Installtion, maintanace,trouble shooting of DT.ppt

Installation, Maintenance & Trouble
shooting

TRANSFORMER INSTALATION INSTRUCTIONS

TRANSFORMER INSTALATION INSTRUCTIONS
EXTERNAL ASSEMBLY
 Check all factory assembled air/gas oil fitting joints for leaks and reseal.
 Use new gaskets supplied with transformer when installing radiators,
coolers or pumps

TRANSFORMER INSTALLATION INSTRUCTIONS
INTERNAL ASSEMBLY
To remove the nitrogen, it is advisable to pull vacuum to fully remove all
nitrogen and Break vacuum with oil.
Bushings to be assembled as per the instructions of the bushing
manufacturer which is available in the instruction manual.
 Bushing CT - Check the CT ratios, lead continuity & polarity at the
terminal points in the control cabinet.
An energized CT is dangerous if the secondary is open circuited. Death
or serious injury can result from contact with the terminals.

If transformer is to be stored after assembly;
 Seal it and pressurize with dry air or nitrogen to 20 kPa; [ 3 PSI (0.2 bar)].
 If the exposure time has been excessive or there are other factors that suggest the
transformer may have been exposed to excessive moisture contamination then:
Evacuate transformer to 2 Torr (.266 Pascal) or less and hold for 4 hours.
Break the vacuum with dry air or nitrogen till the pressure reaches 20 kPa 3-PSI
(.2 bar).
Retain it under pressure for at least 12 hours until equilibrium is reached, and
then measure the dew point.
For surface moisture less than 0.8%, proceed with the final vacuum filling
procedures.
If the dew point is unacceptable, the transformer insulation must be dried.

It is advisable to take the dew point measurement in the early morning hours prior
to sunrise.
If the dew point measurement is taken during periods of extreme ambient
temperature variation or during the afternoon hours, the insulation temperature
should be measured directly after the dew point is taken.

-40º -20º
-20º
Water vapor pressure inside
transformer
40º
30º
20º
10º
0º
-10º
Surface
moistur
e
content
%
2
1.5
1
0.7
0.5
0.4
0.3
0.2
0.01 0.03 0.1 mm Hg
-50º
0.3
-60º -30º
Temperature inside transformer
Dew- point of air inside the Trafo.

ELECTRICAL TESTS
1. Measure the power factor and capacitance of the bushings before installing the
bushings in the transformers. Refer to the appropriate bushing instruction leaflet
for the proper procedures. (Optional Test)
Measure the core resistance to ground.
2. The minimum acceptable value is 500 k Ohm when measured at 1000 volts.
3. Measure the core clamp resistance to ground.
The minimum acceptable value is 500 k-Ohm when measured at 1000 volts.

4. Measure the ratio of all bushing current transformers and verify proper
polarity.
5. Check the turns ratio of the transformer (TTR) at all tap positions. The
measured turns ratio should be + 0.5 % of the nameplate voltage ratio

OIL SPECIFICATION, TESTING, PURIFICATION & STORAGE

OIL SPECIFICATION, TESTING, PURIFICATION AND STORAGE
SPECIFICATION FOR INSULATING OIL (IS:335)
TESTING OF THE OIL – Recommended Tests
A. Dielectric dissipation factor
B. Neutralization value
C. Interfacial tension
D. Electric strength
E. Water content
F. Sludge content
G. Dissolved gas analysis

(Electrical Strength) Breakdown Voltage
Operating Voltage New Transformers prior
to the first Energisation
Transformers having
been in service
(kV) IEC 156 KV / 2.5 mm IEC 156 kV / 2.5 mm
> 170  50 
70 - 170  50 
< 70  50 30

FREQUENCY OF CHECKS
Years after initial
operation
OPERATING VOLTAGE (kV)
73 73 - 170 > 170
(initial operation) Test (A to F) Test (A) to (F) Test (A) to (G)
1 (G)
2
3 (G) (G)
4
 Test (A to F) Test (A) to (F) Test (A) to (F)
6 (G)
afterwards In 5 years
intervals
In 3 year intervals (G) in
5 year intervals: all tests
(A) to (F)
In 2 year
intervals (G)

INTERPRETATION OF TESTS ON OIL
Criteria Operating
Voltage
Test
Method
Permissible
limiting value
Measures to be
taken if values are
not permissible
Breakdown
voltage
> 170 kV
70 - 170 kV
< 70 kV
IEC 156 > 50 kV
> 40 kV
> 30 kV
Filtering
Drying
(Purification)
Water content > 170 kV
< 170 kV
ISO R760 < 20 mg / l
< 30 mg / l
Drying
(Purification)
Dielectric
dissipation factor
All voltages IEC 247
IEC 250
<0.2 (20%) at 90
Deg.C
Exchange of the oil
Neutralisation
value
All voltages IEC 296 < 0.5 mg. KOH/g
oil
Exchange of the oil
Inerfacial tension IEC 296 > 15 mN/m Exchange of oil

OIL SAMPLING
 Take Samples only at the provided extraction points.(drain valves / oil sampling
valves as shown in the outline drawing).
 Before taking an oil sample clean the drain valve and slowly drain off at least 5 liters
of oil.
 Use clean and dry sample containers only. Be sure to remove all residue of cleaning
fluids. Shape of the sampling container and sampling method shall be in
accordance with standard procedures and IS :9497

Rinse it with the oil to be sampled. Protect the oil sample from light. The
following sampling containers are recommended:
o Tinted glass bottles with ground glass stopper
o Aluminum cans with screw-on caps (preferable for long transportation
distances
o Untinted glass bottles, wrapped in non-transparent foils for protection
against light
 Take at least 1 liter of oil for testing.

1. OIL DRAIN VALVE
2. ADAPTER FLANGE
3. SYNTHETIC RUBBER HOSE
4. HOSE CLIP
5. GLASS BOTTLE
Fig: EXAMPLE OIL SAMPING FOR TESTING (DGA & Moisture Content)

DIELECTRIC STRENGTH
 The average value of the six results is considered to be the dielectric strength of
the oil which must comply with the values of table one.
 If any one of the six breakdown voltages lies more than 15% below the specified
value the test must be repeated with a new sample:
 The dielectric strength of the oil can be improved by filtering and drying.

GAS ANALYSIS ON TRANSFORMER OIL
It is recommended that analysis of dissolved gases in transformer oil by gas
chromatographic equipment is made at the time of commissioning and then at
an interval of maximum six months.
Gas Analysis:
1 Gases to be analyzed normally O2, N2 , H2,CO, CO2, CH4
2 Gases to estimate abnormality H2, CH4, C2H2,C2H4,C2H6
3 Gases to estimate deterioration CO, CO2, CH4

Permissible Concentrations of Dissolved Gases in the Oil of a Healthy Transformer (In ppm)
Gas Less than 4 years
in Service
4 - 10 years in
Service
More than 10
years in Service
Hydrogen H2 110- 150 200- 300 200- 300
Methane CH4 50- 70 100- 150 200- 300
Ethane C2H6 30- 50 100- 150 800- 1000
Ethylene C2H4 100- 150 150- 200 200- 400
Acetylene C2H2 20 - 30 30- 50 100- 150
Carbon
Monoxide
200- 300 400- 500 600- 700
Carbon Dioxide 3000 - 3500 4000- 5000 9000- 12000

OIL PURIFICATION – STAGES
 Drying removal of free and dissolved water
 De-gassing removal of dissolved gasses
 Filtering removal of all floating solids above a size to be defined.
Employ only those purification plants which employ vacuum processing.

FIG. FLOW DIAGRAM FOR TRANSFORMER OIL PROCESSING
1. Oil tank (preferably vacuum tight)
2. Oil purification plant
3. Connection to vacuum pump or silica gel breather

STORAGE
 Stored oil in clean containers specially designated for its storage
 Mixing with other type of oil such as used oil, cable oil, lubricating oil, fuel oil and
contamination with solids must be strictly avoided.
 The containers must be protected against penetration of moisture during storage.
 Oil in drums should be stored in a closed room.
SAFE HANDLING
 Avoid inhalation of any mist, fumes or vapour generated during use.
 Avoid contact with the skin.
 Avoid contact with the eyes.
 Wash hands carefully before eating and drinking.
 Change heavily contaminated clothing.

FIRST AID
First Aid due to inhalation is unlikely to be needed under normal use
For skin contact, the first aid is to wash " with soap and water”.
For eye contact, wash out eyes thoroughly with water.
Better consult a doctor if there is risk of swallowing

ERECTION AND ASSEMBLY
Erection and assembly:
 To be carried out by trained staff, familiar with the relevant safety regulations.
 Assembly preferably on a dry day.
 All openings to be re-closed as soon as possible to prevent dust & moisture
entry.
 Accessories to be assembled as per the relevant instructions
 After assembling locking strip/card /pin shall be removed for correct functioning
of Oil Flow Indicator
 supplied gaskets or gaskets of similar quality must be used.

Ensure sealing surfaces are not damaged & they are free from rust, paint, oil,
and grease
Tightening of screws to be done with applicable torque as per table given in the
instruction manual.
Complete connection of all cables as per the relevant cable connection diagram
Repair damaged paint coatings. The paint supplied by or equivalent must be
used for this purpose.

 Complete the assembly of :
Conservator and Brackets
Cooling Equipment
Fans (specific Attention to be paid to the direction of rotation)
Bushings
Pipes & Fittings
Other Accessories as detailed in the outline drawing

OLTC DRIVE MOTOR MECHANISM
NORMALLY MOUNTED ON THE
TRANSFORMER TANK DURING
TRANSPORT.
SHOULD BE RIGIDLY MOUNTED
ON TANK SO THAT THE
STRUCTURE DO NOT VIBRATE
DURING TAP CHANGE
OPERATION.
ALIGNMENT OF DRIVE SHAFT
SHOULD BE CAREFULLY DONE
& REALIGNED.

ON LOAD TAP CHANGER
• OLTC IS MOUNTED IN TRANSFORMER
TANK.
• ALWAYS REFER TO TRANSFORMER
MANUFACTURER FOR ANY PROBLEM IN
TAP CHANGER.
• FOR MAINTENANCE REFER TO
DETAILED MAINTENANCE SCHEDULE
FROM OLTC MANUFACTURER.

CONSERVATOR ASSEMBLY
 CONSERVATOR
ASSEMBLY
SHALL BE
MOUNTED AT
SITE AS PER
GENERAL
ARRANGEMENT
DRAWING.
 ALL OTHER
ACCESSORIES
SHALL ALSO BE
MOUNTED AS
PER GA
DRAWNG.

OIL FILLING
storage
tank
vacuum filter
compound gauge
vacuum gauge
Buchholz
relay
vacuum
pump
transparent hose for level
monitoring
compound gauge right
before fill valve
Oil filling from lower filter valve

OIL FILLING
ARRANGEMENT FOR OIL FILLING - SCHEMATIC PICTURE
1 Transformer
2 Vacuum Treatment Plant
3 Vacuum hose
4 Oil hose
5 Oil filling connection
6 Gate valve for oil
treatment plant
7 Air vent valve
8 Manometer
9 Lower shut-off gate valve
10 Vac. Flange with sight glass
11 Connection for vacuum Gauge
12 Oil inlet slide valve
13 Inlet pump
14 Filter
15 Heater
16 Degassing chamber
17 Discharge pump
18 Oil outlet gate valve
19 Vacuum pump
20 Gas ballast valve
21 Vacuum valve
22 Vacuum gauge

ERECTION & ASSEMBLY
OIL FILLING FOR TRANSFORMERS WITH AIR CELL CONSERVATORS
OIL FILLING PROCEDURE WITHOUT VACUUM IN THE COSERVATOR(AIR CELL)
• Place the separator inside the conservator
• Inflate the same to 0.1 bar (Max.) leaving vent hole open on the conservator.
Adjust the pressure 6 hours later.
• Watch for a possible loss of pressure 24 hours later at appx. same temperature.
• If there is no loss of pressure, then the separator and its fittings on conservator
are considered perfectly tight.
• Push oil slowly by the lower part of conservator till oil overflow by the vent holes
in the upper part.
• Close the vent hole and keep introducing oil by the lower part, while leaving the
separator progressively deflate.
• Stop oil filling at the level selected for the filling temperature.

OIL FILLING PROCEDURE WITH VACUUM IN THE COSERVATOR(AIR CELL)
• Conservator, with its separator as above is connected to its oil filling reserve in its
lower part.
• Create a vacuum in the separator.
• With the same source of vacuum, create vacuum in the conservator.
• Open the oil filing valve on the lower part.
• Because of vacuum in the conservator the oil rises automatically.
• Stop the filling once the required oil volume enters into the conservator.
• Release vacuum inside separator by ambient air or nitrogen. Then the separator
inflates itself to take all the free space.
• During the operation oil shall rise to the top of the conservator.
• Inflate the separator to a max. pressure of 0.1 bar (Max.)
• Allow oil to overflow from vent holes, then close vent holes.

ERECTION & ASSEMBLY (AIR CELL FAMILIARIZATION)
• Air cell supported from top of the
conservator (top left.)
• Complete picture of air cell supported
from top(Top Right).
• Seating structure for air cell inside
conservator(Bot. Left).
• Opening for oil entry/exit into
conservator protected from seating
structure(Bot. Right).

FIELD TEST RECORD AND QUALITY PLAN

FIELD TEST RECORD AND FIELD QUALITY PLAN
Sl
No
Characteristics/ items Types of
check
Quantum/
Frequency of
check
Acceptance
criteria
Remark
(s)
1
1.1
1.1.1
Check on receipt
Main equipment temporary
store
If the permanent location is
not ready, ensure that
temporary storage is done
in a suitable location
Physical At the time of
storage
Hard level
ground --
1.1.2 Check that the equipment
is never stored in a
polluted area
Physical At the
Time of
storage
Unpolluted
--
1.1.3 Check that the equipment
is kept on sleepers/ roller
mounted facilitating free
flow of air underneath.
Physical At the
time of
storage
Normal air
direction
shall be
considered
--

Sl
No
check
Quantum/
Frequency of
check
Acceptance
criteria
Remark
(s)
1.1.4 For gas filled storage ,
periodically check the gas
pressure and ensure the
reading of pressure and
temperature as logged
Reading of
pressure
gauge and
record
Daily Maintain
gas
pressure of
0.1 to 0.2
kg/sqcm
Use
pressure
gauge and
record on
log sheet
1.1.5 Thermometer, flow
indicators etc. Check that
these are stored without
damage to fragile parts.
Physical At the time of
storage
No physical
damage
--
1.1.6 Oil drums , check that the
drums are stored in
protectd area and are not
placed on their side face Physical
At the
Time of
storage
100 %
seals
intact , no
leakages --

Sl
No
check
Quantum/
Frequency of
check
Acceptance
criteria
Remark
(s)
1.1.7 Oil level gauge, buchholz
relay, silica gel breather
etc. Check that these are
stored without damage to
fragile parts
Physical At the
Time of
storage
100 %
No physical
damage --
1.1.8 Cooling system, check that
items connected as pump
motor are stored indoor Physical
At the
Time of
storage 100%
No physical
damage
--
1.1.9 Check that supports and
fabricated parts are not
placed directly on ground
but kept on wooden
battons/planks
Physical At the
Time of
storage 100%
No physical
damage
1.1.10 Bushings- check that
bushings are stored in
respective cases in closed
place
Physical
At the
Time of
storage
Covered
store
--

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No
check
Quantum/
Frequency of
check
Acceptance
criteria
Remark
(s)
1.1.11 Marshalling boxes- check
that the marshalling
boxes are stored in
closed place in the cases
Physical
At the
Time of
storage Covered
store
1.1.12 Loose items-check that
loose items are stored in
closed place
Physical
At the
time of
storage
No physical
damage
1.1.13 Complete receipt/storage
check list
As listed As listed Instruction
manual
Use check
list
2.0
2.1
Erection check
Document check for
availability of all relevant
drawings and documents
Physical
verification
Once before
erection
Complete
set of
erection
drawings,
instructions,
test
certificates
Check list

Sl
No
check
Quantum/
Frequency of
check
Acceptance
criteria
Remark
(s)
2.2 Site preparation – check
that the transformer yard is
properly leveled
Visual Once before
erection
Foundation
drawing
Use
logsheet
2.3 Check that rails are
levelled and exact location
of roller assembly is
marked in permanent
location of the transformer
where applicable.
Physical Once before
erection
Foundation
drawing
Use log
sheet
2.4 Oil filteration plant- check
for availability of oil
filteration plant of adequate
capacity
Physical
Once before
erection
Operation
manual for
filtering
machine
Use log
sheet
2.5 Check for facilities for
operation of filter machine
such as:
-proper power source
-cable of adequate
capacity and length
-hose pipe of adequate
capacity and suitable ends
Physical Once before
erectionat the
time of
storage
Operatinn
manual for
filtering
machine
Use log
sheet

Sl
No
check
Quantum/
Frequency
of check
Acceptance
criteria
Remark
(s)
2.6
Erection check
Check for availability of
suitable and adequate
quantity of oil
Physical
verification
Quantity
check
Once before
erection
Rating and
diagram plate
and
ga.drawing
Also
Oil spec.
2.7 Check that all items and
accessories are inspected for
damage
Physical 100% before
erection
Packing list
No damage
2.8 Check that the pre-erection
survey has been carried out
to ensure that transformer
yard is ready in all respects
and to verify and achieve the
position of various
equipments to be connected,
level of floor/rails, position of
foundation bolts, pockets and
cutouts, alignment of cable
trenches etc.
erection
Foundation
drawing,
Layout drg. In
line with
specifications
--

Sl
No
check
Quantum/
Frequency
of check
Acceptance
criteria
Remark
(s)
2.9 Check that proper tools and
tackles are used for
transporting various items to
erection site
Physical
100% before
commen-
Cement of
erection
Instruction
manual
--
2.10 Check that transformer is
jacked up using only the
jacking lugs provided for the
purpose and that no other
parts are used for this purpose
Physical
verifica-
tion
100% before
erection
No cracks
should
appear near
jacking lugs
2.11 Check that rollers (wherever
applicable) are greased
properly before assembling
under the transformer tank.
erection
Roller
assembly
drawing and
free
movement of
rollers.
2.12 Check that items to be
mounted are cleaned without
leaving any loose fibres with
dry cloth.
erection
Nonflurry dry
cloth
--

Sl
No
check
Quantum/
Frequency
of check
Acceptance
criteria
Remark
(s)
2.14
Check that buchholz relay and
conservator are not subjected
to full vacuum
Operation
al
During
process-ing
Relevant
valves to be
closed as per
valve diag.
Plate
Refer
instructi--
on manual
2.15 Check that the transformer
has been properly dried by
testing oil sample from tank
and oltc diverter switch for -
bdv of oil
-moisture
Content
Operation
al
After
completion
of oil
circulation in
tank
As per
instructional
manual.
Using
Oil testing
set for bdv
and ppm
kit for
moisture
2.16 Ensure that the oil filling in the
conservator (air-cell type) is
done as per the oil filling
instruction given at specified
rate and check the working of
pressure relief valves.
erection
Instruction
manual
Use log
sheet

Sl
No
check
Quantum/
Frequency
of check
Acceptance
criteria
Remark
(s)
2.17 Check for any damage to ct s
and check cleaniness
Commissi-
oning
No damage Log sheet
2.18
Check that ct secondary leads
are all in tact and kept shorted
until respective leads are
connected
commissioni
ng
No damage Use log
sheet
2.19 Complete erection check list
As listed As listed
Instruction
manual
Use check
list
2.20 Complete precommissioning
check list As listed As listed Instruction
manual
Use check
list

Sl
No
check
Quantum/
Frequency
of check
Acceptance
criteria
Remark
(s)
3.
3.1
Commissioning checks
Silica gel colour
Physical 100 % Blue
Use log
sheet
3.2 Oil level in conservator
bushing , breather housing,
oltc diverter each
Physical 100%
Upto the
marking on
gauge
Use log
sheet
3.3 Check that the marshalling
boxes are provided with
gasket and boxes are made
dust proof
Physical 100 % Proper
closing
Use log
sheet
3.4 Check the correctness of the
wiring for connection to oti
coolers, fans
Physical 100% Wiring
drawing
Use log
Sheet
3.5
Correctness of wti, oti, mog,
buchholz relay, cooler control
contacts
Operational 100%
Use
Log sheet

Sl
No
check
Quantum/
Frequency
of check
Acceptance
criteria
Remark
(s)
3.6 Oil sample from transformer
before energising should be
tested for bdv and moisture
content
Operational Before
energising
As per
instruction
manual
oil test set
for bdv,
ppm kit for
moisture
3.7 IR values Operational
Using
motorised
2.5 kv
meggar
100% Test
certificate
value for
general
comparison
3.8 Magnetising current at 400
volts from hv side
Operational 100% Use milli
ammeter
3.9 Check that for purpose of
various protection and alarm
are carried out as per
instruction manual and
recorded in log sheet
Operational 100% Instruction
maual
Contacts
should close
Use log
sheet
3.10 Complete commissioning
checklist
As listed As listed Instruction
manual
Use check
List

Sl
No
check
Quantum/
Frequency
of check
Acceptance
criteria
Remark
(s)
3.11 Trial operation for 24 hours
and check for any abnormal
noise / temperature rise
Operational
100%
Satisfactory
operation for
24 hours
Use log
sheet

DO‘S AND DON‘TS
DO‘S AND DON‘TS FOR POWER TRANSFORMERS
DO‘S FOR POWER TRANSFORMERS
1 Check and thoroughly investigate the transformer whenever any alarm or
protection is operated.
2 Check air cell in conservator
3 Attend the Leakages if any on bushings immediately.
4 Examine the bushings for dirt deposits and coats and clean them periodically
5 Check the oil in transformer and OLTC for di-electric strength and moisture
content and take suitable action for restoring the quality.
6 Check the oil level in oil cup and ensure air passages are free in the breather.
If oil is less make up the oil.
7 Check the oil for acidity and sludge as per IS 1866
8 If the inspection covers are opened or any gasket joint is to be tightened, then
tighten the bolts evenly to avoid uneven pressure.
9 Check and clean the relay and alarm contacts
10 Check the protection circuits periodically
11 Check the pointers of all gauges for their free movement
12 Clean the oil conservator thoroughly before erecting
13 Check the Buchholz relay and readjust the floats and switches etc.
14 Inspect the painting and if necessary retouching should be done.
15 Check the OTI and WTI pockets and replenish the oil if required

DO‘S AND DON‘TS
16 Remove the air through the vent plug of the diverter switch before you
energise the transformer
17 Check the oil level in the divertor switch and if found less top up with fresh oil
conforming to specifications.
18 Check the gear box oil level
19 Examine and replace the burnt or worn out contacts as per maintenance
schedule
20 Check all bearings and operating mechanism and lubricate them as per
schedule
21 Open the equalizing valve between tank and OLTC wherever provided at the
time of filling the oil in the tank.
22 Connect gas cylinder appropriately if transformer is to be stored for long, in
order to maintain positive pressure.
23 Fill the oil in the transformer at the earliest opportunity at site and follow
storage instructions
24 Check the door seals of marshalling box. Change the rubber lining if
required.
25 Do make sure that internal pressure in the transformer is zero gauge before
opening the manhole cover.

DO‘S AND DON‘TS
26 Insulating oil and insulation material for windings and connections are
inflammable. Watch for fire hazards.
27 Make sure that nothing is kept inside the pockets before authorised person
enters inside the main unit. Also remove wrist watches and footwear.
28 There must be protective guard for lamp to be taken inside
29 Keep inspection covers open for supply of fresh air when working inside
30 When one person is working inside, second person must be outside for
emergency.
31 Use fix spanners and tie them to the wrist of the person or somewhere
outside the tank
32 Be careful during connections where bolted joints (jumper connections) are
provided, so that nuts, washers etc. are not dropped inside the tank.
33 If it is necessary to weld some lugs or brackets etc., those should be
welded to tank stiffeners and strictly under the supervision of Transformer
manufacturer’s representatives.
34 De-energise the unit by circuit breakers and line switches while working on
energized unit. Ground the line terminals.
35 Attach the caution tags „DO NOT OPERATE THE SWITCHES“ while
working on energized unit.

DO‘S AND DON‘TS
36 Make sure that the fire-fighting equipments are available at the oil
treatment equipment as well as work place and adjacent to the
transformer.
37 Transformer tank, control cabinets etc. as well as oil treatment equipment
shall be connected with permanent earthing system of the station
38 Check oil level in condensor bushing; ensure proper tightness of top
terminal cap of condenser bushings to avoid rainwater entry.
39 Transport transformers only in upright position
40 Use tools with working surfaces hardened so that they will not peel or
chip.
41 Oil drums at site shall be stored in horizontal position with openings
horizontal

DO‘S AND DON‘TS
DONT’S FOR POWER TRANSFORMERS
1 DO-NOT energise without thorough investigation of the transformer whenever
any alarm of protection has operated.
2 DO-NOT re-energise the transformer unless the Buchholz gas is analyzed.
3 DO-NOT re-energise the transformer without conducting all pre-commissioning
checks. The results must be comparable with the results at works.
4 DO-NOT handle the off circuit tap switch (if any) when the transformer is
energized.
5 DO-NOT energise the transformer unless the off circuit (if any) tap switch handle
is in locked position.
6 DO-NOT leave off circuit tap switch handle unlocked.
7 DO-NOT leave tertiary terminals (if any) unprotected outside the tank, connect
them to tertiary lightning arrestors protection scheme when connected to load.
8 DO-NOT allow WTI/OTI temperature to exceed 65 deg. C during dry out of
transformers and filter machine temperature beyond 70 deg C
9 DO-NOT parallel transformer which DO-NOT fulfill required conditions.

DO‘S AND DON‘TS
10 DO-NOT use low capacity lifting jacks on transformer for jacking
11 DO-NOT move the transformer with bushings mounted
12 DO-NOT overload the transformer other than the specified limits as per IS 6600
13 DO-NOT change the settings of WTI and OTI alarm and trip frequently. The
settings should be done as per the site condition.
14 DO-NOT leave red pointer behind the black pointer in WTI and OTI
15 DO-NOT leave any connections loose.
16 DO-NOT meddle with the protection circuits.
17 DO-NOT allow conservator oil level to fall below 1 / 4 level
18 DO-NOT allow oil level fall in the bushings, they must immediately be topped up
19 DO-NOT switch off the heater in the marshalling box except to be periodically
cleaned.
20 DO-NOT leave marshalling box doors open, they must be locked
21 DO-NOT allow dirt and deposits on bushings, they should be periodically
cleaned.
22 DO-NOT allow unauthorized entry near the transformer.

DO‘S AND DON‘TS
23 DO-NOT leave ladder unlocked
24 DO-NOT change the sequence of valve opening for taking stand- by pump and
motor into circuit
25 DO-NOT switch on water pump(if any) unless oil pump is switched on in case of
OFWF cooling
26 DO-NOT allow water pressure more than oil pressure in differential pressure gauge
(in case of OFWF cooling)
27 DO-NOT mix two transformer oils, unless both conform to the same specification
28 DO-NOT allow inferior oil to continue in transformer. The oil should immediately be
processed and to be used only when BDV/PPM and other properties conform fully
to IS 1866 and oil specification.
29 DO-NOT continue with pink/white silica gel, this should immediately be changed or
regenerated.
30 DO-NOT store the transformer for long after reaching site. It must be erected and
commissioned immediately. Otherwise follow special precautions.
31 DO-NOT leave secondary terminals of unloaded CT open
32 DO-NOT keep the transformer gas filled at site for a longer period.

DO‘S AND DON‘TS
33 DO-NOT take any fibrous material as cotton waste inside while repairing
34 Do not stand on cleats and leads
35 DO-NOT weld/braze/solder inside tank
36 DO-NOT weld any thing to tank wall from outside
37 DO-NOT weld anything to conservator vessel with flxi separator rubber bag
38 DO-NOT smoke on or near transformer.
39 DO-NOT use fibrous cleaning material as it can deteriorate oil when mixed
with it.
40 DO-NOT use pipe flanges and valves as lifting or supporting points
41 DO-NOT drop crates containing porcelain parts
42 DO-NOT open the transformer during periods of inclement weather or when
condensation is forming on the internal surfaces of the transformer.
43 Never enter a transformer with dirty or wet clothing
44 DO-NOT filter oil of energized transformer

MAINTENANCE & TROUBLE SHOOTING

CHECKING LIST– MAINTENANCE
TIME PERIOD
SUBJECT CHECK
YEARS MONTHS
REMARKS
Insulating oil Dielectric strength
Moisture content
Neutralisation value
Interfacial surface tension
Water content
Sludge content
Gas analysis
3
3
3
3
3
3
3
Oil tightness
Tank
Conservator
Cooling equipment
Piping
Bushings
Cable sealing ends
Cable boxes
Buchholz relay
Gate valves
Valves
2
2
2
2
2
2
2
2
2
2
if applicable
if applicable

MAINTENANCE
TIME PERIOD
SUBJECT CHECK
YEARS MONTHS
REMARKS
Oil level
Tank
Conservator
Bushings
Cable sealing ends
Cable boxes
Thermometer pockets
1
1
1
1
1
1
if applicable
if applicable
Venting devices
Tank
Cooling equipment
Intermediate piping
Bushings
Piping
Buchholz relay
cable sealing ends
6
6
6
6
6
6
1
Release
vent screws
until oil
emerges.
Afterwards
screw plugs
tight
if applicable

MAINTENANCE
TIME PERIOD
SUBJECT CHECK
YEARS MONTHS
REMARKS
Earthing
devices
All metal parts
Tank
Motors
Star points
Surge arresters
Control cabinet
Steel armoured cabling
6
6
6
6
6
6
6
if applicable
if applicable
Shut-off devices In position "service" As
required
see plan
"Position of
shut-off
devices"
(if provided)
Buchholz relay Direction of oil flow
Float Contacts
gas sampling device
Functional test
1
1
1
1
if applicable

MAINTENANCE
TIME PERIOD
SUBJECT CHECK
YEARS MONTHS
REMARKS
Dial-type
Thermometers
Contact setting
Position of maximum pointer
Functional test
1
1
1
Setting see
Technical
data
Instrument
Transformers
Polarity
Ratio
Short-circuit connection
3
3
3
Oil level
indicators
Contact setting
Float
Functional test
1
1
1
Breathers
Silicagel
Oil level
Venting pipes
1
1
1
Internal wiring
Insulation resistance
Correct wiring connections
3
3
With 1000 V
Megger
Tester,

MAINTENANCE
TIME PERIOD
SUBJECT CHECK
YEARS MONTHS
REMARKS
Corrosion
Protection
Paint
Blank steel parts
1
1
Touch-up
Grease
Cleanliness
Bushings
Fittings
Indicating devices
Tank cover
Fans
1
1
1
1
1
Remove
loose parts,
if applicable
Terminal box Connections 1
On-load tap
Changer
[as per OLTC Manufacturer’s
catalogues]
See
instructions of
the
manufacturer
Protective relay
for OLTC
as per OLTC Manufacturer’s
catalogues]
See
instructions of
manufacturer

MAINTENANCE
TIME PERIOD
SUBJECT CHECK
YEARS MONTHS
REMARKS
Thermostat Functional test 1 See catalogue
Resistance
thermometer
Functional test 1
Pressure relief
device
Functional test 1 See
Manufacturers
Catalogues

TROUBLE SHOOTING
Components Fault Possible
causes
Remedial
measures
Detailed
description
Buchholz
relay
Buchholz relay
tripping
Oil loss
Violent oil surge
due to inside
flashover.
Violent gas
generation due
to inside failure.
Violent vibration
Fault tripping
Maintain the
shutdown
status.
Carry out tests
and
measurements
as described
above.
Vent the
transformer
and put it back
into operation
when faults
cannot be
found or faults
have been
eliminated

TROUBLE SHOOTING
Components Fault Possible causes Remedial measures Details
Protective
device for
OLTC
Tripping due to
strong oil surge
OLTC
Manufacturer’s
catalogues
Maintain the
shutdown status.
Check the tripping
mechanism.
Remove and check
the diverter switch.
Reset the tripping
mechanism and put
the transformer into
operation
Operating
Instructions
of
OLTC

TROUBLE SHOOTING
Resistance
thermometer
Thermostat
----------------
Dial type
thermometer
for oil or
winding temp.
Oil
temperature
too high
-----------
Winding or
oil temp. too
high
Transformer
overloaded or
inadequate
cooling.
Incorrect
temperature
adjustment
Reduce load of the
transformer
Put fans or cooling
equipment in service
Clean the cooling
equipment
Check the position of
butterfly valves
Adjust incorrect temperature
setting. Check the
thermometer by
comparative measurements
Check the electrical
connections and the tripping
mechanism
Check control devices for
cooling equipment
Check current transformers
and thermometers.
Operating.
instructions
of
Temperature
indicator.

TROUBLE SHOOTING
Component Fault Possible cause Remedial measure Details
Oil level
indicator
Oil level too
low
Not enough oil
(low temperature or
oil loss)
Check for tightness
Top-up oil
Operating
instructions
of
Manufacturer.
Oil flow
monitor
No
Oil
flow
Gate valve closed ,
pipe clogged,, pipe
leaky, oil circulation
pump faulted(no
voltage or voltage too
low, defective
winding, incorrect
direction of rotation,
bearing damage)
Top-up cooling
water to the required
level
Check the electrical
connections
Operating
Instructions.

TROUBLE SHOOTING
Component Fault Possible causes Remedial measures Details
Pressure
relief device
Internal tank
pressure too
high
Conservator pipe
shut-off or
clogged.
Electric flashover
inside the tank
Check the pipes and
shut-off devices Check
the transformer as
described in "Buchholz
relay.
Operating
Instructions.
Motor drive
for OLTC
Drive cannot
be operated
electrically
No voltage supply
at motor-
protective switch
Motor protective
switch not in
operating position.
Open circuit on
one or more motor
phases
Check supply feeders.
See operating
instructions of OLTC
Close motor protective
switch
Correct it.
Operation &
maintenance
manual of
OLTC
manufacturer.

TROUBLE SHOOTING
Drive keeps
on running
contactor stuck Clean or replace
Motor drive of
OLTC
Motor
protective
switch trips
during
operation of
motor drive
Emergency stop
button is on or
stuck.
Motor current
excessive due to
overload or
phase failure
Repair or replace emergency
stop button
Check drive for stiffness with
crank handle. Request a
factory engineer, if a
mechanical fault in the tap-
changer is suspected
Operation &
maintenance
manual of
OLTC
manufacturer
Off-circuit tap
changer
Operation
not possible
Gas in
Buchholz
relay
Adjusting device
defective
Carbon formation
on contacts
Repair adjusting device;
operate multiple the tap
changer once a year over all
positions (extraction
points).Check the
transformer as described for
the Buchholz relay

TROUBLE SHOOTING
Components Fault Possible causes Remidial measures Details
Dehydrating
breather
The drying
crystals turn
from blue to
pink and then to
white
from below
from the top
in general
High atmospheric
humidity, glass
cylinder leaky.
Moisture in
conservator, pipe
leaky, glass
cylinder leaky.
Moisture in
conservator, pipe
leaky, glass
cylinder leaky.
Glass cylinder
burst,
maintenance
interval
Replace dehydrating
agent.
Replace glass cylinder
or seal properly.
seal pipe leaks, check
the oil for
moisture content.
Flush the conservator
with dry air

TROUBLE SHOOTING
Components Fault Possible cause Remedial measure Details
Electrical
breakdown
voltage of the
oil
Breakdown
voltage too low.
Water content
too high
Breather
inoperable or
transformer in
service very low.
Leaks in water
cooling system.
Water pressure
reducer
inoperable.
Put breather into
operation.
Seal or repair coolers.
Contact manufacturer;
dry the oil, if necessary
Protective
spark gap on
bushings
Frequent
operation
Electrical arcing
distance no
longer correct
Adjust the clearance
between the arcing
horns and screw them
tight

TROUBLE SHOOTING
Components Fault Possible causes Remdial measures Detials
Terminal lugs
on bushing
control
Discoloration
of connecting
parts
Poor contact
making
Clear the contact faces.
Tighten the screws
Control cabinet Electrical
apparatus
does not
operate
properly.
Contacts
corroded,
contaminated.
Apparatus
housing bent
Excessive humidity
in control cabinet.
Water or dust
inside the cabinet.
Excessive high
temperature in the
cabinet.
Set the cabinet heater to
a higher temperature
Seal the cabinet door fit
a dust filter if necessary.
Protect the cabinet
against solar irradiation;
provide for better
ventilation

TROUBLE SHOOTING
Components Fault Possible causse Remedial measures Details
Earthing
connection
Earthing line
interrupted
Excessive
currents due to
external
flashovers.
Impermissible
current loops
through multiple
earthing.
Clean the contacts,
tighten the screws and
check the electrical
distances. Open up
current loops. Only one
earthing with a
sufficient cross section

Installtion, maintanace,trouble shooting of DT.ppt

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