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Dr. Sahar Abd El Moneim Moussa 1
Pharos UniversityEE-385
Electrical Power & Machines“Electrical Engineering Dept”
Prepared By:Dr. Sahar Abd El Moneim Moussa
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UGCUNDERGROUND CABLE
(Part 1)
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Uses of UGC
• It is used to transmit electric power, when construction of OHTL is undesirable, for example, in crossing under seawater, highways or rail ways, or in approaches to the territories of high density populated areas.
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Construction of UGC
• UGC consists of:
1) Core conductor2) Core insulation
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1) Core Conductor:
a) Hard drawn Copper Conductors are used in low voltage networks, as it can withstand thermal stresses during overloading
b) Hard drawn Aluminum Conductors are used in medium voltage and high voltage distribution network to decrease costs where 3-phase load are balanced and hence overloading problem is minimized
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1) Cable Insulation:
a) Oil Impregnated-Paper Insulation (OIL):
Advantages: • Highest dielectric strength among all cable
insulation material.• Long life-time.
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OIL FILLED CABLES
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EHV DIRECT GAS PRESSURE CABLES
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b) Polymeric Martials Insulated Cables:
Thermoplastic materials:®Polyetheylene (PE) ® Polyvinyl Chloride (PVC)
Thermosetting materials:®Cross linked Polyethylene (XLPE)® Ethylene-Propylene Rubber (EPR)
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Advantages:
• Reduced weight• Easier to repair faults• Reduced risk of flammability and fire
propagation.• More economical in both initial costs and life time
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Dielectric field of High-voltage Power Cables:
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SHIELDED CABLES
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CABLE CONSTRUCTION
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CABLE PARAMETERS1- Effective Cable Resistance
Where, : is the conductor resistivity in .ml : is the conductor length in mA : is the conductor cross-sectional area in m2
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And,
Where, : is the skin effect : is the proximity effect : is the metallic sheath effect : is the steel tape armoring effect
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2- Cable Inductance
The inductance of a single-core in three-phase power cable
Where,
GMD : is the geometric mean distance between centers of core conductors
GMR : is the geometric mean radius of the core conductors
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2- Cable Capacitance
The inductance of a single-core in three-phase power cable
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Dielectric Losses of Metallic Sheathed Power Cables
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Therefore, the dielectric stress will be:
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