INSTRUCTIONS
INSTALLATION, MAINTENANCE & OPERATION of SHIHLIN DISTRIBUTION TRANSFORMERS
SHIHLIN ELECTRIC & ENGINEERING CORP. 12F. 90. SEC. 6. CHUNG SHAN N. RD.. SHIHLIN. TAIPEI. TAIWAN. REPUBLIC OF CHINA
CONTENTS Description
I. II.
III.
IV.
V.
Page Introduction……………………………………………..................1 Installation……………………………………………………........1 A. Handling……………………………………………….……...1 B. Pole Mounting…………………………………………….…..1 C. Mounting of Station Type Transformers………………………1 D. Storage……………………………………….............………..2 Preparing for Operation…………………………………………....2 A. Quantity of Oil…………………………………………….…..2 B. Transformer Protection…………………………………….….2 C. Tap Changer Position……………………………………….…2 D. External Clamping Parts and Valves……………………….….2 Inspection and Maintenance………………………………….……2 A. Routine Inspection and Maintenance……………………….…2 B. Periodic Inspection and Maintenance………………………....4 Operation Guide for SHIHLIN Transformers…………………..….6 A. Service Conditions………………………………………….…6 B. Insulation Coordination……………………………………..…9 C. Variation of Voltage and Frequency………………………..….9 D. Loading…………………………………………..…………...10 E. Connection………………………………………………..…..10 F. Parallel Operation………………………………………..…...10
INSTRUCTIONS INSTALLATION, MAINTENANCE AND OPERATION OF SHIHLIN DISTRIBUTION TRANSFORMERS I.
Introduction The successful operation of oil-immersed transformers is dependent upon proper installation and maintenance as well as upon proper design and manufacture. As compared with other electric apparatus, transformers require rather little inspection and this instruction is prepared for that purpose.
II.
Installation A. Handling The transformer should always be handled in the normal upright position. Where a distribution transformer cannot be handled by a crane, it may be skidded or moved on rollers, but care must be taken not to tip the transformer excessively so that the base will be damaged. A distribution transformer should never be lifted by placing tackle under the bushings and should not be moved by gripping lightning arresters, bushings, or accessories. When rollers are used, skids should be used to distribute the stress over the base.
B.
Pole Mounting For direct pole mounted transformers support lugs are provided for this purpose. In these cases where crossarm mounting is used, it will be found convenient to fasten the hangers to the case before the transformer is raised up to and slightly above the crossarm and the hooks on the hanger irons made to engage the crossarm by lowering the transformer. If no secondary arm or buck-arm is available, kicker brackets should be used to make the transformer hang parallel to the pole.
C.
Mounting of Station Type Transformers Accessibility, ventilation, and ease of inspection should be given careful consideration in the location of transformers self-cooled transformers depend entirely upon the surrounding air for carrying away their heat, for this reason, care must be taken to provide adequate ventilation. For indoor installation, the room in which the transformers are placed must be well ventilated so that heated air can escape readily and can be replaced by cool air. Inlet openings should be near the floor and distributed so as to be must effective. The outlet openings should be as high above the apparatus as the construction of
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the building will permit. Self-Cooled transformers should always be separated from one another and from adjacent walls, partitions, etc, in order to permit free circulation of air about the tanks. A spacing of 450 mm or more is advisable, depending upon the size of the transformers.
D.
Storage If transformers are not to be put into service immediately, it is advisable to place them, complete with oil, in their permanent location. If this is not convenient, they should be stored in a clean dry place, which is not subject to wide temperature variations. Transformers should not be stored or operated in the presence of corrosive gases, such as chlorine.
III. Preparing for Operation Following precautions must be taken before operating the transformers: A. Quantity of Oil Quantity of oil should be kept so adjusted as to maintain an appropriate oil level for insulation and cooling effects. Voltage should be applied only to transformers filled with oil to the correct level. In case of a remarkable deviation witnessed in the oil level, it is necessary to clarify its causes such as oil leakage, etc.
B.
Transformer Protection Transformers should be protected from excessive overloads and overvoltage surges with approved protective devices.
C.
Tap Changer Position If the unit is equipped with a tap changer, operate the tap changer by turning the handle until the point is directly above the letter or number indicating the desired tap. CAUTION: “Do not operate the tap changer when the transformer is energized”.
D.
External Clamping Parts and Valves Check if foundation bolts, mounting bolts, grounding pads, and all of clamping parts are loosened and if valves are open.
IV. Inspection and Maintenance A. Routine Inspection and Maintenance 2
Rountine inspection and maintenance are ordinarily made at appearance of transformers as in operation during a general inspection trip, taking records with meters which are usually equipped to transformer to ensure their operation and checking most carefully any abnormal noise, bad odor, discoloring, etc. Records thus taken at each time are to be checked in comparison to their normal record values.
1.
Quantity of oil Quantity of oil should be kept so adjusted as to maintain an appropriate oil level for insulation and cooling effects. In case of a remarkable deviation in the oil level, it is necessary to clarify its causes such as oil leakage, etc.
2.
Oil Temperature Care is needed for oil temperature, as it relates to longevity of insulating materials and gradual forming of internal faults.
3.
Noise Sound of transformer, due to magnetostriction of the core, sounds constant with audio frequencies from the fundamental frequency up to approximately 500-600c/s in normal. Therefore, any change in the sound, which is easily noticeable, should be fully examined to find out its cause. There are following causes of noise to be considered. (1) Resonance of the tank, radiator, etc. due to abnormal change in power source frequency. (2) Loosened clamps of core lamination. (3) Faulty electrical contact. (4) Static discharge due to defective earthing. (5) Loosened clamps of accessories.
4.
Leakage of oil Inspection should be made with special care for the welded parts of the main assembly, gasket parts and cemented parts of valves, oil gauge and bushings. In case of large leakage of oil, transformer tank will be stained with oil, while small leakage can be detected from the leakage point being discolored in black.
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5.
Dehydrating Breather Inspection is made if dehydrating breather is normally working. As a dehydrator, a blue sillicagel colored by cobalt chloride is used in principle. As it is wet, its color becomes brown and when it becomes saturated with moisture, its color turns into while pink.
6.
Pressure Relief Device It should be check if there is any trace of outflow of oil.
7.
External Clamping Parts and Valves Check if foundation bolts and grounding pads are loosened and if valves are open.
8.
Cooling Equipment In case of self-cooled type, no other inspections are necessary than the above-mentioned inspection items, but for forced cooled type, the following points should be checked. (1) Forced Air Cooler This is composed of several groups of self cooled coolers, each provided with several units of fan. Check if any abnormal noise is produced from running of fan motor and if the running is proper. (2) Forced Oil Forced Air Cooler In general, one oil pump and several fans compose a unit. Check if there is noise produced from running of pump and fan motor and if the running is smooth. Also check indication of oil flow indicator.
B.
Periodic Inspection and Maintenance Standard items and frequency of periodic inspection and maintenance, as per table below, is to be applied to transformers used under normal conditions. Therefore, it is recommended that transformers used under severe conditions should be checked each time they are used.
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line Items for Inspections
Frequency
Discrimination
1
winding
Insulation resistance
once a year
Please refer to Fig. 1
2
winding
Dielectric loss factor
once in three year
Please refer to Fig. 2
3
oil
Withstand Voltage
once a year
≧30kV/2.5mm
＜30kV/2.5mm no good ＜0.2
4
oil
Acid Value
once a year
oil
Characteristics
6
oil
Filtration
7
tap changer
operation of tap changer once a year
9
Equipment Nitrogen seal Equipment
10 Bushing
of line 1-4 was found abnormal. performance when the test result of line 1-5 was found abnormal.
purity of N2 gas
twice in a year
Seal device
once in two years
cleaning of insulator
twice a year
Mounting bolts and nuts 11 Bushing
and clamping of
once a year
terminals.
Thermometer 12 oil level gauge
cleaning of glass surface alarm contact fault
once a year
indication.
cleaning of transformers 13 Internal
insulation,
no good
performance when the test result
5
Nitrogen seal
good
0.2-0.4 doubtful ＞0.4
8
good
once for ten years
deteriorated lead gasket.
5
Inputy ≧ 95%
good
Inputy ＜ 95%
no good
V.
Operation Guide for SHIHLIN Transformers In the operation of transformers, it is essential to utilize the capability of the transformers to a full extent, as well as to operate them safely without causing any transformer trouble.
This operation guide is prepared for this purpose. A. Service Conditions The service conditions of transformers should satisfy the following conditions. (1) The transformer should be operated at an altitude of 1,000 meters (3,300 feet) above sea level and lower. Note. If the transformer has been designed for the operation at the particular altitude higher than 1,000 meters above sea level, the transformer can naturally be operated at that particular altitude. When the transformer designed for normal service conditions is operated at an altitude higher than 1,000 meters above sea level, care should be taken about the following conditions. (a)
Transformer KVA It is recommended to reduce KVA rating by the percentages given below for each 100 meters (330 feet) that the altitude is above 1,000 meters.
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ANSI std.
BS std.
oil-immersed Self-cooled
0.4%
0.4
0.3
oil-immersed Forced-Air-Cooled
0.5%
0.5
0.4
Forced-oil Forced-Air-Cooled
0.5%
0.5
0.4
0%
0
0
Water Cooled
However, the transformer can usually be used without reducing its rated KVA, because the ambient temperature at such high altitudes is normal service conditions. ANSI standard describes that the transformer designed for normal service conditions can be used at its rated KVA, provided that the average temperature of the cooling air does not exceed the values below for the respective altitudes. Altitude (m. a. s. l.)
Type of Cooling Oil-Immersed Self-Cooled Oil-Immersed Forced-Air-Cooled, Forced-Oil Forced-Air-Cooled.
(b)
1000
2000
3000
4000
30℃
28℃
25℃
23℃
30℃
26℃
23℃
20℃
Dielectric Strength of Bushings The sparkover voltages of bushings decrease as the altitude increases, and the following correction factors should be taken into consideration. Altitude (m. a. s. l.)
Correction Factor
1000
1.00
1200
0.98
1500
0.95
1800
0.92
2100
0.89
2400
0.86
2700
0.83
3000
0.80
3600
0.75
4200
0.70
4500
0.67
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(2) Ambient temperature (cooling water temperature in case of water-cooled) should not exceed the limits specified by the respective standards. Note. If the transformer has been designed for the operation at the particular ambient temperature higher than the specified limit, the transformer can naturally be operated at that particular ambient temperature. When the transformer designed for normal service conditions is operated at an ambient temperature higher than the specified limit, the rated KVA should be reduced by the percentages below for each degree centigrade that the ambient temperature is higher than the limit specified by the respective standards. Oil-Immersed Self-cooled
1.5%
Oil-Immersed Forced-Air-Cooled
1.0%
Forced-oil Forced-Air-Cooled
1.0%
Water Cooled
1.5%
For the purpose of reference, ambient temperature conditions specified by various standards are shown below. JEC 168
ANSI-C57.12 BS-171 IEC-76
VDE 0532/7.55
Maximum
40
40
40
40
35
Air 24 hour Average
35
30
30
30
25
Annual Average
20
-
20
20
20
Maximum
25
30
25
25
25
-
25
20
-
-
Water
24 hour Average
Particular care should be taken for the maintenance of the transformer used in the circumstances listed below, though it is not necessary to reduce the transformer KVA. (c) When the ambient temperature is extremely low. (d) When salt or dust contamination is severe. (e) When cooling water quality is bad. (f) When the humidity is extremely high. (g) When the transformer is used in steam, oil vapour, explosive gas, etc. (h) When the transformer is exposed to severe vibration or mechanical shock.
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B.
Insulation Coordination Each winding of the transformer is so designed that the dielectric strength of the winding complies with the specified B.I.L. (Basic Impulse Level) or insulation level. Therefore, the transformer in operation should be protected by protective devices so that no abnormal voltage higher than that level will attack the transformer terminals. Generally it is recommended to take protection margin of approximately 20% between the abnormal voltage that appears in the system (normally spark-over or discharge voltage of lightning arresters) and the transformer B.I.L. When the winding is connected in wye, make sure that the following conditions are satisfied. (1) The Neutral point of the winding of graded insulation designed for solidly grounded system should be solidly grounded. (2) The winding of full insulation or with neutral point level reduced to approximately (1/√3) of line level can be used without grounding the neutral point, but it is recommended to protect the neutral with a lightning arrester.
C.
Variation of Voltage and Frequency The transformer can be operated as follows when the voltage and/or frequency vary from the rated value. (1) The transformer can be operated continuously at rated output and lower with the voltage 5% higher than the rated voltage on output side (the respective tap voltage if there are taps on output side). (2) The transformer can be operated continuously at no load with a voltage 10% higher than rated voltage (respective tap voltage if there are taps on exciting side) (3) The transformer can be operated as normal with the frequency variation within plus or minus 5%. (4) When the voltage and frequency vary simultaneously, the sum of each variation should be within plus or minus 5%, the increase of voltage and decrease of frequency being.
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D.
Loading The transformer can carry the load higher than rated KVA for a short period or continuously under certain conditions, without causing any damage to the transformer. As various loading guides such as listed below have been published, refer to the guide recommended by the standard with which the transformer complies, for such overloading of the transformer. ANSI C57.91
Guide for Loading Mineral Oil-Immersed Overhead Type Distribution Transformer with 55℃ or 65℃ Average Winding Rise.
ANSI C57.92 BS CP 1010
E.
Guide for Loading Oil-Immersed Distribution and Power Transformers. Guide to Loading of Oil-Immersed Transformers to BS 171.
Connection No connection that is not shown on the nameplate should be made. The transformer should be disconnected from the line when no voltage tap changer position is changed. Never put the no voltage tap changer at the position other than specified, because such operation may cause serious damage such as disconnection or short circuit of the winding. The neutral point of the grade insulation winding designed for solidly grounded system should be solidly grounded. Notify the manufacturer if the transformer should be used without grounding the neutral point.
F.
Parallel Operation Reference should be had to the following clauses when two or more transformers are operated in parallel. (1) Parallel Operation of single phase Transformers The following conditions should be satisfied when single phase transformers are operated in parallel. (a) Transformation ratios of the transformers are same. (b) Polarities of the transformers are same. (c) Percent impedances of the transformers are same. Note. When the polarity of one transformer is additive and that of the other is subtractive, the transformers can be operated in parallel by reversing the connection of primary or second side of wither
10
transformer. In such case check that the dielectric strength is satisfactory when the reversed winding has a graded insulation. Transformers of unequal percent impedances can be operated in parallel, but the capacities of the transformers are not utilized to a full extent because the load allotment is not proportional to their ratings. The total capacity of two paralleled transformers that have unequal percent impedances is given by the formula below.
Where Pa: capacity of the transformer of larger percent impedance. Xa: percent impedance of the transformer of larger percent impedance. Pb: capacity of the transformer of smaller percent impedance. Xb: percent impedance of the transformer of smaller percent impedance. Strictly, it is necessary that both percent resistances and percent reactances of paralleled transformers are same for complete parallel operation, but generally percent resistance need not be considered with Power transformer because it is much smaller than percent reactance. Therefore, satisfactory parallel operation is obtained when the percent impedances are same. (2) Parallel Operation of Three Phase Transformers The following conditions should be satisfied when three phase transformers are operated in parallel. (a) Transformation ratios of the transformers are same. (b) Phase displacements between primary and secondary windings of the transformers are same. Note. The transformers of Group A and B listed below can be operated in parallel by changing the connection as shown below, though these two groups have different phase displacement.
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Star-Delta or Delta-Starr
Star-Star or Delta-Delta
Connection
Connection
Group A
Group B
Connection for Parallel Operation
HV
Group A
Group B
LV
R
S
T
R
S
T
I
II
III
i
ii
iii
III
II
I
iii
ii
i
or II
I
III
ii
i
iii
or I
III
II
i
iii
ii
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(3) Parallel Operation of Three winding Transformers The three winding transformers can be operated with three windings in parallel when the following conditions are satisfied. (a) Ratios of capacities of three windings of the transformers are same. (b) Transformation ratios of the transformers are same. (c) Phase displacements (three phase transformers) or polarities (single phase transformers) of the transformers are same. (d) Percent impedances between primary and secondary, primary and tertiary and secondary and tertiary of the transformers are same respectively. Note. The transformers can be operated in parallel even when the conditions (a) and (b) are not satisfied. Note that the capacities of the transformers are not utilized to a full extent in such cases. When two windings of three winding transformers are operated in parallel with the remaining windings loaded separately, it should be noted that the load allotment may not be proportional to their capacities even when characteristics of two paralleled windings satisfy the parallel operation conditions, due to unequal loadings on the remaining windings.
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