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TD-TSP-0004-2A (1/19)
INSTRUCTIONSMAINTENANCE FOR
POWER TRANSFORMER
Address：No. 23, Chung-Hwa Rd., Huko Hsiang, Hsinchu, Taiwan 303, R.O.C. URL：http: / / ww w . s eec. c o m. t w TEL：+886-3-598-1921 FAX：+886-3-597-6373
TD-TSP-0004-2A (2/19)
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)
TD-TSP-0004-2A (3/19)
(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 inspector’s 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.
TD-TSP-0004-2A (4/19)
3. INSPECTION
3.1 Routine inspection
At least item 1 should be checked daily and recorded.
Table 1
No. Items Method Action
1 Oil 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.
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.Load current
Ambient
temperature
Load current and ambient
temperature should be recorded at
the same time.
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.
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.
(2) in bushing Check the oil level and oil leakage
on all oil-filled bushings.
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.
TD-TSP-0004-2A (5/19)
No. Items Method Action
4 Abnormal noise
and vibration
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.
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 side
check 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.
Note：In case of a self-cooled transformer, there is some difference between top and average oiltemperatures depending on loading conditions and ambient temperature. Strictly speaking, theaverage oil temperature should be referred to for checking oil level.
TD-TSP-0004-2A (6/19)
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.
2(1)
(2)
(3)
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 is
satisfactory 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
Acid value
(Every one year)
Measure acid value and judge it with
the criteria of Table 7.
3 Fan motors and/or
oil pump motors
(At least once every
two years)
(1) Measure insulation resistance of
fan motors and/or oil pump motors
with a 500V megger.
If insulation resistance is less than
2MΩ, check balancing of load
currents of three phase and dry out
the interior of fan motors.
(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.
TD-TSP-0004-2A (7/19)
No. Items Method Action
4 In case of：Cooler
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.
5 Control panel and
terminal box and
cables. (Once
every one year)
(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.
(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.
6
(1)
(2)
Protective relays
(Once every two
years)
(1) oil temperature indicator (2) winding temperature indicator
(3) dial oil gauge (4) oil flow indicator
(5) Buchholz relay (6) gas detector
(7) sudden pressure relay (8) differential pressure relay for oil/water cooler
(9) pressure relief device (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 2MΩ, check dews in the
terminal box.
Operation Operation tests should be made only
when protective relays operated even
if no troubles of a transformer
occurred.
The cause of a maloperation should
be 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.
TD-TSP-0004-2A (8/19)
3.3 Additional inspection
The following inspections and measurements are recommended for a preventive maintenance and in investigating 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 particular occasion.
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 every six months.
Using an appropriate airtight container, oil should be taken from the transformer. The dissolved gas should be extracted from the oil and analyzed.
When the quantities of combustible gases are obtained, evaluationscan be made to a probable location and type of trouble, which may be present in a transformer.
(Refer to Table 10.)
2 Insulation resistance of transformer windings
Measure the insulation resistance between a pair of windings, and between each winding and ground with a 1,000 or 2,000 volt megger at a periodical inspection.
The megger test should be made to check if the transformer is in suitable condition for operation or application of the dielectric test. Refer to Fig. 1.
The insulation resistance is subject to wide variation with temperature, humidity and cleanness of bushing porcelains.It may be low due to the leakage current through the weakest point of inferior insulation, in which case gases dissolved in oil should be analyzed.
3 Ratio test Measure the ratio of a transformer by two voltmeter methods or with a ratio tester.
If the transformer has taps, the turn ratio should be measured for all taps as well as for the full winding.
The test voltage may be between 100 and 200V at the rated frequency.
Compare the test results with those in the test report.
If it is difficult to measure because of fluctuation of voltmeter pointer or because of unbalance of a bridge circuit, more detailed investigation should be made.
4 Winding resistance Measure the winding resistance by bridge method or by drop-of-potential method. If oil pumps are provided, they should be operated during measuring winding resistance. Theoil temperature should be also recorded at the same time.
In case of low voltage and large capacity delta winding (Ex. generator transformer), there is a very difficulty to measure the winding resistance precisely and needs to pay careful consideration for judgment.
If the winding resistance, corrected to a specified temperature, is different from the data obtained previously, more detailed investigation should be made.
5 Excitation current at low voltage
Measure the excitation current at low voltage (100-200 volts) applied onthe lower voltage winding with other windings being open-circuited.
The voltage wave shape should be sinusoidal.
Note (1)
If the measured excitation current is much larger than the original dataat installation, more detailed investigation should be made.
Note (2)
TD-TSP-0004-2A (9/19)
No. Items Method Action or remarks
6 Impedance voltage Measure the impedance voltage at low current (5-10 amperes) applied on the higher voltage winding with lower voltage winding beingshort-circuited.
Note (3)
If the measured impedance voltage is much different from the original data at installation, more detailed investigation should be made.
7 Bushing current transformer
Excitation current and winding resistance should be measured in the same 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 highimpedance measurement.
(2) If the measured values satisfy an expression below, the transformer may not get serious injury such as layer shorting.
VM/IM 10
VR/IR
IR：Rated current IM：Measured current VR：Rated voltage VM：Measured 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.
Shorting cable
TR
(4) If those characteristic values from the item 2 to 6 are abnormally different compared the data with original data, it is recommended to carry out an internal inspection. In this case, you are kindly requested to tell us the information as APPENDIX II.
TD-TSP-0004-2A (10/19)
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, with the grease gun.
Refer to item No.6. It is no necessary when a bearing is sealed type.
2 Porcelain insulator such as bushing, lightning arrester, supporting insulator
Cleaning should be done periodically.
Interval depends on actual circumstance condition at site.
According to insulation book
3 Cooler
(1) Radiator type
Recommended cleaning frequency is once every two years.
With compressed air and/or water.
(2) Forced air type Dust and other foreign materials, accumulated on the finned area, should be blown out to maintain the efficiency of the cooler.
(3) Water cooled type Internal compartment check and cleaning should be done once every two years.
4 Paint for transformer external tank
Repainting should be done once every five years.
5 Bursting plate of transformer
Bursting plate is recommended to be replaced 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 broken bearings.
7 (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 oil leaks from gasket are serious.
(4) Rubber bag or diaphragm in conservator
Expected life is 15 years. If any damage of rubber bag or diaphragm is suspected, exchange with new one.
8 De-energized tap changer
Operate de-energized tap changer more than once a year when the transformer is out of service
Internal inspection is recommendable before operation of the de-energized tap changer, if the de-energized tap changer is not operated more than one year.
Note: As for maintenance of on-load tap changers, please refer to the corresponding insulation books.
TD-TSP-0004-2A (11/19)
OLTC diverter oil should be maintained according to Table 4-b.
Table 4-b
Location of on-load tap changer
Permissible value
Breakdown voltage Water content
Installed to line side
including delta winding≧40 kV/2.5 mm gap ≦30 ppm
Installed to neutral side ≧30 kV/2.5 mm gap ≦40 ppm
TD-TSP-0004-2A (12/19)
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).
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 or
thermal 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.
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.
3 Oil flow indicator The magnetic oil flow indicator
checks the operating condition of an
oil 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 to oil pump motor
3. Radiator valves are shut off.
4. Inverse of power phase sequence.
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 ambient temperature in winter season
3.Oil leakage
4. Damage of rubber bag or diaphragm in conservator.
5. If oil level of OLTC is abnormal, breaking of seal between the OLTC and transformer is suspected.
TD-TSP-0004-2A (13/19)
5.2 Relay function
If any protective relay operates, investigate the cause of a trouble according to the following relay’s functions.First of all, dissolved gas analysis is recommended immediately for the diagnosis of the transformer.
Table 6
No Relay Function and investigation
1 Buchholz relay
(1) First stage
The first stage of a Buchholz relay detects the gas formation due to minor troubles in transformer tank.
Rubber bag or d i aph r a g m t y pe c on s e rv ato r ;
Stop operation of the transformer immediately, and carry out gas analysis of accumulated gas and dissolved gas in oil and internal inspection of the transformer because a local heating and/or arc discharge is suspected.
B r eather t y pe and/ o r n i t r og e n gas s ea l ed t y pe c on s e rv ato r ;
Check if abnormal gas are exist or not by gas analysis of the transformer gas and dissolved gas in oil.
As the result, if abnormal gas are detected, stop operation of the transformer 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.
(2)Second stage The second stage of a Buchholz relay detects the rushing oil due to a serious trouble in the transformer tank.
If other protective relays, such as over-current relay of differential relay operate at the same time, a serious internal damage is suspected.
2 Sudden oil pressure relay
The sudden oil pressure relay detects the high rate of oil pressure increase in a transformer tank due to the gas generation and oil vapour caused 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 pressure increase in a tank due to the gas generation and oil vapour caused by serious troubles in the transformer tank.
4 Pressure relief device The pressure relief device operates when the pressure in the relief vent rises abnormally high enough to reach the pressure of approximately0.7kg/cm2 caused by serious failure in a transformer.
It also operates when the pipe of air breather is choked so as to increase the pressure in the relief vent.
6 OLTC protective relay OLTC protective relay detects some faults in diverter of on-load tap changer.
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 and the output current of a transformer converted by a current transformer.
It also operates sometimes with the inrush current when a transformer is excited.
8 Over current relay and ground fault relay
These relays detect faults in the electrical system including transformers.
Insu
latio
n re
sist
ance
(M
eg o
hm
s)
TD-TSP-0004-2A (14/19)
Fig1. Allowable value of transformer insulation resistance
1200
1000
800
600
400good
300
200
150
System voltage more than 6kV Systme voltage more than 11kV Systme voltage more than 22kV Systme voltage more than 66kV
100
80
60
40poor
30
20
15
10
8
6
4
3
2
0 20 40 60 80 100 120
Transformer oil temperature (° C)
Die
lect
ric
stre
ng
th (
kV
)
2.5m
m g
ap
/12
.5m
mΦ
s
ph
ere
TD-TSP-0004-2A (15/19)
Fig2. Relation between dielectric strength and amount of water in insulating oil
50
40
30
20
10
00 10 20 30 40 50 60
Water-parts per million by weight (PPM)
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 Filter or exchange with
new oil.
in earlier stage
3 More than 0.4 immediately
Table 8. Criteria of cooling water characteristics
No Test item Criteria
1 Hydrogen ion concentration (PH) 6.0 〜 8.0 at 25°C
2 Electrical conductivity Less than 500 (μΩ/cm) at 25°C
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-a：Resistivity criteria of insulation oil, at 80℃
TD-TSP-0004-2A (16/19)
Remarks：New oil should be used added oil.
No Transformer voltage Resistivity (Ω.cm) Judgment Action
1≧400 kV ≧1E
13
goodPeriodical analysis every one year.＜400 kV ＞5E
12
2≧400 kV ≦1E〜5E
PrecautionExchange to new oil is recommendable.＜400 kV ≦5E
12〜＞1E11
3≧400 kV ＜5E
12
Poor Exchange to new oil＜400 kV ≦1E
11
Table 9-b：Power factor criteria of insulation oil, at 80℃
No Transformer voltage Power factor (%) Judgment Action
1≧400 kV ≦0.5
goodPeriodical analysis every one year.＜400 kV ≦1.0
2≧400 kV 0.5〜1.5
PrecautionExchange to new oil is recommendable.＜400 kV ＜1〜3
3≧400 kV ＞1.5
Poor Exchange to new oil＜400 kV ＞3
Table 10 Combustible gas and type of fault with dissolved gas analysis of insulating oil
No Decomposed gases Type of fault
1 H2, CH4, C2H4, C2H6, C3H6, C3H8 Local heating in the oil
2C O , C O 2, H2, CH4, C2H4, C2H6, C3H6,
C3H8
Local heating in the oil impregnated solid insulation.
3 H2, CH4, C2H2, C2H4, C3H6Discharge in the oil
4 C O , C O 2, H2, CH4, C2H2, C2H4, C3H6Discharge in the oil impregnated solid insulation.
Note：Underline means a significant gas.
TD-TSP-0004-2A (17/19)
Table11. Combustible gas levels for maintenance
GasesThe level needed a follow-up survey
Permissible levels
C2H2 ＜0.5ppm 5ppm
H2 ＜400ppm
C2H4＜100ppm
It should be evaluated by necessary and sufficient
conditions with the following two items.
C2H4：more than 100ppm
TCG：more than 700ppm
CO ＜300ppm
It should be evaluated by necessary and sufficient
conditions with the following two items.
CO：more 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 rage：70ppm/month of TCG
C2H4：100ppm
TCG：700ppm
APPENDIX I Actions for safety and quality
TD-TSP-0004-2A (18/19)
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.
Note：When 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.
TD-TSP-0004-2A (19/19)
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 transformer
c. 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.
