This oil transports the heat generated by
convection in the transformer from the windings and core to the transformer
tank. This oil also improves and maintains transformer winding insulation.
• Conservator
It's a small cylindrical tank that sits on top of oil-cooled transformers and is
linked to the main tank by a small pipe. It allows for the expansion and
contraction of oil, which expands when heated and contracts when cooled. It
reduces oil oxidation by reducing the surface area of oil in contact with air.
• Breather
It is the device through which all air movement from and into the
transformer occurs. When the oil expands due to the heating of the transformer,
air is expelled and drawn in when the oil cools. It's mounted at one end of the
conservatory.
• Thermometer
A thermometer is installed on all large-capacity transformers to indicate the
temperature of the hot oil. Temperature-indicating devices are installed in the
winding of very large transformers to record the winding temperature. A
temperature-sensitive alarm system is also installed to sound the alarm whenever
the temperature rises dangerously.
• Explosion Vent Pipe
It's a twisted pipe with a glass cap at the end. It is mounted on top of the
transformer tank. It protects against excessive pressure buildup within a
transformer. In the absence of this device, the transformer may explode.
• Valves
Each transformer has a number of valves for filling and draining the
transformer oil.
• Buchholz Relay
Buchholz relay is a type of gas relay. When a fault develops inside the
transformer, the relay sounds an alarm, and if the fault is dangerous, the relay
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disconnects the transformer circuit. On large-capacity transformers, this relay is
installed between the main tank and the oil conservator.
d. Power Transformer
Definition:
Power transformers are generally used in transmission networks for
stepping up or down the voltage level. It operates mainly during high or peak loads
and has maximum efficiency at or near full load. A power transformer is a passive
electromagnetic device that uses inductive coupling to transfer energy from one
circuit to another. (Power Transformers, 2020)
Parts:
The power transformer has the following parts: (Parts Of A Power Transformer,
2011)
• Transformer Tank (1)
This houses the transformer windings as well as the insulating medium (oilfilled). Transformer tanks must be airtightly sealed in order to isolate their
contents from any environmental contaminants.
• High Voltage Bushing (2)
This is where the transformer's primary windings terminate and serve as an
insulator from the transformer tank. Its creepage distance is determined by the
transformer's voltage rating.
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• Low Voltage Bushing (3)
This is the terminal where the secondary windings of the transformer
terminate and serve as an insulator from the transformer tank, similar to the highvoltage bushing. Because low-voltage bushings are typically smaller in size than
high-voltage bushings, they can be easily distinguished from their high-voltage
counterparts.
• Cooling Fins/Radiator (4)
Cooling fins and radiators are typically attached to transformer tanks in
order for the transformer to dissipate the heat generated in its oil-insulation. The
capacity of the transformer is affected by its temperature, so it must have a
cooling mechanism for improved performance and efficiency.
• Cooling Fans (5)
It is commonly found attached to the cooling fins. Cooling fans can be
controlled by a timer or by winding/oil temperature. Cooling fans assist in
increasing transformer capacity when the temperature of the transformer rises
due to loading. Cooling fans on the transformer are activated by a relaying device
that detects a relatively high temperature and causes the fan to run automatically.
• Conservator Tank (6)
An oil preservation system in which the oil in the main tank is isolated from
the atmosphere over a specified temperature range by an auxiliary tank partially
filled with oil and connected to the fully filled main tank.
• System Ground Terminal (7)
When the connection type of the transformer windings includes a wye,
system ground terminals are usually present. This terminal is located in line with
the transformer's main terminals.
• Drain Valve (8)
It is typically found at the bottom of the transformer tank. Drain valves are
used whenever oil needs to be replaced. This valve allows for the simple
replacement of oil in an oil-filled transformer by simply opening it like a faucet.
• Dehydrating Breather (9)
Dehydrating breathers are used to keep normal air moisture from contacting
the oil in electrical equipment as the load or temperature changes. This helps to
keep the oil's insulation capability and reduces degeneration. It reduces moisture
accumulation in the cell when used with a conservator system and a rubber air
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cell. Some breathers are intended for sealed tank transformers and only breathe
at predetermined pressure levels.
• Oil Temperature/Pressure gauges (10)
These are used to monitor the transformer's internal characteristics,
particularly its windings. These gauges assist the operator in determining the
temperature and pressure levels within the transformer (oil & winding). This will
also serve as an alarm if a certain level is reached that may be hazardous to the
transformer windings.
• Bushing Current Transformers (11)
These are typically found near transformer terminals that will later be used
for metering and relaying. Its terminals are located in the transformer's control
panels.
• Control Panel (12)
This contains all of the transformer's monitoring devices, terminals, and
auxiliary devices, as well as the terminals of the bushing current transformers
and cooling fans. Control panels are extremely useful, especially when
constructing a remote control house; this will serve as their connection point.
• Surge Arresters (13)
This type of arrester is installed directly before and after the transformer
terminals to reduce the transformer's exposure. Its purpose, like any other surge
arrester, is to clip sudden voltage surges that can damage the transformer
winding.
e. Distribution Transformer
Definition:
A distribution transformer is also mentioned as a common type of isolation
transformer. The basic function of this transformer is to convert high voltage to
standard output voltages such as 240/120 V for use in electric energy distribution.
In the distribution system, transformers of various types are available, including
single-phase, three-phase, pad-mounted, underground, and pole-mounted
distribution transformers. (Linquip Team, 2021b)
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Parts:
The distribution transformer has the following parts: (Distribution Transformer |
MBT Transformer, 2020)
• Oil Tank
The oil tank is used to soak the coils by placing it in.
• Conservator
On the outside of the transformer frame, above the oil tank, is a conservator.
It is linked to the main tank through a metal tube. The oil in the tank can be easily
contacted and expanded during loading, allowing the oil's temperature to rise and
fall.
• Buchholz relay
When using a conservator tank, the Buchholz relay is used. Because it
indicates errors such as oil loss when it runs low, the flow of oil between the tank
and transformer is incorrect.
• Dehydrating Breather
The oil in the breather unit contains desiccant silica gel. It will not be
hygroscopic in oil if its color changes from blue to pink.
• Oil Level Indicator
The oil indicator displays the level of oil in the conservatory unit.
• Temperature Detector
The temperature detector keeps track of the oil's temperature. When the oil
temperature reaches a certain threshold, the transformer is turned off.
• Pressure relief device
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The pressure relief device reduces the pressure inside the transformer to
prevent it from exploding.
• Thermal relay
The thermal relay serves as a temperature indicator for the winding.
• Radiators
Radiators are used to improve the transformer's cooling efficiency.
• Bushings
Bushings are used to connect a transformer's inner windings to an external
electrical network.
f. Current Transformer
Definition:
Current transformers are measurement transformers that are used to
measure the amount of current flowing through a circuit. Direct measurement of
high currents with measuring instruments is not only costly but also dangerous and
difficult at times. As a result, in order to be measured, the current passing through
the circuit must be reduced to a specific value. The current transformer, which is
connected in series to the circuit, reduces the magnetic field created by the current
passing through the primary circuit and transfers it to the secondary circuit. The
amount of current flowing in the primary circuit can be measured by the measuring
device connected in parallel to the secondary winding due to the cyclic current
occurring in the secondary circuit. (Entes, 2023)
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Parts:
Current transformers are made up of three parts: a magnetic iron core, a
primary winding wound on this core, and a secondary winding wound in the
opposite direction on this primary winding. The primary winding current generates
a magnetic flux on the magnetic iron core. The magnetic flux in the core induces a
voltage on the secondary winding. Because the current passing through the
secondary circuit is opposite to the winding direction, the measuring device
connected in parallel to the secondary winding generates a magnetic flux in the
magnetic iron core in the opposite direction.
The magnetic flux created by the current passing through the primary
winding is balanced by this magnetic flux. As a result, the current transformers'
secondary ends must be short-circuited by a measuring device or a load. Otherwise,
there will be no magnetic flux in the opposite direction, and because the flux is
unbalanced, the magnetic iron core will heat up and fail. Furthermore, this situation
endangers users by increasing the voltage at the secondary ends. (Entes, 2023)
g. Potential Transformer
Definition:
A potential transformer is a type of instrument transformer (also known as a
voltage transformer). It is a step-down voltage transformer that converts high-level
voltage to lower-level voltage. An ordinary voltmeter can be used to measure the
potential transformer's output voltage. (Electrical Technology, 2021)
Parts:
The potential transformer has the following parts: (Construction of Potential
Transformer, 2017)
• Core
The potential transformer's core can be either a core or a shell. The windings
surround the core in a core-type transformer, while the core surrounds the
winding in a shell-type transformer. The shell-type transformer is intended for
low-voltage applications, whereas the core-type transformer is intended for highvoltage applications.
• Windings
The primary and secondary windings are coaxially placed to reduce the
potential transformer's leakage reactance.
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• Insulation
Cotton tape and cambric materials are used as insulation
between the potential transformer's windings. Low voltage
transformers do not use compound insulation. Oil is used as
an insulation medium in high voltage transformers. Porcelain
is used as an insulator in transformers with ratings greater
than 45kVA.
• Bushing
The bushing is an insulated device that connects the
transformer to the external circuit. The transformer's bushings
are made of porcelain material. The oil-filled bushing is used
in transformers that use oil as an insulating medium. When
the line through which it is connected is not at ground
potential, a two bushings transformer is used in the system.
The transformer that connects to the neutral ground uses only
one high voltage bushing.
V.
Reference
Construction of Potential Transformer. (2017, December 7). Circuit Globe.
https://circuitglobe.com/construction-of-potential-transformer.html
Distribution Transformer | MBT Transformer. (2020). Vietnamtransformer.com.
https://vietnamtransformer.com/our-news/distribution-transformer-mbttransformer
Electrical Technology. (2021). Potential Transformer (PT) - Types of Voltage
Transformers.
ELECTRICAL
TECHNOLOGY.
https://www.electricaltechnology.org/2021/09/voltage-potentialtransformer.html
Elprocus. (2020). Three-Phase Transformer - Working Principle and Its Construction.
ElProCus
Electronic
Projects
for
Engineering
Students.
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Entes. (2023). What is current transformer? Where do we use current transformers?
ENTES Elektronik. https://www.entes.eu/what-is-current-transformer-wheredo-we-use-currenttransformers/#:~:text=Current%20transformers%20basically%20consist%20of
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Industrial Quick Search. (n.d.). Electric Transformers: Types, Applications, Benefits,
and
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Www.iqsdirectory.com.
https://www.iqsdirectory.com/articles/electrictransformer.html#:~:text=Electric%20transformers%20are%20basically%20ma
chines
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Linquip Team. (2021a). Step Up Transformer: Construction & Working Principles |
Linquip. Linquip. https://www.linquip.com/blog/what-is-step-up-transformer/
Linquip Team. (2021b, May 23). Distribution Transformer: Parts, Types & Working
Principles. Linquip. https://www.linquip.com/blog/what-is-a-distributiontransformer/#:~:text=The%20main%20components%20of%20this
Power
Transformers.
(2020).
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PARTS
OF A POWER TRANSFORMER. (2011, June). Blogspot.com.
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Sorting Hat Technologies Pvt Ltd. (n.d.). Parts Of A Single-Phase Transformer.
Unacademy. Retrieved from https://unacademy.com/content/upsc/studymaterial/physics/parts-of-a-single-phasetransformer/#:~:text=The%20single%2Dphase%20transformer%20is%20comp
osed%20of%20the%20following%20parts
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