Dry Transformer Course.pptx

Mapna Group
| Slide 1
Dry Type Transformers

Mapna Group
| Slide 2
Content
Useful References
Dry Transformer Maintenance
Dry Transformer Operation
Dry Transformer Commissioning
Dry Transformer Installation
Dry Transformer Components
Standard technical features
Main advantages
What is a dry transformer?

Mapna Group
| Slide 3
What is a dry transformer?
 A dry transformer does not utilized any kind of
liquid for cooling, it has windings encapsulated
under Vacuum, in epoxy resin reinforced with
glass net.
 It is the most technologically advanced design
for extreme conditions.
 These transformers meet strict parameters with
respect to electrical system demands, are
virtually maintenance free and are manufactured
in accordance with industry and international
standards including, IEC 60076-11.

Mapna Group
| Slide 4
Main advantages: safe and environmental friendly
• Reduced environmental contamination.
• Zero risk of leakage of flammable
or contaminating substances.
• Environmental safe in production.
• Well suited to damp and contaminated areas.
• No fire hazard.
• Transformers are non flammable
and self-extinguishing.
• High resistance to short circuits.
• High capacity to support overloads.
• High performance in dealing with seismic
phenomenon.
• Capable of withstanding the most severe of rolling
and vibrating conditions.

Mapna Group
| Slide 5
Main advantages: The most economical
• Less space needed.
• Less civil work needed.
• No special safety features required.
(fire detection)
• Maintenance free.
• Longer transformer life due to low thermal
and dialectic ageing.
• Can be installed closer to the point of consumption
reducing load cable losses.
• Optimal design subject to constant improvements
in design as new materials become available.

Mapna Group
| Slide 6
Environmental, climatic and fire classes
Environment
• E0 Normal indoor installation, no condensation, no considerable pollution.
• E1 Limited pollution, occasional condensation eg off circuit periods.
• E2  Heavy pollution, frequent condensation.
Climate
• C1 Lower ambient temperatures:
• Operation -5 °C
• Storage and transport -25 °C
• C2  Lower ambient temperatures:
• Operation -25 ºC/-25 ºC
• Storage and transport
Fire
• F0 No special requirements except typical characteristics for dry type
transformers.
• F1  Increase demands.
• All material practically free of halogens
• Limited formation of fumes
• Limited contribution with calorific energy to the source of fire
• Self extinguishing transformer fire

Mapna Group
| Slide 7
Dry transformers VS Oil transformers
The best alternative due to:
 Suitable to operate in humid or heavily polluted
environments (E2).
 Suitable for operation, transport and storage at ambient
temperatures down to -25 ºC (C2).
 Restricted flammability, self fire extinction (F1).
 Emission of toxic substances and opacity of fumes is
minimized (F1).
 Withstand the same impulse test even for exposed
situation.
 Have more ability to withstand thermal and dynamic short
circuit effects.
 Mechanically stronger, safer against vibrations,
earthquakes, etc..
 No liquid, neither leaks and no risk of polluting spills.
 Fire hazard
 Safety for people and property
 Respect for natural life

Mapna Group
| Slide 8
Types and Designs
• Types:
• Standard three phase transformer.
• Multi winding transformer.
• Low Voltage transformer.
• Autotransformer.
• Drive systems transformers.
• Excitation systems transformers.
• Standard designs:
• High Voltage winding material: foil disks.
• Low Voltage winding material:
aluminum/copper foils.
• Insulation class: F (155°), H (180°).

Mapna Group
| Slide 9
1
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3
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5
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9
10 1
2
3
4
5
6
7
8
9
10
Wheels
Foundation
Lower clamp
High-voltage connecting rod
Insulating cylinder
iron core
Neutral bar
Low-voltage winding
High-voltage winding
Upper clamp

Mapna Group
| Slide 10
1. Magnetic Core:
The magnetic core is made from laminations of
grain-oriented silicon steel insulated with 0.25- 0.3
mm thickness. The choice and grade of steel and the
45 degrees cutting pattern and method of step-lap
assembly minimize the loss level and the no-load
current with the effect of a very low noise level.

Mapna Group
| Slide 11
2. Low Voltage Winding:
The low voltage winding is made of aluminum or copper foil to
achieve zero axial stresses under short circuit conditions; the foil is
insulated by a class F or H inter-layer film, pre-impregnated with
heat-activated, epoxy resin.
The ends of the winding are protected and insulated using a class F
or H insulator.
The whole winding is polymerized by being placed in an autoclave
for 2 hours at 130°C which guarantees:
• Outstanding resistance to industrial atmosphere aggression,
• Excellent dielectric withstand,
• Excellent resistance to radial stresses under bolted short circuit
conditions.
Each LV winding terminates in a tin-plated aluminum or copper
connection point, enabling connections to be made without using a
contact interface (grease, bi-metal strip). Assembly is carried out
according to current practices, including using spring pressure
washers under nuts and screw heads.

Mapna Group
| Slide 12
3. High Voltage Winding:
The high voltage winding is usually made and wounded by series
aluminum foil. This kind of wounding method is because of the high
turn numbers and small cross-section in high voltage winding.
These methods are used to obtain very low stress levels between
adjacent conductors. This winding is cast and moulded under vacuum
in a class F or H loading and fireproofed resin

Mapna Group
| Slide 13
Spacer strips (LV)
• Glass random non-woven with B-stage epoxy
resin impregnation
• Polyester non-woven with B-stage epoxy resin
impregnation
Support and spacers (LV)
dog bones
Layer insulation (LV)
Multi-layer insulation with B-stage epoxy resin coating
• Glass fabric with B-stage epoxy resin impregnation
• NOMEX with epoxy resin coating
Outer bandings (LV)
• Thread reinforced polyester non woven with B-
stage epoxy resin impregnation
Insulation cylinders
• PET Folie
• NOMEX
• PET Vlies
• Polyester folien-Laminat
Cast-resin reinforcement (HV)
• Glass roving fabric with cured epoxy resin

Mapna Group
| Slide 14
4. Voltage regulation
Some tap voltages are designed at high voltage side to control the
voltage at the low voltage side and keeping it constant.
The variation step voltages are ±2 × 2.5% according to the rated
voltage.
The variation of tap voltages is done via a piece of brass or copper at
the high-voltage side.
The variation of tap voltages in dry transformers is off-circuit type, and
the transformer must be turned off.
Low Voltage
(V)
High Voltage
(V)
Tap
Number
Connection Status
400
21000 1 6-5
20500 2 7-5
20000 3 7-4
19500 4 8-4
19000 5 8-3
5
4
3
7
6
8
5
4
3
7
6
8

Mapna Group
| Slide 15
Dry Transformer transportation guidelines
Handling
• lifting with slings
Lifting is carried out using the 4 lifting holes for a transformer
without an enclosure and by 2 lifting lugs in the case of a
transformer with an enclosure. The slings should not form an
inside angle greater than 60°.
• lifting with a fork lift truck
The lifting capacity of the fork lift truck should first be checked.
If suitable, the forks should be inserted inside the base channels
after removing the rollers.
• towing.
Towing the transformer with or without enclosure should be
done from the under base. For this purpose hole of 27 mm
diameter are provided on every side of the under base. owing
can be done in two directions : in the axis of the under base and
perpendicular to that axis.

Mapna Group
| Slide 16
Dry Transformer Maintenance guidelines
Storage
The transformer should be protected in storage from
water drops and dust generating work (masonry,
sanding, etc.).
a) The transformer can be stored at a temperature
down to - 25°C.
b) The place of transformer storage should be
protected from water drops, and if the transformer
is delivered with a plastic cover, it should be kept
over the equipment while it is in storage. It is better
to place a dehumidifier such as silica gel close to
the windings in humid environments and provide
proper ventilation.
c) The dry transformer is resilient against fire. It
means that no anti-fire precautions are necessary.

Mapna Group
| Slide 17
Installation and Commissioning
It's not the dry transformer manufacturer's
responsibility to install it basically, but it's
recommended for commissioning to take advice from
the manufacturer's professionals.
For installation, the following guidelines are followed :
• The transformer should be installed on a flat surface
and indoor (IP 00), and for outdoor installation, use
an enclosure with appropriate IP (eg. IP 35).
• the altitude should not be above 1000 meters
unless a higher altitude is specified at the time of
enquiry ;
the ambient temperature for the transformer to be
within the following limits :
-minimum : – 25°C ;
-maximum : + 40°C (unless a higher temperature is
designed for based on information provided at the time
of enquiry).

Mapna Group
| Slide 18
For an altitude and a daily average temperature higher
than 1000 meters above the sea and 30° C respectively, the
dry transformer must be de-rated according to IEC 60076
and IEEE C57.91:
Type of cooling
% of kVA rating
Decrease load
for each °C
higher
temperature
Increase load
for each °C
lower
temperature
Decrease load
per
100m (330 ft)
AN, AF, AN/AF 1.0 1.0 ~2.0

Mapna Group
| Slide 19
• Ground the transformer and all metal parts including
the enclosure.
• Check the terminal connections and the similarity of all
taps in three phases
• Check the connection of thermal sensors via ohmmeter
from the terminal box
• All steel and brass bolts should be tightened with the
recommended torques below.
Thread size
Torques
steel bolts
(N.m)
brass bolts
(N.m)
M8 20 10
M10 40 20
M12 75 35
M12 140 70

Mapna Group
| Slide 20
Installation and Commissioning (forced ventilation )
In the event of temporary overloading, to avoid
overheating of the windings, it is possible to install forced
ventilation.
For powers equal or greater than 1000 kVA, it is possible
to install forced ventilation to achieve a temporary
increase in power of 40%, without any special
modification.
However, if an increase in power is requested, account
must be taken of the impact of this choice on the
following points :
-Sections of cables and of Prefabricated Busbar Trunking
(PBT),
-The rating of the transformer's protective circuit breaker,
-The size of inlet and outlet openings for air in the
transformer room,
-The life span of fans in service, which is considerably
shortened compared with that of the transformer

Mapna Group
| Slide 21
High voltage side cable connection
The cable connection holes are reserved at the upper and lower
ends of the connecting rod on the high voltage side of the
transformer. Taking the delta connection as an example, the
phase sequence at the upper end is U-V-W and the phase
sequence at the lower end is V-W-U. Attention should be paid to
correct phase sequence when connecting high voltage cables.
Fasteners shall be used during the connection, and loosening
preventive measures shall be taken to fix the cable at the terminal
of the high-voltage connecting rod of the transformer.
High voltage cable junction
Corresponding connection phase
sequence
Upper terminal U-V-W
Lower terminal V-W-U

Mapna Group
| Slide 22
Low voltage side bus-bar or cable connections
The low-voltage terminal of the transformer has reserved cable
connection holes, and fasteners with loosening preventive
measures are required to fix the cable or bus bar. If it is required
to be equipped with copper-aluminium composite foil (cupal) as
specially specified in the contract, the copper-aluminium
composite foil (cupal) shall be installed between the low-voltage
terminal of the transformer and the cable, or between the low-
voltage terminal of the transformer and the bus bar. Please refer
to the figure.
 In the installation of copper-aluminum composite foil, the
copper surface should be in contact with the copper bars, and
the aluminum surface should be in contact with the aluminum
bars.

Mapna Group
| Slide 23
Cable installation layout (with enclosure)
For the transformer with protective enclosure, cables in its high-
voltage side and low-voltage side can be imported to internal part
of the enclosure through the top or bottom of the enclosure,
which can be connected to the corresponding wiring site of the
transformer. •
The bending radius of the cable needs noting, to prevent force
on end of cable connection.

Mapna Group
| Slide 24
Cable installation layout (without enclosure)
The high voltage side cable can be connected to the
transformer after layout in the bottom cable tray or after
layout the top cable tray. Cable or bus bar can used for
the low-voltage side connection. If the bus bar
connection is used, soft connection transition is
recommended to avoid mechanical impact on the low-
voltage winding and reduce noise level due to structural
reasons.
• High-voltage cables are not allowed to pass through the
high-voltage connecting rod (delta connection) of the
transformer.

Mapna Group
| Slide 25
Electrical safety clearance
Sufficient space must be ensured around the transformer to
ensure a smooth connection of the cable and the necessary
electrical distance. The minimum clearance value for flashover
protection is as below.
• These electrical distances are for installation equal to or
below 1000 m above the sea level, and for each 500 m
increase above the 1000 m, the mentioned distances must
increase by 10%.
• After the transformer is installed, ensure that the
transformer body and enclosure are reliably grounded.
Maximum voltage of
the equipment (kV)
Minimum clearance value
A (mm) B (mm) C (mm)
12 125-150 50 40
24 225-280 100 50-70
36 325-400 160 90-110

Mapna Group
| Slide 26
Commissioning of temperature control system
The transformer may be equipped with a temperature control system to monitor the
temperature of the winding to prevent abnormal temperature rise of the winding, thereby
protecting the transformer.
The temperature control system includes a temperature controller and a temperature sensor
(PT100). The temperature sensor (PT100) is placed in the three-phase winding of the
transformer. When the temperature reaches the set value, the temperature sensor (PT100)
feeds back the corresponding temperature change to the temperature controller. After the
temperature controller receives the corresponding feedback signal, it corresponds to different
functional responses. The over-temperature alarm and over-temperature trip functions need
to be connected with the relay protection system of the front-end equipment so that the
higher-level equipment can be linked when the temperature controller acts.
Temperature controller function
description
Parameter settings
Over-temperature trip 140˚C
Over-temperature alarm 130˚C
Fan on 90˚C

Mapna Group
| Slide 27
Ventilation of the Transformer Room
 In the case of natural cooling(AN):
the ventilation of the substation or of the enclosure
must ensure by natural convection the dissipation of the
heat produced by the transformer’s total losses.
 In the case of a sufficiently ventilated substation,
appropriate ventilation will consist of a fresh air
intake opening of S section at the bottom of the
substation and an outgoing air opening S’ located
above on the opposite wall at height H metres above
the intake opening.
 To ensure efficient cooling of the transformer and
sufficient air circulation, it is essential to maintain a
minimum height of 150 mm under the live section,
by installing rollers or an equivalent booster.
 It must be noted that restricted air circulation reduces
the transformer’s continuous and short term
overload capacity.
𝑆 = 0.185 ×
𝑃𝑡
𝐻
𝑚2
𝑆′
= 1.1 𝑡𝑜 1.15 × 𝑆 𝑚2
𝑃𝑡= Sum of the transformer’s no-load and load losses
expressed in kW at 120°C.
S = Area of the lower air intake opening (allow for mesh
factor) expressed inm2.
S’ = Area of the air outlet opening(allow for mesh factor)
expressed in m2.
H = Height difference between the two openings expressed
in metres.

Mapna Group
| Slide 28
Ventilation of the Transformer Room
 In the case of Air cooling(AF):
Forced ventilation of the substation is necessary for
ambient temperatures above 20°C, or small or badly
ventilated rooms for applications with frequent
overloads.
The fan can be thermostat controlled and operate as an
extractor in the top part of the room.
𝑄 (Advised flow) = 0.1 × 𝑃𝑡
𝑚3
𝑠
𝑃𝑡= Sum of the transformer’s no-load and load losses
expressed in kW at 120°C.
Ventilation (AN) of the Transformer Room (Example)
- Transformer 1000kVA,
-Po = 2300 W ,Pcc at 120°C = 11000 W,
i.e. P= 13.3 kW. If the distance between the grills = 2 m, then S = 1.7 m2of net surface area
necessary. If we imagine a grill obstructing the air inlet by 30% ; the air inlet grill surface
area should then be 1.5 m×1.5 m, and that of the air outlet should be 1.5 m×1.6 m.

Mapna Group
| Slide 29
Pre-commissioning test
 Voltage ratio test: Measure the voltage ratio of the
winding under all taps and the connection group. The
allowable deviation of rated tap voltage ratio shall not
exceed ± 0.5%, except for special transformers.
Tips:
 Earth the transformer
𝑅𝑊 = 𝑅𝑘.
225+𝜃𝑤
225+𝜃𝑘
𝜃𝑤: Base Temperature
𝜃𝑘: Ambient Temperature
𝑅𝑤: Base Resistance
𝑅𝑘: Ambient Resistance
1. DC Current source/ DC Battery
2. Varying Resistor
3. Ampere meter
4. Volt meter
5. Dry Transformer
 Wingding resistance test: Measure the DC resistance of
the winding at all taps and records the winding
temperature. (Measure the DC resistance shows the
accuracy of transformer connections)
Tips:
 DC current for low voltage winding: 10 A
 DC current for high voltage winding: 1A
 Maximum DC current: 10% rated current
 Minimum DC current: 1.2 times the maximum of no-
load
HV winding
LV winding
200 V- 380 V

Mapna Group
| Slide 30
Pre-commissioning test
 Insulation resistance test: Measure the insulation resistance
values of the windings and cores and record ambient
temperature and humidity.
Tips:
 The insulation resistance is measured at ambient temperature
of -25 º C ~ 50 º C, humidity ≤ 90%
 If the insulation resistance is not less than 2 MΩ, a voltage
can be applied to the low-voltage side of the transformer and
the transformer can be dried by no-load heating.
 If the insulation resistance value is less than 2 MΩ, it can be
dried by air drying or baking with heat lamp.
1. HV Winding
2. LV winding
3. Body
4. Megger
Test position
Test equipment
(1 min)
Test value requirements
HV- E 2500 V ≥100 MΩ
LV- E 2500 V ≥50 MΩ
HV- LV 2500 V ≥100 MΩ
1
2
3
4

Mapna Group
| Slide 31
I. Voltage regulation
If the actual grid voltage deviates from the rated voltage of
the transformer, the tapping gear of the transformer can be
adjusted appropriately to control the output voltage value.
 For no-load voltage regulation, the transformer gear tap
shall be adjusted to the appropriate gear to keep in line
with the grid voltage.
Tips:
 The gear of transformer is set at rated gear (4-7) by
default when it leaves factory. Make sure that the
transformer is powered off before adjusting the gear.
 The three-phase tap must be adjusted at the same time.
The rear gear bolt must be tightened after adjustment
and the torque value must be restored.

Mapna Group
| Slide 32
II. No load operation
When large capacity no-load transformers are put into operation, visible sparks may be
generated at the joints of external components (especially at the core and clamps), but this
phenomenon will soon disappear. This is due to physical reasons, and will not affect the safe
operation of the transformer, so it is not a product defect.
III. inrush current
There is inrush current when the transformer is switched on, and the peak value can reach 6-8
times of rated current. The setting value of current quick protection for the transformer shall
be larger than the peak value of inrush current, and the time limit shall be ≤ 0. 5 s. Therefore,
no-load inrush impulse test shall be carried out before operation to check whether the relevant
protection of the transformer is malfunction or not. If the protection value is set improperly, it
will cause the tripping phenomenon in the later closing.
IV. long-term storage or overhauled
For long-term storage (storage time more than 3 months) or overhauled transformers or
transformers to be used at ambient temperature below 0 ℃, it is recommended to operate
without load for 12 hours before putting the transformers into load, and the load shall be
gradually increased.

Mapna Group
| Slide 33
V. overload operation
The transformers are designed to operate at rated
power at ambient temperature defined by IEC
60076 :
 40 °C maximum
 30 °C monthly average of the hottest month
 20 °C annual average
 If operated normally, the transformer should
attain its expected lifetime consumption. In
particular, the average annual temperature and
the load significantly affect the lifetime
consumption. Environment temperatures
differing from the annual average have an effect
on the system’s load capacity.
 The three-phase voltage, current and
temperature values shall be recorded
periodically during the operation of the
transformer so that the historical data of the
transformer can be consulted in case of overhaul
or fault.
Ambient
temperature
(Average Annual
temperature)
Load rating
–20 °C 124 %
–10 °C 118 %
0 °C 112 %
+10 °C 106 %
+20 °C 100 %
+25 °C 97%
+30 °C 93 %
+35 °C 90%
https://www.worldweatheronline.com/

Mapna Group
| Slide 34
Maintenance
Cast-resin transformers are maintenance-free.
Routinely inspect and clean the windings, bolt
connections, alarm devices and all fan functions
once a year. If the transformer is in dusty
environment or close to the pollution source, it is
recommended to clean the equipment every six
months. It is recommended to fully inspect and
clean the transformer every 5 years. Before
maintenance, the transformer must be powered
off and all terminals must be short-circuited and
grounded.
 Transformer cleaning
Blow off the transformer with dry compressed air
or wipe with dry cloth and alcohol
(concentrations above 85%) to prevent the
formation of creepage paths and blockage of
cooling air passages.
Sediment Cleaning method
Oily 2
Carbonaceous 1+2
Metal-containing 1+2
Saline 1+2
Dry dust 1+2
Wet dust 2
 Cleaning method 1
Use compressed air to blow the
transformer. The compressed air must be
oil-free and water-free, and the air
pressure ≤ 6 bar. Vacuum cleaners can
also be used instead of compressed air for
dust collection.
Cleaning method 2
Wipe with a dry rag and alcohol
(concentrations above 85%).

Mapna Group
| Slide 35
S/N Maintenance items
Maintenance cycle
(recommended)
Use Tools Methods:
1
Clean the surface stains of
windings, pads and cores and
stains at the heat dissipation
holes of the enclosure
Normally, each year or
more. Every 6 months
for dusty and other
polluted environment
Dry compressed
air, pressure ≤ 3
bar, dry rags
and alcohol
Select cleaning
method according to
Form 1
2
Check winding surface
condition
Normally, each year or
more. Every 6 months
for dusty and other
polluted environment
Visual
inspection
No blackening or
cracks on the surface
of the winding (if any,
please contact the
manufacturer)
3
Check bolt and nut tightening
status at cable connections
Each year or after
maintenance
Torque wrench
According to the
torque table
4
Check correct tapping
connections and bolt
tightening
Each year or after
maintenance
Torque wrench
According to the
torque table
5
Check grounding condition of
transformer body and
enclosure
Each year or after
maintenance
Torque wrench
and visual
inspection
According to the
torque table

Mapna Group
| Slide 36
Maintenance
cycle
(recommended)
Use Tools Methods:
6
Check whether temperature
controller settings,
temperature probe and
PT100 are normal.
Each year or after
maintenance
Heat gun,
power
supply
The temperature of the
temperature controller can be
displayed normally by blowing
the temperature probe with a heat
gun.
7 Check the cooling fan
Each year or after
maintenance
Power
supply
Turn on the power supply, start
the operation according to the
manual of the temperature
controller, and observe whether it
rotates
8 Insulation resistance test
Each year or after
maintenance or 5
years
Insulation
resistance
tester
Refer to for test values

Mapna Group
| Slide 37
Maintenance cycle
(recommended)
Use Tools Methods:
9
Transformation ratio
test
Every 5 years or after
maintenance
Transformation ratio
tester
Refer to test
10 DC resistance test
maintenance
DC resistance tester Refer to test
11
Power frequency
withstand voltage test*
maintenance
Power frequency
withstand voltage
tester
Refer to test
* Applied withstand voltage test: The withstand voltage strength of the transformer is tested. The on-site tested
withstand voltage value is 80% of the factory test voltage value. The factory test withstand voltage value can be shown
in the factory test report and nameplate.

Mapna Group
| Slide 38
Dry Transformer Maintenance (Frequently asked questions guidelines (chart))
S/N Question Possible cause Corrective measure
1
Temperature controller does
not display
Temperature controller power
cord is not connected
Measure whether the
temperature controller power
interface is energized and
required to reconnect the power
supply (85 ~ 250 V)
It is internal failure of temperature
controller, power interface of
temperature controller is
energized, but panel indicator
lamp is not on
Contact Service Center to
replace with a new temperature
controller
2
Temperature controller three
phase temperature display
FOC or FCC
Wrong or poor connection or
loose connection of temperature
sensor
Check and press the
temperature sensor wiring and
tighten it according to the
auxiliary wire diagram on the
transformer certificate of
conformity
Temperature sensor probe is
damaged
controller

Mapna Group
| Slide 39
2
Three-phase temperature
display of temperature
controller differs greatly
Temperature sensor probe is not
fully inserted into thermometer tube
(three-phase probe is inserted at
different depths)
Check the position of the
temperature probe and place it
correctly
Cooling fan is damaged
controller
Temperature sensor probe is
damaged
controller
Three-phase load of transformer is
not balanced
Check three-phase load and
voltage, current
3
The temperature controller
cannot communicate
properly with the
monitoring device
Wrong address setting for
temperature controller
Please refer to the use manual
for the temperature controller
The communication cable of the
temperature controller and the strong
electric cable are arranged together,
which causes the interference of the
communication signal
Properly lay out the cables

Mapna Group
| Slide 40
4
Noise is
abnormal
Primary side voltage exceeds tapping rated voltage
Disconnect the power of
transformer and adjust tap gear
The bus bar is not fixed well and there is
resonance. The transformer is not well fixed with
the ground, and the resonance enclosure plate is
not fixed tightly, and there is resonance
Bus bar, enclosure board and
transformer base are well fixed
There are unclamped free ends in the iron core or
clamping parts, and there are high frequency
vibrations during the excitation of the iron core,
resulting in abnormal noise
Check the fastening core and
clamping piece and press the free
end tight with insulating material
Within the same power distribution room, multiple
devices are placed close together, causing wall
reflections and noise overlapping
Reasonably lay out equipment
position in power distribution
room
In the transformer load, equipment such as
frequency converter produces large harmonics in
the system, which makes the core excitation
uneven and causes noise*
Filter device is designed in low
voltage system
Transformer is under overload operation state
Check the load and distribute the
load reasonably
*De-rating the Transformers according to non sinusoidal currents (Slide 44)

Mapna Group
| Slide 41
5
Cooling fan is not
running
Temperature does not reach fan start
temperature value
Refer to factory temperature
setting value and setting
method
Cooling fan is damaged
replace with a new cooling fan
6
Low side output
voltage is high or low
Grid input voltage is high or low
Adjust the tap gear of
transformer
7
Transformer over-
temperature alarm,
trip
Transformer overload (overvoltage, over
current) operation
Check transformer load
Cooling of transformer fails
Check whether the cooling fan
is working properly and check
whether the cooling air duct is
blocked
8
Winding surface
discharge
Severe stains (dust, etc.) on the surface
of the winding
Clean stains on windings, pads,
etc.
Short circuit on high and low voltage
lines
Check high-voltage lines
High and low voltage transmission lines
suffer from overvoltage impulse
Optimize system protection
functions

Mapna Group
| Slide 42
8
Winding surface
discharge
There is insufficient distance between
metal structure and winding
minimum insulation clearance
requirements
9
Winding ablation and
blackening
Upon the service life of the transformer
and natural damage; poor heat
dissipation; long-term overload; short
circuit of external wiring; system
overload; wrong cable connection; metal
foreign body falling into the cooling air
duct of the winding; unscrewed torque of
tap gear bolt; short circuit fault inside
the winding, etc.
On-site inspection is required.
Please contact service center
for such inspection.
Dry Transformer Maintenance (Frequently asked questions guidelines (chart))

Mapna Group
| Slide 43
Loading transformers with non sinusoidal currents
 All ratings for transformers are based on sinusoidal rms values, rated power, rated
voltage, losses, temperature rise, etc.
𝐼𝑟 =
𝑆𝑟
3𝑈𝑟
𝑆𝑟: Rated Power
𝑈𝑟: Rated Voltage
𝐼𝑟: Rated Current
 Load losses and temperature rise are based on sinusoidal rms rated current.
𝑃𝐿𝐿 = 𝑃𝐷𝐶+𝑃𝑊𝐸−50+𝑃𝑂𝑆
𝑷𝑫𝑪: DC losses produced by a DC current of the same value that rms fated current.
𝑷𝑾𝑬−𝟓𝟎: Winding eddy losses at the rated frequency produced by circulation current (eddy) in the windings due
to leakage flux.
𝑷𝑶𝑺: Other stray losses, produced in bus bars and steel parts due to leakage flux, these losses have not any
influence on winding temperature rise.
All losses referred to the reference temperature.
When transformer supply a non sinusoidal load current with the same rms value than rated
current, DC losses remain constant but winding eddy losses increase due to the higher
frequency of the harmonics, as a result, winding temperature rise increases and temperature
limits can be exceed.

Mapna Group
| Slide 44
 A transformer requested to supply non sinusoidal loads, shall be oversized in order to
guarantee that windings temperature limits are not exceed in service.
 Total Harmonic Distortion:
It is a measurement of the harmonic distortion present in
a signal and is defined as the ratio of the sum of the
powers of all harmonic components to the power of the
fundamental frequency.
THD = ℎ=2
𝑛
𝐼(𝑝𝑢)ℎ
2
 K- factor:
K-factor defines the non-linear load a transformer can tolerate without overheating or damage.
The basis for K factor is seen in the ABB Document (Loading transformers with non sinusoidal
currents). This document identifies the method for correctly de-rating transformers for non-
linear loads.
α =
𝑇𝐻𝐷
0.463
𝑰𝒉(pu): rms current for harmonic “h”
in pu of rms rated current I rated
h: is the harmonic number
α = [
𝐾 − 1
12 − 0.2145 × 𝐾
]0.5 𝐾 = 𝐾 − 𝐹𝑎𝑐𝑡𝑜𝑟

Mapna Group
| Slide 45
* Remark: this equivalence list is valid up to 3150kVA transformers

Mapna Group
| Slide 46
Loading transformers with non sinusoidal currents (Example)
 Fundamental Power – 2MVA
 Net harmonic content – K-17 => Factor K equals to 1.28
 Equivalent Power – 2000 × 1.28 = 2560kVA
 As a result of this, the transformer shall be physically sized as 2560kVA rated power and
the temperature rise limit shall be guaranteed at such equivalent power as well.
Therefore, should the temperature rise test is requested, during the full load part of the test
the current must be equal to the rated current multiplied by the proper Factor-K, i.e.
assuming the no load voltage level on LV side is 417V (Dyn11), rated current will be
2000/ (417×√3) = 2.77kA, however test must be run at 2.77×1.28= 3.54kA (corresponding
to 2560kVA).

Mapna Group
| Slide 47
Excitation Transformer
Dry Transformer

Mapna Group
| Slide 48
Dry Transformer
Electrostatic shielding
• Electrostatic shielding is a metallic barrier (aluminum
or copper foil ) built into a transformer between the
primary and secondary winding. The shield is
grounded.
I. Providing an electrostatic shield between the primary
and the secondary windings thus avoiding transfer of
surge/impulse voltages passing through inter-winding
capacitance.
II. The stray capacitance between windings can generate
asymmetry currents and could lead to high common
mode noise and is found to emphasize the noise
transmission in a converter,.

Mapna Group
| Slide 49
Dry Transformer

Mapna Group
| Slide 50
Dry Transformer
Power (kVA) Height (m) Temperature (°C) THD (%)
2410 1650 40 29.7
2770.11 1000 40 29.7
2541.39 1000 40 0
I. Height: 6.5 × 2% = 13% → 𝑆 =
2410
1−0.13
=2770.11 kVA
𝐼𝐼. α =
0.297
0.463
= 0.642, 0.642 = [
𝐾 − 1
12 − 0.2145 × 𝐾
]0.5
= 𝐾 = 5.5
𝐾 = 5.5 → 𝑂𝑣𝑒𝑟 𝑟𝑎𝑡𝑖𝑛𝑔 𝐹𝑎𝑐𝑡𝑜𝑟 = 1.09 → 𝑆 =
2770.11
1.09
=2770.11 kVA

Mapna Group
| Slide 51
Dry Transformer
The First Indoor 110KV/35KV 31.5MVA Cast Resin Transformer (CRT) and GIS
Substation Layout

Mapna Group
| Slide 52
Dry Transformer
Useful References
1. Electric Power Transformer Engineering, Second Edition
Edited by James H. Harlow
2. Spotlight on Modern Transformer Design
by Pavlos S. Georgilakis
3. Transformer Engineering: Design and Practice
by S.V.Kulkarni & S.A.Khaparde
4. Transformer Design Principles: With Applications to Core-Form Power
Transformers, Second Edition
by By Robert M. Del Vecchio, Bertrand Poulin, Pierre T. Feghali, Dilipkumar
M. Shah, Rajendra Ahuja

Mapna Group
| Slide 53
Dry Transformer
Useful References
5. The J & P Transformer Book
by Martin Heathcote
6. Transformer and Inductor Design Handbook
by Colonel William T. McLyman
7. ABB Transformer Handbook
8
.
‫و‬ ‫فازه‬‫یک‬ ‫ترانسفورماتور‬
‫فازه‬‫سه‬
(
‫جلد‬
1
‫و‬
2
)
‫مطلبی‬ ‫علی‬ ‫دکتر‬ ‫تالیف‬

Mapna Group
| Slide 54
Dry Transformer
Useful References
8
.
‫بولر‬ ‫هانس‬ ‫قدرت‬ ‫الکترونیک‬
‫قدیر‬ ‫دکتر‬ ‫ترجمه‬
‫قنادی‬ ‫عزیزی‬
Useful Telegram channel & Web site
https://t.me/transformermag_group
‫گروه‬ ‫ادمین‬
:
‫فر‬ ‫آقایی‬ ‫آرش‬ ‫مهندس‬
-
‫فصلنامه‬ ‫مسئول‬ ‫مدیر‬
‫ترانسفورماتور‬
https://electrical-engineering-portal.com

Mapna Group
| Slide 55
Dry Transformer
Learn from yesterday, live for
today, hope for tomorrow. The
important thing is “Not to stop
questioning”
Albert Einstein
Thank you
Question ?

Dry Transformer Course.pptx

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