The most complete basic knowledge of power distribution transformer in history!
Writer： Hengfeng you electric Time：2023-04-18 views：times
The most complete basic knowledge of power distribution transformer in history!
Source: hengfengyou electric Author: Martin time: July 26, 2021
1、 Classification and model of power transformer
1. Classification by use
(1) Step up transformer: used for power transmission from power plant.
(2) Step down transformer: the substation of the power supply bureau is used for voltage conversion.
(3) Distribution transformer: used to supply power to users.
(4) Auxiliary transformer: provide internal power for the power plant.
(5) Station transformer: provide internal power for the substation.
(6) Converter transformer: for DC transmission, one side is connected with AC and one side is connected with converter valve.
(7) Rectifier transformer: a transformer that converts the grid power supply into the power supply required by rectifier equipment
(8) Electric furnace transformer is a professional transformer planned according to the working principle, load characteristics and operation characteristics of various electric furnaces, including steelmaking electric arc furnace transformer, ladle refining furnace transformer, electroslag furnace transformer, submerged arc furnace transformer, power frequency furnace transformer and other communication electric furnace transformers, medium frequency induction furnace transformer, silicon carbide Transformer for DC electric furnace such as graphitization furnace transformer
2. Classification by winding
(1) Double winding transformer: used for step-up transformer, step-down transformer, auxiliary transformer, etc.
(2) Three winding transformer: used for step-down transformer, tie transformer, etc.
(3) Self coupling transformer: used for step-down transformer, tie transformer, etc.
(4) Split transformer: there are axial split and radial split, which are used for auxiliary transformer and start-up standby transformer.
3. Classification by structure
(1) Single phase transformer: used for 110 ~ 1000V transformer.
(2) Three phase transformer: used for 6 ~ 500kV transformer.
(3) Combined transformer: the transformer is divided into several parts and combined after arriving at the site, which is used in areas with inconvenient transportation.
4. Classification by cooling mode
(3) SF6 transformer: currently used for 110kV transformer.
5. Model of power transformer
(1) Meaning of letters in model
D - single phase F - oil immersed air cooling
O - from P - forced oil circulation
S-three-phase or three coil j-oil immersed self cooling
Z - on load voltage regulation L - aluminum coil
*Copper coils and double coils do not need symbols
(2) Examples
Sfpsl-120000 / 110: 110KV, 120mva three-phase three coil forced oil circulation air-cooled aluminum coil transformer
Osfpsz-240000 / 330: 330kV, 240MVA three-phase three coil on load pressure regulating forced oil circulation air-cooled self coupling voltage transformation
2、 Coil of power transformer
Coil is the most important and complex part of power transformer. It is composed of copper (or aluminum) conductor wound and special insulating parts.
1. Spiral coil
The main feature of spiral coil is that there are many parallel wires, the wire cake is wound into a spiral, and one wire cake is a coil with one turn. Spiral coil has good mechanical stability, good heat dissipation and processability. It is widely used in low voltage and high current coils of transformers.
The spiral coil can be wound into three structures: single helix, double helix and four helix according to the current.
2. Continuous coil
When the coil is composed of several axially distributed segments that do not need to be welded to each other, it is called continuous coil.
The end support surface of the continuous coil is large, bears large axial force, has strong short-circuit resistance, and has large heat dissipation capacity on each section. This kind of coil is widely used in both voltage level and capacity range.
3. Tangled coil
The tangled coil is composed of several tangled segments (cakes). Coils with all tangled segments (cakes) are called fully tangled coils, which are widely used in transformers with voltage of 220kV and above. The coil composed of a part of tangled line segment (cake) and a part of continuous line segment is called tangled continuous coil, which is applied to transformers with voltage of 66kV and above.
Because it inserts non adjacent wire turns between adjacent wire turns of the coil, forms staggered tangled segments and forms a tangled coil, so as to increase the longitudinal capacitance of the coil and improve the impulse voltage distribution characteristics at the axial height of the coil along the line, it has been widely used in various high voltage coils.
4. Inner shielded coil
The inner shielding continuous coil improves the impulse voltage distribution by increasing the series capacitance between line segments. The structure is characterized in that the additional capacitance wire turn is directly wound inside the continuous line segment, the end of the capacitance wire turn is wrapped with insulation and suspended in the line segment, and the capacitance wire turn does not carry current and only works under impulse voltage.
The internal shielding continuous coil has two-stage jumper, four stage jumper, eight stage jumper and sectional connection in structure.
3、 Core of power transformer
Iron core is also an important component of power transformer. It is composed of high magnetic conductivity silicon steel sheets stacked, and then clamped with steel clamps or bound with glass ribbon.
1. Silicon steel sheet
The silicon steel sheet for power transformer is 0.3 ~ 0.5mm thick cold gadolinium silicon steel sheet. At present, only Wuhan Iron and steel plant and Shanghai Baosteel can produce this cold gadolinium silicon steel sheet in China. However, the silicon steel sheets for large transformers have to be imported from Japan.
2. Structural form of iron core
(1) Single phase two column iron core is used for various single-phase transformers.
(2) Single phase section column side yoke iron core is used for high-voltage large capacity single-phase transformer.
(3) Single phase two column side yoke iron core is used for high voltage and ultra-high voltage large capacity single-phase transformer.
(4) Three phase three column is an iron core, which is used for various three-phase transformers.
(5) Five column iron core is used for high-capacity three-phase transformer.
4、 Oil tank of oil immersed transformer
1. Cylindrical oil tank is mainly used for various small oil immersed transformers and extra large oil immersed transformers.
2. Bell jar oil tank is widely used in 110 ~ 500kV oil immersed transformer.
3. The fully sealed oil tank is about to be welded. It has only been used in oil immersed transformers of 110kV and above in recent years.
5、 Oil conservator of oil immersed transformer
The oil conservator of the transformer has two functions: one is to provide space for thermal expansion and cold contraction of the transformer oil in the oil tank; The transformer oil is separated from the atmosphere to prevent the transformer oil from aging.
1. The capsule oil conservator uses rubber capsules to separate the transformer oil from the external atmosphere and provide space for thermal expansion and cold contraction of the transformer oil.
2. Diaphragm oil conservator separates transformer oil from the external atmosphere with rubber diaphragm, and provides space for thermal expansion and cold contraction of transformer oil.
3. The corrugated oil conservator uses a metal expander composed of metal corrugated sheets to separate the transformer oil from the external atmosphere and provide space for thermal expansion and cold contraction of the transformer oil. Corrugated oil conservator is divided into internal oil type and external oil type. The internal oil type has good performance but large volume.
6、 Cooling mode of oil immersed transformer
1. Symbol indicating cooling mode
The first letter: O - mineral oil, K - synthetic insulating fluid, L - insulating gas.
The second letter: n - natural convection circulation, F - forced oil circulation, D - forced pilot circulation.
The third letter: a - air, W - water.
The fourth letter: n - natural convection, F - forced circulation (fan, pump).
2. Examples
Onan - natural cooling
ONAF - air cooling
Ofaf - forced oil circulation air cooling
ODAF - forced oil circulation pilot cooling
7、 Transformer bushing
1. Pure porcelain insulated bushing of 40kV and below
The casing has two structures: guide rod type and cable threading type. Guide rod type low voltage bushing for transformer; Cable threading type is used for 10 ~ 20kV high voltage outgoing line.
2. 40kV and below high current bushing
The bushing has two structures: guide rod type and capacitance type. Guide rod type pure porcelain bushing is used for low-voltage winding outgoing line of medium capacity generator transformer; Capacitive bushing is used for low-voltage winding outgoing line of large generator transformer.
3. 66kV and above oil paper capacitive bushing
The inner insulation of the bushing is a capacitor core formed by alternately winding insulating paper and aluminum foil. The capacitor core and the porcelain bushing are filled with insulating oil. The connection between the bushing and the winding has two structures: guide rod type and cable threading 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. Tape capacitive bushing of 66kV and above
The inner insulation of the sleeve is a capacitor core formed by alternately winding adhesive paper and aluminum foil. The capacitor core and the porcelain sleeve are filled with insulating oil, and the porcelain sleeve is not required at the lower part of the sleeve. But the Tan of this casing δ The adhesive paper is easy to crack and produce partial discharge. At present, the production has been stopped.
5. Resin casting capacitive bushing
The main insulation of the sleeve is also a capacitor core formed by alternating winding of insulating paper and aluminum foil, and epoxy resin is poured outside to become a solid insulating sleeve. The casing can be used as oil-gas casing, the upper part is sleeved in the GIS pipeline, and SF6 gas is filled between them; The lower part is immersed in transformer oil.
8、 Voltage regulation mode of power transformer
1. Voltage regulation mode
The voltage regulation mode of transformer includes non excitation voltage regulation and on load voltage regulation. No excitation voltage regulation, also known as no-load voltage regulation, is to regulate the voltage when the transformer stops running without load; On load voltage regulation refers to voltage regulation under the condition of transformer operation and load. The voltage regulating device without excitation voltage regulation is called no-load tap changer; The device of on load voltage regulation is called on load tap changer.
2. On load voltage regulation position
There are three positions of on load voltage regulation of transformer: neutral point voltage regulation, medium voltage line end voltage regulation and high voltage coil line end voltage regulation. The structure and process of neutral point voltage regulation are relatively simple, and there are many applications.
3. On load voltage regulating switch
The voltage regulating switch is also a tap changer. At present, the quality of on load tap changers produced in China is not good enough. Most on load tap changers rely on imports, most of which are imported from MR in Germany and ABB in Sweden.
9、 Transformer oil
1. Composition of transformer oil
Transformer oil is a mineral oil, which is a mixture of many hydrocarbon molecules with different molecular weights. It is mainly alkanes, cycloalkanes and a small amount of aromatic hydrocarbons.
2. Function and brand of transformer oil
Transformer oil for insulating oil of oil immersed transformer. Transformer oil not only has the function of insulation, but also has the function of heat dissipation.
Transformer oil is divided into 25 oil and 45 oil according to its freezing point. The freezing point of No. 25 oil is minus 25 ℃; The freezing point of No. 45 oil is minus 45 ℃.
No. 25 transformer oil belongs to paraffin base oil, and No. 45 transformer oil is naphthenic base 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 body and accessories. The body is also composed of coils, insulating parts, iron cores, tap changers, transformer oil and oil tanks. The accessories of the transformer include oil conservator, cooler, casing, gas relay, pressure relief device, thermometer, etc. The cooler, insulating oil, casing, tap changer, gas relay, pressure relief device and thermometer are purchased from outside. The following is a brief introduction to the manufacturing process of several main components.
1. Coil winding: installation of winding frame - winding coil - wire welding - package insulation - coil shaping - coil test.
2. Core assembly: silicon steel sheet cutting - deburring - stacking core - installing pulling plate and shielding - binding core - core test - installing core clamp.
3. Processing of insulating parts: cutting of insulating parts - deburring - chamfering - moisture-proof treatment.
4. Oil tank and oil conservator processing: steel plate cutting - oil tank and oil conservator welding - rust removal - sand blasting - primer painting - Painting - mechanical strength test.
5. General Assembly: install iron core - install oil tank pipe - set coil - stack iron yoke - install tap changer - weld lead - wrap lead insulation - semi-finished product test - body drying - finishing body - oil tank assembly - accessory assembly - oil injection - sealing test - hot oil circulation - static discharge.
11、 Factory test of power transformer
The delivery test of power transformer produced by hengfengyou Electric is divided into routine (delivery) test, type test and special test. Routine test is a test item to be carried out for each transformer before delivery, which is usually called delivery test; Type test is a test item conducted by sampling 1 ~ 2 transformers in a type of product; Special test is a test item proposed by the user and agreed with the manufacturer.
1. Basic requirements and regulations for high voltage insulation test
The transformer winding is inspected according to the maximum operating voltage um and the corresponding insulation level. The following table is the insulation test items specified in the national standard gb1094.3-2003 power transformers Part III: insulation level, insulation test and external insulation air gap.
2. Routine (delivery) test items
(1) Winding DC resistance measurement: measurement on all tap leads.
(2) Transformation ratio measurement: measure at all tapping positions.
(3) Wiring group detection: test at the rated tapping position.
(4) Insulation resistance, absorption ratio and polarization index measurement: polarization index measurement shall be carried out for 220kV and above transformers.
(5) Winding Tan δ And capacitance test: Tan shall be conducted for 35kV and above transformers δ Measurement
(6) Casing Tan δ And capacitance test: Tan shall be conducted for 66kV and above capacitive bushings δ And capacitance test
(7) Test of transformer oil: oil analysis, insulation strength, Tan δ、 For chromatographic analysis and other projects, 750kV and above transformers shall also be tested for particle size in oil. Moreover, the oil analysis and oil chromatographic analysis should be repeated in the whole test process.
(8) No load loss and no-load current measurement: the test shall be carried out under the rated voltage wiring.
(9) Load loss and short-circuit impedance measurement: the test shall be carried out under the rated voltage wiring.
(10) Partial discharge test: the discharge amount is not used as an assessment, but only as a reference for whether the high voltage test can be carried out.
(11) Lightning full wave impulse test: 220kV and above, 120mva and above transformers
(12) Operation impulse test: 330kV and above transformers.
(13) Induced voltage withstand test with partial discharge measurement: 110kV and above transformers.
(14) External power frequency withstand voltage test of low voltage winding and neutral point.
(15) Partial discharge test: this test is an assessment test as factory test value.
(16) Live measurement of oil flow: 330kV and above transformers with oil pumps.
(17) Partial discharge test of rotating oil pump: 330kV and above transformers with oil pump.
3. Type test items
(1) Temperature rise test.
(2) Lightning cut-off test.
(3) Lightning full wave impulse test of neutral point.
(4) Radio interference test
4. Special test items
(1) Sound level measurement.
(2) Zero sequence impedance measurement of three-phase transformer.
(3) Harmonic measurement of no-load current.
(4) Measurement of power absorbed by fan motor and oil pump motor.
(5) Measurement of transient voltage transmission characteristics.
(6) Short circuit withstand capacity test.
