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INSTRUCTIONS
MAINTENANCE FOR
POWER TRANSFORMER
Address No. 23, Chung-Hwa Rd., Huko Hsiang, Hsinchu, Taiwan 303, R.O.C.
URL http://www.seec.com.tw TEL +886-3-598-1921 FAX +886-3-597-6373
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1. FOREWORD
Power transformers are getting larger in their capacity to meet increasing power demand. So emergency
or unexpected power demand due to transformer trouble cause much loss of production as well as
inconvenience.
Therefore it is essential to assure trouble-free performance by a well-planned maintenance program.
Daily or periodical inspections will result in detecting abnormal conditions of a transformer and parts
before they cause any more serious troubles. A regular program of inspection should be established and
rigidly carried out for preventive maintenance of power transformers.
This instruction book describes inspection and maintenance methods to keep transformers in good
condition. As for construction, functions and handling of accessories, the corresponding instruction book
should be referred to for more detailed information.
2. REQUIREMENTS FOR INSPECTION AND MAINTENANCE
2.1 General
(1) The inspection items are classified into three categories in this instruction book.
(a) Routine inspection items (Table 1)
The routine inspection should be made, preferably daily, on every transformer in service.
Especially oil leak, oil temperature and/or winding temperature, load current, ambient
temperature and oil level in transformer should be daily checked and recorded.
(b) Periodical inspection items (Table 2)
The periodical inspection should be made each item, at least once every six months to once
every three years in order to ascertain the good performance of a transformer and its parts. Most
of the periodical inspections should be made in detail when the transformer is de-energized.
(c) Additional inspection items (Table 3)
Some additional inspections or measurements of electrical characteristics of a transformer are
recommended as preventive maintenance actions and when any transformer trouble should be
investigated thoroughly.
(2) Repainting of radiators and transformer tanks, and exchange of parts, gaskets and bearings of motors
should be planned and prepared previously for preventive maintenance, which will result in
continuous good performance of transformers. (Refer to Table 4)
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(3) If any protective relays give alarm, investigate the trouble causes according to Table 5 and Table 6.
It is essential in investigating the right causes to check whether differential relay, overcurrent relay
and/or ground fault relay have operated or not, in combination with other relays such as Buchholz
relay, sudden pressure relay and pressure relief device, which have physically operating
mechanisms.
(4) Transformer should be inspected internally whenever they have been subjected to unusually severe
operating conditions such as overloads and frequent short-circuits of outer bus or transmission line.
(5) Any symptoms such as unusual noises, high or low oil levels, rupturing of bursting plate, etc., should
be investigated thoroughly.
2.2 Inspection records
(1) The establishment of the report and recording of the condition and repair of the transformers is
required for a good maintenance program.
(2) A preventive maintenance system will operate satisfactorily with the following records.
(a) An equipment record
This may be simply a card, which contains the basic information of a transformer itself such as
the serial number, the location, size, etc.
(b) A repair record card
This may keep a running record as to costs of maintaining a transformer. It is the essential
diagnostic record for avoiding future difficulties.
(c)An inspection check list or inspectors record
This may be simply a listing of the points to be checked on a transformer and the establishment
of the time that these checks should be made.
(3) Without these records it would be very difficult for a preventive maintenance program to work,
because the knowledge gained form regular inspections would be quickly lost.
2.3 Actions for safety
Always inspection and maintenance works are to be done very carefully so that their schedule should
be planned in detail in view of safekeeping of human life and equipment according to APPENDIX I.
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3. INSPECTION
3.1 Routine inspection
At least item 1 should be checked daily and recorded.
Table 1
No. Items Method ActionOil temperature
and winding
temperature
Read indications of dial and/or
alcohol thermometers, and winding
thermal relays, if provided.
Compare them with the data
previously obtained.
When oil and/or winding
temperature
are much higher or lower
considering load current and
ambient temperature,
Thermometers should be inspected.
1
Load current
Ambient
temperature
Load current and ambient
temperature should be recorded at
the same time.
Check if indication of a thermometer
is correct or not.
If the temperature is not correct,
exchange with a new one.
If oil temperature is too high due to
dust and other foreign materials on
the finned area of radiators or the
inner surface of cooling water tube
(In case of water cooler type) clean
up them.
If indication of thermometer is not
correct, check oil level in the sensor
pocket and adjust to correct the
level.
2(1) Oil level
See note.
Read indication of the dial oil level
gauge on the conservator with a
telescope.
Compare it with the oil level-oil
temperature curve for the
transformer. Oil level is deemed to
be normal when its difference is
within one graduation of the gauge
on the curve.
(2) in bushing Check the oil level and oil leakage
on all oil-filled bushings.
When the indicated oil level is
constant with the changing oil
temperature, inspect the dial gauge
and check the actual oil level.
If the oil level is abnormal, adjust it
according to instructions.
If the oil level shows low, in case of
rubber bag or diaphragm type,
damage of rubber bag or diaphragm
is suspected.
If oil level of OLTC is abnormal,
breaking of seal between OLTC and
transformer is suspected.
3 Oil leaks Check oil leaks visually from
radiators flanges, pipes,
transformer tank and so on.
If oil leaks are due to gasket, tighten
bolts or exchange gasket.
In case of oil leaks from welded
parts, apply adhesive material or
weld again on the leaking part.
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No. Items Method Action
Abnormal or unusual noise,
especially from oil pump motors and
fan motors, should be carefully
listened to.
When oil pump or fan motor is
getting noisier, exchange the
bearings with new ones.
4 Abnormal noise
and vibration
Abnormal vibration can be checked
comparatively easily by hand.
When any supporters, pipes and
other parts are vibrating due to loose
bolts, tighten them.
5 Silica gel breather Check the breathing action in oil pot
and discoloration of silica gel
visually. Check the color of oil in oil
pot.
If the breathing action is not
satisfactory, check choking such as
filter in oil pot.
If the color of silica gel became to
pink from blue (or became to dark
green from orange) from upper sidecheck air leaks and fix it up.
If the oil color in oil pot blackened,
replace with new oil.
6 Gas trapped in
buchholz relay
Check whether any gas trapped in
buchholz relay with telescope.
If any gas trapped in the relay, the
transformer should be stopped for
investigation including accumulated
gas analysis.
7(1)Appearance
Bolt connection
Check any looseness of bolt
connection visually.
When any loose bolts are found,
tighten them.
(2) Discoloration Check visually that all connections
are normal without any
discoloration due to local heating.
When any connections show signs
of having been hot, clean and tighten
bolts and nuts.
(3) Dust Inspect visually for dust, especially
on radiators.
Clean up dust if it may reduce
cooling capacity of radiators.
(4) Rust Inspect visually for rust, especially
on radiators.
Re-painting is recommendable once
every five years.
Anti-rust and final paint should be
applied after rubbing off rust and old
paint.
(5) Dew Inspect visually for dew in the
terminal box, control cabinets and
protective relays.
If any dew is found, dry it out, and
ensure space heaters are in use if
they are provided.
NoteIn case of a self-cooled transformer, there is some difference between top and average oil
temperatures depending on loading conditions and ambient temperature. Strictly speaking, the
average oil temperature should be referred to for checking oil level.
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3.2 Periodical inspection
The recommended inspection frequency is described in parenthesis under each inspection item.
Table 2
No. Items Method Action
1 Breather silica gel
(Once every six
months)
Check the discoloration of silica gel in
breather due to moisture in breathed
air.
If the color of silica gel has turned to
pink from blue (or turned to dark
green from orange) by more than
two thirds of total quantity, dry out or
exchange it.
If the color of silica gel has turned to
pink by more than two thirds of total
quantity, dry out or exchange it.
Insulation oil
Dielectric strength
(Every one year)
Measure dielectric strength with an oil
tester and confirm it is more than 40
kV/2.5 mm gap.
If any measured values are not
satisfactory, filtering and/or
degassing of insulating oil are
recommended. The permissible
value of OLTC oil shows in Table
4-b.
Moisture content in
oil
(Every one year)
Measure moisture content in oil with
Automatic Coulometric Karl-Fischer
Titration method and confirm that it issatisfactory to the criteria. Criteria of
OLTC oil is show in Table 4-b.
(Criteria of Transformer oil)
TR. Voltage 69kV > 69kV~230kV
M. Content 35 ppm 25 ppm
TR. Voltage > 345 kV
M. Content 20 ppm
2(1)
(2)
(3)
Acid value
(Every one year)
Measure acid value and judge it with
the criteria of Table 7.
(1) Measure insulation resistance of
fan motors and/or oil pump motors
with a 500V megger.
If insulation resistance is less than
2M, check balancing of load
currents of three phase and dry out
the interior of fan motors.
3 Fan motors and/or
oil pump motors
(At least once every
two years)
(2) Check if temperature rise of oil
pump motors cases, based on oil
temperature, is less than 10 deg. C.
If it is more than 10 deg. C, check its
insulation resistance, winding
resistance and three phase
balancing of load current.
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No. Items Method Action
4 In case ofCooler
of water-cooled
type
(At least once every
two years)
(1) Analyze the characteristics of
cooling water as shown in Table 8.
(2) Check scale deposit on the inside
of the cooling tube to reduce the
water flow required, resulting in
excessive heating of a transformer
at normal load.
If any characteristics are not
satisfactory according to the criteria
shown in Table 8, shorten inspection
interval of coolers. If any heavy
scale is found on the inside of the
cooling tubes, clean them up.
(1) Check the water-tightness of a
control cabinet and a terminal box.
If the rubber gasket is worn out,
exchange it with a new one.
(2) Ascertain the tightness of all
control wiring connections.
Tighten the loose bolts.
(3) Operate all switches, annunciators
and lamps to observe proper
functions according to schematic
diagrams.
If any part maloperates, adjust or
exchange them with new one.
5 Control panel and
terminal box and
cables. (Once
every one year)
(4) Measure insulation resistance of
cable with 500V megger.
Check any crack or abrading on
cable insulation.
If such defect is found, put tape on it
or exchange it with new one.
Protective relays
(Once every twoyears)
(1) oil temperature indicator
(3) dial oil gauge(5) Buchholz relay
(7) sudden pressure relay
(9) pressure relief device
(2) winding temperature indicator
(4) oil flow indicator(6) gas detector
(8) differential pressure relay
(10) leak detector
Insulation
resistance
(Once every two
years)
Measure insulation resistance of
protective relays including their
wirings with a 500V megger.
When the insulation resistance is
less than 2M, check dews in the
terminal box.
6
(1)
(2)
Operation Operation tests should be made onlywhen protective relays operated even
if no troubles of a transformer
occurred.
The cause of a maloperation shouldbe investigated by operation tests
according to instruction books for
protective relays.
7 Connections
(Occasionally)
All connections outside of a
transformer should be inspected to
see whether they are in good
conditions without any discoloration,
which indicates hot connection.
Any connection that shows signs of
having been hot should be
thoroughly cleaned and bolted
together tightly.
for oil/watercooler
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3.3 Additional inspection
The following inspections and measurements are recommended for a preventive maintenance and ininvestigating a transformer trouble.For preventive maintenance, items 1 and 2 are recommended.
If a transformer was failed, all items (1 to 7) are recommended for the investigation on that particularoccasion.
Table 3
No. Items Method Action or remarks
1 Insulation oil
Analysis of gas
dissolved in oil
After a transformer is put into service,a periodic analysis of gas dissolvedin oil is recommended at least everysix months.
Using an appropriate airtightcontainer, oil should be taken fromthe transformer. The dissolved gasshould be extracted from the oil andanalyzed.
When the quantities of combustiblegases are obtained, evaluationscan be made to a probable locationand type of trouble, which may bepresent in a transformer.
(Refer to Table 10.)
2 Insulation resistance oftransformer windings
Measure the insulation resistancebetween a pair of windings, andbetween each winding and groundwith a 1,000 or 2,000 volt megger ata periodical inspection.
The megger test should be made tocheck if the transformer is in suitablecondition for operation or applicationof the dielectric test. Refer to Fig. 1.
The insulation resistance is subjectto wide variation with temperature,humidity and cleanness of bushingporcelains.
It may be low due to the leakagecurrent through the weakest pointof inferior insulation, in which casegases dissolved in oil should beanalyzed.
3 Ratio test Measure the ratio of a transformer bytwo voltmeter methods or with a ratiotester.
If the transformer has taps, the turnratio should be measured for all tapsas well as for the full winding.
The test voltage may be between 100and 200V at the rated frequency.
Compare the test results with thosein the test report.
If it is difficult to measure because
of fluctuation of voltmeter pointer orbecause of unbalance of a bridgecircuit, more detailed investigationshould be made.
4 Winding resistance Measure the winding resistance bybridge method or by drop-of-potentialmethod. If oil pumps are provided,they should be operated duringmeasuring winding resistance. Theoil temperature should be alsorecorded at the same time.
In case of low voltage and largecapacity delta winding (Ex. generatortransformer), there is a very difficultyto measure the winding resistanceprecisely and needs to pay carefulconsideration for judgment.
If the winding resistance, correctedto a specified temperature, isdifferent from the data obtainedpreviously, more detailedinvestigation should be made.
5 Excitation current at lowvoltage
Measure the excitation current at lowvoltage (100-200 volts) applied onthe lower voltage winding with otherwindings being open-circuited.
The voltage wave shape should besinusoidal.
Note (1)
If the measured excitation current ismuch larger than the original dataat installation, more detailedinvestigation should be made.
Note (2)
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No. Items Method Action or remarks
6 Impedance voltage Measure the impedance voltage atlow current (5-10 amperes) appliedon the higher voltage winding withlower voltage winding beingshort-circuited.
Note (3)
If the measured impedance voltageis much different from the originaldata at installation, more detailedinvestigation should be made.
7 Bushing currenttransformer
Excitation current and windingresistance should be measured in thesame way as items 4 and 5.
Same as above 4 and 5.
Note(1) The ammeter should be connected inside of voltmeter as shown below to avoid error due to high
impedance measurement.
(2) If the measured values satisfy an expression below, the transformer may not get serious injury such aslayer shorting.
10/IV
/IV
RR
MM
IRRated current
IMMeasured current
VRRated voltage
VMMeasured voltage
(3) The shorting cable should be more than 100mm2
in its section and be as shorter as possible in its length,to avoid measuring error.
(4) If those characteristic values from the item 2 to 6 are abnormally different compared the data withoriginal data, it is recommended to carry out an internal inspection. In this case, you are kindlyrequested to tell us the information as APPENDIX II.
TR
Shorting cable
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4. MAINTENANCE
Maintenance of parts and materials should be planned according to the following Table 4-a.
Table 4-a
No. Material and parts Maintenance frequency Remarks
1 Grease of fan motors Grease them up once a year, withthe grease gun.
Refer to item No.6. It is nonecessary when a bearing is sealedtype.
2 Porcelain insulator suchas bushing, lightningarrester, supportinginsulator
Cleaning should be doneperiodically.
Interval depends on actualcircumstance condition at site.
According to insulation book
Cooler
(1) Radiator type
Recommended cleaning frequencyis once every two years.
(2) Forced air type Dust and other foreign materials,
accumulated on the finned area,should be blown out to maintain theefficiency of the cooler.
3
(3) Water cooled type Internal compartment check andcleaning should be done once everytwo years.
With compressed air and/or water.
4 Paint for transformerexternal tank
Repainting should be done onceevery five years.
5 Bursting plate oftransformer
Bursting plate is recommended to bereplaced once every five years.
6 Bearing of fan motors
and oil pump motors
Expected life is ten years.
Expected life is three years, whenbearing is sealed type. (only fanmotors)
Exchange with new ones, if a motor
becomes noisy due to brokenbearings.
(1) Gasket
(Cork-neoprene)
(2) Thermometer
(Oil, winding)
(3) Pressure relay
(Water, nitrogen,sudden pressure relay,water/oil differential
pressure relay)
Expected life is ten years. Exchange with new gaskets, if oilleaks from gasket are serious.
7
(4) Rubber bag ordiaphragm inconservator
Expected life is 15 years. If any damage of rubber bag ordiaphragm is suspected, exchangewith new one.
8 De-energized tapchanger
Operate de-energized tap changermore than once a year when thetransformer is out of service
Internal inspection isrecommendable before operation ofthe de-energized tap changer, if thede-energized tap changer is notoperated more than one year.
Note: As for maintenance of on-load tap changers, please refer to the corresponding insulation books.
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OLTC diverter oil should be maintained according to Table 4-b.
Table 4-b
Permissible value
Location of on-load tap changer
Breakdown voltage Water content
Installed to line side
including delta winding40 kV/2.5 mm gap 30 ppm
Installed to neutral side 30 kV/2.5 mm gap 40 ppm
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5. TROUBLE SHOOTING
5.1 Diagnosis of protective relays in operationIf any protective relay gives an alarm, investigate its causes according to the following Table 5.
Table 5
No Relay Function Cause and Action
1 Dial type thermometer The dial type thermometer indicates
the top oil temperature and highest
oil temperature experienced. It gives
an alarm when oil temperature gets
to the alarm setting (80 for
example).
2 Thermal relay for oil
temperature or winding
temperature
The thermal relay detects and
indicates maximum oil or winding
temperature of a transformer.
It also has protective functions to
give an alarm or tripping signal, and
automatic functions to control
cooling system.
1.Overloading
2. Insufficient efficiency of cooler
units due to dust and other
foreign materials accumulated
on the finned area or due to a
heavy scale in the water-cooling
coils.
3. Maloperation of thermometer orthermal relay due to their own
defects.
4. If indication of thermometer is
not correct, check oil level in the
sensor pocket and adjust to
correct oil level.
3 Oil flow indicator The magnetic oil flow indicator
checks the operating condition of anoil pump. When an oil pump stops,
the pointer returns to the stop
position and the micro-switch
contact closes to give an alarm.
1.Trouble of oil pump motor
2.Trouble of wiring connection tooil pump motor
3. Radiator valves are shut off.
4. Inverse of power phasesequence.
4 Oil level gauge-dial type The dial type oil level gauge
indicates the oil level in a
conservator of an oil-immersed
transformer.
When the oil level comes down to
the bottom of a conservator, its
pointer indicates zero and give an
alarm.
1.Shortage of oil
2.Abnormally low ambienttemperature in winter season
3.Oil leakage
4. Damage of rubber bag ordiaphragm in conservator.
5. If oil level of OLTC is abnormal,breaking of seal between theOLTC and transformer issuspected.
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5.2 Relay function
If any protective relay operates, investigate the cause of a trouble according to the following relaysfunctions.First of all, dissolved gas analysis is recommended immediately for the diagnosis of the transformer.
Table 6
No Relay Function and investigation
Buchholz relay
(1) First stage
The first stage of a Buchholz relay detects the gas formation due to minortroubles in transformer tank.
Rubber bag or diaphragm type conservator;
Stop operation of the transformer immediately, and carry out gas analysisof accumulated gas and dissolved gas in oil and internal inspection of thetransformer because a local heating and/or arc discharge is suspected.
Breather type and/or nitrogen gas sealed type conservator;
Check if abnormal gas are exist or not by gas analysis of the transformergas and dissolved gas in oil.
As the result, if abnormal gas are detected, stop operation of thetransformer and carry out of internal inspection.
The type and location of trouble may be predicted by gas analyses of oil.
Note: Nitrogen gas dissolved in oil could supersaturate and accumulate inthe relay and actuate the relay when oil-temperature drops rapidlyon a cold day in case of a gas-sealed transformer.
1
(2)Second stage The second stage of a Buchholz relay detects the rushing oil due to aserious trouble in the transformer tank.
If other protective relays, such as over-current relay of differential relayoperate at the same time, a serious internal damage is suspected.
2 Sudden oil pressurerelay
The sudden oil pressure relay detects the high rate of oil pressureincrease in a transformer tank due to the gas generation and oil vapourcaused by serious troubles. In case of correct operation, the transformer
operation should be stopped.3 Sudden pressure relay [In case of nitrogen sealed conservator]
The sudden pressure relay detects the high rate of nitrogen pressureincrease in a tank due to the gas generation and oil vapour caused byserious troubles in the transformer tank.
4 Pressure relief device The pressure relief device operates when the pressure in the relief ventrises abnormally high enough to reach the pressure of approximately0.7kg/cm
2caused by serious failure in a transformer.
It also operates when the pipe of air breather is choked so as to increasethe pressure in the relief vent.
6 OLTC protective relay OLTC protective relay detects some faults in diverter of on-load tapchanger.
Check the following items;
1.Fault of diverter insert
2.Fault of whole of OLTC
Malfunction of OLTC relay due to normal deterioration.
7 Differential relay The differential relay detects the difference between the input current andthe output current of a transformer converted by a current transformer.
It also operates sometimes with the inrush current when a transformer isexcited.
8 Over current relay andground fault relay
These relays detect faults in the electrical system including transformers.
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100 120806040200
2
3
4
6
8
10
15
20
30
40
60
80
100
150
200
300
400
600
800
1000
1200
Transformer oil temperature (C)
Insulationresistance(Megohms)
good
poor
System voltage more than 6kV
Systme voltage more than 11kV
Systme voltage more than 22kV
Systme voltage more than 66kV
Fig1. Allowable value of transformer insulation resistance
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Fig2. Relation between dielectric strength and amount of water in insulating oil
Table 7. Acid value criteria
No Acid value (mg KOH/g) Action
1 Less than 0.2 Good
2 From 0.2 to 0.4 in earlier stage
3 More than 0.4
Filter or exchange
with new oil. immediately
Table 8. Criteria of cooling water characteristics
No Test item Criteria
1 Hydrogen ion concentration (PH) 6.0 8.0 at 25C
2 Electrical conductivity Less than 500 (/cm) at 25C
3 Chlorine ion (C1
) Less than 100 ppm
4 Total hardness (CaCO3) Less than 150 ppm
5 Sulfuric acid ion (SO4 ) Less than 200 ppm
6 M-Alkalinity (CaCO3) 15 60 ppm
7 Sulfur ion (S
) undetectable
8 Ammonium ion (NH4+
) undetectable
9 Total iron ion (Fe+++
) Less than 0.5 ppm
10 Silica (SiO2) Less than 30 ppm
Table 9-aResistivity criteria of insulation oil, at 80
50
40
30
20
10
020 30 40 50 600 10
Water-parts per million by weight (PPM)
Dielectricstrength(kV)
2.5
mm
gap/12.5
mm
sphe
re
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Table11. Combustible gas levels for maintenance
GasesThe level needed a
follow-up surveyPermissible levels
C2H2 0.5ppm 5ppm
H2 400ppm
C2H4 100ppm
It should be evaluated by necessary and sufficient
conditions with the following two items.
C2H4more than 100ppm
TCGmore than 700ppm
CO 300ppm
It should be evaluated by necessary and sufficient
conditions with the following two items.
COmore than 300ppm
Ratio of CO2/CO
Normal ratio is more than 3
Abnormal ratio is less than 3
TCG
(Total Combustible Gas)700ppm
It should be evaluated by necessary and sufficient
conditions with the following three items.
Increasing rage70ppm/month of TCG
C2H4100ppm
TCG700ppm
APPENDIX I Actions for safety and quality
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Table 11
No Working condition Actions for safety
1 Exterior check (1) Be careful not to approach live parts.
2 Electrical test and
remedial work
(1) De-energize the transformer by circuit breakers and line switches.
(2) Ground the line terminals of the transformer.
(3) Attach caution tags not to operate switches for circuit breakers and line
switches. See note.
(4) De-energize the control cabinets for coolers and tap changer by AC and DC
switches.
(5) Attach caution tags on switch boxes.
3 When internal
inspection is to be
made
Same as above except the following additional items.
(1) Replace nitrogen gas completely with dry fresh air, if it was filled in the
transformer.
(2) Make sure there is 18% or more oxygen to sustain life in a transformer
tank.
(3) Make sure your pockets are empty.
(4) Take off a wrist watch and any other accessories on your body.
(5) List up name and quantity of all tools to be brought into a transformer
tank.
(6) Spread out clean cloth on coil groups when repairing.
(7) Protect lamps with guards not to break them in a tank.
(8) Be careful not to drop any tool and foreign material into the transformer.
Secure all tools with hand lines. Any metallic item dropped into a
transformer must be removed to prevent serious trouble in future.
4 After inspection
work
(1) Make sure all foreign materials are clear before closing manhole and
energizing.
(2) Check the quantity of all tools brought out from a tank.
(3) Remove the grounding wires on the line terminals of the transformer.
NoteWhen test and remedial work must be carried out under the live conditions for any special reasons, pay
attention to live parts to protect yourself against electrical shock.
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APPENDIX II Technical information to be sent to the manufacturer
Whenever you need technical advice for any troubles of parts and/or a transformer itself from Shihlin Electric
Corporation, you are kindly requested to let us know the following technical information.
(1) Name of the power station or sub-station where the transformer is in service
(2) Serial number and ratings of the transformer in trouble
(3) Name, type and serial number of the parts in trouble
(4) Detailed explanation in case of more severe troubles
a. Duration and amperes of over current
b. Overvoltage and/or surge applied on the transformerc. Protective relays in operation
d. Load conditions (voltage, current and power factor)
e. Copies of p/s or s/s layout drawings which show location of the transformer and other electrical
equipment such as circuit-breakers, lightning arresters and line switches
f. Copies of skeleton sequence drawings for control panels
(5) Any other information available about the trouble
Your quick and detailed information is being expected, which would result in quick and more appropriate
actions for its recovery.