In high-voltage grid equipment, “Partial Discharge (PD)” is one of the most common causes of aging and failure of insulation systems.PD is not a monolithic breakdown, but a discharge phenomenon in a localized area of the insulation interior or surface.Seemingly weak, but each discharge will cause irreversible damage to the insulating material, long-term accumulation will inevitably lead to insulation breakdown, equipment downtime, and even power grid accidents.
1.1 Definition and Classification of Partial Discharge
According to the discharge position, PD is divided into three categories:
| Type | Discharge Location | Typical Scenario | Degree of Hazard |
|---|---|---|---|
| Internal Discharge | Insulated Internal Air Gap | Paint Film, Impregnated Paint, Composite Insulation | Medium |
| Surface discharge | Insulated surface | Insufficient end, creepage distance | Serious |
| Corona discharge | Gas medium | Conductor tip, winding end | Severe |
1.2 4 Hazards of Partial Discharge
- Insulation corrosion : high-energy electrons, ozone, nitric acid directly attack the insulation molecular chain
- Local temperature rise : The instantaneous temperature at the discharge point can reach 1000°C, and the conductor is locally melted
- Chemical degradation : The discharge produces strong oxidizing agents (O, NO) to age the insulation
- Electromagnetic interference : High frequency pulse interference relay protection, communication, control system
1.3 Typical PD scenarios in grid equipment
- High voltage transformer : inter-turn insulation, end insulation, lead insulation
- GIS combo appliances : basin insulator, SF gas insulation
- High voltage motor : stator winding, winding end, slot wedge
- High voltage cables : XLPE insulation, connectors, terminals
- Transformer (CT/PT) : secondary winding, core insulation
- High voltage reactor : winding, inter-turn insulation
II. International standard system for partial discharge: IEC 60270/IEC 60885
2.1 IEC 60270 Partial Discharge Measurement Standard
IEC 60270 High-voltage test techniques – Partial discharge measurements is the international standard for PD measurements.The test methods for core parameters such as PD charge (pC), apparent discharge, and discharge repetition rate are specified.
2.2 Enameled wire PD test related standards
| Standard Number | Name | Scope of Application | Key Parameters |
|---|---|---|---|
| IEC 60270 | High Voltage Testing Technology – Partial Discharge Measurement | All High Voltage Equipment | Apparent Charge (pC) |
| IEC 60851-5 | Enameled wire test method – Electrical properties | Enameled wire | Breakdown voltage, PD starting voltage |
| IEC 60885-1 | Cable PD Testing | Power Cables | PD Start Voltage, Extinction Voltage |
| ASTM D1868 | Enameled Wire PD Pulse Detection | Enameled Wire North America | Discharge Charge Capacity |
| ASTM D2275 | Enameled Wire Voltage Durability | Enameled Wire North America | Time to Failure |
| IEEE 4 | General Principles of High Voltage Testing Technology | North American High Voltage Equipment | PD Test Methods |
| IEEE 1434 | Motor Stator Winding PD Measurement | Rotating Motor | PD Strength Evaluation |
| GB/T 7354 | Partial discharge measurement | China | Equivalent to IEC 60270 |
2.3 Detailed explanation of PD key parameters
- PD start voltage (PDIV, Partial Discharge Inception Voltage) : the lowest voltage at which PD is initiated
- PD Extinction Voltage (PDEV, Partial Discharge Extinction Voltage) : maximum voltage when PD is off
- Apparent Charge : Instantaneous charge transfer caused by PD, in pC
- Pulse Repetition Rate : PD pulses per second
- PD Magnitude : Discharge Energy Composite
2.4 Typical PD Limits
| Equipment Type | Operating Voltage | Allowed PD Amount | Test Criteria |
|---|---|---|---|
| High voltage transformer | 110 kV | < 50 pC | IEC 60270 |
| High Voltage Cables | 35 kV | < 5 pC | IEC 60885 |
| High Voltage Motor | 6 kV | < 100 pC | IEEE 1434 |
| GIS | 110 kV | < 10 pC | IEC 60270 |
| Transformer | 35 kV | < 20 pC | IEC 60270 |
III. Core design of PD-resistant enameled wire: paint film chemistry and structure
3.1 Mechanism of PD penetrating the paint film
PD destroys the paint film through three mechanisms:
1. Electron bombardment : high-energy electrons directly interrupt C-C, C-H bonds
2. Chemical oxidation : Strong oxidizing agents such as O, NO, etc. react with the paint film
3. Thermal effect : Thermal degradation due to local temperature rise
3.2 Core ingredients of PD-resistant paint film
| Ingredients | Action | Typical Materials | Content |
|---|---|---|---|
| Polymer Matrix | Foundation Insulation, Adhesion | PI/PEI/Pai | 70-90% |
| Nanofiller | Dispersive electric field, barrier discharge | TiO ₂/Al ₂ O ²/SiO ₂/BN | 5-20% |
| Plasticizers | Improved Flexibility | Phthalates | 1-5% |
| Crosslinkers | Improved Temperature Resistance | Melamine | 1-3% |
| Antioxidants | Anti-aging | Phenolic Antioxidants | 0.1-1% |
3.3 Paint film structure design
The modern PD-resistant enameled wire film adopts a “gradient structure”:
| Layer | Location | Thickness | Key Ingredients | Features |
|---|---|---|---|---|
| Bottom | Copper conductor interface | 5-10 μm | PEI/Pai | Adhesion, buffering |
| Intermediate layer | Body | 30-50 μm | PI + nanofiller | Insulation, barrier PD |
| Surface | Air contact | 5-15 μm | PD resistant coating | Ozone and UV resistant |
| Shielding layer (optional) | Outermost layer | 3-5 μm | Semiconductor paint | Dispersed surface electric field |
3.4 Key Performance Indicators for PD Resistant Paint Film
| Metrics | Test Methods | Typical (PEI-based) | Typical (PI-based) |
|---|---|---|---|
| PDIV | IEC 60851-5 | > 1.5 kV | > 2.0 kV |
| Breakdown Voltage | IEC 60851-5 | > 6 kV | > 8 kV |
| Voltage Durability | ASTM D2275 | > 100 h | > 200 h |
| Dielectric Loss tan δ @ 1 kHz | IEC 60250 | < 0.01 | < 0.008 |
| Volume resistivity | IEC 60093 | > 10 ¹ ² Ω · cm | > 10 ¹ ² Ω · cm |
| Temperature rating | ASTM D2307 | 180°C | 220°C |
IV. ASTM D2275 Voltage Durability Test: PD Performance Evaluation
4.1 Test principle
ASTM D2275 is the core method for evaluating PD resistance of enameled wires.Principle: Apply a 50/60 Hz AC voltage (typically 1-3 kV) to the twisted pair sample until the film breaks down (short circuit), recording duration (in hours).PD-resistant life is measured in hours.
4.2 Test parameters
| Parameters | Typicals | Description |
|---|---|---|
| Test Voltage | 1.0-3.0 kV | Much higher than rated voltage, accelerated aging |
| Frequency | 50/60 Hz | Power Frequency |
| Temperature | 23-180°C | Room or Operating Temperature |
| Sample | Twisted Pair | IEC 60851-5 specification |
| Failure Criteria | Paint Film Breakdown | Sudden Current Increase |
| Typical lifetime | 50-500 h | PD-resistant enameled wire |
4.3 Relationship between life and voltage
The relationship between PD life and test voltage follows the inverse power law:
L = K × V^(-n)
where L is the lifetime, V is the test voltage, K and n are constants (n is usually 2-4). This means:
– Voltage increased by 20%, life shortened by 30-50%
– Voltage reduced by 20%, life extended by 50-100%
4.4 Comparison with other aging tests
| Dimensions | ASTM D2275 PD Aging | ASTM D2307 Heat Aging | ASTM D3137 Moisture Resistance |
|---|---|---|---|
| Main stresses | Voltage | Temperature | Humidity |
| Failure mechanism | Electrochemical corrosion of paint film | Thermal oxidative degradation | Hydrolysis |
| Typical life | 50-500 h | 1,000-20,000 h | 100-1,000 h |
| Main applications | High voltage power grid equipment | All enameled wires | Outdoor, humid environments |
V. Five typical applications of power grid equipment: PD-resistant enameled wire engineering practice
5.1 Case 1: 110 kV power transformer
A power grid company’s 110 kV oil-immersed power transformer with a capacity of 50 MVA. The low-voltage winding (10 kV side) uses NEMA MW 35-C PD-resistant enameled wire, which has been operated for 15 years without PD failure.
5.2 Case 2: High Voltage Motor
A large chemical company’s 6 kV high-voltage motor, 800 kW. Ordinary PEI enameled wire was originally used, but a PD alarm occurred after 3 years of operation. Switched to IEC 60317-42 PD-resistant enameled wire, and it has been running without abnormality for 8 years.
5.3 Case 3: GIS combined electrical transformer
A 220 kV GIS station uses an electromagnetic voltage transformer (PT). The secondary winding uses PD-resistant enameled wire (PI-based). The PD test has always been <10 pC after 12 years of operation.
5.4 Case 4: Wind farm box transformer
A 35 kV box-type transformer (ZGS11-Z.F series) in a wind farm, located at an altitude of 3000 m, in a high-humidity, low-pressure environment (exacerbating PD). Using IEC 60317-56 PD-resistant enameled wire, there have been zero PD failures in 5 years.
5.5 Case 5: High voltage cable intermediate joint
A certain 110 kV high-voltage cable intermediate joint uses PD-resistant enameled wire (PI-based, 200°C) for wrapping insulation. There is no PD signal after 10 years of operation.
VI. Five engineering suggestions for selecting PD-resistant enameled wires
6.1 Recommendation 1: Select according to voltage level
| Operating voltage | Recommended PD resistance level | Paint film thickness | Standard |
|---|---|---|---|
| < 1 kV | No special resistance to PD required | Grade 1 | IEC 60317-8/13 |
| 1-3 kV | Basic PD resistant | Grade 2 | IEC 60317-42 / NEMA MW 35-C |
| 3-10 kV | Enhanced PD | Grade 3 | IEC 60317-56 / NEMA MW 36-A |
| 10-35 kV | Top PD resistant + shielding | Grade 3 + shielding | Custom solutions |
| > 35 kV | Multi-layer insulation system | Multi-layer structure | Customized |
6.2 Recommendation 2: Selection based on PD severity
Three elements of PD severity assessment:
– Voltage Amplitude: The higher, the harsher
– Frequency: High frequencies (such as PWM) are more severe
– Environment: High humidity, low pressure, and filth are more severe
6.3 Recommendation 3: Selection based on temperature and heat dissipation conditions
| Temperature Rating | Recommended Paint Films | PD Resistance Lifetime | Typical Applications |
|---|---|---|---|
| Class 130 (130°C) | PU + PD-resistant coating | > 50 h | Small transformers |
| Class 155 (155°C) | PE + PD-resistant coating | > 80 h | Industrial motors |
| Class 180 (180°C) | PEI + PD-resistant coating (IEC 60317-42) | > 150 h | Power transformers, high-voltage motors |
| Class 200 (200°C) | PAI + PD-resistant coating | > 200 h | High-end power equipment |
| Class 220 (220°C) | PI + PD-resistant coating (IEC 60317-56) | > 300 h | UHV, traction |
6.4 Suggestion 4: Pay attention to the “four resistance” properties of the paint film
- PD resistant: ASTM D2275 Lifetime > 100 h
- Heat Resistance: ASTM D2307 Lifetime > 20,000 h @ temperature grade
- Moisture Resistance: ASTM D3137 Lifetime > 500 h @ 95% RH
- Chemical Resistant: Resistant to transformer oil, SF₆, SF₆ decomposition products
6.5 Recommendation 5: Consider manufacturing and quality
- Paint uniformity: film thickness tolerance < ±2 μm
- Degree of cure: Degree of cure > 95% (DSC test)
- Pinhole control: number of pinholes < 5 / 100m
- Adhesion: no cracking in winding test (IEC 60851-3)
VII. PD online monitoring and diagnosis technology
7.1 The necessity of PD online monitoring
Traditional periodic maintenance is difficult to catch the early signs of PD. Online monitoring can:
– Capture PD pulses in real time
– Identify PD type and location
– Evaluate the remaining life of the insulation
– Early warning of potential failures
7.2 4 major methods of PD monitoring
| Methods | Principles | Advantages | Limitations |
|---|---|---|---|
| Electrical pulse method | Monitor PD current pulses | Highly sensitive and quantitative | Susceptible to interference |
| UHF ultra-high frequency method | Monitoring 300-3000 MHz electromagnetic waves | Anti-interference, accurate positioning | Expensive equipment |
| Acoustic emission method | Monitor the sound generated by PD | Accurate positioning | Low sensitivity |
| Chemical methods | Monitoring SF₆ decomposition products | Suitable for GIS | Slow reaction |
7.3 Typical PD monitoring system
- Transformer PD Monitoring: UHF sensor + acoustic emission + oil chromatography
- GIS PD monitoring: mainly UHF sensors
- Motor PD Monitoring: Stator Slot Coupler + Offline/Online Monitoring
- Cable PD Monitoring: High Frequency Current Transformer (HFCT)
VIII. Future trends: Development direction of PD-resistant enameled wire technology
8.1 Trend 1: Development of UHV power grid
The development of 1100 kV UHV transmission in China and ±800 kV / ±1100 kV DC transmission worldwide has put forward higher requirements for PD-resistant enameled wires. As the voltage level increases to 1000 kV, the difficulty of PD control increases exponentially.
8.2 Trend 2: New insulation materials
- Polyetheretherketone (PEEK): temperature resistance 250°C, excellent mechanical properties
- Polyimide Aerogel (PI Aerogel): Ultra-low dielectric constant
- Boron Nitride Nanotubes (BNNT): Ultra-high breakdown strength
- MXene 2D material: tunable dielectric properties
8.3 Trend 3: Intelligent PD Monitoring
- 5G + IoT PD monitoring network
- AI algorithm identifies PD type
- Digital twin predicts insulation life
- Blockchain ensures the credibility of monitoring data
8.4 Trend 4: Environmental protection and sustainability
- Solvent-free paint film process (zero VOC emissions)
- Bio-based paint film (soybean oil, citric acid)
- Recyclable paint film design
- Life cycle assessment (LCA)
IX. FAQ: Frequently asked questions about PD-resistant enameled wire
9.1 What is the difference between PD-resistant enameled wire and corona-resistant enameled wire?
PD-resistant enameled wire focuses on partial discharge inside and on the surface of the insulation, and the evaluation methods are mainly PDIV and ASTM D2275. Corona-resistant enameled wire focuses on the discharge (corona) of gas medium, and the evaluation method is mainly ASTM D2275. The two often overlap in practical applications, Modern PD-resistant enameled wires usually also have corona-resistant properties.
9.2 How old does a PDIV need to be to qualify?
PDIV (PD Inception Voltage) should be at least 1.5-2 timesof the operating voltage. For example, for a high-voltage motor with an operating voltage of 6 kV, the PDIV should be > 9-12 kV.
9.3 What is the price of PD-resistant enameled wire?
Usually 30-100% more expensive than ordinary enameled wire. However, considering the catastrophic consequences of insulation failure (equipment damage, power outage, fire), the cost performance is much higher than that of ordinary enameled wire.
9.4 How does the PD life of enameled wire match the life of equipment?
The design life of power grid equipment is usually 30-40 years. Enameled wires with PD life > 100 h (ASTM D2275 @ 2 kV, 50 Hz) should be selected during the design stage.
9.5 How to prevent enameled wire PD failure?
- Strictly control paint film quality (thickness, uniformity, pinholes)
- Optimize winding design (avoid electric field concentration)
- Control operating environment (temperature, humidity, cleanliness)
- Install PD online monitoring system
X. Conclusion: PD-resistant enameled wire is the cornerstone of long life of power grid equipment
Although PD-resistant enameled wire only accounts for 1-5% of the cost of power grid equipment, it directly determines the reliability and life of the equipment. In major projects such as UHV, underground cables, offshore wind power, and urban power grid transformation, PD-resistant enameled wire is an irreplaceable key basic material.
When selecting, you should comprehensively consider the voltage level, PD severity, temperature level, application scenarios, certification standards, and supplier strength, and select qualified products that comply with IEC 60270, IEC 60851-5, ASTM D2275, and IEEE 1434 standards. Suppliers should provide complete test reports, PD life curves, and application cases.
LP Winding Wire offers a full range of PD-resistant enameled wire products, including IEC 60317-42 (180°C PEI), IEC 60317-56 (220°C PI), NEMA MW 35-C, NEMA MW 36-A, NEMA MW 38-C, and more. All products are certified by ASTM D2275, IEC 60270, UL 1446, VDE, TÜV, CCC. For technical consultation, PD life testing, and application solution design, please contact LP Winding Wire sales engineers.
XI. Appendix: Key Parameters Cheat Sheet
11.1 PD parameter quick check
| Parameters | Symbol | Units | Typical range |
|---|---|---|---|
| PD onset voltage | PDIV | kV | 0.5-5.0 |
| PD extinction voltage | PDEV | kV | 0.4-4.5 |
| Apparent discharge | q | pC | 1-1000 |
| Discharge repetition rate | n | pps | 1-10⁶ |
| PD intensity | Q | nC/s | 0.1-1000 |
| Average discharge current | I | μA | 0.001-10 |
11.2 Quick check of paint film thickness
| Paint film grade | Thickness range | Breakdown voltage (PEI) | Breakdown voltage (PI) |
|---|---|---|---|
| Grade 0 | < 18 μm | < 1.5 kV | < 2.0 kV |
| Grade 1 | 18-30 μm | 1.5-3.5 kV | 2.0-4.5 kV |
| Grade 2 | 30-50 μm | 3.5-6.0 kV | 4.5-8.0 kV |
| Grade 3 | 50-80 μm | 6.0-9.0 kV | 8.0-12.0 kV |
| Grade 4 (Special) | > 80 μm | > 9.0 kV | > 12.0 kV |
11.3 Temperature level quick check
| Temperature Rating | Operating Temperature | Recommended Paint Films | Typical Lifetime |
|---|---|---|---|
| Class A | 105°C | PVF | 20,000 h |
| Class E | 120°C | PVF / PE | 20,000 h |
| Class B | 130°C | PU / PE | 20,000 h |
| Class F | 155°C | PE | 20,000 h |
| Class H | 180°C | PEI | 20,000 h |
| Class N | 200°C | PAI | 20,000 h |
| Class R | 220°C | PI | 20,000 h |
| Class 240 | 240°C | PI / PEEK | 20,000 h |
11.4 PD-resistant enameled wire selection process
1.Determine the working voltage: rated voltage, maximum working voltage
2. Assess PD severity: voltage amplitude, frequency, environment
3. Determine the temperature level: operating temperature, maximum temperature rise
4. Select paint film grade: Grade 1/2/3
5. Select paint film type: PEI / PAI / PI
6. Determine PDIV requirements: ≥ 1.5-2 times operating voltage
7. Verified PD life: ASTM D2275 ≥ 100 h
8. Confirm certification standards: UL / VDE / TÜV / CCC
9. Select suppliers: quality, production capacity, service
10. Establish a testing mechanism: incoming material inspection, PD online monitoring
XII. 20 Glossary of terms
| Chinese | English | Abbreviation | Definition |
|---|---|---|---|
| Partial Discharge | PD | A discharge in a localized area of the insulation that does not penetrate the entire insulation | |
| Apparent discharge | Apparent Charge | q | Instantaneous charge transfer caused by PD, unit pC |
| PD Inception Voltage | PD Inception Voltage | PDIV | The lowest voltage that induces PD |
| PD Extinction Voltage | PD Extinction Voltage | PDEV | The highest voltage when PD is extinguished |
| Dielectric Loss Tangent | tan δ | Energy loss index of insulating materials in AC electric field | |
| Dielectric constant | Dielectric Constant | εr | Polarization ability of materials |
| Glass transition temperature | Glass Transition Temperature | Tg | The temperature at which the paint film changes from the glass state to the rubber state |
| Film Grade | Film Grade | – | Paint film thickness grade specified by IEC 60317 |
| Temperature Class | Thermal Class | – | Rated operating temperature of enameled wire |
| Breakdown Voltage | Breakdown Voltage | BDV | The critical voltage when the paint film is broken down |
| Twisted Pair | Twisted Pair | – | Sample preparation method for enameled wire withstand voltage test |
| Nano Filler | Nano Filler | – | Inorganic particles with particle size < 100 nm |
| Volume Resistivity | ρv | DC resistance per unit volume | |
| Surface Resistivity | Surface Resistivity | ρs | DC resistance per unit surface area |
| Relative Permittivity | Relative Permittivity | εr | Dielectric constant of material relative to vacuum |
| UHF Sensor | UHF Sensor | – | Sensor that monitors 300-3000 MHz electromagnetic waves |
| High Frequency Current Transformer | HFCT | High Frequency Transformer for monitoring PD current | |
| Acoustic Emission | Acoustic Emission | AE | Elastic waves generated when materials are deformed or damaged |
| Oil Chromatography Analysis | Dissolved Gas Analysis | DGA | Diagnose transformer faults by analyzing dissolved gases in oil |
| Gas Insulated Combined Electrical Equipment | Gas Insulated Switchgear | GIS | High-voltage power distribution equipment using SF₆ gas insulation |
XIII. LP Winding Wire Company Introduction
LP Winding Wire is an international enterprise specializing in the R&D, production and sales of high-performance enameled wire. Its main products include enameled round copper wire, enameled round aluminum wire, enameled flat copper wire, paper-covered wire, fiberglass winding wire, transposed wire, etc.
Core Advantages:
– Complete product certifications: UL, VDE, TÜV, CCC, CSA fully covered
– Production Capacity Scale: Annual production capacity of 50,000 tons, ranking among the top in the industry
– Application areas: motors, transformers, home appliances, new energy, rail transit, wind power, photovoltaics
– Core Technology: PD-resistant enameled wire (Partial Discharge Resistant), Corona-resistant enameled wire (Corona Resistant), high-temperature resistant enameled wire (200°C / 220°C), new energy-specific enameled wire
– Service Commitment: Technical consultation, sample testing, PD life assessment, customized development, global logistics
Contact Information:
– Official website: https://www.lpwindingwire.com
– Email: sales@lpwindingwire.com
– Phone: +86 138-XXXX-XXXX
– WhatsApp: +86 138-XXXX-XXXX
XIV. Practical suggestions and misunderstandings for engineers
14.1 3 common misunderstandings when selecting a model
Myth 1: The higher the PDIV, the betterA PDIV that is too high may mean that the paint film is too thick, affecting heat dissipation and winding slot fill ratio. PDIV should be selected based on 1.5-2 times the actual operating voltage.Myth 2: Ignoring environmental factorsHigh humidity, low air pressure, and pollution can significantly aggravate PD. The actual operating environment must be considered when selecting.Misunderstanding 3: Only look at the price but not the PD lifeCheaper enameled wire often has short PD life and the cost of insulation failure is much higher than the initial cost savings.
14.2 3 key points of manufacturing process
1.Paint Uniformity: Paint film thickness deviation < ±2 μm
2. Pinhole control: Number of pinholes < 5 / 100m
3. Cure Degree: > 95% (DSC test)
14.3 3 major precautions in use
- Avoid mechanical damage: Prevent scratches on the paint film during the wire winding and wire embedding processes.
- Avoid chemical corrosion: Avoid long-term contact with strong acids, strong alkali, and organic solvents
- Periodic testing: Key equipment undergoes PD testing every 2-3 years
14.4 PD fault diagnosis and processing
| Troubleshooting | Possible causes | Solutions |
|---|---|---|
| PD alarm | Insufficient PDIV of paint film | Clean and check electric field distribution |
| PD continues to rise | Insulation aging | Shorten inspection cycle and plan replacement |
| PD mutation | Sudden insulation defect | Emergency power outage, detailed diagnosis |
| PD intermittent | Environmental factors | Improve operating environment |
XV. Summary and Outlook
As a key basic material for power grid equipment, PD-resistant enameled wire plays an irreplaceable role in UHV, underground cables, offshore wind power, rail transportation, new energy and other fields. As the voltage level of the power grid continues to increase and the operating environment becomes increasingly harsh, the performance requirements for PD-resistant enameled wires will become increasingly higher.
Future development directions include:
– Higher voltage level: 1100 kV UHV, ±800 kV DC
– Longer Life: 30, 40, 50 year life design
– More Harsh Environment: high humidity, low pressure, strong pollution, strong radiation
– Smarter Monitoring: 5G + AI + Digital Twin
– Greener materials: solvent-free, bio-based, recyclable
LP Winding Wire is willing to work together with global power grid equipment manufacturers, power companies, and research institutions to jointly promote the progress and innovation of PD-resistant enameled wire technology and contribute to global energy transformation and grid security.
XVI. In-depth analysis: PD physical mechanism and breakdown process
16.1 Microscopic process of partial discharge
The microscopic process of partial discharge can be divided into four stages:
Initiation: There are air gaps, impurities, and electric field concentration points inside or on the insulation. When the external electric field reaches a critical value, the air in the air gap is ionized and initial electrons are produced.
Propagation: The initial electrons gain energy under the acceleration of the electric field and collide with gas molecules to generate new electrons (electron avalanche). Photons are released during the avalanche process, which further trigger photoionization.
Sustainment: Under AC voltage, PD occurs repeatedly in each half-wave cycle. Each discharge releases a certain amount of charge.
Extinction: When the applied voltage is lower than the extinction voltage (PDEV), the PD stops.
16.2 Damage mechanism of PD to paint film
There are three main mechanisms by which PD damages paint films:
- Electron bombardment mechanism: High-energy electrons (energy 2-10 eV) directly break the C-C bonds (bond energy 3.5 eV) and C-H bonds (bond energy 4.3 eV) of the paint film
- Chemical oxidation mechanism: O₃, NO, NO₂ and other strong oxidants generated by discharge react with the paint film
- Thermal degradation mechanism: The temperature at the discharge point instantly reaches 200-1000°C, causing thermal degradation of the paint film
16.3 Time evolution of breakdown process
The PD breakdown process can be divided into three stages:
- PD initial period(0-10% life span): PDIV decreases and PD begins to occur frequently
2.PD development period(10-80% lifespan): PD intensity gradually increases, and visible damage begins to appear on the paint film
3.PD expiration date(80-100% life span): PD strength increases sharply, and eventually the paint film breaks down
16.4 Factors affecting PD lifespan
-Electric field strength: The higher the electric field strength, the shorter the PD life (inverse power law)
– Frequency: The higher the frequency, the shorter the PD life
– Temperature: Rising temperature accelerates paint film aging
– Humidity: PD is significantly aggravated in high-humidity environments
– Air Pressure: PD starting voltage decreases under low air pressure
– Mechanical stress: Bending and vibration cause micro-cracks in the paint film and shorten the life of the PD
XVII. The relationship between PD-resistant enameled wire and reliability of power grid equipment
17.1 Statistical rules of power grid equipment failures
According to statistics from the International Conference on Large Power Grids (CIGRE), the causes of high-voltage equipment failures are distributed as follows:
| Reasons for failure | Proportion | Main causes |
|---|---|---|
| Insulation failure | 45% | PD accumulation, thermal aging |
| Mechanical failure | 20% | Vibration, wear |
| Thermal failure | 15% | Overload, poor cooling |
| Chemical corrosion | 10% | Oil deterioration, SF₆ decomposition products |
| Others | 10% | Design, manufacturing, operation and maintenance |
Insulation failure is the number one cause of grid equipment failure, and PD is the main cause of insulation failure.
17.2 Impact of PD-resistant enameled wire on equipment life
Take a 110 kV power transformer as an example:
– Using ordinary enameled wire: design life is 30 years, actual life is 20-25 years
– Use PD-resistant enameled wire: design life is 30 years, actual life is 30-40 years
The economic benefits of extended life are much greater than the additional cost of PD-resistant enameled wire.
17.3 Life cycle cost analysis (LCC)
| Cost item | Ordinary enameled wire | PD-resistant enameled wire | Difference |
|---|---|---|---|
| Initial Purchase | 100% | 130% | +30% |
| Installation Cost | 100% | 100% | 0 |
| Maintenance Cost | 100% | 70% | -30% |
| Failure Cost | 100% | 30% | -70% |
| Lifespan | 20 years | 30 years | +10 years |
| LCC (30 years) | 100% | 80% | -20% |