Power Transformer ( Summer Training presentation BHEL )
Summer Training Report
Presented by :
Electrical & Electronics Engineering
They have rating above 200 Kva
and used in generating station and substation
used for power transmission line for stepping
up and stepping down the voltage.
Stages of Power Transformers
manufacturing are :
Design & Drawing
Unlacing of Core
Fitting Bottom insulation
Core Coil Assembly
Fitting of Top insulation
Relacing of core
Design & Drawing :
Winding Used :
R-S Coil : reverse section winding.
Helical coil : winded in shape of
Spiral coil : simply wounded on the
Interleaved coil : winding current
rotates in same conductor
Composite winding : more than one
conductor winded with each other.
Core of Transformer :
Material Used :
CRGO : Cold rolled grain oriented silicon
steel is used to build the core.
Purpose of using CRGO is to reduce the
Hysteresis losses. Laminations of these
sheets minimizes eddy current loss.
Unlacing of core :
This is basically the phenomena of removal
of top end frame of the core assembly so
that the coils can be mounted on the core.
Core – Coil Assembly :
Core coil assembly consists of assembling the windings to the core assembly. Core
assembly is placed on a suitable leveled platform.
Tighten the three limbs with webbing tape. Top channels and top yoke laminations
are removed and placed on a table in the same sequence. Bottom insulation items
like pressboard rings, petals; perma wood rings are placed on bottom yoke on each
core limb. Core wraps as specified in the design details are covered to the core
limbs and tightened with cotton tape.
L.V Coil : primary coil for step down transformer, made in order to allow the flow
of large current through it .
H.V Coil : Secondary coil for step down transformer, made in order to allow high
voltage and hence small current through it.
T.V Coil : this is known as the tertiary voltage coil.
Relacing Of Core :
The top yoke is again attached to
The Rest of the Core, the sheets
Are attached one by one or in
Packets (generally 2 to 4 in
numbers) to the core limb in
erect position. Then the job is
dipped in oil and then heated to
remove any kind of moisture in
it. After that the job is
compressed i.e. pressure is
applied from the top to compress
the coil and achieve the required
CD of the coil as specified in
Processing and DRY OUT :
The presence of the moisture brings about the
reduction in the electric strength of material and
also increases its volume.
Dry out is necessary in this condition.
The final drying out is commenced either when
the core and winding are placed or when they
are fitted in to there tank, all main connections
made and the tank placed in an oven and
connected to the drying system
Final Tanking :
assembling the core coil
assembling job into
transformer tank with
all necessary accessories
according to bill
and design diagram.
Testing of Power
Tests during manufacture :
Core plate checks
Core frame insulation resistance
Core loss measurement
Winding copper checks
Final Testing :
Voltage ratio and polarity.
impedance voltage, short-circuit impedence and load
(a) separate source AC voltage.
(b) Induced voltage.
no-load losses and current.
on-load tap changers, where appropriate.