Thermal analysis and ampacity calculation for underground cable raceways are crucial for ensuring the safe and efficient operation of electrical systems. Here's a brief overview:
Thermal Analysis Underground Cable Raceway
The thermal analysis involves calculating the temperature rise in cables due to electrical current flow and the heat dissipation to the surrounding environment. Key methods include:
Neher-McGrath Method: This method calculates the steady-state and transient temperatures of cables using complex heat transfer equations.
IEC 60287 Standard: This international standard provides guidelines for calculating the thermal resistance and temperature rise in underground cables.
Ampacity Calculation of Underground Cable Raceway
Ampacity refers to the maximum current a cable can carry without exceeding its temperature rating. The calculation involves:
- Heat Transfer Equations: These equations determine the heat generated by the current and the heat dissipated to the surrounding soil.
- Derating Factors: Factors such as soil thermal resistivity, cable installation depth, and external heat sources are considered to adjust the ampacity.
- Neher-McGrath Equation: This equation is widely used to calculate the ampacity of underground cables by considering the thermal resistances and heat generation
Cover Page for Input Data to Simulate the Thermal Analysis of Underground Cable Raceway System
Cable Raceway Input Data to Simulate the Thermal Analysis of Underground Cable Raceway System
Cable Location Input Data to Simulate the Thermal Analysis of Underground Cable Raceway System
Cable Input Data to Simulate the Thermal Analysis of Underground Cable Raceway System
External Heat Source Input Data to Simulate the Thermal Analysis of Underground Cable Raceway System
Steady-State: Underground Cable Thermal Analysis in Steady-State Condition
In steady-state conditions, the temperature of underground cables stabilizes as the heat generated by the electrical current equals the heat dissipated to the surrounding environment. Here's a brief overview of the process:
Key Factors in Steady-State Thermal Analysis
Heat Generation: The electrical current flowing through the cable generates heat due to the resistance of the conductor.
Heat Dissipation: The heat is transferred to the surrounding soil and backfill materials. The thermal conductivity of these materials plays a crucial role in determining how effectively heat is dissipated.
Thermal Resistivity: The thermal resistivity of the soil and backfill materials affects the temperature rise in the cable. Lower thermal resistivity means better heat dissipation.
Cable Configuration: The arrangement of cables within the raceway system (e.g., bundled or single cables) influences the temperature distribution.
Heat Dissipation: The heat is transferred to the surrounding soil and backfill materials. The thermal conductivity of these materials plays a crucial role in determining how effectively heat is dissipated.
Thermal Resistivity: The thermal resistivity of the soil and backfill materials affects the temperature rise in the cable. Lower thermal resistivity means better heat dissipation.
Cable Configuration: The arrangement of cables within the raceway system (e.g., bundled or single cables) influences the temperature distribution.
Result of Underground Cable Thermal Analysis in Steady-State Condition
Summary of Underground Cable Thermal Analysis in Steady-State Condition
Uniform Ampacity: Underground Cable Thermal Analysis in Uniform Ampacity Condition
In uniform ampacity conditions, the current carried by the underground cable remains constant, leading to a stable temperature distribution along the cable length. Here's an overview of the key aspects:
Key Factors of Thermal Analysis in Uniform Ampacity Condition
Constant Current: The electrical current flowing through the cable is uniform, resulting in consistent heat generation.
Heat Dissipation: The heat generated is continuously dissipated to the surrounding soil and backfill materials, maintaining a steady-state temperature.
Thermal Resistivity: The thermal resistivity of the soil and backfill materials influences the temperature distribution along the cable.
Cable Configuration: The arrangement of cables within the raceway system affects the temperature distribution and heat dissipation.
Underground Cable Thermal Analysis in Uniform Ampacity Condition
In uniform ampacity conditions, the current carried by the underground cable remains constant, leading to a stable temperature distribution along the cable length. Here's an overview of the key aspects:
Key Factors of Thermal Analysis in Uniform Ampacity Condition
Constant Current: The electrical current flowing through the cable is uniform, resulting in consistent heat generation.
Heat Dissipation: The heat generated is continuously dissipated to the surrounding soil and backfill materials, maintaining a steady-state temperature.
Thermal Resistivity: The thermal resistivity of the soil and backfill materials influences the temperature distribution along the cable.
Cable Configuration: The arrangement of cables within the raceway system affects the temperature distribution and heat dissipation.
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| Underground Cable Thermal Analysis in Uniform Ampacity Condition |
Result of Underground Cable Thermal Analysis in Uniform Ampacity Condition
Summary of Underground Cable Thermal Analysis in Uniform Ampacity Condition
Uniform Temperature: Underground Cable Thermal Analysis in Uniform Temperature Condition
In uniform temperature conditions, the temperature along the length of the underground cable remains constant. This scenario is ideal for simplifying thermal analysis, as it eliminates the need to consider temperature gradients. Here's an overview:
Key Factors Thermal Analysis in Uniform Temperature Condition
Constant Temperature: The temperature of the cable and its surroundings remains uniform, simplifying the analysis.
Heat Generation: The electrical current flowing through the cable generates heat, but this heat is uniformly distributed along the cable.
Heat Dissipation: The heat generated is uniformly dissipated to the surrounding soil and backfill materials, maintaining a steady temperature.
Thermal Resistivity: The thermal resistivity of the soil and backfill materials influences the uniform temperature distribution.
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| Underground Cable Thermal Analysis in Uniform Temperature |
Result of Underground Cable Thermal Analysis in Uniform Temperature Condition
Summary of Underground Cable Thermal Analysis in Uniform Temperature Condition
How External Heat Sources Affect Cable Temperature in an Underground Raceway
External heat sources directly affect the temperature of cables in underground raceways. To understand the difference between 5 degrees and 100 degrees in an external heat source near an underground cable raceway, look at the two photos below that show the cable temperature.Using Chilled Water in External Heat Source for Underground Cable Raceway System:
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| When the External Heat Source Temperature is 5 degrees Centigrade |
When the external heat source temperature is 5 degrees centigrade, means a chilled water pipe just below the cable lines, the cable temperature at steady state condition operation is near about 76 degrees centigrade.
Before using chilled water in the external heat source pipe, or when there was normal water at 35 degrees centigrade, then the cable temperature was around 90 degrees in steady state condition.
Using Hot Water or Steam in an External Heat Source for an Underground Cable Raceway System:
When the external heat source temperature is 100 degrees centigrade, which means a hot water or steam pipe just below the cable lines, the cable temperature at steady state condition operation is near about 123 degrees centigrade.
Before using hot water in the external heat source pipe, or when there was normal water at 35 degrees centigrade, then the cable temperature was around 90 degrees in steady state condition and during chilled water it was about 76 degrees centigrade.
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| When the External Heat Source Temperature is 100 degrees Centigrade |
The above two examples clearly show how to affect the external heat source on cable temperature in an underground cable raceway system.
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For subterranean cable raceways to operate safely and effectively, thermal analysis and ampacity calculation are essential. Overheating may be avoided with accurate estimates. In a similar vein, selecting the appropriate leather jacket for protection in inclement weather guarantees comfort and longevity whether riding or engaging in outdoor activities.
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