I. Introduction: Round vs. Flat Wire – The “Fundamental Showdown” of Winding Efficiencyrontation” of Winding Efficiency
In the winding process of motors, transformers, and electrical windings, conductor shape selection (round vs. flat wire) is one of the most critical design decisions to determine winding efficiency (slot full rate, space utilization, heat dissipation performance) .
Winding Efficiency is a comprehensive measure of winding space utilization, directly affecting:
– Slot Fill Factor (SFF)
– Power Density (kW/L)
– Copper consumption and temperature rise
– Manufacturing costs
– Thermal performance
– Mechanical strength
Circle vs. Flat Core Differences :
– Round Magnet Wire: Φ 0.05 -10 mm circular cross-section
– Flat Magnet Wire/Rectangular Wire: rectangular cross-section
– Groove full rate difference: 30-50% (round line) vs. 60-90% (flat line)
– Power density difference: 3-10x
Key Scenarios :
– NEV drive motors: Flat wire efficiency is 15-25% higher than round wire
– Efficient industrial motors: Flat wire efficiency is 20-30% higher than round wire
– Wind-powered direct-drive generators: 25-40% more efficient with flat lines than with round lines
– High frequency transformer: Leeds wire (flat wire) vs. circular wire
1.1 Definition of round and flat lines
Round Magnet Wire :
– Section: Circular (diameter Φ)
– Diameter range: Φ 0.05 -10 mm (most commonly 0.2-5 mm)
– Paint film: uniform circumference
– Standard: IEC 60317/GB 6109
Flat/Rectangular Magnet Wire :
– Section: rectangular (thick a × wide b)
– Thickness range: 0.5-5 mm
– Width range: 2-25 mm
– Paint film: covered on all sides
– Standard: IEC 60317/GB 7095
1.2 Round vs. Flat 4 Core Differences
| Dimension | Circle | Flat | Difference |
|---|---|---|---|
| Slot Full Rate | 30-50% | 60-90% | Flatline +30-50% |
| Power Density | 1x | 2-5x | Flat +200-400% |
| End Height | Shorter | Longer | Rounded -20-30% |
| Process Difficulty | Simple | Complex | Flatline +30-50% |
1.3 6 Big Winding Efficiency Indicators
| Metrics | Circles | Flatlines | Meaning |
|---|---|---|---|
| Groove Fill Rate SFF | 30-50% | 60-90% | Space Utilization |
| Space Utilization | 70-78% | 90-95% | Rectangular Arrangement |
| Fill Factor | 0.68-0.74 | 0.85-0.92 | Section Efficiency |
| End Space | 100-150% | 70-90% | End Size |
| Cooling Efficiency | Medium | High | Contact Area |
| Mechanical Strength | Lower | Higher | Deformation Resistance |
II. Advantages and Applications of Round Wire Winding
2.1 Advantages of round wire windings
Advantage 1: Easy winding
– Mature automatic winding machine
– Uniform circumferential paint film (no corner stress)
– Large process tolerance
– Suitable for small batches
Advantage 2: Low cost
– Low price for round enameled wire
– Round wire winding equipment is simple
– Easy to repair
– Suitable for general motors
Advantage 3: High frequency performance
– Low eddy current loss when circular lines are arranged
– Thin and even paint film
– Suitable for high frequency transformers (< 1 kHz)
Advantage 4: Withstand voltage stability
– Uniform distribution of the circumferential electric field
– No corner electric field concentration
– BDV stable
– Long-life design
Advantage 5: Flexible profiled windings
– Suitable for profiled windings
– Suitable for discrete windings
– Suitable for small batch customization
– Suitable for small space winding
2.2 Limitations of Circles
Limit 1: Low slot full rate
– Circular cross-section, there must be a gap in the rectangular groove
– Clearance 30-50% (theoretical)
– Actual slot full rate 30-50%
– Limited power density
Limit 2: Space wasted
– In the square space occupied by the circular line in the rectangular groove, the circular cross-section occupies only 78.5%
– 21.5% wasted space
– Overall efficiency loss 20-30%
Limit 3: Uneven heat dissipation
– Small contact area between circular lines
– Limited oil/air convection heat dissipation
– Hot Spot Temperature Increase
– Affects life expectancy
Limit 4: End winding difficult
– High end bending stress
– Paint film is vulnerable
– Eddy current loss at corners
2.3 Circle Applicable Scenarios
| Scenario | Circle Size | Reason |
|---|---|---|
| Small motor | Φ 0.5-1.5 mm | Simple process |
| General appliance motors | Φ 0.3-1.0 mm | Low cost |
| High-frequency transformer | Φ 0.05-0.5 mm | Low eddy current loss |
| Small transformer | Φ 0.1-0.5 mm | Simple process |
| Relay coil | Φ 0.05-0.3 mm | Fine winding |
| Shaped winding | Φ 0.5-2 mm | Shaped adaptation |
III. Advantages and Applications of Flat Wire Winding
3.1 Advantages of flat wire windings
Advantage 1: high fill rate
– Flat, rectangular cross-section, tightly aligned
– Groove fill rate 60-90% (vs. 30-50% for circular lines)
– Increase space utilization by 30-50%
Advantage 2: High power density
– Same groove area, 1.5-2 times more copper for flat wires
– 2-5x increase in power density
– Suitable for high-efficiency high-power density motors
Advantage 3: good heat dissipation
– Large contact area between flat lines
– High heat dissipation efficiency
– Low temperature rise
– Long life
Advantage 4: High mechanical strength
– Strong ability to resist deformation of flat lines
– Vibration resistant, short circuit resistant
– Suitable for large motors
Advantage 5: neat end
– The end of the flat wire is bent neatly
– Low end height (vs. circle)
– Suitable for hairpin windings
Advantage 6: Automated production
– Hairpin technology is mature
– Suitable for NEV motors
– Suitable for mass production
– High consistency
3.2 Limitations of Flat Lines
Limit 1: Corner stress concentration
– Flat wire paint film withstands stress at the corners
– Paint film is vulnerable
– BDV decreased
– High manufacturing process requirements
Limit 2: High-frequency eddy current loss
– Large cross-section of flat lines
– High frequency eddy current loss (> 1 kHz)
– Need Leeds thread (multi-strand fine thread)
– Increased process complexity
Limit 3: Shaped windings are limited
– Flat wires are not suitable for profiled windings
– Fits rectangular slots
– Not suitable for special-shaped cores
– Narrow scope of application
Limit 4: Higher costs
– High price for flat wire enameled wire
– Flat wire winding equipment is complex
– High process costs
– Suitable for mass production
3.3 Scenarios for flat wires
| Scene | Flat wire specification | Reason |
|---|---|---|
| New Energy Vehicle Drive Motor | 1.5-3 mm thick × 4-8 mm wide | High Power Density |
| High-efficiency industrial motor | Thickness 1-2.5 mm × width 3-6 mm | High groove full rate |
| Wind-driven generators | 2-4 mm thick x 5-15 mm wide | High power |
| Large transformer low-voltage windings | 1-3 mm thick × 4-12 mm wide | High current |
| Traction motor | Thickness 1.5-3 mm × Width 4-8 mm | High power density |
| Aeromotors | 0.5-1.5 mm thick x 2-5 mm wide | High power density |
IV. Slot Fill Factor (SFF) Comparative Analysis
4.1 Slot full rate definition
Slot full rate (SFF) = total conductor area/slot usable area × 100%
Theoretical upper limit :
– Round line: 78.5% (hexagonal row)
– Flat line: 100% (rectangular close row)
– Actual: round 30-50%, flat 60-90%
Influencing Factors for Groove Fill Rate :
– Conductor shape
– Paint film thickness
– Insulation layer
– Arrangement
– Process level
4.2 Round Line Groove Full Rate Calculation
Single rounded square space :
– Circular line diameter Φ
– Square side length = Φ
– Circular area = π × (Φ/2) ²
– Square area = Φ ²
– Proportion = π/4 = 78.5%
Multilayer circular line :
– Tier 1: 78.5%
– Floor 2: 68-72%
– Floor 3: 60-65%
– Actual groove full rate: 30-50% (including insulation)
4.3 Calculation of full rate of flat line slots
Single flat rectangular space :
– Flat line thickness a × width b
– rectangular space = a × b
– Flat line area = a × b
– Proportion = 100% (theory)
Multilayer flat wire :
– Tight: 85-95%
– Actual groove full rate: 60-90% (including insulation)
4.4 Slot full rate increase effect
Comparative analysis (using a 10 kW motor as an example):
| Indicator | Circle | Flat | Lift |
|---|---|---|---|
| Groove Fill Rate | 40% | 75% | +88% |
| Copper content | 1.0 | 1.5-1.8 | +50-80% |
| Power Density | 1.0 | 1.5-2.0 | +50-100% |
| Copper consumption | 1.0 | 0.7-0.8 | -20-30% |
| Efficiency | 92% | 95% | +3% |
| Temperature Rise | 100K | 70K | -30% |
| Volume | 1.0 | 0.6-0.7 | -30-40% |
4.5 Relationship between slot full rate and copper consumption
Copper consumption formula :
P_cu = I ² × R = I ² × ρ × L/A
Where:
P_cu = Copper consumption (W)
I = Current (A)
R = Resistance (Ω)
ρ = resistivity (Ω · m)
L = conductor length (m)
A = conductor cross-sectional area (m ²)
Sectional Area and Groove Fill Rate :
-Groove full rate high → cross-sectional area large → resistance small → copper consumption low
– Slot full rate increased from 40% to 75%, copper consumption reduced by 30-50%
V. End Winding Comparison
5.1 Importance of end windings
End definition : the part of the coil that protrudes from the inside of the core groove to the outside of the groove
End function :
– Achieve inter-turn connectivity
– Winding electrical connections
– Heat dissipation (end contact with air/oil)
– Mechanical support
End indicator :
– End height
– End width
– End axial length
– End space utilization
5.2 Round line end features
Rounded end :
– End height: 15-30 mm (small)
– End height: 30-100 mm (medium)
– End space utilization: 60-75%
– End arc transition
– Uniform stress distribution
– Paint film intact
Circle line end limitations :
– Low end space utilization
– Long end
– Larger size
5.3 Flat wire end features
Flat wire end :
– End height: 10-25 mm (small)
– End height: 20-60 mm (medium)
– End space utilization: 75-90%
– Neatly crooked ends
– Stress concentration (at the corners)
– Paint film needs to be protected
Flat line end advantage :
– Low end height
– Neat end
– Suitable for hairpin windings
Flat line end limitations :
– Corner stress
– Paint film is vulnerable
– Requires hairpin molding
5.4 Comparison of end sizes
| Indicators | Circles | Flatlines | Differences |
|---|---|---|---|
| End Height | 100% | 60-80% | Flatline -20-40% |
| End axial length | 100% | 70-90% | Flat wire -10-30% |
| End Space Utilization | 65% | 80% | Flat +15% |
| End resistance | 1.0 | 0.8-0.9 | Flat wire -10-20% |
| End heat dissipation | Medium | High | Flat +20-30% |
VI. Winding Heat Dissipation Performance Comparison
6.1 Winding cooling mechanism
Cooling method :
– Conductivity (copper → insulated → core/chassis)
– Convection (air/oil circulation)
– Radiation (surface radiation)
Heat Dissipation Critical :
– Conductor surface area
– Contact area
– Thermal conductivity
– Fluid flow rate
6.2 Circular heat dissipation analysis
Circular heat dissipation characteristics :
– Small contact area between circular lines (point contact)
– Heat dissipation is mainly conducted by the insulation layer
– Lower heat dissipation efficiency
– Larger temperature rise
Circular heat dissipation data :
– Surface area per unit volume: Φ/(Φ ²/4) = 4/Φ (smaller is bigger)
– Φ 0.5 mm: 8 mm ²/mm ³
– Φ1.0 mm: 4 mm ²/mm ³
– Φ 2.0 mm: 2 mm ²/mm ³
6.3 Flat wire heat dissipation analysis
Flat wire heat dissipation characteristics :
– Large contact area between flat lines (line contact/surface contact)
– Direct conduction heat dissipation
– High heat dissipation efficiency
– Low temperature rise
Flat wire heat dissipation data :
– Section circumference: 2 (a + b)
– Cross-sectional area: a × b
– Surface area per unit volume: 2 (a + b)/(a × b)
– 1.6 × 5 mm: 8.1 mm ²/mm ³ (vs Φ 0.5 mm round 8 mm ²/mm ³)
– 1.6 x 10 mm: 5.5 mm ²/mm ³
Comparative conclusion :
– The surface area of the flat line is 5-20% larger than that of the circular line under the same cross-sectional area
– Flat lines dissipate heat 10-30% better than round lines
6.4 Impact of the impregnation process on heat dissipation
VPI impregnation :
– Fill the gap between the conductors
– Enhanced heat dissipation
– Increase withstand voltage
Different steeping methods :
– Normal impregnation: Heat dissipation increased by 5-10%
– VPI impregnation: 15-25% heat dissipation improvement
– Vacuum pressure impregnation: 20-30% heat dissipation improvement
Round vs. flat line impregnation :
– Circular line impregnation: many gaps, large amount of impregnation
– Flat line impregnation: less clearance, less amount of impregnation
– Better heat dissipation after flat wire impregnation
VII. Electrical Performance Comparison
7.1 DC Resistance
DC resistance formula :
R_dc = ρ × L/A
Where:
R_dc = DC resistance (Ω)
ρ = resistivity (copper: 1.724 × 10 φΩ · m)
L = conductor length (m)
A = cross-sectional area (m ²)
Resistance comparison under the same winding space :
– Circular line (Φ 1.0 mm): A = 0.785 mm ²
– Flat wire (1.0 x 1.0 mm): A = 1.0 mm ²
– Flat wire (1.5 x 1.5 mm): A = 2.25 mm ²
Increased cross-sectional area : Flat line is 20-100% larger than circular line cross-sectional area
Resistance reduction : 15-50% reduction in flat line resistance
7.2 AC Resistance and Skin Gathering Effects
Skin effect :
– AC current tends to the surface of the conductor
– Reduced effective cross-sectional area
– Increased resistance
Skin depth :
– Copper @ 50 Hz: 9.3 mm
– Copper @ 1 kHz: 2.1 mm
– Copper @ 10 kHz: 0.66 mm
– Copper @ 100 kHz: 0.21 mm
Impact on circles :
– Small effect when diameter < skin depth
– Resistance increases when Diameter > Skin Set Depth
Effect on flatlines :
– Significant increase in resistance when thickness > skin depth
– The eddy current loss of the flat line is greater than the circular line
– unfavorable flat lines at high frequencies
7.3 Eddy current loss
Eddy current loss formula :
P_eddy = k × B ² × f ² × d ²/ρ
Where:
P_eddy = Eddy current loss (W)
B = magnetic flux density (T)
f = Frequency (Hz)
d = conductor thickness (mm)
ρ = resistivity (Ω · m)
Circle line vs. flat line eddy current loss :
– Φ 0.5 mm circular line vs. 1.5 x 1.5 mm flat line
– Eddy current loss: round line < flat line (thicker)
– Circular lines have clear advantages in high-frequency applications
7.4 Proximity Effects
Proximity effects :
– Magnetic field interaction of adjacent conductors
– Uneven current distribution
– Increased wear and tear
Effect on round and flat lines :
– Circle line: smaller proximity effect (circular symmetry)
– Flat line: large proximity effect (rectangular asymmetry)
– Flat wires need to be considered in dense windings
7.5 Dielectric properties
BDV (breakdown voltage) :
– Round wire paint film is thin and even
– Flat line paint film is vulnerable in the corners
– High stability of circular BDV
Insulation resistance :
– Round line: homogeneous thin paint film
– Flat wire: covered on all sides, slightly low insulation resistance
-Not much difference
VIII. Mechanical Performance Comparison
8.1 Anti-short circuit electric power
Electric power formula :
F = B × I_sc × L
Electrodynamic Differences :
– Round line: weak resistance (easy to deform)
– Flat wire: strong resistance (resistant to deformation)
– Anti-short circuit ability of flat wire is 50-100% higher than that of round wire
Design highlights :
– Flat wire for low-voltage windings of large transformers
– Flat wire for large motors
– Circular line for small and medium-sized
8.2 Anti-vibration
Circle line :
– Circular symmetry
– Consistent anti-vibration in all directions
– Moderate vibration resistance
Flat wire :
– Rectangular cross-section
– Strong bending resistance on the long side
– Weak resistance to bending in the short side direction
– Anti-vibration directivity
Compare :
– The circular line is more stable in random vibrations
– Strong vibration resistance of the flat wire in a specific direction
– Preferred circular line when anti-vibration needs are high
8.3 Deformation resistance
Circle line :
– Tensile: 30-40% (elongation)
– Stress resistance: easily deformed
– Bending resistance: evenly rounded
Flat wire :
– Tensile: 15-25%
– Stress resistance: Strong deformation resistance
– Bending resistance: directionality
Compare :
– Flat wire is 30-50% more resistant to deformation than round wire
– High current winding preferably flat wire
8.4 Assembly process
Circle line :
– Discrete windings (manual/automatic)
-Easy to embed wires
– Suitable for small batches
Flat wire :
– Hairpin windings
– Automation equipment
– Suitable for large volumes
IX. Typical Application Case Comparison
9.1 NEV Drive Motor
Application : 160 kW PMSM
Circle Schemes :
– Circle: Φ 1.0-1.4 mm
– Slot full rate: 45-50%
– Power density: 5-6 kW/kg
– Efficiency: 93-95%
– End height: 30-40 mm
– Weight: 30-35 kg
Hairpin :
– Flat wire: 1.5 x 4 mm or 1.6 x 5 mm
– Slot Fill Rate: 70-75%
– Power density: 8-10 kW/kg
– Efficiency: 95-97%
– End height: 20-25 mm
– Weight: 20-25 kg
Comparative conclusion :
– Flat wire has 60-80% higher power density than round wire
– Flat wire is 2-3% more efficient than round wire
– Flat line is 25-30% lighter than round line
– The flat line is 30-40% shorter than the rounded end
9.2 High-efficiency industrial motors
Application : 15 kW IE4 three-phase asynchronous motor
Circle Schemes :
– Circle: Φ 1.0-1.3 mm
– Slot Fill Rate: 40-45%
– Efficiency: 93-94%
– Cost: 100%
Flat wire solution :
– Flat wire: 1.2 x 3 mm or 1.5 x 4 mm
– Slot full rate: 65-70%
– Efficiency: 95-96%
– Cost: 120-130%
Comparative conclusion :
– Flat wire is 1.5-2% more efficient than round wire
– Flat wire costs 20-30% more than round wire
– Flat line investment payback period < 1 year (energy saving)
9.3 Wind power direct drive generator
Application : 3 MW permanent magnet direct drive wind turbine
Circular scheme (rare) :
– Circle: Φ 1.5-2.5 mm
– Slot Fill Rate: 35-45%
– Power density: low
– End height: higher
Flat Wire Scheme (Standard) :
– Flat wire: 2 x 6 mm or 2.5 x 8 mm
– Slot full rate: 70-80%
– Power Density: High
– End height: lower
– Efficiency: 97-98%
Comparative conclusion :
– Flat wire is standard for direct drive wind power
– High groove fill rate and efficiency
– Mature manufacturing process
9.4 Traction transformer
Application : 25 MVA traction transformer low voltage winding
Circle Schemes :
– Circular line: Φ 2-3 mm (multiple strands in parallel)
– Slot Fill Rate: 45-55%
– Anti-short circuit: General
Flat wire solution :
– Flat wire: 2 x 6 mm or 2.5 x 8 mm
– Slot Fill Rate: 65-75%
– Short circuit resistance: Strong
Comparative conclusion :
– Preferred flat wires for high current occasions
– Anti-short circuit ability flat wire height 50-100%
– Flat wires are commonly used for traction transformers
9.5 5 Application Scenarios Comprehensive Comparison
| Apply | Circle | Flat | Recommend |
|---|---|---|---|
| NEV motor | Φ 0.8-1.4 mm | 1.5-3 × 4-8 mm | Flat wire |
| Efficient industrial motor | Φ 0.8-1.5 mm | 1.2-2 × 3-6 mm | Flat wire |
| Wind direct drive | Φ 1.5-2.5 mm | 2-3 × 6-10 mm | Flat wire |
| Traction transformer | Φ 2-3 mm | 2-3 × 5-10 mm | Flat wire |
| HF transformer | Φ 0.05-0.3 mm | Leeds wire | Circular wire |
X. Calculation and evaluation of winding efficiency
10.1 Winding efficiency composite index
Winding efficiency W_eff = f (slot full rate, power density, copper consumption, temperature rise, cost)
Overall Efficiency Score (out of 100):
– Circle: Overall score 70-80
– Flatline: Overall score 85-95
10.2 Key Calculation Formula
Cross-sectional area formula :
– Circle: A = π × Φ ²/4
– Flat wire: A = a × b
Resistance calculation :
-R = ρ × L/A
Copper consumption calculation :
-P_cu = I ² × R
Slot full rate calculation :
– Circle: SFF = n × A_cu/A_slot
– Flat wire: SFF = n × A_cu/A_slot
10.3 Efficiency assessment 6 dimensions
| Dimension | Circle Score | Flat Score |
|---|---|---|
| Slot Full Rate | 60-70 | 85-95 |
| Power Density | 65-75 | 90-95 |
| Cooling | 70-80 | 80-90 |
| Manufacturing | 90-95 | 70-80 |
| Cost | 85-95 | 70-80 |
| Lifespan | 80-90 | 85-95 |
| Composite | 75-85 | 80-90 |
10.4 Selection Decision Tree
Identify scenarios
↓
High power/high power density?
├─ It's a → flat line.
└─ No → Continue
↓
High Frequency/Low Voltage?
├─ Is → Circle Line (Thin Line)
└─ No → Continue
↓
Small batches/special shapes?
├─ Is → Circle Line
└─ No → Continue
↓
Budget sensitive?
├─ Is → Circle Line
└─ No → Flat wire
XI. Selection Guide
11.1 6 Major Dimension Selection Comparison
| Dimension | Circular Line Advantage | Flat Line Advantage |
|---|---|---|
| Groove Full Rate | Disadvantages (30-50%) | Strengths (60-90%) |
| Power Density | Disadvantages | Advantages (2-5x) |
| End size | Medium | Advantages (20-40% shorter) |
| Cooling | Medium | Advantages (10-30% better) |
| Short circuit resistance | Disadvantages | Advantages (strong 50-100%) |
| High Frequency | Strengths | Disadvantages |
| Simple process | Advantages | Disadvantages |
| Cost | Benefits | Disadvantages |
| Shaped windings | Advantages | Disadvantages |
| High Volume | Medium | Benefits |
11.2 7 Major Selection Recommendations
Recommendation 1: New energy vehicle drive motor → flat wire (Hairpin)
Recommendation 2: High-efficiency industrial motor → flat wires
Recommended 3: Wind turbine direct drive generator → flat line
Recommended 4: Traction Transformer Low Voltage Winding → Flat Wire
Recommended 5: High-frequency transformer → circular line (thin line or Leeds line)
Recommended 6: Universal appliance motor → circular wire
Recommended 7: Special-shaped/small-batch → circular lines
11.3 Criteria for upgrading circular → flat lines
Need to upgrade :
– Insufficient power density → upgrade
– Inefficient → escalation
– Over-volume/weight → upgrades
– Anti-short circuit → escalation
Upgrade costs :
– Enameled wire cost: +30-50%
– Winding equipment: +200-500%
– Process cost: +20-30%
– Overall: +30-50%
Upgrade payback period :
– Energy saving: 1-3 years
– Performance improvement: 5-10 years
– Combined: 1-2 years
XII. 20 Glossary of Terms
| Chinese | English | Abbreviations | Definitions |
|---|---|---|---|
| Circular wire | Round Magnet Wire | – | Enameled wire with circular cross-section |
| Flat Wire | Flat/Rectangular Magnet Wire | – | Enameled Wire with Rectangular Section |
| Groove Fill Rate | Slot Fill Factor | SFF | Conductor Area as % of Groove Area |
| Power Density | PD | Power per volume or weight | |
| Copper consumption | Copper loss | P_cu | Loss of current through winding copper wire |
| Skin Effect | – | Phenomena of AC Current Tending to the Surface of a Conductor | |
| Proximity Effect | – | Proximity Effect | |
| Eddy Current Loss | – | Loss due to eddy current in conductor | |
| End Winding | – | Part of the coil that protrudes from the inside of the core groove to the outside of the groove | |
| Hairpin Winding | – | How to insert the winding into the slot after preforming the flat wire | |
| VPI Impregnation | Vacuum Pressure Impregnation | VPI | Vacuum + Pressure Impregnation Process |
| Litz Wire | – | High Frequency Line with Strands | |
| BDV | Breakdown Voltage | BDV | Breakdown Voltage |
| Dielectric Loss | tan δ | Dielectric Loss in AC Field | |
| DC Resistance | DC Resistance | R_dc | Resistance measured under DC conditions |
| AC Resistance | AC Resistance | R_ac | Resistance measured under AC conditions |
| Conductor Cross-Section | Conductor Cross-Section | A | Conductor Vertical Cross-Section Area |
| Lacquer Film | Enamel Coating | – | Insulation on the surface of the enameled wire |
| Inserting Winding | – | Inserting a Winding into a Core Groove | |
| Winding Efficiency | Winding Efficiency |
XIII. LP Winding Wire Company Introduction
LP Winding Wire is the world’s leading manufacturer of winding wires. Its main products include enameled wires, paper coated wires, glass fiber coated wires, Nomex paper coated wires, PI film coated wires and other series.
Round line products :
– Ultra-fine circular line : Φ 0.05-0.3 mm (high-frequency transformer)
– Fine circular line : Φ 0.3-1.0 mm (appliance motor, relay)
– Standard circular line : Φ 1.0-3.0 mm (general motors, transformers)
– Thick circular line : Φ 3.0-10 mm (large transformer, low-voltage winding)
– Leeds wire : Φ 0.05-0.2 mm multi-stranded (high frequency)
Flat wire products :
– Thin flat wire : 0.5-1.0 × 2-5 mm (small motor, special application)
– Standard flat wire : 1.0-2.0 × 3-8 mm (new energy vehicles, industrial motors)
– Thick flat wire : 2.0-3.0 × 5-12 mm (wind power, traction)
– Large flat wire : 3.0-5.0 × 8-25 mm (large transformer, direct drive generator)
– Hairpin flat wire : 1.5-3.0 × 4-10 mm (Hairpin motor)
Top 8 Dedicated Products :
– Hairpin for NEV motors :
– High groove full rate flat wire
– Heat resistant H grade paint film
– Supporting automated production
– For wind power direct drive generators :
– Large cross-section flat wire
– Thick paint film (> 80 μm)
– VPI impregnation
– For efficient industrial motors :
– Medium cross-section flat wire
– Paint film heat-resistant grade F
– IE4/IE5 efficiency
– For traction transformers :
– Large cross-section flat wire
– Anti-short circuit
– Elastomer potting
– For high-frequency transformers :
– Circular line Φ 0.05-0.5 mm
– Leeds Line
– Low dielectric loss
– For General Motors :
– Standard circle
– Enameled wire
– IEC 60317 certified
– Special for special-shaped windings :
– Circle line
– Abnormal adaptation
– Small batch customization
– For large transformers :
– Round + flat combination
– Anti-short circuit
– 60 year lifespan
Core strengths :
– Full size circular wire (Φ 0.05 -10 mm)
– Full size flat wire (0.5-5 × 2-25 mm)
– Round + Flat Wire Combination Scheme
– UL, VDE, TÜV, CCC, CSA, Keri fully certified
– IEC 60317/GB 6109/GB 7095
– Dedicated Hairpin Hairpin Winding Line
– Annual capacity of 50,000 tons
Contact :
– Official Website : https://www.lpwindingwire.com
– Email : sales@lpwindingwire.com
XIV. Summary and Outlook
Circular vs. flat lines is a core issue in winding line selection, flat lines are preferred in most high power applications , but circular lines still have an irreplaceable position in high frequency and profiled scenarios.
14.1 Core Comparison Conclusions
| Dimension | Circle Line | Flat Line | Winner |
|---|---|---|---|
| Groove Fill Rate | 30-50% | 60-90% | Flat |
| Power Density | 1x | 2-5x | Flat |
| End Height | 100% | 60-80% | Flat |
| Cooling | Medium | Good | Flat |
| Short circuit resistance | Weak | Strong | Flat wire |
| High Frequency | Good | Bad | Circle |
| Shaped Winding | Good | Bad | Round Line |
| Process | Simple | Complex | Circular |
| Cost | Low | High | Circle |
| composite | 75-85 points | 80-90 points | flat wire |
14.2 5 Future Trends
- Increased flatline penetration : from 30% → 50% (5-10 years)
- Hairpin hairpin popularization : NEV standard
- Circular line + Leeds line high-frequency : high-frequency transformer mainstream
- Appearance of special-shaped flat wires : Application of heterogeneous iron cores
- Smart Manufacturing Upgrade : Round + Flat Wire Automation
14.3 6 Tips for Action
- Clarify application scenarios : power, frequency, space, budget
- Evaluate groove full rate needs : > 60% → flat line, < 50% → circular line
- Assess Power Density Requirements : → High Power Flats
- Assess process capability : Hairpin capability → flat line priority
- Assess cost budget : budget tight → circle
- Long-term return on investment : energy saving + performance → flat line long-term better
14.4 Selection decision table
| Apply | Circle | Flat | Best Choice |
|---|---|---|---|
| NEV Drive | Φ 0.8-1.4 mm | 1.5-3 × 4-8 mm | Flat Wire |
| High-efficiency industrial motors | Φ 0.8-1.5 mm | 1.2-2 × 3-6 mm | Flat wire |
| Wind Direct Drive | Φ 1.5-2.5 mm | 2-3 × 6-10 mm | Flat Wire |
| Traction Transformer | Φ 2-3 mm | 2-3 × 5-10 mm | Flat Wire |
| High-frequency transformer | Φ 0.05-0.5 mm | Leeds wire | Circular wire |
| General appliances | Φ 0.3-1.0 mm | 1-1.5 × 2-4 mm | Circular wire |
| Shaped winding | Φ 0.5-2 mm | – | Circular line |
| Relay Coil | Φ 0.05-0.3 mm | – | Circular Wire |
LP Winding Wire offers circular + flat all-scene winding wire solutions – from new energy vehicles to industrial motors, from wind power to traction, from high frequency transformers to profiled windings.
XV. Appendix A: Round vs. Flat 5 Key Technical Parameters Quick ReferenceCheck
| Parameters | Circle Typicals | Flatline Typicals | Units | Impacts |
|---|---|---|---|---|
| Slot Fill Rate SFF | 30-50 | 60-90 | % | Space Utilization |
| Space Utilization | 70-78 | 90-95 | % | Section Efficiency |
| Power Density | 1.0 | 2-5 | Double | Volume Efficiency |
| End Height | 100 | 60-80 | % | Overall Dimensions |
| Short Circuit Resistance | 1.0 | 1.5-2.0 | Times | Reliability |
XVI. Appendix B: 6 Key Control Points in Flat Wire Production Processn process
B.1 Paint film thickness control
The thickness of the flat wire paint film is uneven on all sides and at the corners, the thinest paint film at the corners (stress concentration), which requires special processes to ensure:
| Part | Film Thickness | Film Uniformity |
|---|---|---|
| Middle of Long Edge | 60-80 μm | Excellent |
| Middle of short edge | 50-70 μm | Good |
| Corner | 30-50 μm | Poor |
| End | 40-60 μm | Medium |
Control method :
– Mold Design Optimization (Pultrusion Mold Angle)
– Multiple paint processes
– Online Paint Film Thickness Gauge
– Rounded corner treatment (instead of sharp corners)
B.2 Rounding of corners
Flat line corners changed from sharp corners to R0.3-1.0 mm rounded corners :
– Reduced stress concentration
– Uniform film thickness
– 20-30% increase in BDV
– 30-50% longer life
B.3 Embedding process
Flat Wire Embedding :
– Hairpin: Flat wire preform → insertion groove → welding
– Waveform winding: flatline direct waveform winding
– Automation equipment: Accuracy ± 0.1 mm
B.4 Welding process
Flat wire end welding :
– TIG welding (preferred)
– Laser welding (high precision)
– Ultrasonic welding (specific applications)
– Connector resistance < 1.2x busbar resistance
B.5 Insulation treatment
Flat wire insulation :
– Outsourced Insulation: Paper/Film/Nomex
– Impregnation: VPI Vacuum Pressure Impregnation
– End: insulating paint/insulating sleeve
– Surface treatment: epoxy coating
B.6 End forming
Hairpin end :
– Preform: Flat bend 90-180°
– Insertion slot: Automation equipment
– End expansion: laser cutting
– Welded end: TIG welded
– Insulation treatment: paint/sleeve
XVII. Appendix C: Round Wire + Flat Wire Hybrid Application Plan
C.1 Hybrid scenarios
Scenario 1: NEV drive motor
– Flat wire stator windings (high power density)
– Circular rotor winding (simple process)
– Comprehensive advantages: high power density + controllable cost
Scenario 2: Efficient industrial motors
– Flat wire high voltage winding (high efficiency)
– Circular low-voltage windings (cost)
– Comprehensive advantages: high efficiency + low cost
Scenario 3: Traction transformer
– Flat wire low voltage winding (high current)
– Round wire high-voltage windings (HV)
– Comprehensive advantages: short circuit resistance + high voltage
Scenario 4: Wind power direct drive generator
– Flat wire stator windings (high power)
– Circular rotor winding (permanent magnet protection)
– Comprehensive advantages: high efficiency + safety
C.2 Circular + Flatline Economy Analysis
| Scenario | Round Line Cost | Flat Line Cost | Mixed Cost | Recommended Scenario |
|---|---|---|---|---|
| Pure Circular | 100% | – | – | General Motors |
| Pure Flat Wire | – | 130% | – | High Efficiency Motor |
| Hybrid | 30% | 100% | 80% | Performance + Cost Balance |
| Circular + Leeds | 100% | – | – | HF Transformer |
C.3 Round + Flat Line Transition Scheme
Transition from round to flat line :
1. Evaluate the need for escalation
2. Invest in Hairpin equipment
3. Train craftsmen
4. Trial production validation
5. Mass production
Transitional costs :
– Equipment investment: 5-20 million
– Process validation: 1-3 million
– Training costs: $500-1 million
– Total investment: 6.5-24 million
Transitional gains :
– 60-80% increase in power density
– 1-3% increase in efficiency
– Energy-saving payback period: 1-2 years
– Long-term return on investment: 5-10x
XVIII. Appendix D: 5 Major Typical Industry Application Selections
D.1 New energy vehicles
Application : Drive motor
Recommended : Flatline Hairpin
Specifications : 1.5-3 × 4-8 mm
Slot full rate : 70-75%
Benefits : High power density, high efficiency
D.2 Industrial motors
Application : IE4/IE5 High Efficiency Motor
Recommended : Flat wire
Specifications : 1.2-2 × 3-6 mm
Slot full rate : 65-70%
Benefits : High efficiency and energy savings
D.3 Wind power generation
Applications : direct/semi-drive generators
Recommended : Large flat wire
Specifications : 2-3 × 6-10 mm
Slot full rate : 70-80%
Benefits : High power, high efficiency
D.4 Traction system
Application : traction motor, traction transformer
Recommended : Flat wire
Specifications : 1.5-3 × 4-10 mm
Slot full rate : 65-75%
Benefits : Short circuit resistance, high power density
D.5 High frequency power supply
Applications : high-frequency transformers, inductors
Recommended : Round or Leeds line
Specifications : Φ 0.05-0.5 mm
Advantages : low eddy current loss, low impedance