Paper Covered Wire in Transformer Coil Design – A Complete Guide
I. Introduction: Transformer Coil Design – The Core Application for Paper Covered Wiref paper wrapped wires
The Transformer Coil/Winding is the core component of the transformer and carries out the key tasks of power conversion, voltage conversion, and energy transfer . In the field of transformer design, coil design accounts for 50-60% of the transformer design workload and is a key factor in determining transformer performance, life, volume, and cost.
Paper Covered Wire (PCW) As the main insulation material for transformer coils, it has been 130 + years of application since its invention in the 1890s, and is still the preferred material for oil-immersed transformer coils.
6 core parameters for coil design :
– Voltage class: 220 V – 1,000 kV
– Capacity range: 1 kVA – 1,500 MVA
– Impedance voltage: 4-25%
– Short circuit current: 10-100 kA
– Temperature Limit: 65-75 K
– Insulation class: A/E/B/F/H/N/C
Coil type : cylindrical, pie (continuous/spiral/kinky), foil, layered, multilayer cylinder, shielded winding
Core Design Objectives :
– Electrical performance: impedance, efficiency, waveform, noise
– Mechanical properties: short circuit resistance, vibration resistance, impact resistance
– Thermal performance: temperature rise, heat dissipation, lifetime
– Cost: materials, manufacturing, transportation, maintenance
– Reliability: failure rate, lifetime, insulation coordination
1.1 8 Major Trends in Transformer Coil Design
| Trends | Key Points | Impact on Paper Envelopes |
|---|---|---|
| High Voltage | 1,000 kV + | Thick Insulation |
| Large Capacity | 1,500 MVA + | Large Section |
| Energy Saving and Low Loss | SCB/HV Steel | Thin Insulation |
| High Reliability | Short Circuit Resistance | VPI Immersion |
| High Frequency Switching Power Supply | High Frequency | Stranded Cable |
| Intelligent | Digital Twin | Online Monitoring |
| New Energy | Wind/Photovoltaic/Energy Storage | Special Insulation |
| Extreme Environment | Extreme Cold/Extreme Heat/Corrosion | Composite Insulation |
1.2 Six core roles of paper wrapped wires in transformer coil design
| Role | Mechanism | Proportion |
|---|---|---|
| Main Insulation | Paper + Oil Combo | 70% |
| Turn Insulation | Paper Layer Isolation | 60% |
| Layer Insulation | Paper Insulation Cartridge | 80% |
| Electrostatic Shielding | Shielding Paper/Foil | 100% |
| Mechanical support | Short circuit resistance | 50% |
| Cooling tunnel | Oil tunnel | 100% |
II. 8 Basic Structures of Transformer Coils
2.1 Cylindrical Winding/Layer Winding
Structural characteristics :
– Multilayer winding in axial direction
– Circular/rectangular cross-section
– For transformers with lower voltage (< 35 kV) and smaller capacity
– Single or Multilayer
Applicable :
– Distribution transformer (630 kVA or less)
– Voltage 35 kV and below
– Larger current and fewer turns
Application of paper wrapping :
– Single layer winding, 4-6 layers of paper
– Interlayer insulation: cable paper 0.12-0.5 mm
– End insulation: reinforced tape
– Oil channel: strut + cardboard
Benefits :
– Simple structure and easy to manufacture
– Good heat dissipation
– Low cost
Cons :
– Weak resistance to short circuits
– Difficult to do high voltage
– Fewer turns
2.2 Continuous Winding
Structural characteristics :
-Continuous winding by multiple wire cakes
– No solder joints
– for 110-220 kV, 5-50 MVA
– Circular/rectangular conductors
Applicable :
– 110-220 kV medium transformer
– Oil-immersed power transformers
– Medium Capacity
Application of paper wrapping :
– Insulation between cakes: cable paper + strut
– Turn insulation: 6-10 layers of cable paper
– Electrostatic shielding: metal foil
– VPI impregnation (optional)
Benefits :
– Strong resistance to short circuits
– Good heat dissipation
– High manufacturing efficiency
Cons :
– Complex workmanship
– Difficult to maintain
– Medium cost
2.3 Spiral Winding
Structural characteristics :
– Multiple conductors spirally wound in parallel
-Inter-turn insulation is paper layer
– For high current (> 1,000 A) low voltage windings
– Circular/translocation conductor
Applicable :
– High-current low-voltage windings
– 35 kV and below
– 5-50 MVA transformer low voltage windings
Application of paper wrapping :
– Multiple parallel conductors
– Displacement treatment (elimination of eddy current)
– Turn Insulation: Cable Paper 4-6 Layers
– End: transposition paper + insulated end ring
Benefits :
– High current capacity
– Good heat dissipation
– Strong resistance to short circuits
Cons :
– Complex workmanship
– Highly restricted
– Higher costs
2.4 Interleaved Winding
Structural characteristics :
– Special winding process (tangle type)
– Inter-turn voltage is 2x turn voltage
– For high-voltage transformers
– For 110-500 kV high voltage windings
Applicable :
– 110-500 kV high voltage windings
– Coils with higher starting voltages
– Transformers with high lightning impact requirements
Application of paper wrapping :
– Turn insulation: 8-12 layers of cable paper (thick insulation)
– Inter-segment insulation: insulated cardboard
– Electrostatic shielding: foil/paper
– VPI impregnation (recommended)
Benefits :
– Optimization of the initial voltage distribution
– Resistant to lightning shock
– High voltage adaptation
Cons :
– Extremely complex workmanship
– Difficult to maintain
– High cost
2.5 Foil Winding
Structural characteristics :
– Copper/Aluminum Foil Winding
– Interlayer insulation: paper/film
– For low-voltage high current
– Simple and reliable
Applicable :
– 10 kV and below
– Welding transformer
– High current rectifier transformer
– Capacity 1-5 MVA
Application of paper wrapping :
– Foil + Paper Layer Combo
– Interlayer insulation: cable paper 0.2-0.5 mm
– End: lead insulation
– Electrostatic shielding: metal foil
Benefits :
– High current capacity
– Compact structure
– Good heat dissipation
– Low cost
Cons :
– Voltage restricted
– Risk of insulation damage
– Uneven heat dissipation
2.6 Shielded Winding
Structural characteristics :
– Main winding + shielded winding
– Shielded winding open circuit
– Improved voltage distribution
– For high-voltage transformers
Applicable :
– 110-500 kV high voltage windings
– High starting voltage
– High requirements for lightning strikes
– Harmonic suppression is demanding
Application of paper wrapping :
– Shielded winding: 2-4 layers of paper wrapped wire
– Main winding: 6-10 layers of paper
– Shielding: metal foil + insulation paper
– VPI impregnation (recommended)
2.7 Multilayer Cylindrical Winding
Structural characteristics :
– Multilayer winding
– Interlayer insulation: cable paper
– For high-voltage transformers
– Voltage 110-500 kV
Applicable :
– High voltage 110 kV and above
– High-voltage windings for distribution transformers
– Transformer
Application of paper wrapping :
– Multilayer paper wrapping (1-3 turns per layer)
– Interlayer insulation: cable paper 0.5-2 mm
– End: Insulated end ring
– VPI impregnation
2.8 Comparison Table of 8 Coil Structures
| Coil Type | Voltage | Capacity | Current | Complexity | Cost | Anti-short circuit |
|---|---|---|---|---|---|---|
| Cylinder | Low | Small | Medium | ★ | ★ | |
| Continuous | High | Medium | Medium | ★★★ | ★★ | |
| Spiral | Low | Medium | Large | ★★★ | ★★★ | ★★★★ |
| Tangled | Tall | Large | Medium | ★★★★ | ★★★★ | |
| Foil | Low | Small | Large | ★★ | ★ | ★★★ |
| Shielded | High | Medium | Medium | ★★★★ | ★★★★ | |
| Multilayer Cylinder | Medium High | Medium Small | Medium | ★★★ | ★★★ |
III. Application of Paper Covered Wire in Main Coil Design
3.1 Conductor Selection Design
Conductor material :
– Soft copper (T1/T2/TU1/TU2)
– Silver-copper alloy (high-strength soft copper)
– Soft aluminum (1060/1350)
– Copper clad aluminum (CCA)
Conductor shape :
– Circular wire (Φ 1.0-10 mm)
– Flat conductor (1.0-5 mm thick, 4-20 mm wide)
– Transposed wire (stranded)
– Foil (0.5-3 mm thick)
Selection calculation :
– Current density: 2-4 A/mm ²
– Voltage Design: Upper Current Density Limit
– Temperature rise check: matched with load, heat dissipation
3.2 Number of turns and insulation design
Calculation of the number of turns :
N = V/(4.44 × f × A × B)
Where:
N = number of turns
V = Voltage (V)
f = Frequency (Hz)
A = cross-sectional area of iron core (m ²)
B = magnetic flux density (T)
Voltage per turn (V/turn) :
– Power distribution: 1-10 V
– Electricity: 20-100 V
– Large power: 50-200 V
– UHV: 100-300 V
Turn insulation thickness :
– Below 10 kV: 0.3-0.5 mm
– 10-35 kV: 0.5-1.0 mm
– 35-110 kV: 1.5-3 mm
– 110-500 kV: 3-8 mm
– Above 500kV: 8-15mm
Number of wrapping layers :
– Circle: Floors 4-12
– Flat wire: 6-10 layers
– Shielding: Add 2-4 layers
3.3 Impedance voltage design
Impedance voltage formula :
U_k % = Z × I/V × 100%
Where:
Z = Leak impedance (Ω)
I = rated current (A)
V = rated voltage (V)
Design Objectives :
– Power distribution: 4-6%
– Electricity: 6-12%
– UHV: 12-25%
Three elements of impedance design :
1. Conductor cross-sectional area : The larger the cross-sectional area, the smaller the resistance
2. Coil spacing : The greater the spacing, the greater the leakage resistance
3. Core window : The larger the window, the greater the adjustable range of impedance
Short circuit impedance matching :
– Matches system impedance
– Meet the needs of parallel operation
– Meet the short-circuit current limit
3.4 Main insulation design
Main insulation composition :
– Paper wrapped wire insulation
– Oil-immersed insulation
– Oil gap
– Insulated cardboard
– Struts, cushion blocks
– Electrostatic plate
Oil-paper insulation system :
– Oil-immersed cable paper (density 0.8-1.2 g/cm ³)
– High density cable paper (HV)
– Transformer oil (mineral/synthetic)
-Oilway design
Insulation distance design :
– Between high and low pressure: carton + oil channel
– Coil to core: insulated barrel + strut
– Coil-to-fuel tank: insulated cardboard
– End insulation: insulated end ring
IV. Application of Paper Covered Wire in Layer Insulation Designsign
Function of layer 4.1 insulation
Layer insulation :
-Wire layers isolating different potentials
– Provide mechanical support
– Form oil channel (heat dissipation + insulation)
Interlayer voltage :
– Cylindrical: voltage per layer = number of layers × turn voltage
– Multilayer cylinder: voltage per layer = total voltage/number of layers
– Continuous: voltage per pie = number of pies/total turns
Layer insulation thickness design :
– Voltage per layer < 1 kV: paper layer 0.5 mm
– 1-3 kV: paper layer 1.0 mm
– 3-5 kV: paper layer 1.5 mm
– 5-10 kV: paper layer 2.0 mm
4.2 Cable paper layer insulation design
Cable paper type :
– DL series: low dielectric loss cable paper (dielectric loss ≤ 0.002)
– DLD Series: Low Dielectric Loss High Density Cable Paper
– BLL series: thin insulated cable paper
– RX series: wrinkled cable paper
Cable Paper Specifications :
– Thickness: 0.07-0.5 mm
– Density: 0.75-1.30 g/cm ³
– Tensile strength: longitudinal ≥ 50-80 N/15mm
– Transverse ≥ 25-40 N/15mm
Design highlights :
– Thickness matches voltage
– Tensile strength meets winding stress
– Low dielectric loss
– Moisture content < 8%
4.3 Insulation design of insulated cardboard layers
Insulated cardboard thickness :
– Cylindrical layer insulation: 1-2 mm
– Continuous support: 2-4 mm
– End insulation: 5-10 mm
Insulated cardboard requirements :
– Density: 1.0-1.2 g/cm ³
– Compressive strength: ≥ 80 MPa
– Dielectric strength: ≥ 25 kV/mm
– Moisture content: < 6%
4.4 Oil passage design
Duct width :
– Cylindrical: 6-10 mm
– Continuous: 8-15 mm
– Spiral: 10-20 mm
– Tangle: 12-20 mm
Oil channel action :
– Heat dissipation
– Increase insulation distance
– Improved electric field distribution
Strut cushion block :
– Struts: cardboard strips (axial)
– Cushion blocks: cardboard blocks (circumferential)
– Number of struts: 8-24
– Number of cushion blocks: 8-36 cubes
V. Application of Paper Covered Wire in Turn Insulation Designgn
5.1 Importance of turn insulation
Turning insulation characteristics :
– Minimum withstand voltage (1-100 V/turn)
– but the damage is most severe (direct short-circuit)
– 50-70% of insulation failures
– Must be 100% reliable
Insulating material for turns :
– Enameled wire film
– Cable paper (outer layer)
– DDP rhombus dispensing paper (bonded)
– Resin (bonding, potting)
Turn insulated structure :
-Paint film (enameled wire)
– Paper layers 1-12 (outer layer)
– Impregnated resin (VPI)
– Air/oil clearance
5.2 Turn Insulation Thickness Design
Formula for insulation thickness of turns :
d = V_turn/E_allowance
Where:
d = turn insulation thickness (mm)
V_turn = Voltage between turns (V)
E_allowance = Design dielectric strength (kV/mm)
Typical Design Value :
– 220 V/turn: paper layer 0.1-0.2 mm
– 1 kV/turn: paper layer 0.2-0.4 mm
– 3 kV/turn: paper layer 0.4-0.8 mm
– 10 kV/turn: paper layer 1.0-2.0 mm
– 30 kV/turn: paper layer 3.0-5.0 mm
5.3 Enameled wire + cable paper composite turn insulation
Structure :
– Interior: Enameled wire coating (100-200 μm)
– Middle layer: cable paper 4-8 layers (0.5-3 mm)
– Outer layer: adhesive resin
Benefits :
– Paint film provides uniform thin insulation
-Paper layer provides main insulation
– Resin bonding in one piece
– VPI impregnation enhancement
5.4 Turn insulation breakdown risk
Cause of breakdown :
– Broken paint film (mechanical damage)
– Paper layer defects (pinholes, delamination)
– High moisture content
– Process defects (welding, crimping)
– Running aging
Risk control :
– 100% factory test
– Automatic winding equipment
– Moisture content < 8%
– Manufacturing environmental controls
VI. Application of Paper Covered Wire in Main-Longitudinal Insulation Designn design
6.1 Main – Vertical Insulation Design Principles
Main Insulation :
– Insulation between high and low voltage coils
– Withstand lightning shock + power frequency voltage
– Design strength ≥ long-term withstand voltage
Longitudinal Insulation :
– Insulation between different parts within the same winding
– Between turns, between layers, between cakes
– Withstand Lightning Shock + Operational Shock
– Designed strength ≥ lightning shock resistance
4 challenges of vertical insulation :
1. Uneven start voltage distribution (uneven turn voltage at high frequencies)
2. Lightning Impact Gradient (4-6x power frequency)
3. Operating impact gradient (1.5-2x power frequency)
4. Resonant overvoltage
6.2 Voltage distribution under lightning shock
Lightning wave equivalent frequency : 100 kHz – 1 MHz
Voltage distribution characteristics :
– The first few turns carry most of the voltage
– Damped oscillation
– Is prone to insulation breakdown
Countermeasures :
– Tangled winding (improved voltage distribution)
– Electrostatic shielding
– Shielded winding
– Lightning arrester protection
6.3 Electrostatic shielding design
Block type :
– Electrostatic plate (copper/aluminum foil)
– Shielded windings (separate windings)
– Semiconducting paper (new)
Electrostatic plate action :
– Improved electric field distribution
– Limit starting voltage
– Prevents metal particles from discharging
Shielding design :
– Thickness: 0.05-0.2 mm (copper/aluminum foil)
– Insulation: cable paper 0.5-1.0 mm
– End insulation: reinforced
– Lead insulation: insulated sleeve
6.4 Role of VPI impregnation in insulation design
VPI (Vacuum Pressure Impregnation) :
– Vacuum → pressurized impregnation → curing
– Resin-filled paper gap
– Integrity enhancement
VPI effect :
– 30-50% increase in BDV
– 50% better short-circuit resistance
– 20% reduction in dielectric loss
– 50% longer life
Scenario for VPI :
– High voltage transformer
– Traction transformer
– Wind Power Transformer
– Dry transformer (included)
VII. Application of Paper Covered Wire in Special Coil Design
7.1 Traction transformer coil design
Traction transformer characteristics :
– Strong vibration (10-100 m/s ²)
– Frequent short circuits
– High temperature fluctuations
– Limited installation space
Wrapper selection :
– Soft copper + high density cable paper
– Elastomer potting
– VPI impregnation
– DDP diamond dispensing
Coil Design Essentials :
– Anti-vibration structure
– Elastomer fixation
– Vibration damping installation
– Strong oil circulation cooling
Cases :
– Qinghai-Tibet Railway Traction Transformer
– High-speed rail EMU transformers
– Urban rail transit transformer
7.2 Wind Power Transformer Coil Design
Wind Power Transformer Characteristics :
– High humidity (coastal)
– Salt spray corrosion
– Strong vibration
– Frequent stops and starts
Wrapper selection :
– Soft copper + corrosion resistant paper
– Corrosion resistant coating
– Fully sealed design
– VPI impregnation
Coil Design Essentials :
– Corrosion resistant housing
– Vibration damping installation
– Strong oil circulation
– On-line temperature monitoring
7.3 Offshore wind power transformer coil
Special challenges :
– High humidity (> 95%)
– Salt spray corrosion
– Strong winds (> 60 m/s)
– Vibration (10-30 m/s ²)
Wrapper selection :
– Soft copper + corrosion resistant paper
– Tinned copper conductor
– Stainless steel enclosure
– Fully sealed design
7.4 Nuclear Power Transformer Coil Design
Nuclear power transformer characteristics :
– High reliability (> 99.99%)
– Long life (60 years)
– Radiation resistant
– Safety related (Level 1E)
Wrapper selection :
– PI enameled wire
– Radiation resistant cable paper
– Radiation resistant mineral oil
– 60 year lifespan design
Design Requirements :
– High quality standards
– Earthquake resistant
– Radiation resistant
– Online monitoring
– Redundant design
7.5 Test transformer coil design
Test transformer characteristics :
– High voltage (> 1,000 kV)
– Short-term use (intermittent work)
– High insulation strength
– Low current
Wrapper selection :
– Soft copper + thick paper layer
– High density cable paper
– Multi-layer insulated tubes
– Special oil treatment
7.6 HVDC converter transformer coil
HVDC converter transformer characteristics :
– Bidirectional commutation voltage stress
– High DC component
– Harmonics
– High reliability
Wrapper selection :
– High density cable paper (HV)
– Low moisture content
– Special oil treatment
– VPI impregnation
VIII. Application of Paper Covered Wire in Temperature Rise Designe design
8.1 Transformer temperature rise
Temperature Limit (IEC 60076/GB 1094):
– Oil top layer temperature rise: ≤ 55-60 K
– Average oil temperature rise: ≤ 50-55 K
– Winding temperature rise (resistance method): ≤ 65 K
Hotspot temperature :
– Design hotspot temperature: < 98°C
– Alarm temperature: < 110°C
– Trip temperature: < 120°C
Relationship between envelope life and temperature :
– Arrhenius’ Law
– For every 10°C increase in temperature, life is halved
-98°C: 30-40 years
– 110°C: 15-20 years
8.2 Thermal design
Cooling method :
– Oil-immersed self-cooling (Onan)
– Oil-immersed air cooling (ONAF)
– Strong oil circulation (OF)
– Forced Oil Circulation Guide (OD)
Cooling channel :
– Oil passage (vertical + horizontal)
– Strut oil passage
– Cardboard oil lanes
– End oil channel
Covered wire heat dissipation :
– Paper layer porous structure (oil flow)
– Paper + oil composite insulation
-Oilway design
– Strong oil circulation
8.3 Hotspot temperature control
Hotspot temperature rise control 6 major technologies :
1. Strong oil circulation (OF)
2. Forced Oil Direction (OD)
3. Multiple parallel oil channels
4. Coil temperature monitoring
5. Fiber Optic Temperature Sensor
6. Intelligent online load control
IX. Application of Paper Covered Wire in Short Circuit Resistance Designt design
9.1 Short circuit electrodynamic analysis
Short circuit electrodynamic formula :
F = B × I_sc × L
Where:
F = Electrodynamic (N)
B = magnetic flux density (T)
I_sc = short-circuit current (A)
L = conductor length (m)
Short circuit current multiple :
– Three-phase short circuit: 10-25 times rated current
– Single-phase short-circuit: 5-15 times rated current
– Large transformers: > 50 kA
3 key features of electrodynamics :
1. Sudden : lasts only 0.1-1 s
2. Transient : 100-1,000 times normal operation
3. Cumulative : multiple short-circuit cumulative damage
9.2 Anti-short circuit design 6 major measures
Measure 1: Use soft copper
– Elongation 30-40%
– Strong deformation resistance
– High strength soft copper preferred
Action 2: Add paper layer
– Floors 8-12 (vs. Floors 4-6)
– Overall mechanical strength +20-30%
Measure 3: VPI impregnation
– Integrity enhancement
– +50% resistance to displacement
Measure 4: End Reinforcement
– DDP diamond dispensing
– Epoxy ties
– End ring reinforcement
Action 5: Tightening optimization
– Spring platen
– Anti-loose fastening
– Overall potting
Action 6: Simulation optimization
– Finite Element Analysis
– Short circuit test validation
– Optimized winding structure
9.3 Anti-short circuit test
Short circuit test standard (IEC 60076-5):
– Number of tests: 6-9
– Test current: 10-25 times rated
– Duration: 0.5-1 s
– Judgment criteria: deformation of winding < 1%, change in reactance < 5%
Post-test testing :
– Impedance measurement (impedance change)
– Visual inspection
– Disassembly inspection (if necessary)
– BDV test
X. Process Design of Coil Manufacturing
10.1 Winding process
Wrapping equipment :
– Automatic winding machine (CNC)
– Horizontal winder
– Vertical winder
– Foil winder
Winding parameters :
– Tension: 5-50 N (matches conductor cross-section)
– Speed: 10-100rpm
– Routing: automatic routing
– Counting: Automatic counting
10.2 Welding and connection
Welding method :
– Silver welding (preferred)
– TIG welding
– Laser welding
– Brazing
Welding requirements :
– Minimum connector resistance
– High mechanical strength
-No false soldering
– Solder joints are smooth
Connection method :
– Welding (preferred)
– Crimping (specific application)
– Bolted (removable)
10.3 VPI impregnation process
VPI Process Flow :
1. Pre-drying: moisture removal (80-100°C/8-24 h)
2. Vacuum: Remove air (< 100 Pa)
3. Pressure impregnation: resin infiltration (0.6-0.8 MPa)
4. Pressure relief: atmospheric drip drying (1-2 h)
5. Curing: Heat curing (80-150°C/8-12h)
VPI resin :
– Epoxy
– Polyester
– Modified epoxy
– Flame retardant epoxy
10.4 Drying and oil immersion
Drying process :
– Vacuum drying (< 100 Pa/110-130°C/48-96 h)
– Dew point temperature < -40°C
– Moisture content < 0.5% (winding)
Oil immersion process :
– Vacuum infusion (< 100 Pa/rt – 60°C)
– Mineral or synthetic oils
– Oil temperature 60-80°C
– Time 24-48 h
XI. Insulation Testing and Quality Control
11.1 Factory test
Winding DC resistance test :
– With double-armed bridges
– Deviation < 2% (phase to phase)
– Temperature conversion
Insulation resistance test :
– 5 kV insulation resistance meter
– R60/R10 ratio
– Absorption ratio > 1.3
– Polarization Index > 1.5
Dielectric loss test (tanδ):
– High voltage bridge
– Intermediate < 0.5%
– Capacitance measurement
Pressure withstand test (AC withstand):
– Power frequency withstand voltage: 2.5-3 times the rated voltage
– 1 minute
– No breakdown
11.2 Type test
Lightning Impact Test (LI):
– 1.2/50 μs wave
– Peak voltage (kV)
– Chopping test
– Full wave test
Operational Impact Test (SI):
– 250/2500 μs waves
– High voltage transformer
Temperature rise test :
– Total loss method
– Direct load method
– Short circuit method
11.3 Online monitoring
Monitoring 6 parameters :
1. Temperature (Fiber/Thermocouple)
2. Partial discharge (UHF/ultrasound)
3. Moisture content (oil-water separation)
4. Vibration (Accelerometer)
5. Noise (Sound Level Meter)
6. Oil chromatography (DGA)
XII. 20 Glossary of Terms
| Chinese | English | Abbreviations | Definitions |
|---|---|---|---|
| Transformer Coil | Transformer Coil/Winding | – | Key components of a transformer that consist of conductors and insulation |
| Paper Covered Wire | PCW | Cable Paper Covered Winding Wire | |
| Main Insulation | – | Insulation between high and low voltage coils | |
| Longitudinal Insulation | Longitudinal Insulation | – | Insulation between different parts within the same winding |
| Turn Insulation | – | Insulation between adjacent turns | |
| Electrostatic Shield | – | Metal Shield for Improved Voltage Distribution | |
| Lightning Arrester | Surge Arrester | – | Overvoltage Limiting Protector |
| Lightning Impulse | Lightning Impulse | LI | Analog Lightning Impulse Voltage |
| Operating Impulse | Switching Impulse | SI | Impulse voltage to simulate switch action |
| Voltage per Turn | V/t | Voltage per Turn | |
| Short Circuit Impedance | Short-Circuit Impedance | Zk | Short Circuit Impedance Percentage |
| Temperature Rise | Temperature Rise | ΔT | Temperature Rise of Winding or Oil |
| Oil Duct | – | Oil Duct | |
| Vacuum Pressure Impregnation | Vacuum Pressure Impregnation | VPI | Vacuum + Pressure Impregnation Process |
| DDP Rhombus Dispensing | Diamond Dotted Paper | DDP | Surface Glued Insulating Paper |
| Cylindrical Winding | – | Multilayer Winding Axially | |
| Continuous Coil | Continuous Winding | – | Continuous Winding of Multiple Wire Cakes |
| Spiral Winding | – | Multiple Parallel Spirals | |
| Tangled Coil | Interleaved Winding | – | Specially Winded High Voltage Coil |
| Foil Coil | Foil |
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.
Products for transformer coils :
– For cylindrical coils :
– Soft copper + cable paper 4-6 layers
– Flat copper wire
– Round copper wire
– Applicable: 10 kV and below distribution transformers
– For continuous coils :
– Soft copper + cable paper 6-10 layers
– Transposed copper wire
– Applicable: 110-220 kV medium transformer
– For spiral coils :
– Multiple strands of parallel soft copper
– Transposition Handling
– Applicable: 5-50 MVA low voltage windings
– For tangled coils :
– High strength soft copper
– High density cable paper 8-12 layers
– Applicable: 110-500 kV high voltage windings
– For foil coils :
– Copper foil + cable paper
– Applicable: Welding transformer
– For shielded coils :
– Special winding wire for electrostatic shielding
– Applicable: 110-500 kV high voltage windings
– Multi-layer cylinder dedicated :
– High density cable paper
– Applicable: High voltage 110 kV and above
– For VPI impregnation :
– Matching VPI envelope
– Good resin compatibility
– Applicable: Transformers with high strength requirements
Special products for 8 special coils :
– For traction transformers :
– Vibration resistant + cold resistant
– Elastomer potting
– Applicable: Qinghai-Tibet railway, high-speed railway
– For wind power transformers :
– Anti-corrosion + damping
-Salt spray resistance
– Applicable: Onshore/Offshore Wind
– For nuclear power transformers :
– PI + radiation resistance
– Level 1E certification
– 60 year lifespan
– Applicable: Nuclear Power Level 1E
– For HVDC converter transformers :
– DC resistant component
– Low dielectric loss
– Applicable: HVDC system
– For test transformers :
– High voltage (> 1,000 kV)
– Multi-layer insulated tubes
– Applicable: High pressure test
– For EAF transformers :
– High current
– Anti-short circuit
– Applicable: electric arc furnace
– For rectifier transformers :
– Resistant to harmonics
– High current
– Applicable: electrolysis, frequency conversion
– For Phase Shifting Transformers :
– Multiple windings
– Applicable: Tide control
Core strengths :
– Full coil construction coverage (8 types)
– Full voltage rating (220V – 1,000kV)
– Full capacity range (1 kVA – 1,500 MVA)
– Full temperature rise (65-75 K)
– UL, VDE, TÜV, CCC, CSA, Keri fully certified
– IEC 60076/GB 1094/IEEE standard
– Annual capacity of 50,000 tons
Contact :
– Official Website : https://www.lpwindingwire.com
– Email : sales@lpwindingwire.com
XIV. Summary and Outlook
Application of paper wrapped wire in transformer coil design covers all 8 major aspects of coil design – conductor, turn insulation, layer insulation, main insulation, longitudinal insulation, temperature rise, short circuit resistance, special applications.
14.1 8 large coil structure + paper wrapping scheme
| Coil Structure | Applicable Voltage | Applicable Capacity | Wrapped Wire Scheme |
|---|---|---|---|
| Cylindrical | < 35 kV | < 2.5 MVA | Soft copper + 4-6 layers of paper |
| Continuous | 110-220 kV | 5-50 MVA | Soft copper + 6-10 layers of paper |
| Spiral | < 35 kV | 5-50 MVA | Transposition Copper + Paper Layer 4-6 |
| Tangled | 110-500 kV | > 50 MVA | High strength soft copper + 8-12 layers of paper |
| Foil type | < 10 kV | < 5 MVA | Copper foil + paper layer 0.5 mm |
| Shielded | 110-500 kV | Medium | Shielded windings + 6-10 layers of paper |
| Multilayer Cylinder | 35-220 kV | < 5 MVA | Soft Copper + Paper Layer 6-8 Layers |
14.2 5 Core Design Principles
- Insulation coordination : Main insulation + vertical insulation + turn insulation coordination design
- Temperature rise control : 75K temperature rise limit + life guarantee
- Anti-short circuit : soft copper + VPI + reinforcement
- Reliability : 100% factory test + online monitoring
- Economy : material + manufacturing cost balance
14.3 6 Tips for Action
- Define transformer parameters : voltage, capacity, impedance, temperature rise
- Choose the coil structure : Choose the most suitable of the 8
- Design insulation system : main + longitudinal + turn insulation coordination
- Select paper wrapping : voltage level, insulation thickness, conductor material
- Simulation verification : Electromagnetic, thermal, mechanical simulation
- Test verification : ex-factory + type + special test
14.4 Top 5 Development Directions for the Future
- New structure : efficient winding structure, smart winding
- New insulation : PI + film + composite
- New process : Smart winding, automated VPI
- New applications : HVDC, superconducting, new energy
- New digitalization : digital twins, smart coils
LP Winding Wire is committed to providing all-scene paper wrapping solutions for transformer coil design – from distribution transformers to 1,000 kV UHV, from civil to nuclear, traction, wind, HVDC.
XV. Appendix A: 3 Major Fixed Selection Decision Tables
A.1 Selection by voltage level
| Voltage Level | Recommended Coil | Recommended Paper Wrap | Turn Insulation |
|---|---|---|---|
| < 10 kV | Cylindrical | Soft copper + paper layer 4-6 | 0.5-1.0 mm |
| 10-35 kV | Cylindrical/Continuous | Soft Copper + Paper Layer 6-8 Layers | 1.0-1.5 mm |
| 35-110 kV | Continuous/multilayer cylinder | Soft copper + 8-10 layers of paper | 1.5-2.5 mm |
| 110-220 kV | Continuous/Tangled | High Strength Soft Copper + Paper Layer 8-12 Layers | 2.5-4.0 mm |
| 220-500 kV | Tangled/Shielded | PI + High Density Paper 10-14 Layers | 4.0-6.0 mm |
| > 500 kV | Shielded + Tangled | PI + High Density Paper 14-20 Layers + Shielded | 6.0-10.0 mm |
A.2 Selection by capacity
| Capacity | Recommended coil | Current density | Paper wrapping specifications |
|---|---|---|---|
| < 630 kVA | Cylindrical | 3-4 A/mm ² | Φ1-3 mm |
| 0.63-2.5 MVA | Cylindrical | 2.5-3.5 A/mm ² | Flat 2-5 mm |
| 2.5-10 MVA | Cylindrical/Continuous/Foil | 2.5-3 A/mm ² | Flat 3-8 mm |
| 10-50 MVA | Continuous/Spiral | 2-3 A/mm ² | Displacement 5-15 mm |
| 50-200 MVA | Continuous/Tangled | 2-2.5 A/mm ² | Displacement 10-25 mm |
| > 200 MVA | Tangle/Shield | 1.5-2 A/mm ² | Displacement 15-50 mm |
A.3 Selection by insulation level
| Insulation Rating | Maximum Temperature Rise | Envelope Scheme | Application |
|---|---|---|---|
| Class A (105°C) | 60 K | Regular Paper + Mineral Oil | Vintage Transformers |
| Class E (120°C) | 75 K | Modified Paper + Mineral Oil | Universal Transformer |
| Class B (130°C) | 80 K | Modified Paper + Mineral Oil | Universal Transformer |
| Class F (155°C) | 100K | PE + Paper + Hot Oil | General Power Distribution |
| Class H (180°C) | 125 K | PI + Paper + Hot Oil | Traction, Specialty |
| Class N (200°C) | 145K | PI + Nomex + Silicone | Specialty, Wind |
| Class C (> 220°C) | > 150 K | PI + ceramic + silicone oil | Special high temperature |
XVI. Appendix B: 4 Major Special Application Selection Tables
B.1 New energy applications
| Applications | Capacity | Coils | Cords | Lifetime |
|---|---|---|---|---|
| Onshore wind | 5-10 MVA | Continuous | Soft copper + corrosion resistant paper | 25 years |
| Offshore wind | 5-15 MVA | Continuous | Soft copper + salt spray resistance | 30 years |
| Centralized PV | 5-20 MVA | Cylindrical/Continuous | Soft Copper + Class H | 25 years |
| Energy Storage pcs | 5-25 MVA | Cylindrical/Continuous | Soft Copper + Class H | 25 years |
B.2 Rail transit
| Applications | Capacity | Coils | Cords | Lifetime |
|---|---|---|---|---|
| High Speed Rail | 20-50 MVA | Cylindrical/Spiral | High Strength + Elastomer | 30 Years |
| Urban Rail Transit | 5-15 MVA | Cylindrical | Soft Copper + Anti-Vibration | 30 Years |
| Traction substation | 25-80 MVA | Continuous | Soft copper + elastomer | 30 years |
B.3 Industrial specialty
| Applications | Capacity | Coils | Cords | Lifetime |
|---|---|---|---|---|
| Arc furnace | 30-200 MVA | Spiral | Soft copper + Anti-short circuit | 20 years |
| HVDC | 100-500 MVA | Tangle/Shield | PI + Anti-DC | 30 years |
| Chemical Rectification | 5-50 MVA | Cylindrical | Corrosion Resistance + Soft Copper | 20 years |
| Test Transformer | 0.1-5 MVA | Multilayer Cylinder | High Strength + Thick Paper Layer | 30 Years |
B.4 High voltage special
| Applications | Capacity | Coils | Cords | Lifetime |
|---|---|---|---|---|
| UHV DC | 500-1500 MVA | Tangle/Shield | PI + HDPE + VPI | 40 years |
| Nuclear 1E | 1-10 MVA | Cylinder/Continuous | PI + Radiation Resistance | 60 years |
| Polar Extreme Cold | 1-50 MVA | Cylinder/Continuous | Soft Copper + Low Temperature Oil + Reinforcement | 30 Years |