Three-phase to single-phase transformer with midpoint symmetrical output

Abstract

This invention belongs to the field of power transformer technology, specifically relating to a three-phase to single-phase transformer with symmetrical output at a neutral point. The transformer includes a main transformer winding unit with a Scott connection structure, comprising an M-transformer winding and a T-transformer winding. The secondary output winding unit includes two sets of identical output windings, each containing a secondary winding with the same number of turns coupled to the M-transformer and T-transformer and orthogonal in phase. The two sets of output windings are connected in series in the same direction to form a common neutral point. This invention can achieve symmetrical positive and negative voltage output with a neutral point, solving the problem that existing Scott transformers cannot meet the positive and negative voltage output requirements, while ensuring the balance of the three-phase power grid.

Description

Technical Field

[0001] This invention belongs to the field of power transformer technology, specifically relating to a three-phase to single-phase transformer with symmetrical output at the midpoint. Background Technology

[0002] In the power distribution field, there is a common demand for converting three-phase AC to single-phase AC in scenarios such as industrial special loads and power electronic conversion devices. Scott-connected transformers have become the mainstream equipment for three-phase to single-phase conversion because they can achieve load balancing on the three-phase grid side. However, their secondary windings only have two sets of windings with a 90-degree phase difference, which cannot create a symmetrical positive and negative output voltage with a common neutral point, making it difficult to meet the power supply requirements of special loads and power electronic conversion devices for symmetrical positive and negative voltage. While conventional V-connected three-phase to single-phase transformers have a simple structure, they can cause severe imbalance in the three-phase grid, leading to grid voltage distortion, interfering with the stable operation of other electrical equipment on the same grid, and even inducing equipment failure. Currently, the industry lacks a three-phase to single-phase transformer solution that balances the operation of the three-phase grid and provides symmetrical positive and negative voltage output with a neutral point, making it difficult to adapt to the rapidly developing needs of special single-phase power supply scenarios.

[0003] Based on the above problems, there is an urgent need for a three-phase to single-phase transformer technology that can stably output symmetrical positive and negative single-phase voltages with a common neutral point while maintaining the balanced operation of the three-phase power grid, and adapt to the power supply needs of special loads and power electronic conversion equipment. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a three-phase to single-phase transformer with symmetrical output at the midpoint, comprising a main transformer winding unit and a secondary output winding unit. The main transformer winding unit adopts a Scott transformer connection structure and includes an M-type transformer winding and a T-type transformer winding. The secondary output winding unit includes a first output winding group and a second output winding group. The first output winding group and the second output winding group have the same structure. The first output winding group includes a first M-side secondary winding and a first T-side secondary winding. The second output winding group includes a second M-side secondary winding and a second T-side secondary winding. The first M-side secondary winding and the second M-side secondary winding have the same number of turns and are both coupled to the M-type winding. The first T-side secondary winding and the second T-side secondary winding have the same number of turns and are both coupled to the T-type winding. The first M-side secondary winding and the first T-side secondary winding are orthogonal in phase. The second M-side secondary winding and the second T-side secondary winding are orthogonal in phase. The first output winding group and the second output winding group are connected in series in the same direction to form a common midpoint.

[0005] Preferably, the same-name end of the first M-side secondary winding is connected to the non-same-name end of the first T-side secondary winding to form a first combined output terminal, the same-name end of the second M-side secondary winding is connected to the non-same-name end of the second T-side secondary winding to form a second combined output terminal, and the same-name end of the first T-side secondary winding is connected to the non-same-name end of the second T-side secondary winding to form the common midpoint.

[0006] More preferably, a positive output voltage is formed between the first combined output terminal and the common midpoint, and a negative output voltage is formed between the second combined output terminal and the common midpoint. The amplitude of the positive output voltage is the same as the amplitude of the negative output voltage, and the phase difference between the positive output voltage and the negative output voltage is 180 degrees.

[0007] More preferably, the winding directions of the first M-side secondary winding and the second M-side secondary winding on the core assembly are the same, and the winding directions of the first T-side secondary winding and the second T-side secondary winding on the core assembly are the same.

[0008] More preferably, the two ends of the M-type transformer winding are respectively connected to the B-phase input terminal and the C-phase input terminal of the three-phase AC power supply, the first end of the T-type transformer winding is connected to the A-phase input terminal of the three-phase AC power supply, the tail end of the T-type transformer winding is connected to the electrical midpoint of the M-type transformer winding, and the electrical midpoint of the M-type transformer winding is located at the midpoint of the number of turns of the M-type transformer winding.

[0009] More preferably, the output voltage phase difference between the first M-side secondary winding and the first T-side secondary winding is 90 degrees, the output voltage phase difference between the second M-side secondary winding and the second T-side secondary winding is 90 degrees, the phase difference between the combined output voltage of the first output winding group and the combined output voltage of the second output winding group is 180 degrees, and the phase of the combined output voltage is offset by 45 degrees relative to the output voltage phase of the M-type winding.

[0010] More preferably, the transformer includes a three-phase three-column core assembly, which includes three parallel core columns and two yokes connected to the two ends of the three core columns. The M-phase transformer winding is wound on the B-phase core column and the C-phase core column of the three core columns, and the T-phase transformer winding is wound on the A-phase core column of the three core columns.

[0011] More preferably, all secondary windings of the secondary output winding unit are wound with enameled copper flat wire, the wire diameter of all secondary windings of the secondary output winding unit is determined according to the rated output current, and an insulating isolation layer is provided between adjacent secondary windings of the secondary output winding unit, the insulating isolation layer being made of NOMEX insulating paper.

[0012] More preferably, the rated input voltage of the transformer is 10kV three-phase AC, the rated output voltage of the transformer is 0-110V-220V single-phase AC, and the rated operating frequency of the transformer is 50Hz.

[0013] More preferably, the first combined output terminal, the second combined output terminal, and the common midpoint are all connected to terminals, the terminals are made of tin-plated copper, and the rated current carrying capacity of the terminals is not less than the rated output current of the transformer.

[0014] The technical effects include: This invention overcomes the limitation of existing Scott transformers in being unable to output symmetrical positive and negative voltages with a midpoint by connecting two sets of identical output windings in series in the same direction to form a common midpoint. It solves the core problem that existing technologies cannot meet the power supply requirements of symmetrical positive and negative voltages. At the same time, it retains the advantage of Scott transformers in three-phase load balance and will not cause imbalance to the three-phase power grid. The structure is simple, easy to implement, and has outstanding creativity and practicality. Attached Figure Description

[0015] Figure 1 Schematic diagram of the overall winding architecture of a Scott transformer with a common midpoint; Figure 2 Schematic diagram of the basic wiring and phasor relationship of the Scott connection transformer; Figure 3 A schematic diagram of the wiring and phasor synthesis of a Scott transformer with dual secondary symmetrical outputs. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0017] Traditional technical solutions have the following technical problems: the existing Scott transformer secondary winding only has two windings with a 90-degree phase difference, which cannot form a symmetrical positive and negative output voltage with a common midpoint, and cannot meet the load demand for symmetrical positive and negative voltage power supply. Other three-phase to single-phase solutions will cause three-phase grid imbalance and affect the stable operation of the grid.

[0018] Based on this, please refer to Figures 1-3 , Figure 2 As shown, the product input coil consists of two coils, namely M-transformer and T-transformer, and the two secondary windings are ax and by, with a 90-degree phase difference between the secondary windings. Figure 3As shown, the improved winding has the same input, consisting of M and T, but the output consists of four windings with the same windings: a1-x1, a2-x2, b1-y1, and b2-y2. Then, the secondary windings a1-x1 and y1-b1 form a 45-degree voltage, and a2-x2 and y2-b2 form another 45-degree voltage. After being connected in series, they form a new midpoint O. Thus, a1-O-b2 forms a symmetrical voltage with a midpoint, which can realize the positive phase voltage at a1-O and the negative phase voltage at b2-O. This embodiment provides a three-phase to single-phase transformer with symmetrical output at the midpoint, including a main transformer winding unit and a secondary output winding unit. The main transformer winding unit adopts a Scott transformer connection structure and includes an M-type transformer winding and a T-type transformer winding. The secondary output winding unit includes a first output winding group and a second output winding group. The first output winding group and the second output winding group have the same structure. The first output winding group includes a first M-side secondary winding and a first T-side secondary winding. The second output winding... The group includes a second M-side secondary winding and a second T-side secondary winding. The first M-side secondary winding and the second M-side secondary winding have the same number of turns and are both coupled to the M-type winding. The first T-side secondary winding and the second T-side secondary winding have the same number of turns and are both coupled to the T-type winding. The first M-side secondary winding and the first T-side secondary winding are orthogonal in phase. The second M-side secondary winding and the second T-side secondary winding are orthogonal in phase. The first output winding group and the second output winding group are connected in series in the same direction to form a common midpoint.

[0019] This scheme, through the design of two sets of output windings with identical structures, retains the three-phase balance advantages of the Scott transformer and achieves symmetrical positive and negative voltage output with a neutral point by connecting them in series in the same direction to form a common neutral point. This solves the core problem that existing technologies cannot simultaneously satisfy both three-phase balance and symmetrical positive and negative voltage output. The Scott transformer connection structure adopted by the main transformer winding unit is the core foundation for achieving balanced operation of the three-phase power grid. The voltages of the M-transformer winding and the T-transformer winding satisfy a fixed phase orthogonal relationship, and the corresponding phasor formula is: ; In the formula, This is the voltage phasor across the T-turn winding, in volts. This is the voltage phasor across the M-type transformer winding, in volts. The imaginary unit indicates that the phase of the corresponding phasor is 90 degrees ahead; This is the amplitude matching coefficient, dimensionless. The M transformer winding is connected between phases B and C of the three-phase power grid. The voltage phasor of the M transformer winding completely coincides with the line voltage phasor of the three-phase power grid. The first end of the T transformer winding is connected to phase A of the three-phase power grid, and the last end of the T transformer winding is connected to the midpoint of the turns of the M transformer winding, so that the voltage phasor at both ends of the T transformer winding forms a 90-degree phase difference with the voltage phasor at both ends of the M transformer winding. Simultaneously, through... The amplitude matching coefficient ensures that the voltage amplitude across the T transformer winding is exactly equal to the voltage amplitude of a single-phase winding of the M transformer winding, thus ensuring that the three-phase load of the three-phase power grid is completely balanced and that there is no problem of three-phase current imbalance.

[0020] Both the first M-side secondary winding and the second M-side secondary winding are electromagnetically coupled to the M-type winding. The number of turns of the first M-side secondary winding and the second M-side secondary winding are exactly the same, so that the induced voltage amplitude at both ends of the first M-side secondary winding is exactly equal to the induced voltage amplitude at both ends of the second M-side secondary winding. The voltage phasor of the first M-side secondary winding is completely in phase with the voltage phasor of the M-type winding, and the voltage phasor of the second M-side secondary winding is also completely in phase with the voltage phasor of the M-type winding, ensuring that the voltage phasors of the first M-side secondary winding and the second M-side secondary winding are completely in phase and have the same amplitude. Both the first T-side secondary winding and the second T-side secondary winding are electromagnetically coupled to the T-type transformer winding. The number of turns of the first T-side secondary winding and the second T-side secondary winding are exactly the same, so that the induced voltage amplitude at both ends of the first T-side secondary winding is exactly equal to the induced voltage amplitude at both ends of the second T-side secondary winding. The voltage phasor of the first T-side secondary winding is completely in phase with the voltage phasor of the T-type transformer winding, and the voltage phasor of the second T-side secondary winding is also completely in phase with the voltage phasor of the T-type transformer winding, ensuring that the voltage phasors of the first T-side secondary winding and the second T-side secondary winding are completely in phase and have the same amplitude. The voltage phasor of the T-type transformer winding and the voltage phasor of the M-type transformer winding have a 90-degree phase difference. This ensures that the voltage phasors of the first T-side secondary winding and the second T-side secondary winding coupled to the T-type transformer winding, and the voltage phasors of the first M-side secondary winding and the second M-side secondary winding coupled to the M-type transformer winding, form a fixed 90-degree phase difference, providing a fixed phase basis for the subsequent 45-degree phasor synthesis. The first output winding group and the second output winding group have identical structures, ensuring that the electrical parameters of the two winding groups are completely consistent. The first output winding group and the second output winding group are connected in series in the same direction, so that the phase difference of the synthesized output voltage phasors of the two winding groups is 180 degrees. The common midpoint formed after series connection is located at the electrical midpoint of the series circuit of the two winding groups. The output voltage amplitudes on both sides of the common midpoint are completely equal and the phases are completely opposite, forming symmetrical positive and negative output voltages. The turns deviation between the first M-side secondary winding and the second M-side secondary winding is controlled within ±0.5%, and the turns deviation between the first T-side secondary winding and the second T-side secondary winding is controlled within ±0.5%, ensuring that the electrical parameters of the two sets of output windings are completely matched and avoiding problems such as midpoint offset and voltage asymmetry. The first M-side secondary winding, the second M-side secondary winding, the first T-side secondary winding, and the second T-side secondary winding are all wound using the same batch of conductor materials, ensuring that the DC resistance of the windings is completely consistent, further improving the symmetry of the output voltage.

[0021] Traditional technical solutions have the following technical problems: the existing connection method of the secondary winding cannot stably form a common midpoint, cannot guarantee the symmetry of the output voltage, and is prone to midpoint offset.

[0022] Based on this, the same-name terminal of the first M-side secondary winding is connected to the non-same-name terminal of the first T-side secondary winding to form a first combined output terminal; the same-name terminal of the second M-side secondary winding is connected to the non-same-name terminal of the second T-side secondary winding to form a second combined output terminal; and the same-name terminal of the first T-side secondary winding is connected to the non-same-name terminal of the second T-side secondary winding to form the common midpoint. This scheme, through a clearly defined connection method between the same-name and non-same-name terminals, ensures that the series connection direction of the two sets of output windings is consistent, avoids midpoint offset, stably forms a common midpoint, guarantees the symmetry of the output voltage, and solves the problems of unstable midpoint and voltage asymmetry in existing technologies.

[0023] The corresponding terminals are those with the same phase of the induced voltage in the winding. The determination of the corresponding terminals is based on the winding direction and the magnetic circuit direction of the core. The winding directions of the first M-side secondary winding and the second M-side secondary winding on the core are exactly the same, ensuring that the corresponding terminals of the two windings correspond completely. Similarly, the winding directions of the first T-side secondary winding and the second T-side secondary winding on the core are also exactly the same, ensuring that the corresponding terminals of the two windings also correspond completely. The corresponding terminal of the first M-side secondary winding is the one with the same phase of the induced voltage as the corresponding terminal of the M-side winding. The non-corresponding terminal of the first M-side secondary winding is the one with the opposite phase of the induced voltage as the corresponding terminal of the M-side winding. The corresponding terminal of the first T-side secondary winding is the one with the same phase of the induced voltage as the corresponding terminal of the T-side winding. The non-corresponding terminal of the first T-side secondary winding is the one with the opposite phase of the induced voltage as the corresponding terminal of the T-side winding. The same-name terminal of the first M-side secondary winding is directly connected to the non-same-name terminal of the first T-side secondary winding, so that the voltage phasor of the first M-side secondary winding and the voltage phasor of the first T-side secondary winding are positively superimposed. The resulting composite voltage phasor is the total output voltage phasor of the first output winding group. The phase difference between the voltage phasor of the first M-side secondary winding and the voltage phasor of the first T-side secondary winding is 90 degrees, and the amplitudes of the two voltage phasors are exactly equal. The phase of the composite voltage phasor is offset by 45 degrees relative to the voltage phasor of the first M-side secondary winding, and the amplitude of the composite voltage phasor is equal to the voltage amplitude of a single winding. times.

[0024] The same-name terminal of the second M-side secondary winding is directly connected to the non-same-name terminal of the second T-side secondary winding, so that the voltage phasor of the second M-side secondary winding and the voltage phasor of the second T-side secondary winding are positively superimposed. The superimposed composite voltage phasor is the total output voltage phasor of the second output winding group. The phase difference between the voltage phasor of the second M-side secondary winding and the voltage phasor of the second T-side secondary winding is 90 degrees, and the amplitudes of the two voltage phasors are completely equal. The phase of the superimposed composite voltage phasor is offset by 45 degrees relative to the voltage phasor of the second M-side secondary winding, and the amplitude of the composite voltage phasor is completely equal to the amplitude of the composite voltage phasor of the first output winding group.

[0025] The same-name terminal of the first T-side secondary winding is directly connected to the non-same-name terminal of the second T-side secondary winding to form a series connection node of two sets of output windings. This node is the common midpoint. The tail end of the resultant voltage phasor of the first output winding set and the head end of the resultant voltage phasor of the second output winding set are connected at the common midpoint, so that the voltage phasor between the first combined output terminal and the common midpoint and the voltage phasor between the second combined output terminal and the common midpoint have completely equal amplitudes and completely opposite phases, forming a stable symmetrical positive and negative output voltage without the problem of midpoint offset.

[0026] The connections between the windings are all made by silver-copper brazing. The contact resistance at the weld is no more than 10 microohms. After the welding is completed, the weld is fully covered with insulating material to avoid partial discharge and insulation breakdown. At the same time, it ensures the long-term reliability of the connection and will not loosen due to vibration or temperature rise during operation, further ensuring the long-term stability of the common midpoint.

[0027] Traditional technical solutions suffer from the following problems: existing three-phase to single-phase transformers cannot output symmetrical positive and negative voltages with the same amplitude but opposite phase, thus failing to meet the load requirements that symmetrical positive and negative power supply is needed. Therefore, a positive output voltage is formed between the first combined output terminal and the common neutral point, and a negative output voltage is formed between the second combined output terminal and the common neutral point. The amplitudes of the positive and negative output voltages are the same, and the phase difference between the positive and negative output voltages is 180 degrees.

[0028] This scheme uses two sets of output windings connected in the same direction to form symmetrical voltages with the same amplitude and opposite phases on both sides of the common midpoint, which fully meets the load requirements for symmetrical positive and negative power supply and solves the problem that existing technologies cannot output symmetrical positive and negative voltages.

[0029] The positive output voltage is the voltage of the first combined output terminal relative to the common midpoint, and the negative output voltage is the voltage of the second combined output terminal relative to the common midpoint. The amplitude of the positive output voltage is exactly the same as the amplitude of the negative output voltage, so that the voltage output capabilities on both sides of the common midpoint are completely consistent, which is suitable for the power supply needs of power electronic equipment and special industrial loads that require symmetrical positive and negative voltage power supply.

[0030] The phase difference between the positive output voltage and the negative output voltage is 180 degrees, so that the amplitude of the total output voltage between the first combined output terminal and the second combined output terminal is twice the amplitude of the positive output voltage, forming a symmetrical output voltage system with a midpoint, which can realize graded output from 0 to midpoint to full voltage, adapting to different load power supply requirements.

[0031] The amplitude deviation between the positive and negative output voltages is controlled within ±0.5%, and the phase deviation is controlled within ±1 degree, ensuring that the symmetry of the output voltage meets the power supply requirements of high-precision loads. The amplitude deviation is controlled by precise matching of the number of winding turns, and the phase deviation is guaranteed by precise control of the winding direction and the connection method of the same-name terminals.

[0032] The waveform distortion rate of the positive output voltage and the negative output voltage is no greater than 3%, ensuring that the output voltage is a standard sine wave and will not cause harmonic interference to the load equipment. The waveform distortion rate is controlled by the reasonable selection of the working magnetic flux density of the iron core and the optimization of the winding distribution. The working magnetic flux density of the iron core is set between 1.5 Tesla and 1.7 Tesla to ensure that the iron core works in the linear magnetization region and avoids waveform distortion caused by magnetic saturation.

[0033] Traditional technical solutions suffer from the following problems: inconsistent winding directions of the secondary windings can easily lead to phase misalignment of the output voltage, preventing the formation of the expected composite voltage and affecting the normal operation of the transformer. Therefore, the winding directions of the first M-side secondary winding and the second M-side secondary winding on the core assembly are the same, as are the winding directions of the first T-side secondary winding and the second T-side secondary winding on the core assembly.

[0034] This solution ensures that the output voltage phase of the two sets of output windings is consistent by unifying the winding direction of secondary windings of the same type, avoiding phase misalignment and ensuring that the phase of the synthesized voltage meets the design requirements. This solves the phase anomaly problem caused by inconsistent winding directions in existing technologies.

[0035] The first M-side secondary winding and the second M-side secondary winding are continuously wound in the same direction on the same core column of the core assembly. During the winding process, the turn spacing and layer spacing of the windings are kept completely consistent to ensure that the parasitic parameters and induced voltage phases of the two windings are completely matched and there is no phase deviation. The first M-side secondary winding and the second M-side secondary winding are wound in layers, with the first M-side secondary winding wound in the inner layer and the second M-side secondary winding wound in the outer layer. An insulating isolation layer is set between the two layers of windings to ensure that the coupling coefficients of the two windings and the M-type transformer winding are completely consistent and that the amplitude and phase of the induced voltage are completely matched.

[0036] The first T-side secondary winding and the second T-side secondary winding are continuously wound in the same direction on the same core column of the core assembly. During the winding process, the turn spacing and layer spacing of the windings are kept completely consistent to ensure that the parasitic parameters and induced voltage phases of the two windings are completely matched and there is no phase deviation. The first T-side secondary winding and the second T-side secondary winding are wound in layers, with the first T-side secondary winding wound in the inner layer and the second T-side secondary winding wound in the outer layer. An insulating layer is set between the two layers of windings to ensure that the coupling coefficients of the two windings and the T-transformer winding are completely consistent and that the amplitude and phase of the induced voltage are completely matched.

[0037] The winding is performed using a horizontal winding machine, maintaining a constant tension during the winding process. The tension value is set according to the wire diameter of the winding conductor to ensure that the winding is tightly and neatly wound, preventing loosening or misalignment between turns, and further ensuring the stability and consistency of the induced voltage in the winding. After winding, the winding is fully wrapped and fixed with heat-shrinkable insulating tape to prevent displacement during assembly and operation, which could lead to phase anomalies caused by changes in the coupling coefficient.

[0038] Traditional technical solutions suffer from the following problems: the input wiring structure of the Scott transformer is unclear, which can easily lead to phase misalignment of the three-phase inputs, making it impossible to achieve balanced operation of the three-phase power grid. Therefore, the two ends of the M-transformer winding are connected to the B-phase and C-phase input terminals of the three-phase AC power, respectively. The first end of the T-transformer winding is connected to the A-phase input terminal of the three-phase AC power, and the last end of the T-transformer winding is connected to the electrical neutral point of the M-transformer winding. The electrical neutral point of the M-transformer winding is located at the midpoint of the number of turns of the M-transformer winding.

[0039] This scheme clarifies the input wiring method of the Scott wiring structure, ensures three-phase input phase matching, achieves balanced operation of the three-phase power grid, and solves the three-phase imbalance problem caused by non-standard input wiring in existing technologies.

[0040] The M-type transformer winding is a continuously wound single-phase winding. The midpoint of the M-type transformer winding is located at half the total number of turns. This position is the electrical midpoint of the M-type transformer winding. The electrical midpoint of the M-type transformer winding divides the M-type transformer winding into two winding segments with completely equal number of turns. The electrical parameters of the two winding segments are completely identical, ensuring that after being connected to a three-phase power grid, the voltage amplitude between phase B and the midpoint, and the voltage amplitude between phase C and the midpoint are completely equal, with a phase difference of 180 degrees.

[0041] The tail end of the T-type transformer winding is directly connected to the electrical neutral point of the M-type transformer winding using silver-copper brazing. The contact resistance at the weld joint is no greater than 10 microohms, ensuring stable electrical performance and preventing three-phase load imbalance caused by excessive contact resistance. The number of turns in the T-type transformer winding is matched to the number of turns in the M-type transformer winding, and the effective number of turns in the T-type transformer winding is a fraction of the total number of turns in the M-type transformer winding. This ensures that the voltage amplitude across the T transformer winding is exactly equal to the voltage amplitude of a single section of the M transformer winding, thus achieving complete balance of the three-phase load in the three-phase power grid.

[0042] The three-phase AC power supply is equipped with terminals for phase A, phase B, and phase C. The terminals are made of tin-plated copper and have a rated current carrying capacity not less than the rated input current of the transformer. The terminals are equipped with anti-loosening structures to ensure the long-term reliability of the three-phase input wiring and prevent the wiring from becoming loose due to vibration or temperature rise, which could lead to phase misalignment or poor contact in the three-phase input.

[0043] After the transformer is connected to the three-phase power grid, the three-phase current imbalance of the three-phase power grid is no more than 1%, which will not cause interference to other electrical equipment in the same power grid and fully meets the relevant standard requirements for power grid operation. The three-phase current imbalance is guaranteed by precise matching of the number of winding turns and standardized control of the input wiring method.

[0044] Traditional technical solutions suffer from the following problems: the phase of the synthesized voltage of the secondary winding is unclear, making it impossible to guarantee that the output voltages of the two sets of output windings are out of phase, thus failing to form symmetrical positive and negative voltages. Therefore, the phase difference between the output voltages of the first M-side secondary winding and the first T-side secondary winding is 90 degrees, the phase difference between the output voltages of the second M-side secondary winding and the second T-side secondary winding is 90 degrees, the phase difference between the synthesized output voltage of the first set of output windings and the synthesized output voltage of the second set of output windings is 180 degrees, and the phase of the synthesized output voltage is offset by 45 degrees relative to the phase of the output voltage of the M-type winding.

[0045] This scheme clarifies the phase relationship of the secondary windings. The phase of the combined voltage of a single output winding group satisfies a 45-degree offset, and the phase difference between the two combined voltage groups is 180 degrees, ensuring that the voltages on both sides of the common midpoint are completely symmetrical. The formula for calculating the combined voltage is: ; In the formula, The phasor of the combined output voltage of a single set of output windings, in volts; This is the output voltage phasor of the secondary winding on the M side, in volts. This is the output voltage phasor of the secondary winding on the T side, in volts.

[0046] because and With the same amplitude and a 90-degree phase difference, the combined phase is relative to... The 45-degree offset provides the basis for the formation of symmetrical positive and negative voltages.

[0047] Output voltage phasor of the first M-side secondary winding Phasor of the output voltage of the first T-side secondary winding The phase difference is 90 degrees, and and The amplitudes are exactly equal, and the phasor of the combined output voltage of the first output winding group is The phase of the synthesized phasor is relative to With a lead of 45 degrees, the amplitude of the synthesized phasor is Amplitude times.

[0048] The output voltage phasor of the second M-side secondary winding Phasor of the output voltage of the second T-side secondary winding The phase difference is 90 degrees, and and The amplitudes are exactly equal, and the phasor of the combined output voltage of the second output winding group is The phase of the synthesized phasor is relative to Leading by 45 degrees, the synthesized phasor amplitude and The amplitudes are exactly the same.

[0049] The first output winding group and the second output winding group are connected in series in the same direction, so that and The phase difference is 180 degrees. The tail end of the composite output voltage phasor of the first output winding group is connected to the head end of the composite output voltage phasor of the second output winding group to form a common midpoint, so that the voltage phasor amplitudes on both sides of the common midpoint are completely equal and the phases are completely opposite, forming a stable symmetrical positive and negative output voltage.

[0050] The phase deviation of the synthesized output voltage is controlled within ±0.5 degrees, which is ensured by precise control of the winding direction, the connection method of the same-name terminals, and the coupling coefficient. This ensures that the phase of the synthesized voltage fully meets the design requirements and prevents voltage asymmetry caused by phase deviation. The waveform of the synthesized output voltage is a standard sine wave with a waveform distortion rate of no more than 3%, ensuring that the power quality of the output voltage meets the power supply requirements of high-precision loads.

[0051] Traditional technical solutions suffer from the following problems: the core assembly structure is unclear, making it impossible to guarantee the electromagnetic coupling effect between the main transformer winding and the secondary winding, which easily leads to excessive transformer losses and low efficiency. Therefore, the transformer includes a three-phase, three-limb core assembly, comprising three parallel core limbs and two yokes connected to the ends of the three core limbs. The M-phase winding is wound on the B-phase and C-phase core limbs, and the T-phase winding is wound on the A-phase core limb.

[0052] This solution clarifies the structure and winding position of the three-phase three-column core assembly, ensuring the electromagnetic coupling effect between the main transformer winding and the secondary winding, reducing the no-load loss and load loss of the transformer, improving operating efficiency, and solving the problem of excessive loss caused by the unclear core structure in existing technologies.

[0053] The three-phase, three-column core assembly is constructed from stacked cold-rolled grain-oriented silicon steel sheets with a thickness of 0.3 mm to 0.5 mm. The surface of the silicon steel sheets is coated with an insulating layer, and the stacking factor is not less than 0.97. This ensures that the core's permeability meets design requirements while reducing eddy current and hysteresis losses. The core column has a stepped circular cross-section with a fill factor of not less than 0.95, maximizing the utilization of the core window area and improving the winding coupling effect.

[0054] The three iron core columns are arranged in parallel and equidistant, with their center lines located in the same plane. Two iron yokes are connected to the upper and lower ends of the three iron core columns, respectively, forming a closed three-phase magnetic circuit. The cross-sectional area of ​​the iron yokes is exactly equal to that of the iron core columns, ensuring that the magnetic resistance of the magnetic circuit is evenly distributed and preventing magnetic saturation caused by excessive local magnetic flux density.

[0055] The M-type transformer winding is divided into two sections, which are wound on the B-phase and C-phase core columns respectively. The two sections have the same number of turns and are wound in the same direction, ensuring that the induced voltage amplitudes are equal and the phases are opposite, forming a complete M-type transformer winding magnetic circuit. The T-type transformer winding is wound entirely on the A-phase core column, with its winding direction matching that of the M-type transformer winding, ensuring that the induced voltage phase of the T-type winding forms a fixed 90-degree phase difference with that of the M-type transformer winding.

[0056] The main transformer winding is wound on the inner layer of the iron core column, and the secondary output winding is wound on the outer layer of the main transformer winding. A main insulation layer is provided between the main transformer winding and the secondary output winding. The thickness of the main insulation layer is designed according to the rated voltage level of the transformer to ensure that the insulation performance between the windings meets the requirements, while ensuring the electromagnetic coupling effect between the main transformer winding and the secondary winding and reducing the additional losses caused by leakage flux.

[0057] The surface of the core assembly is provided with a grounding plate made of copper. The grounding plate is reliably connected to the core assembly to ensure that the core assembly is reliably grounded during transformer operation, avoid partial discharge problems caused by floating potential, and improve the operational safety and long-term reliability of the transformer.

[0058] Traditional technical solutions suffer from the following problems: the material and insulation structure of the secondary winding are unclear, making it impossible to guarantee the operational safety and service life of the transformer, and making it prone to winding breakdown and short circuit faults. Therefore, all secondary windings of the secondary output winding unit are wound with enameled copper flat wire. The wire diameter of all secondary windings in the secondary output winding unit is determined according to the rated output current. An insulating isolation layer is provided between adjacent secondary windings of the secondary output winding unit, and the insulating isolation layer is made of NOMEX insulating paper.

[0059] This solution clarifies the conductor material, wire diameter design rules, and insulation structure of the secondary winding, ensuring the current carrying capacity and insulation performance of the winding, improving the operational safety and service life of the transformer, and solving the safety hazards caused by the unclear winding structure in existing technologies.

[0060] The conductor of the enameled copper flat wire is made of oxygen-free copper with a purity of not less than 99.95%. A polyesterimide enameled insulation layer is applied to the surface of the conductor. The thickness of the insulation layer is designed according to the operating voltage level of the winding, and the breakdown voltage of the insulation layer is not less than three times the operating voltage of the winding, ensuring that the inter-turn insulation performance of the winding meets the requirements. The width-to-thickness ratio of the copper flat wire is controlled between 2:1 and 4:1 to maximize the utilization of the winding window area while reducing skin effect losses and improving the transformer's operating efficiency.

[0061] The wire diameter of the secondary winding is designed based on the rated output current, and the current density of the winding is set between 2.5 amperes per square millimeter and 3.5 amperes per square millimeter to ensure that the temperature rise of the winding under rated load does not exceed the limit specified by national standards, and to prevent insulation aging and shortened lifespan due to overheating. The wire diameter design of the winding also considers short-term overload conditions, ensuring that the temperature rise of the winding remains within the allowable range even after the transformer has been running continuously for 2 hours under 1.2 times the rated load.

[0062] The insulating isolation layer between adjacent secondary windings is made of NOMEX insulating paper with a thickness of 0.08 mm to 0.18 mm. The number of insulating isolation layers is designed according to the working voltage difference between the windings to ensure that the insulation breakdown voltage between the windings is not less than 5 times the working voltage, thus avoiding insulation breakdown and short circuit faults between windings. The NOMEX insulating paper has excellent high-temperature resistance and mechanical strength, with a long-term operating temperature of up to 200 degrees Celsius. It also has good anti-aging properties, significantly improving the long-term operational reliability and service life of the windings.

[0063] After the secondary winding is wound, it is subjected to a vacuum pressure impregnation process for insulation treatment. The impregnation varnish is a high-temperature resistant solvent-free insulating varnish. After impregnation, it is dried and cured to ensure that the insulating varnish completely penetrates into the gaps between the turns and layers of the winding, thereby improving the overall insulation performance, mechanical strength and heat dissipation performance of the winding and avoiding problems such as inter-turn short circuits and vibration loosening during operation.

[0064] The winding ends are provided with insulating end rings made of epoxy glass cloth. The size of the insulating end rings is perfectly matched with the size of the winding ends, which reliably fixes and insulates the winding ends, avoids partial discharge problems caused by electric field concentration at the winding ends, and further improves the insulation performance and operational safety of the winding.

[0065] Traditional technical solutions suffer from the following problems: the rated parameters of the transformer are unclear, making it unsuitable for specific industrial power supply scenarios and failing to guarantee operational stability and reliability. Therefore, the rated input voltage of the transformer is 10kV three-phase AC, the rated output voltage is 0-110V-220V single-phase AC, the rated operating frequency is 50Hz, and the three-phase imbalance does not exceed 1%.

[0066] This solution clarifies the rated input and output parameters, operating frequency, and three-phase imbalance index of the transformer, adapts to common scenarios in China's 10kV distribution network, meets the positive and negative symmetrical voltage output requirements of 0-110V-220V, ensures operational stability, and solves the problem of poor scenario adaptability caused by unclear existing technical parameters.

[0067] The transformer has a rated input voltage of 10kV three-phase AC, with an allowable input voltage fluctuation range of ±10% of the rated value, ensuring stable operation within the normal fluctuation range of the grid voltage and meeting design requirements for output voltage accuracy. The transformer's rated output voltage is 0-110V-220V single-phase AC, with a common neutral point of 110V. The rated output voltage between the first combined output terminal and the common neutral point is 110V, the rated output voltage between the second combined output terminal and the common neutral point is 110V, and the rated output voltage between the first and second combined output terminals is 220V, forming a symmetrical ±110V output voltage system with a neutral point, fully adaptable to loads requiring symmetrical positive and negative voltage power supply.

[0068] The transformer has a rated operating frequency of 50Hz, which is compatible with the operating standards of domestic power frequency distribution networks. It can operate normally within a frequency range of 45Hz to 55Hz, and the output voltage performance meets design requirements. The rated capacity of the transformer is designed according to load demand, covering a commonly used capacity range from 10kVA to 1000kVA. Transformers of different capacity levels maintain the same winding structure and wiring method to ensure the symmetry and three-phase balance of the output voltage.

[0069] The three-phase imbalance of the transformer does not exceed 1%. This three-phase imbalance is the ratio of the negative-sequence to the positive-sequence components of the three-phase grid input current under rated load. This ensures that the transformer will not cause significant imbalance to the three-phase grid during operation, fully complying with relevant grid connection standards. The transformer's output voltage regulation rate is no greater than 5% across the entire load range from no-load to rated load, ensuring output voltage stability under different load conditions and meeting the power supply accuracy requirements of the load.

[0070] The transformer's no-load loss is no more than 80% of the national standard limit for the same capacity, and its load loss is no more than 90% of the national standard limit for the same capacity, demonstrating excellent energy-saving performance and significantly reducing power loss during long-term operation. The transformer's temperature rise meets national standards, with the average temperature rise of the windings not exceeding 65K and the core temperature rise not exceeding 55K, ensuring long-term continuous operation under rated conditions without overheating leading to insulation aging or shortened lifespan.

[0071] Traditional technical solutions suffer from the following problems: the wiring structure between the output terminal and the common neutral point is unclear, which cannot guarantee the convenience and reliability of load wiring and easily leads to equipment failure due to wiring errors. Therefore, the first combined output terminal, the second combined output terminal, and the common neutral point are all connected to terminal blocks. These terminal blocks are made of tin-plated copper, and their rated current carrying capacity is not less than the rated output current of the transformer.

[0072] This solution clarifies the terminal structure of the output end and the common midpoint, ensuring the convenience and reliability of load wiring, avoiding wiring errors, and ensuring that the current carrying capacity of the terminal matches the rated output of the transformer. This solves the wiring failure problem caused by the unclear wiring structure in the existing technology.

[0073] The terminals are made of oxygen-free copper with a tin-plated surface. The tin plating layer is at least 8 micrometers thick, providing excellent conductivity and corrosion resistance, thus preventing oxidation and increased contact resistance during long-term operation. The terminals employ a bolt-fitting structure, equipped with anti-loosening washers and flat washers to ensure reliable connection of the load cable. This prevents loosening due to vibration or temperature rise, which could lead to poor contact, overheating, or even fire hazards.

[0074] The rated current carrying capacity of the terminals is not less than 1.25 times the rated output current of the transformer, ensuring that the terminals can withstand the short-term overload current of the transformer without overheating damage. The rated voltage of the terminals is not less than twice the rated output voltage of the transformer, ensuring that the insulation performance of the terminals meets the design requirements and prevents insulation breakdown.

[0075] The terminals of the first combined output terminal, the second combined output terminal, and the common midpoint are all installed on the low-voltage outgoing panel of the transformer. The outgoing panel is made of epoxy fiberglass cloth, which has excellent insulation performance and mechanical strength. The three terminals are arranged in a fixed order on the outgoing panel, and the electrical clearance and creepage distance between adjacent terminals meet the national standard requirements to avoid short circuits and discharges between terminals.

[0076] The outgoing panel has clear markings corresponding to the location of each terminal, with the markings matching the terminal's function perfectly. This ensures that wiring errors are avoided during field wiring, preventing damage to load equipment and transformer malfunctions caused by incorrect wiring. The terminals are connected to the winding leads using silver-copper brazing, with a contact resistance of no more than 10 microohms at the weld. After welding, the weld is fully covered with insulating material to ensure that the electrical and insulation performance of the connection meets long-term operational requirements.

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A three-phase to single-phase transformer with mid-point symmetrical output, comprising a primary winding unit and a secondary output winding unit, the primary winding unit adopting a Scott transformer connection structure, the primary winding unit comprising an M winding and a T winding, characterized in that, The secondary output winding unit includes a first output winding group and a second output winding group. The first output winding group and the second output winding group have the same structure. The first output winding group includes a first M-side secondary winding and a first T-side secondary winding. The second output winding group includes a second M-side secondary winding and a second T-side secondary winding. The first M-side secondary winding and the second M-side secondary winding have the same number of turns and are both coupled to the M-type winding. The first T-side secondary winding and the second T-side secondary winding have the same number of turns and are both coupled to the T-type winding. The first M-side secondary winding and the first T-side secondary winding are orthogonal in phase. The second M-side secondary winding and the second T-side secondary winding are orthogonal in phase. The first output winding group and the second output winding group are connected in series in the same direction to form a common midpoint.

2. The three-phase to single-phase transformer with mid-point symmetrical output according to claim 1, characterized in that, The same-name terminal of the first M-side secondary winding is connected to the non-same-name terminal of the first T-side secondary winding to form a first combined output terminal. The same-name terminal of the second M-side secondary winding is connected to the non-same-name terminal of the second T-side secondary winding to form a second combined output terminal. The same-name terminal of the first T-side secondary winding is connected to the non-same-name terminal of the second T-side secondary winding to form the common midpoint.

3. The three-phase to single-phase transformer with mid-point symmetrical output according to claim 2, characterized in that, A positive output voltage is formed between the first combined output terminal and the common midpoint, and a negative output voltage is formed between the second combined output terminal and the common midpoint. The amplitude of the positive output voltage is the same as the amplitude of the negative output voltage, and the phase difference between the positive output voltage and the negative output voltage is 180 degrees.

4. The three-phase to single-phase transformer with mid-point symmetrical output according to claim 1, characterized in that, The first M-side secondary winding and the second M-side secondary winding are wound in the same direction on the core assembly, and the first T-side secondary winding and the second T-side secondary winding are wound in the same direction on the core assembly.

5. The three-phase to single-phase transformer with symmetrical output at the midpoint according to claim 1, characterized in that, The two ends of the M-type transformer winding are respectively connected to the B-phase input terminal and the C-phase input terminal of the three-phase AC power. The first end of the T-type transformer winding is connected to the A-phase input terminal of the three-phase AC power. The tail end of the T-type transformer winding is connected to the electrical midpoint of the M-type transformer winding. The electrical midpoint of the M-type transformer winding is located at the midpoint of the number of turns of the M-type transformer winding.

6. The three-phase to single-phase transformer with symmetrical output at the midpoint according to claim 1, characterized in that, The output voltage phase difference between the first M-side secondary winding and the first T-side secondary winding is 90 degrees, the output voltage phase difference between the second M-side secondary winding and the second T-side secondary winding is 90 degrees, the phase difference between the combined output voltage of the first output winding group and the combined output voltage of the second output winding group is 180 degrees, and the phase of the combined output voltage is offset by 45 degrees relative to the output voltage phase of the M-side variable winding.

7. The three-phase to single-phase transformer with symmetrical output at the midpoint according to claim 1, characterized in that, The transformer includes a three-phase three-column core assembly, which includes three parallel core columns and two yokes connected to the two ends of the three core columns. The M-phase winding is wound on the B-phase core column and the C-phase core column of the three core columns, and the T-phase winding is wound on the A-phase core column of the three core columns.

8. The three-phase to single-phase transformer with symmetrical output at the midpoint according to claim 1, characterized in that, All secondary windings of the secondary output winding unit are wound with enameled copper flat wire. The wire diameter of all secondary windings of the secondary output winding unit is determined according to the rated output current. An insulating isolation layer is provided between adjacent secondary windings of the secondary output winding unit. The insulating isolation layer is made of NOMEX insulating paper.

9. The three-phase to single-phase transformer with symmetrical output at the midpoint according to claim 1, characterized in that, The transformer has a rated input voltage of 10kV three-phase AC, a rated output voltage of 0-110V-220V single-phase AC, and a rated operating frequency of 50Hz.

10. The three-phase to single-phase transformer with symmetrical output at the midpoint according to claim 2, characterized in that, The first combined output terminal, the second combined output terminal, and the common midpoint are all connected to terminals. The terminals are made of tin-plated copper and the rated current carrying capacity of the terminals is not less than the rated output current of the transformer.

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