Transformer works by increasing or decreasing voltage levels without changing frequency. It has a core made of silicon steel laminations and winding coils. Key parts include the core, HV and LV windings, bushings, conservator tank, breather, and Buchholz relay. Transformer types depend on whether the core surrounds the coil or vice versa. Windings are insulated and sectioned or wound continuously. Tests ensure safety and performance. Recent trends focus on more efficient designs using improved materials.

1. TRANSFORMER
BY
pradeeprajr93@gmail.com

2. What is it ?
▪ It transforms theVOLTAGE level without changing
FREQUENCY.
V v
▪ Rated in
– MVA (POWERTRANSFORMERS)
– KVA (DISTRIBUTIONTRANSFORMERS)
int const f = 50;
Static
Device

3. Let’s Explore it
▪ Various parts
– Core
– Winding
▪ HV winding
▪ LVWinding
– HV and LV Bushings
– ConservatorTank
– Breather
– Buchholz Relay
– Cooling Fins and Fans
▪ Tests involved
▪ Recent trends

4. CORE OF A TRANSFORMER
CONSTRUCTION Laminated core is made of
SILICON STEEL.(prevent
eddy current loss)
It has low hysteresis area
and high permeability.
Core is also used to give
mechanical support to the
windings.
Proper distribution of flux

5. Types involved
▪ In case of Shell type transformer Core surrounds
the coil.
▪ In case of core type transformer coil surrounds the
core.

6. Transformer Winding
HV windings
– It carries very low current
– So it’s thickness is less compared to
LV winding
– We can fully wound the entire coil
continuously (DRUMType coil).
But during fault entire coil has to be
replaced.
– We can section/segment the coil
into two to four sections for ease of
winding and replacement.
– DPC (Double Paper Coating) is used
as insulation
Section 1
Section 2
Section 3
Section 4
Section 5
Section 6
Section 7
Section 8
Sectioned coil

7. Transformer Winding
LVWindings
– As we know LV winding has to carry
more current than HV, it’s thickness
is large.
– Based on number of turns in LV
winding and primary secondary
Voltage/Current, we can calculate
the primary turns.
𝑁1
𝑁2
=
𝐸1
𝐸2
=
𝐼2
𝐼1

8. Transformer Winding
▪ In general, LV windings are wounded around the core
first, then HV windings.
▪ So less amount of insulation is enough.
▪ Every windings in LV have two terminals (Inner and
Outer)
▪ In this case, all inner terminals of three phases(R,Y,B)
are shorted and welded together to form neutral
winding
▪ The remaining three outer terminals forms the phases
R,Y,B.

9. Transformer Bushings
▪ The HT windings are mostly Δ (delta) connected
and LT windings areΥ (star) connected.
▪ The terminals are taken out and connected to
bushings.

10. Arrangement of Bushings
Primary
R Y B
Secondary
E N R Y B
Earth* Neutral
* Newly introduced especially in Star rated Energy Efficient transformers

11. CONSERVATOR TANK
▪ Reservoir forTransformer oil situated at top.
▪ It should be half-filled, because to provide space
for oil during expansion while heating and to
supply oil when oil level reduced in transformer
during cooling.

12. Breather
▪ As we know that level of oil rise and fall during
heating and cooling.
▪ Cooling takes air in and heating let the air out.
▪ This aspirated air contain some moisture to
breather is filled with SILICA GEL (desiccant air
drier) else oil will be deteriorated.

13. Buchholz Relay (Only in power Transformers)
▪ On a slow accumulation of gas, due to slight
overload, gas produced by decomposition of
insulating oil accumulates in the top of the relay
and forces the oil level down.
▪ A float switch in the relay is used to initiate an
alarm signal. Depending on design, a second float
may also serve to detect slow oil leaks.

14. Cooling fins and fans
▪ Due to convection hot oil rise up and flow through
cooling tubes and fins. The oil is cooled by either
natural air or forced air using Fans.
Cooling tubes

15. Tap Changing
▪ It allows a variable number of
turns to be selected in discrete
steps.
▪ A transformer with a variable
turns ratio is produced, enabling
stepped voltage regulation of the
output.
▪ The tap selection may be made
via an automatic or manual tap
changer mechanism.

16. Types of TAP-CHANGING
▪ OLTC (On LoadTap Changer)
– Used in large PowerTransformer where
power interruption is unaccepted.
▪ NLTC (No LoadTap Changer)
– Due to short circuit problems, the power
is shut down during tap changing
operation

17. Power Transformer Protection
▪ OTA - OilTemperature Alarm (if exceeds 85°C)
▪ WTA- WindingTemperature Alarm (if exceeds 90°C)
▪ WTT- WindingTemperatureTrip
▪ BA – Buchholz Alarm
▪ BT – BuchholzTrip
▪ MOGA- Minimum Oil Gauge Measurement
▪ PRV – Pressure ReleaseValve
▪ OSTC – OLTC Surge RelayTrip
▪ DRT- Differential RelayTrip

18. Transformer Tests
▪ Short CircuitTest
▪ Open CircuitTest
▪ InducedVoltageTest
▪ Back-to-BackTest
▪ Megger test
– Ground-Ground (zero resistance)
– Line-Ground (infinite resistance)
– Line-Line (infinite resistance)
▪ Heated in HOTAIR CHAMBER at 200°C around 6hours

19. Transformer Oil Tests
▪ Medium used for cooling and insulation is
hydro carbonatedTransformer oil.
▪ Tests involved are
– BDV (Break DownVoltage test)
– AcidityTest
– InterfacialTensionTest

20. Recycling of Transformer Oil
▪ It has
– Three chambers
– 3 x 3 kW heater
– Propulsion System
– Belt driven Clay

21. Process in Recycling chamber
▪ Chamber 1 & 2
– Impure oil is circulated inside chamber at 60°C
– Then heated clay at 110°C is mixed and kept circulated for
three hours.
– Leave 16hours for settling of clay with carbon and impurities
(REST PERIOD)
– Pure oil is let out and further filtered using bladder
▪ Chamber 3
– It takes in the pure oil from bladder and mixes with chemicals
and CO2
– This improves the quality of transformer oil and immune to
corrosion problems in transformer.
▪ Finally the output is filtered in cartridge and filled in
Drums for transportation.

22. Energy Efficient Transformers
▪ In a typical power distribution grid, electric
transformer power loss typically contributes about
40-50% of the total transmission and distribution
loss.
▪ Energy efficient transformers are therefore an
important means to reduce transmission and
distribution loss.
▪ With the improvement of electrical steel (silicon
steel) properties, to achieve higher efficiency
▪ E.g.: Amorphous MetalTransformers
▪ These transformers are star-rated. ✭✭✭

23. Features of Energy Efficient
Transformers
▪ Addition Earth bushing to ground fault current
instantly, high safety and better efficiency.
▪ Guaranteed maximum temperature rise in
Oil/Winding is 35/40°C.
▪ GuaranteedTotal loss @ 100% loading is 3320watts.
▪ GuaranteedTotal loss @ 50% loading is 1050watts.
▪ These losses are double the amount in case of
ordinary distribution transformers.

24. Some specifications for your
REFERENCE*
▪ Type of cooling involved – ONAN (Oil Natural Air
Natural)
▪ Weight of Core andWindings – around 775Kg
▪ Weight of Oil – around 418Kg (480 litres)
▪ Total weight – around 1433 Kg
*The above mentioned values vary based on the capacity of
transformer, it is 250KVA Energy Efficient distribution
transformer

25. And finally, it’s my turn to