1 Overview

Transformer is an electrical device that uses electromagnetic induction to exchange AC voltage or current between two or more windings at the same frequency.

The electric energy generated from the power plant has to be transmitted to remote users through a long transmission line. In order to reduce the power loss on the transmission line, high-voltage or ultra-high-voltage transmission must be used. At present, the voltage generated by the general power plant is limited by the insulation level, and the voltage cannot be too high. This requires a transformer to increase the voltage generated by the power plant to the power grid. Such transformers are collectively referred to as step-up transformers. For each user, the voltage required by various electrical equipment is not too high, and a transformer must be used to convert the high voltage of the power system into a rated voltage that meets the requirements of the user's various electrical equipment. The transformers used for this purpose are collectively referred to as step-down transformers.

It can be seen from the above that the power transformer is the main electrical equipment used to change the voltage in the power system.

From the perspective of the power system, a power grid connects many power plants and users together, and is divided into a main system and several sub-systems. The voltage of each sub-system is not necessarily the same, and the main system must have a uniform voltage level, which also requires transformers of various specifications and capacities to connect the various systems. Therefore, the power transformer is an indispensable electrical equipment in the power system.

2. Classification of transformers

Transformers have different usage conditions, installation environments, different voltage levels and capacity levels, and different structural forms and cooling methods, so they should be classified according to different principles.

3. Operation principle

Simply put, the basic principle of a transformer is: the principle of electromagnetic induction, that is, "electricity generates magnetism, and magnetism generates electricity."

Take one of the three phases of the transformer as an example: it consists of two windings and an iron core. When an AC voltage U1 is applied on the primary side, and the current flowing is I1, an alternating magnetic flux Φ will be generated in the core, so that the two windings are electromagnetically connected. According to the principle of electromagnetic induction, the alternating magnetic flux passes through this The two windings will induce electromotive force E1.E2. When the secondary side is connected to the load, under the action of the electromotive force E2, a secondary current I2 will pass, and the magnetomotive force F2 generated by the current will also act on the same iron core. , Plays the role of reverse demagnetization. But because the main magnetic flux Φm is fixed at the power supply voltage U1, and U1 is basically unchanged, so the main magnetic flux Φm is also basically the same. Therefore, the primary winding current I1 will automatically increase a component to produce Magnetomotive force F1 to offset the magnetomotive force F2 generated by the secondary winding current I2.

4. Structure

1. an iron core

Ordinary transformers are laminated with silicon steel sheets, and the iron core of the wound core transformer is made of silicon steel strips. It has two functions: one is to form a power frequency alternating magnetic flux Φ under the action of the alternating current of the primary coil; the other is to induce the electromotive force in the secondary coil through the alternating magnetic flux in the iron core to form a low-voltage power supply. The iron core is the main body that completes the conversion of electrical energy-magnetic energy-electrical energy.

2. Winding (commonly known as coil)

Generally, insulated rectangular copper wire or round copper wire is wound on the winding die. Contains two sets of primary and secondary (high pressure and low pressure). The primary coil introduces one part of the primary side electric energy into the transformer to complete the excitation process, and the other part fills the electric energy in the secondary coil. The secondary coil converts magnetic energy into electric energy and transmits it. The coil is usually connected according to a certain electrical circuit connection method (D angle connection or Y star connection).

3. Body insulation

Including primary and secondary insulation, turn-to-turn insulation and insulation with iron core, and insulation between shells. The materials used are: cardboard, epoxy resin, various insulating materials, transformer oil, electrical wood, etc. Among them, transformer oil not only has a good insulation effect, but also helps the transformer to dissipate heat, and is used to cool the running iron core and coil. Our company’s products use national standard 25# (freezing point -25℃)

4. Fuel tank and base

The oil tank is equipped with transformer oil for insulation and cooling, which is made of steel plate, which requires high mechanical strength, small deformation, and no leakage at the weld.

5. Appendix

1) Casing and lead
1. The connecting part of the secondary winding and the external circuit. It can not only fix the lead, but also insulate the lead to the ground.

2) Tap switch
A device that connects and cuts off transformer winding taps to achieve voltage regulation. There are no-load tap-changers and on-load tap-changers. Our company's products use
No-load tap changer, the no-load tap changer must adjust the voltage after cutting off the transformer power supply.

3) Pressure relief valve:
When the internal pressure of the transformer reaches a certain value, the pressure release valve will act to eliminate the overpressure in the tank. After the internal pressure is released, the release valve automatically closes.

4) Gas relay
Gas relay is an important protection component for transformers. When a fault occurs in the transformer, gas is generated in the oil or the oil is flowing, the gas relay will act to send a signal or cut off the power supply to protect the transformer. In addition, after a fault, you can observe the gas color through the window of the gas relay and take the gas. Analyze to make a judgment on the nature of the fault.

5. Model meaning

S 9（11）-M.（R）-10~2000/10
Voltage level
Rated Capacity
Rolled iron core
Sealed type
Performance level code
Three-phase

6. Main technical parameters
 

The main technical data of the transformer is generally marked on the nameplate of the transformer under the specified operating environment and operating conditions. It mainly includes: rated capacity, rated voltage and its tapping, rated frequency, winding connection group and rated performance data (impedance voltage, no-load current, no-load loss and load loss) and total weight.

1. Rated capacity (kVA): rated voltage. The capacity that can be delivered during continuous operation at rated current.

2. Rated voltage (kV): The working voltage that the transformer can withstand when it is running for a long time. In order to adapt to the needs of grid voltage changes, the high-voltage side of the transformer has taps, and the low-voltage side output voltage is adjusted by adjusting the number of turns of the high-voltage winding.

3.Rated current (A): The current that the transformer is allowed to pass for a long time under the rated capacity.

4. No-load loss (kW): The active power drawn when the rated voltage of the rated frequency is applied to the terminal of one winding and the other windings are open. It is related to the performance and manufacturing process of the core silicon steel sheet, and the applied voltage.

5. No-load current (%): When the transformer is no-load on the secondary side under the rated voltage, the current passing through the primary winding. Generally expressed as a percentage of the rated current.

6. Load loss (kW): Short-circuit the secondary winding of the transformer, and apply the rated current at the rated tapping position of the primary winding. The power consumed by the transformer at this time.

7. Impedance voltage (%): Short-circuit the secondary winding of the transformer, and slowly increase the voltage in the primary winding. When the short-circuit current of the secondary winding is equal to the rated value, the voltage applied on the primary side at this time. Generally rated voltage Is expressed as a percentage.

8. Phase number and frequency: the beginning of three-phase is indicated by S, and the beginning of single-phase is indicated by D. The Chinese national standard frequency f is 50 Hz. There are 60Hz countries abroad (such as the United States).

9. Temperature rise and cooling: The difference between the temperature of the transformer winding or the upper oil temperature and the surrounding environment of the transformer is called the temperature rise of the winding or upper oil surface. The temperature rise limit of the oil-immersed transformer winding is 65K, and the oil surface temperature rise is 55K. There are also many cooling methods: oil-immersed natural cooling, forced air cooling, water cooling, tube type, chip type, etc.

10. Insulation level: there is an insulation level standard. An example of how to indicate the insulation level is as follows: the high-voltage rated voltage is 35kV, and the low-voltage rated voltage of the transformer is 10kV. The insulation level of the transformer is expressed as LI200AC85/LI75AC35, where LI200 means that the transformer's high-voltage lightning impulse withstand voltage is 200kV, and the power frequency withstand voltage It is 85kV, the low-voltage lightning impulse withstand voltage is 75kV, and the power frequency withstand voltage is 35kV. The current oil-immersed transformer products of Aux High-Tech Co., Ltd. have an insulation level of LI75AC35, which means that the transformer’s high-voltage lightning impulse withstand voltage is 75kV, power frequency The withstand voltage is 35kV, because the low voltage is 400V, so it can be ignored.

11. Connection group label: According to the phase relationship of the primary and secondary windings of the transformer, the transformer windings are connected into various combinations, which are called winding connection groups. In order to distinguish between different connection groups, clock notation is often used, that is, the phasor of the high-voltage side line voltage is used as the long needle of the clock and fixed to 12, and the phasor of the low-voltage side line voltage is used as the short needle of the clock. A number is used as the label of the connection group. For example, Dyn11 means that the primary winding is (triangular) connection, and the secondary winding is (star) connection with a center point, and the group number is (11) point.

1. Star connection (Y-connection): One end of each phase winding of a three-phase transformer or one end of three windings of the same rated voltage of a single-phase transformer forming a three-phase group is connected to a common point (neutral point), And the other end is connected to the corresponding line terminal.

2. Delta connection (D-connection): Three phase windings of a three-phase transformer or three windings of the same rated voltage of a single-phase transformer forming a three-phase group are connected in series to form a closed circuit.
K. Physical indicators: weight, volume (L,, W, H)

7. S11-MR transformer performance characteristics

1. Good energy-saving characteristics. (The iron core is designed as a rolled iron core structure with a circular cross-section, no joints, fully enclosed magnetic circuit, and a natural tightening state. No clamps are required for tightening, which avoids the deterioration and loss of iron core performance caused by iron core clamping. Increase. After the iron core is annealed, its magnetic permeability can be restored to the original level before machining. The no-load loss is reduced by 30~40% compared with the S9 series, and the no-load current is reduced by 70~80% compared with the S9 series.)

2. Low noise. (The wound core itself is a seamless whole, and the structure is compact, the noise level during operation is reduced to 30 ~ 45dB, which is much better than the national standard (44 ~ 57dB), which protects the environment.)

3. The fuel tank adopts a fully sealed corrugated sheet structure, and the transformer oil is well isolated from the air, which reduces the oxidation rate of the oil, prolongs the service life and maintenance period, and reduces the operating cost.

4. The high and low voltage sides adopt barrel-type skeletons to enhance the mechanical strength of the coils, and cooperate with the wound core structure to significantly enhance the short-circuit resistance of the transformer. Among them, the foil winding process is adopted for transformers above 500KVA.

5. The low-voltage winding adopts paper-covered flat wire and the interlayer adopts the technique of dot gluing paper to increase the capacitance between the layers, thereby increasing the lightning resistance of the transformer.

6. The vacuum oil injection process is adopted to completely remove the water molecules in the oil to ensure the maintenance-free operation of the transformer.

7. Strengthen the insulation between the end and the tail to improve the ability of the transformer to withstand high-voltage shocks.

8. The coil and the iron core cannot be separated from each other, and the use of agricultural electricity has a certain degree of anti-theft.

二 production process

1. Core manufacturing process

1
Silicon steel sheet coil

Slitting

Silicon steel sheet curve cutting

Core winding

Core annealing

Core cooling

Iron core paint

Core measurement

Qualified product transfer

) Rolled iron core

2
Silicon steel sheet coil

Slitting

Strip inspection

Iron core horizontal shear

Piece inspection

Core stack inspection

Core inspection

Core measurement

Qualified product transfer

) Stacked core

1. All silicon steel sheets for transformer core use imported 27RGH110, 27ZH110 high permeability and low loss grain-oriented cold-rolled silicon steel sheets. The transverse shearing of the laminated transformer silicon steel sheet is carried out on the silicon steel sheet cutting production line imported by Georg Company, Germany, and the burr is less than 0.02mm. The core stacking factor is high, and the eddy current loss is small.

2. The core of the wound core transformer is a three-phase three-column inner and outer frame rolling structure, with a high degree of mechanization, a large lamination coefficient, and a core cross-section close to a circle (the width of the core silicon steel sheet is stepless structure). The filling factor is high; at the same time, the magnetic flux is completely along the lattice arrangement direction of the cold-rolled silicon steel sheet, which greatly reduces the no-load loss and no-load current; the iron core must be annealed after being wound into shape. The iron core is continuously wound with seamless gaps, which reduces the additional process coefficient of no-load loss, thereby reducing the no-load loss and no-consumption current, and greatly reducing the noise of the iron core.

3. The clamping of the iron core adopts a frame structure composed of slot plate clamps, pull plates and beams, which has good mechanical strength. Through the action of laminated wood and clamps, the iron core is subjected to a uniform and reasonable clamping force, so that the right iron core is formed as a whole, which has strong mechanical strength, and does not increase the loss of the iron core due to too much force. noise.

4. Due to the above measures, the no-load loss of the low-loss coiled core transformer produced by our company is at least 30% lower than the national standard, the no-load current is reduced by 70%, and the noise is greatly reduced.

2. Coil manufacturing process

Stacked core coil
roll
Insulator

Mould tool

Electromagnetic wire

Coil winding

Plastic surgery

Inspection

Qualified product transfer

Rolled iron core installation

Gear installation

Paper tube installation

test

Iron core coil
Insulator

Mould tool

Electromagnetic wire

Low voltage coil winding

High-voltage insulation cylinder installation

High-voltage coil winding

Coil handling

Qualified product transfer

1. The magnet wire used for the coil is made of oxygen-free copper with low resistivity. Control reasonable selection of current density to reduce load loss. The load loss of the low-loss transformer is reduced by more than 10% compared with the national standard.

2. For distribution transformer products with a low-voltage voltage of 0.4kV and a capacity of 500kVA and above, use foil-type or new-type spiral low-voltage coils to improve short-circuit resistance. The high-voltage coils of oil-immersed transformers are multi-layer cylindrical, while the high-voltage coils of dry-type transformers are continuous or tangled continuous.

3. The coil ampere turns are balanced, the insulation is reliable, and the heat dissipation is reasonable to meet the requirements of transformer insulation, temperature rise and short-circuit resistance.

4. Oil-immersed transformer turn-insulated enameled magnet wire adopts QQ-2 type high-strength acetal enameled wire, and oil-immersed paper-covered wire adopts ZB-0.45 or ZB-0.6 type

5. In the coil winding and pre-compression, the ampere-turn balance is achieved. In addition to ensuring the equal height of the inner and outer coils, the ampere-turn sections of the inner and outer coils must be equal, thereby improving the ability of the coil to withstand short circuits.

3. Body structure and general assembly

1. Manufacturing of insulating parts
All insulating parts requiring mechanical strength, such as insulating end rings, spacers, stays, etc., are hot-pressed to ensure the mechanical strength of the insulating parts and reduce the shrinkage rate of the insulating parts.

2. The high-voltage coil of the wound core transformer is directly wound on the low-voltage coil to make the coil as a whole and improve the mechanical strength and short-circuit resistance.

3. The upper part of the machine adopts a special positioning device to ensure the stability of the transformer during transportation. All fasteners are fastened with anti-loosening bolts, and the lead wire adopts the company's unique fixed structure.

4. The transformer body adopts more advanced transformer vacuum drying treatment, so that the transformer can be completely dried. The transformer adopts full vacuum oil injection, which greatly improves the insulation strength of the transformer.

5. The treatment of transformer oil is carried out in vacuum purification oil treatment equipment. The voltage strength of the purified transformer oil is more than 40kV, the moisture content is below 20PPM, and the dielectric loss is far less than 0.5% (national standard).

6. Before the transformer leaves the factory, pre-hoist the core and fasten all fasteners to ensure that the core can be free of hoisting on site.

The factory not only has advanced and complete process equipment, but also in accordance with the requirements of the ISO9001-2000 version of the standard, set up control points for key processes and special processes that directly affect product quality, and strictly process discipline to ensure that the entire production process is always under control.

4
Wire loop

Appendix

Lead

Insulator

Iron core

fastener

Body assembly

Inspection

Tap switch and switch operating mechanism

Transformer assembly process
Fuel tank

Factory inspection

Fuel tank assembly

Finished product test

Qualified products in storage

5. List of main parts and materials of oil transformer