短路额定值：为什么3GI3 EPR绝缘VDE电缆的短路温度设定为250°C，这对(N)TSCGECEWÖU的屏蔽层尺寸有何影响？
Short-Circuit Rating: Why is the Short-Circuit Temperature for 3GI3 EPR-Insulated VDE Cables Set at 250°C, and How Does This Impact Screen Sizing for (N)TSCGECEWÖU?
短路额定值：为什么3GI3 EPR绝缘VDE电缆的短路温度设定为250°C，这对(N)TSCGECEWÖU的屏蔽层尺寸有何影响？
Technical Analysis by Anhui Feichun Special Cable Co., Ltd.
安徽飞纯特种电缆有限公司技术分析
1. Introduction 引言
In the design of medium voltage mining and reeling cables such as the (N)TSCGECEWÖU, the short-circuit temperature rating of the insulation material fundamentally determines the cable’s fault current withstand capability. The 3GI3 EPR (Ethylene Propylene Rubber) compound specified in DIN VDE 0207 Part 20 has a maximum permissible short-circuit temperature of 250°C, which directly influences how engineers must size the metallic screen to safely conduct earth fault currents without thermal damage.
在设计诸如(N)TSCGECEWÖU等中压矿用和卷筒电缆时，绝缘材料的短路温度额定值从根本上决定了电缆的故障电流承受能力。DIN VDE 0207第20部分规定的3GI3 EPR（乙丙橡胶）化合物的最大允许短路温度为250°C，这直接影响工程师必须如何确定金属屏蔽层的尺寸，以安全传导接地故障电流而不会造成热损坏。
This technical analysis explains the thermodynamic basis for the 250°C limit, demonstrates the calculation methodology per IEC 60949 and IEC 60364-5-54, and shows how the (N)TSCGECEWÖU cable’s copper wire braid screen must be sized to meet specified fault current requirements in mining applications.
本技术分析解释了250°C限值的热力学基础，演示了根据IEC 60949和IEC 60364-5-54的计算方法，并展示了(N)TSCGECEWÖU电缆的铜丝编织屏蔽层必须如何确定尺寸以满足采矿应用中规定的故障电流要求。
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2. Understanding Insulation Thermal Limits 了解绝缘热极限
Every cable insulation material has three critical temperature thresholds that define its operational envelope. These temperatures are determined by the material’s molecular structure and its ability to maintain dielectric integrity under thermal stress. For 3GI3 EPR compound used in VDE mining cables, these thresholds represent carefully established limits beyond which the insulation risks permanent degradation.
每种电缆绝缘材料都有三个关键温度阈值，定义其操作范围。这些温度由材料的分子结构及其在热应力下保持介电完整性的能力决定。对于VDE矿用电缆中使用的3GI3 EPR化合物，这些阈值代表了经过仔细确定的极限，超过该极限绝缘有永久降解的风险。
| Insulation Type 绝缘类型 | Continuous Operation 持续运行 | Emergency Overload 紧急过载 | Short-Circuit Maximum 短路最大值 |
|---|---|---|---|
| PVC (Thermoplastic) PVC（热塑性） | 70°C | 100°C | 160°C (≤300mm²) / 140°C (>300mm²) |
| 90°C PVC (High-Temp) 90°C PVC（高温型） | 90°C | 110°C | 160°C / 140°C |
| 3GI3 EPR (VDE 0207-20) 3GI3 EPR | 90°C | 130-140°C | 250°C |
| XLPE (Cross-Linked PE) XLPE（交联聚乙烯） | 90°C | 130°C | 250°C |
| EPR 105°C Grade EPR 105°C等级 | 105°C | 140°C | 250°C |
| Silicone Rubber 硅橡胶 | 180°C | 220°C | 350°C |
The significantly higher short-circuit temperature of thermosetting insulations (EPR, XLPE) compared to thermoplastic PVC reflects the fundamental difference in their molecular structures. Thermosetting materials have cross-linked polymer chains that maintain structural integrity at elevated temperatures, while thermoplastic PVC softens and deforms, potentially causing insulation displacement and dielectric failure.
热固性绝缘（EPR、XLPE）的短路温度明显高于热塑性PVC，这反映了它们分子结构的根本差异。热固性材料具有交联聚合物链，可在高温下保持结构完整性，而热塑性PVC会软化和变形，可能导致绝缘位移和介电失效。
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3. Why 250°C for 3GI3 EPR Insulation 为什么3GI3 EPR绝缘是250°C
The 250°C short-circuit temperature limit for 3GI3 EPR insulation is not arbitrary but derives from extensive thermal aging studies and the material’s cross-linking chemistry. EPR (Ethylene Propylene Rubber) is a copolymer of ethylene and propylene monomers that undergoes vulcanization (cross-linking) during cable manufacturing. This cross-linking process creates a three-dimensional molecular network that provides thermal stability far beyond that of thermoplastic materials.
3GI3 EPR绝缘的250°C短路温度限制不是任意的，而是来源于广泛的热老化研究和材料的交联化学。EPR（乙丙橡胶）是乙烯和丙烯单体的共聚物，在电缆制造过程中经过硫化（交联）。这种交联过程创建了三维分子网络，提供了远超热塑性材料的热稳定性。
3.1 Material Science Basis 材料科学基础
The 3GI3 designation in DIN VDE 0207 Part 20 specifies a high-grade EPR compound with enhanced mechanical and electrical characteristics suitable for flexible cables under demanding conditions. The “3” prefix indicates a rubber-based insulation, “G” denotes general purpose application, “I” signifies insulation compound, and “3” represents the specific formulation grade.
DIN VDE 0207第20部分中的3GI3名称指定了一种高等级EPR化合物，具有增强的机械和电气特性，适用于要求苛刻条件下的柔性电缆。”3″前缀表示基于橡胶的绝缘，”G”表示通用应用，”I”表示绝缘化合物，”3″代表特定配方等级。
| Property 性能 | Requirement 要求 | Test Standard 测试标准 |
|---|---|---|
| Tensile Strength (min.) 拉伸强度（最小） | ≥5 N/mm² | DIN VDE 0472 |
| Elongation at Break (min.) 断裂伸长率（最小） | ≥200% | DIN VDE 0472 |
| Continuous Operating Temperature 持续工作温度 | 90°C | DIN VDE 0207-20 |
| Maximum Short-Circuit Temperature 最大短路温度 | 250°C | DIN VDE 0207-20 |
| Ozone Resistance 耐臭氧性 | No cracking after 72h | DIN EN 60811-403 |
| Volume Resistivity (min.) 体积电阻率（最小） | ≥10¹² Ω·cm | DIN VDE 0472 |
3.2 Thermal Degradation Mechanism 热降解机制
At temperatures approaching and exceeding 250°C, EPR insulation begins to experience accelerated thermal oxidation and chain scission of the polymer backbone. While the material does not melt (unlike thermoplastics), prolonged exposure above this threshold causes irreversible chemical degradation that compromises dielectric strength and mechanical properties. The 250°C limit represents the temperature at which short-duration exposure (typically less than 5 seconds) causes acceptable, recoverable stress without permanent insulation damage.
当温度接近并超过250°C时，EPR绝缘开始经历加速的热氧化和聚合物主链的链断裂。虽然材料不会熔化（与热塑性塑料不同），但长时间暴露在该阈值以上会导致不可逆的化学降解，从而损害介电强度和机械性能。250°C限制代表短时间暴露（通常少于5秒）导致可接受的、可恢复的应力而不会造成永久性绝缘损坏的温度。
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4. The Adiabatic Calculation Principle 绝热计算原理
Short-circuit current calculations for cable sizing are based on the adiabatic assumption, which states that during a fault of short duration, all heat generated by the I²R losses in the conductor or screen is retained within the metallic component without any heat transfer to the surrounding insulation or environment. This assumption is conservative and places the calculation on the safe side.
电缆尺寸的短路电流计算基于绝热假设，该假设指出在短时间故障期间，导体或屏蔽层中I²R损耗产生的所有热量都保留在金属部件内，不会传递到周围的绝缘或环境中。这种假设是保守的，使计算处于安全一侧。
4.1 Fundamental Energy Balance 基本能量平衡
The adiabatic temperature rise derives from the basic energy balance equation where the electrical energy dissipated during the fault equals the thermal energy stored in the conductor. The governing equation per IEC 60949 is expressed as follows:
绝热温度上升源自基本能量平衡方程，其中故障期间耗散的电能等于存储在导体中的热能。根据IEC 60949的控制方程表示如下：
| Variable 变量 | Description 描述 | Unit 单位 |
|---|---|---|
| I | Short-circuit current (RMS) 短路电流（有效值） | A (Amperes) |
| t | Fault duration 故障持续时间 | s (seconds) |
| A (or S) | Cross-sectional area of conductor/screen 导体/屏蔽层的横截面积 | mm² |
| θᵢ | Initial conductor temperature 导体初始温度 | °C |
| θf | Final (maximum) conductor temperature 导体最终（最高）温度 | °C |
| k | Material constant (derived from thermal properties) 材料常数（由热性能推导） | A·s0.5/mm² |
The fundamental adiabatic equation relates the short-circuit current, duration, and conductor area through the relationship: A = (I × √t) / k, where k is dependent on the conductor material and the allowable temperature rise (θf – θᵢ).
基本绝热方程通过以下关系将短路电流、持续时间和导体面积联系起来：A = (I × √t) / k，其中k取决于导体材料和允许的温度升高（θf – θᵢ）。
Source: IEC 60949 – Calculation of thermally permissible short-circuit currents
5. The K-Factor and Its Derivation K因子及其推导
The k-factor is the critical parameter linking conductor material properties to short-circuit withstand capability. It incorporates the volumetric heat capacity, electrical resistivity, and temperature coefficient of resistance of the conductor material. The k-factor is calculated using the formula specified in IEC 60364-5-54 Annex A.
k因子是将导体材料性能与短路耐受能力联系起来的关键参数。它包含了导体材料的体积热容、电阻率和电阻温度系数。k因子使用IEC 60364-5-54附录A中规定的公式计算。
5.1 K-Factor Formula K因子公式
The k-factor is derived from the following equation, which accounts for the temperature-dependent resistance of the conductor:
k因子由以下方程推导，该方程考虑了导体的温度相关电阻：
k = √[(Qc × (β + 20)) / ρ₂₀ × ln((β + θf) / (β + θᵢ))]
| Parameter 参数 | Description 描述 | Copper Value 铜值 | Aluminium Value 铝值 |
|---|---|---|---|
| Qc | Volumetric heat capacity at 20°C 20°C时的体积热容 | 3.45 × 10⁻³ J/(K·mm³) | 2.5 × 10⁻³ J/(K·mm³) |
| β | Reciprocal of temperature coefficient at 0°C 0°C时温度系数的倒数 | 234.5°C | 228°C |
| ρ₂₀ | Electrical resistivity at 20°C 20°C时的电阻率 | 17.241 × 10⁻⁶ Ω·mm | 28.267 × 10⁻⁶ Ω·mm |
| θᵢ | Initial temperature (screen at ambient) 初始温度（屏蔽层在环境温度） | 30°C (typical for screen not incorporated in cable) | |
| θf | Final temperature (limited by insulation) 最终温度（受绝缘限制） | 250°C for 3GI3 EPR | |
5.2 Standard K-Factor Values 标准K因子值
IEC 60364-5-54 Table A.54.2 provides pre-calculated k-values for common insulation/conductor combinations. For copper conductors with 90°C thermosetting insulation (EPR/XLPE) with a 250°C short-circuit limit, the standard k-factor is 176.
IEC 60364-5-54表A.54.2为常见的绝缘/导体组合提供了预先计算的k值。对于具有250°C短路限制的90°C热固性绝缘（EPR/XLPE）铜导体，标准k因子为176。
| Insulation Type 绝缘类型 | Initial Temp. 初始温度 | Final Temp. 最终温度 | k (Copper) k（铜） | k (Aluminium) k（铝） |
|---|---|---|---|---|
| 70°C PVC 70°C PVC | 30°C | 160/140°C | 143/133 | 95/88 |
| 90°C PVC 90°C PVC | 30°C | 160/140°C | 143/133 | 95/88 |
| 90°C Thermosetting (EPR/XLPE) 90°C热固性（EPR/XLPE） | 30°C | 250°C | 176 | 116 |
| 60°C EPR Rubber 60°C EPR橡胶 | 30°C | 200°C | 159 | 105 |
| 85°C EPR Rubber 85°C EPR橡胶 | 30°C | 220°C | 166 | 110 |
| 185°C Silicone Rubber 185°C硅橡胶 | 30°C | 350°C | 201 | 133 |
The higher the k-factor, the greater the short-circuit current a given conductor cross-section can withstand. The 250°C limit for 3GI3 EPR yields k=176 for copper, which is 23% higher than the k=143 for PVC-insulated cables limited to 160°C. This directly translates to smaller screen cross-sections for the same fault current requirement, or higher fault current capacity for the same screen size.
k因子越高，给定导体横截面能够承受的短路电流就越大。3GI3 EPR的250°C限制使铜的k=176，比限制为160°C的PVC绝缘电缆的k=143高23%。这直接转化为相同故障电流要求下更小的屏蔽层横截面，或相同屏蔽层尺寸下更高的故障电流容量。
Source: Schneider Electric – Electrical Installation Guide: Sizing of Protective Earthing Conductor
6. Screen Sizing for (N)TSCGECEWÖU Cables (N)TSCGECEWÖU电缆的屏蔽层尺寸
The (N)TSCGECEWÖU cable is a specialized medium voltage mining cable designed to DIN VDE 0250 Part 813 with enhanced flexibility and a Protective Earth Conductor consisting of individual copper wire braid for added safety. The “CE” in the designation indicates the presence of a concentrically applied copper earth (screen) conductor, and “W” denotes the copper wire braid construction.
(N)TSCGECEWÖU电缆是根据DIN VDE 0250第813部分设计的专业中压矿用电缆，具有增强的柔韧性和由单独铜丝编织组成的保护接地导体，以增加安全性。名称中的”CE”表示存在同心敷设的铜接地（屏蔽）导体，”W”表示铜丝编织结构。
6.1 Screen Functions in Mining Cables 矿用电缆中屏蔽层的功能
The metallic screen in (N)TSCGECEWÖU cables performs multiple critical functions. It contains the electric field within the cable insulation system, provides a defined return path for capacitive charging currents, carries earth fault currents during single-phase-to-earth faults, and enables continuous ground fault monitoring for mine safety systems.
(N)TSCGECEWÖU电缆中的金属屏蔽层执行多个关键功能。它将电场限制在电缆绝缘系统内，为电容性充电电流提供确定的回路，在单相对地故障期间传导接地故障电流，并为矿山安全系统提供连续接地故障监测。
| Parameter 参数 | Specification 规格 |
|---|---|
| Screen Construction 屏蔽层结构 | Copper wire braid (individual wires concentrically applied) |
| Screen Material 屏蔽层材料 | Tinned copper wires per DIN VDE 0295 |
| Coverage 覆盖率 | ≥80% surface coverage |
| Voltage Ratings 电压等级 | 3.6/6 kV to 18/30 kV |
| Conductor Sizes 导体尺寸 | 25 mm² to 150 mm² |
| Insulation Type 绝缘类型 | EPR type 3GI3 per DIN VDE 0207 Part 20 |
| Short-Circuit Temperature Limit 短路温度限制 | 250°C |
6.2 Minimum Screen Cross-Section Calculation 最小屏蔽层横截面计算
The minimum screen cross-sectional area required to withstand a specified earth fault current is calculated using the adiabatic formula. Rearranging the fundamental equation gives the minimum required screen area.
承受指定接地故障电流所需的最小屏蔽层横截面积使用绝热公式计算。重新排列基本方程得到所需的最小屏蔽层面积。
Amin = (If × √t) / k
Where: Amin is the minimum screen cross-section (mm²), If is the earth fault current (A), t is the fault clearing time (s), and k is the material factor (176 for copper with 3GI3 EPR at 250°C).
其中：Amin是最小屏蔽层横截面（mm²），If是接地故障电流（A），t是故障清除时间（s），k是材料因子（3GI3 EPR在250°C时铜为176）。
Source: Power and Cables – HV Cable Optimization: Screen Sizing per IEC 60949
7. Practical Calculation Example 实际计算示例
Consider a (N)TSCGECEWÖU 3×95mm² 6/10 kV cable installation in an underground mining application where the earth fault current is 8 kA and the protection system clearing time is 0.5 seconds.
考虑在地下采矿应用中安装(N)TSCGECEWÖU 3×95mm² 6/10 kV电缆，接地故障电流为8 kA，保护系统清除时间为0.5秒。
7.1 Calculation with 3GI3 EPR (k=176) 使用3GI3 EPR计算（k=176）
| Step 步骤 | Calculation 计算 | Result 结果 |
|---|---|---|
| 1. Given Data 给定数据 | If = 8,000 A, t = 0.5 s, k = 176 | — |
| 2. Calculate √t 计算√t | √0.5 = 0.707 | 0.707 s0.5 |
| 3. Calculate I×√t 计算I×√t | 8,000 × 0.707 = 5,656 | 5,656 A·s0.5 |
| 4. Calculate Amin 计算Amin | 5,656 / 176 = 32.1 | 32.1 mm² |
| 5. Select Screen Size 选择屏蔽层尺寸 | Next standard size ≥32.1 mm² | 35 mm² copper screen |
7.2 Comparison: Impact of 250°C vs 160°C Limit 比较：250°C与160°C限制的影响
To demonstrate the significance of the 250°C short-circuit temperature limit, consider the same calculation if the insulation were limited to 160°C (as with PVC), giving k=143 instead of k=176.
为了证明250°C短路温度限制的重要性，考虑如果绝缘限制为160°C（如PVC），k=143而不是k=176时的相同计算。
| Insulation System 绝缘系统 | Max. SC Temp. 最大短路温度 | k-Factor k因子 | Amin Required 所需Amin | Difference 差异 |
|---|---|---|---|---|
| 3GI3 EPR (VDE) | 250°C | 176 | 32.1 mm² | Baseline |
| PVC Insulation | 160°C | 143 | 39.6 mm² | +23% larger |
| 60°C EPR | 200°C | 159 | 35.6 mm² | +11% larger |
The 250°C short-circuit capability of 3GI3 EPR insulation allows a 23% reduction in screen cross-sectional area compared to PVC-insulated cables. In mining cable applications where weight, flexibility, and cost are critical factors, this advantage translates directly to reduced cable weight, improved flexibility, and lower material costs.
3GI3 EPR绝缘的250°C短路能力允许与PVC绝缘电缆相比减少23%的屏蔽层横截面积。在重量、柔韧性和成本是关键因素的矿用电缆应用中，这一优势直接转化为减轻电缆重量、提高柔韧性和降低材料成本。
8. Design Implications for Mining Cables 矿用电缆的设计影响
The 250°C short-circuit temperature limit of 3GI3 EPR has several important implications for (N)TSCGECEWÖU cable design and application in mining environments.
3GI3 EPR的250°C短路温度限制对(N)TSCGECEWÖU电缆在采矿环境中的设计和应用有几个重要影响。
| Aspect 方面 | Implication 影响 | Benefit 益处 |
|---|---|---|
| Screen Weight 屏蔽层重量 | Smaller screen cross-section for same fault rating | Reduced cable weight, improved handling |
| Cable Flexibility 电缆柔韧性 | Less copper in screen construction | Better bending performance for reeling |
| Material Cost 材料成本 | 23% less copper required vs. PVC systems | Lower cable procurement costs |
| Fault Current Capacity 故障电流容量 | Higher I²t withstand for same screen size | Enhanced safety margins |
| Protection Coordination 保护协调 | Longer allowable fault clearing times | More flexibility in protection settings |
| Cable Diameter 电缆直径 | Potentially smaller overall cable OD | Easier installation, smaller reeling drums |
8.1 Non-Adiabatic Considerations 非绝热考虑因素
For screens and sheaths (as opposed to main conductors), IEC 60949 permits non-adiabatic calculations that account for heat dissipation from the metallic component during the fault. This can further increase the permissible short-circuit current by applying a factor ε to the adiabatic rating: I = ε × IAD. For cable screens surrounded by insulation materials, this factor can provide an additional 5-15% improvement in fault current capacity, particularly for longer fault durations exceeding 1 second.
对于屏蔽层和护套（与主导体相对），IEC 60949允许非绝热计算，考虑故障期间金属部件的散热。这可以通过将因子ε应用于绝热额定值来进一步增加允许的短路电流：I = ε × IAD。对于被绝缘材料包围的电缆屏蔽层，这个因子可以在故障电流容量方面提供额外的5-15%的改进，特别是对于超过1秒的较长故障持续时间。
Source: ELEK Software – Short Circuit Power Cable Sizing Explained
9. Applicable Standards Reference 适用标准参考
| Standard 标准 | Title 标题 | Application 应用 |
|---|---|---|
| IEC 60949 | Calculation of thermally permissible short-circuit currents | Adiabatic and non-adiabatic methods |
| IEC 60364-5-54 | Earthing arrangements and protective conductors | K-factor tables, PE sizing |
| DIN VDE 0207-20 | Rubber compounds for insulation (3GI3) | EPR insulation specifications |
| DIN VDE 0250-813 | Medium voltage reeling cables for mining | (N)TSCGECEWÖU cable construction |
| IEC 60228 | Conductors of insulated cables | Conductor classes and dimensions |
| DIN VDE 0295 | Conductors for cables and cords | German implementation of IEC 60228 |
| DIN EN 60811-404 | Oil resistance tests for cable materials | Sheath material qualification |
| IEC 60724 | Short-circuit temperature limits of cables | Maximum temperature guidance |
10. Conclusion 结论
The 250°C short-circuit temperature limit for 3GI3 EPR-insulated VDE cables is established based on the thermosetting nature of the EPR compound and its ability to maintain dielectric integrity during brief thermal excursions. This limit, significantly higher than the 160°C limit for thermoplastic PVC, enables the use of smaller copper screen cross-sections in (N)TSCGECEWÖU mining cables while maintaining adequate earth fault current capacity.
3GI3 EPR绝缘VDE电缆的250°C短路温度限制是基于EPR化合物的热固性特性及其在短暂热波动期间保持介电完整性的能力而确定的。这个限制明显高于热塑性PVC的160°C限制，使得(N)TSCGECEWÖU矿用电缆能够使用更小的铜屏蔽层横截面，同时保持足够的接地故障电流容量。
The practical significance is substantial: the higher k-factor (176 vs 143) translates to approximately 23% reduction in required screen cross-section for the same fault current and clearing time. For mining operations where cable weight, flexibility, and cost are critical factors, the 3GI3 EPR insulation system offers clear advantages over alternative insulation materials with lower short-circuit temperature ratings.
实际意义是重大的：更高的k因子（176对143）意味着在相同的故障电流和清除时间下，所需的屏蔽层横截面减少约23%。对于电缆重量、柔韧性和成本是关键因素的采矿作业，3GI3 EPR绝缘系统比具有较低短路温度额定值的替代绝缘材料具有明显优势。
Engineers specifying (N)TSCGECEWÖU cables should ensure that screen sizing calculations properly account for the 250°C short-circuit limit, using k=176 for copper screens, and should coordinate with protection system designers to verify that fault clearing times are within the cable’s thermal withstand capability.
指定(N)TSCGECEWÖU电缆的工程师应确保屏蔽层尺寸计算正确考虑250°C短路限制，对铜屏蔽层使用k=176，并应与保护系统设计人员协调以验证故障清除时间在电缆的热耐受能力范围内。
11. Contact Information 联系方式
Anhui Feichun Special Cable Co., Ltd.
安徽飞纯特种电缆有限公司
| Technical Inquiries 技术咨询 | [email protected] |
| Sales (Zihao Yang) 销售（杨子豪） | [email protected] |
| Sales (Ziyu Huang) 销售（黄子煜） | [email protected] |
| +86 138 5512 3218 |
Our engineering team provides technical support for short-circuit calculations, screen sizing verification, and custom cable design for mining, tunnelling, and heavy industrial applications.
我们的工程团队为采矿、隧道和重工业应用提供短路计算、屏蔽层尺寸验证和定制电缆设计的技术支持。
