Power transformer basic knowledge (entry consolidation must see)
1. Classification by use
(1) Booster transformer: power plant to transmit electricity.
(2) step-down transformer: the substation of the power supply bureau is used as a voltage conversion.
(3) Distribution transformer: power supply to users. (4) Plant transformer: to provide internal electricity for the power plant.
(5) Station transformer: to provide internal electricity for the substation.
(6) Converter transformer: DC transmission, one side is connected to AC, one side is connected to the converter valve.
(7) Rectifier transformer: thermal power plant for electric dust supply.
2. Classification by winding
(1) Double-winding transformer: used for boost voltage change, buck voltage change, factory change, etc.
(2) Three-winding transformer: used for step-down transformer, liaison transformer, etc.
(3) Autotransformer: used for buck change, contact change, etc.
(4) Split transformer: there are two kinds of axial split and radial split, which are used for factory changes and start-up changes.
3. Classification by structure
(1) Single-phase transformer: used for 330~1000kV transformer.
(2) Three-phase transformer: for 10~500 kV transformer.
(3) Combined transformer: the transformer is divided into several parts, and then combined after the scene of the transformer, used in inconvenient areas.
4. Classification by cooling method
(1) Oil-immersed transformer: for 10~1000kV transformer.
(2) Dry transformer: for 10~110 kV transformer.
(3) SF6 transformer: Currently used for 110 kV transformer.
5, the model of power transformer
(1) The meaning of the letters in the model
D - Single phase F - oil immersed air cooling
O - self-P - forced oil circulation
S - three phase or three coil J - oil immersed self cooling
Z - Pressure regulation on load L - Aluminum coil
* Copper coils and double coils do not need to be marked
(2) Examples
SFPSL - 120,000/110:110kV, 120MVA three-phase three-coil forced oil circulation air-cooled aluminum coil transformer
OSFPSZ - 240000/330:330 kV, 240MVA three-phase three-coil pressure regulation forced oil circulation air-cooled autotransformer
Second, the power transformer coil
The coil is the most important and complex component of a power transformer, which is wound with copper (or aluminum) wire and composed of specialized insulating parts.
1, spiral coil
The main feature of the spiral coil is that the number of parallel wires is more, the wire cake is wound into a spiral, and a coil of the wire cake is a turn. Spiral coil has good mechanical stability, good heat dissipation and good technology, and is widely used in transformer low voltage and high current coil.
According to the size of the current, the spiral coil can be wound into a single helix, double helix and four helix three structures. 2, continuous coil
When the coil is composed of a number of axial distribution, and by each other do not need to weld the line segment of the coil, called continuous coil.
The end of the continuous coil has large supporting surface, large axial force, strong short-circuit resistance, and large heat dissipation capacity on each line segment. This coil is widely used in both voltage level and capacity range.
3, tangled coil
The entangled coil is composed of several entangled segments (cakes). The coils that are all entangled segments (cakes) are called fully entangled coils, which are widely used in transformers of 220kV and above voltage. A coil composed of a part of the tangled line segment (pie) and a part of the continuous line segment is called the tangled continuous coil, which is used in transformers with a voltage of 66 kV and above.
Because it inserts non-adjacent turns between the adjacent turns of the coil, forms a staggered entangled line segment and forms a entangled coil, thereby increasing the longitudinal capacitance of the coil and improving the impulse voltage distribution characteristics along the axial height of the coil, so it has been widely used in various high-voltage coils.
4. Inner shielded coil
The internally shielded continuous coil is designed to improve the impulse voltage distribution by increasing the series capacitance between line segments. The structure features that the additional capacitor turns are directly wound inside the continuous line segment, and the end of the capacitor turns is wrapped in insulation and suspended in the line segment. The capacitor turns do not carry current and only work under the impulse voltage.
The continuous coil with internal shielding has two segments, four segments, eight segments and segment connections in structure.
Third, the core of the power transformer
The core is also an important component of the power transformer, which is composed of highly magnetic silicon steel sheets stacked and then clamped with steel clips or tied with glass ribbons.
1. Silicon steel sheet
The silicon steel sheet used for power transformers is 0.3~0.5mm thick cold gadolinium silicon steel sheet, at present, only Wuhan Iron and Steel Works and Shanghai Baosteel can produce this kind of cold gadolinium silicon steel sheet. However, silicon steel sheets for large transformers are also imported from Japan.
2, the structure of the iron core
(1) Single-phase two-column core for various single-phase transformers.
(2) single-phase section column side yoke type core, used for high-voltage large-capacity single-phase transformer.
(3) Single-phase two-column side-yoke core for high-voltage and ultra-high-voltage large-capacity single-phase transformers.
(4) three-phase three-column is an iron core used for various three-phase transformers.
(5) Five-column core for large-capacity three-phase transformers.
Four, oil immersed transformer oil tank
1, cylindrical tank, mainly used for a variety of small oil-immersed transformers and large oil-immersed transformers.
2, bell tank, widely used in 110~500kV oil-immersed transformer.
3, the fully sealed tank, that is, the tank is welded to death, and it has been used for oil-immersed transformers of 110kV and above in recent years.
5. Oil storage tank of oil-immersed transformer
The oil storage tank of the transformer has two functions, one is to provide space for the thermal expansion and cold contraction of the transformer oil in the tank; The other is to separate the transformer oil from the external atmosphere to prevent the aging of the transformer oil.
1, capsule type oil storage tank, which uses rubber capsules to separate the transformer oil from the external atmosphere, and provides the transformer oil with space for thermal expansion and contraction.
2, diaphragm type oil storage tank, with a rubber diaphragm to separate the transformer oil from the external atmosphere, and to provide the transformer oil thermal expansion and contraction space.
3. The corrugated oil storage tank is separated from the external atmosphere by a metal expander composed of metal corrugated sheets, and provides space for thermal expansion and contraction of the transformer oil. The corrugated oil storage tank is divided into internal oil type and external oil type, the internal oil type has better performance, but the volume is larger. Six, oil-immersed transformer cooling mode
1. Symbol for cooling method
First letter: O - mineral oil, K - synthetic insulating liquid, L - insulating gas.
Second letter: N - natural convective circulation, F - forced oil circulation, D - forced guided circulation.
Third letter: A - air, W - water.
Fourth letter: N - natural convection, F - forced circulation (fan, pump).
2. Examples
ONAN - Naturally cooled
ONAF - Wind cooling
OFAF - forced oil circulation air cooling
ODAF - Forced oil circulation guided cooling
Seven, transformer bushing
1, 40kV and below pure porcelain insulation sleeve
This kind of casing has two kinds of structure: guide rod type and cable type. Guide rod type for transformer low voltage bushing; Cable type for 10~20kV high voltage outlet.
2, 40kV and below large current bushing
This kind of bushing has two kinds of structure: guide rod type and capacitance type. Guide rod type pure porcelain bushing is used for low voltage winding of medium capacity generator transformer. Capacitive bushing is used for low voltage winding of large generator transformer. 3, 66kV and above oil-paper capacitive bushing
The inner insulation of the sleeve is a capacitor core which is alternately wound by insulating paper and aluminum foil. The capacitor core and the porcelain sleeve are filled with insulating oil. The connection between the sleeve and the winding has two structures: guide rod type and cable type. The oil paper capacitor core is alternately wound on the conductive tube by 0.08-0.12mm thick cable paper and 0.01mm thick aluminum foil. 4, 66 kV and above adhesive paper capacitive sleeve The inner insulation of this sleeve is made of adhesive paper and aluminum foil alternately wound capacitor core, capacitor core and porcelain sleeve filled with insulation oil, the lower part of the sleeve does not need porcelain sleeve. However, the tanδ of this sleeve is large, and the adhesive paper is prone to crack and generate partial discharge, and the production has been stopped.
5, resin pouring capacitive sleeve
The main insulation of this kind of sleeve is also a capacitor core made of insulating paper and aluminum foil alternately wound, and the epoxy resin is poured outside to become a solid insulating sleeve. This kind of casing can be used as oil-gas casing, the upper part of the GIS pipe, filled with SF6 gas between; Lower part immersed in transformer oil.
Viii. Voltage regulation mode of power transformer
1. Pressure regulation method
Transformer voltage regulation mode with or without excitation voltage regulation and load voltage regulation two kinds. No excitation voltage regulation, also known as no-load voltage regulation, is to adjust the voltage when the transformer stops running and is not loaded. On-load voltage regulation is the operation of transformer in the state of load regulation. The voltage regulating device without excitation is called no-load tap changer; The device of on-load voltage regulation is called on-load tap-changer.
2. Load regulating position
There are three kinds of voltage regulation in the position of transformer on load: neutral point voltage regulation, medium voltage line end voltage regulation and high voltage coil line end voltage regulation. The structure and process of neutral voltage regulation are relatively simple, and the application is more.
3, load regulator switch
The voltage regulator is also a tap changer. At present, the quality of on-load tap-changer produced in China is not good enough, and most of the on-load tap-changer depends on imports, of which more are imported from German MR And Swedish ABB.
Nine, transformer oil
1. Composition of transformer oil
Transformer oil is a mineral oil, which is a mixture of many different molecular weights of hydrocarbon molecules, alkane, cycloalkane and a small number of aromatic hydrocarbons.
2. The role and grade of transformer oil
Transformer oil for insulation oil of oil-immersed transformers. Transformer oil not only has insulation effect, but also has the role of heat dissipation.
Transformer oil is divided into No. 25 oil and No. 45 oil according to its freezing point. The freezing point of No.25 oil is minus 25℃; The freezing point of oil 45 is minus 45℃.
No. 25 transformer oil is paraffin based oil, and No. 45 transformer oil is naphthenic oil. In the past, No. 45 transformer oil was imported from abroad, and now Xinjiang Karamay Refinery can also produce it.
10. Manufacturing process of power transformer
The power transformer consists of two parts: the body and the accessories. The body is composed of coil, insulation, core, tap-changer, transformer oil and oil tank. The accessories of the transformer include oil storage tank, cooler, bushing, gas relay, pressure release device and thermometer. The coolers, insulating oils, bushings, tap switches, gas relays, pressure relievers and thermometers are all purchased from outside. The following is only a brief introduction to the manufacturing process of several main components.
1, coil winding: installation of wire skeleton - coil winding - wire welding - insulation - coil shaping - coil testing.
2, core assembly: silicon steel sheet cutting - deburring - stacked core - installation of pull plate and shield - binding core - core test - installation of core clips.
3, insulation processing: insulation cutting - deburring - corner - moisture-proof treatment.
4, oil tank and oil storage tank processing: steel plate cutting - oil tank and oil storage tank welding - rust removal - sand blasting - priming - painting - mechanical strength test.
5, total assembly: install the core - install the oil tank pipe - set of coils - stack the iron yoke - install the tap changer - welded lead - cover lead insulation - semi-finished product test - body drying - organizer body - oil tank assembly - accessories assembly - oil injection - sealing test - hot oil cycle - static release. 11. Factory test of power transformer
The factory test of power transformer is divided into three types: routine (factory) test, type test and special test. Routine test is a test item for each transformer factory, usually known as factory test; Type test is a test project carried out by sampling 1~2 transformers in a type of product; Special test is a test project proposed by the user and agreed with the manufacturer.
1, the basic requirements and regulations of high voltage insulation test transformer winding is tested according to the highest operating voltage Um and the corresponding insulation level, the following table is the national standard GB10994.3-2003 "Power transformer Part III: insulation level, insulation test and external insulation air gap" stipulated in the insulation test items.
