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Cables Classification.................pptx
- 1. Cable Classification • Operating voltage •Operating frequency • Conductor type • Insulation level • Core number • Neutral and Earthing cable • Derating factors • Cross section area (mm2)
- 2. Operating Voltage • Low voltagecable [ 1 V-1000 V ] , 0.6 /1 KV • Medium voltage cable [ 1 KV-66 KV ], 12 /20 KV 11 KV, 18 /30 KV 22 KV, 6 /10 KV 3.3 KV 6.6 KV. • Overhead conductor [ 66 KV-500 KV]
- 3. Operating Voltage • The higherthe operating voltage, the more insulation required, also lower crossectional area required due to the presence of lower current.
- 4. 🔍 Summary Table— Voltage Class Overview Classification Nominal System Voltage Range Typical Rating (U₀/U) Example Applications Low Voltage (LV) Up to 1 kV 0.3/0.5, 0.45/0.75, 0.6/1 kV Building wiring, domestic distribution Medium Voltage (MV) 3.3 kV – 33 kV 3.6/6 to 18/30 kV Industrial feeders, substations High Voltage (HV) 66 kV – 220 kV (+) 64/110 to 127/220 kV Transmission networks
- 5. Operating Frequency • The frequencyat which the cables are operating are 50 Hz and 60 Hz.
- 6. Cables Classification According toConductor Type
- 7. Conductor Types • Aluminum(Al) and Copper (Cu). • According to the International Annealed Copper Standard (IACS), although aluminum only has 61% of the conductivity of copper it is only 30% of the weight, and therefore significantly cheaper. • All medium voltage cables are made from Al because of two reasons:- Low current and Underground cable cost, except cables used to fed motors load. • Low voltage cables are preferred from Cu in the electrical distribution network. • The voltage drop (mV/A.m) for aluminium cables is higher than the equivalent copper cable.
- 8. Conductor Types • Aluminumcables appear cheaper, but this doesn’t take into consideration the extra cost and effort involved in installing less pliable aluminum cables. Therefore, copper cables are still primarily used for the low voltage network, except in situations where overhead cables are installed, and weight is a factor. • Aluminum cable requires a larger cross-sectional area to match the conductivity of the equivalent copper cable. An aluminum cable needs a 56% larger cross-sectional area to achieve the same conductive capability as a copper cable. • If run underground, the size and number of conduits would need to increase to match the increased aluminum cable cross-sectional area. If run above ground, the width of cable tray would need to increase to accommodate larger and additional aluminum cables. • Installation of aluminum cables are more difficult due to the flexibility and size.
- 9.
- 10. Conductor Types Key Insight💡 • Larger cross-sections reduce resistance and improve current capacity. •Copper cables carry more current and handle higher short- circuit stress than Aluminum.
- 11. Cables Classification According toInsulation Level
- 12. Insulation levels Type Standard normal temperature MaxTemp. at short circuit level COST ($/m) PVC 70°c 150°c Low XLPE 90°c 250°c High
- 13. Layer Function MaterialType Copper Conductor Carries current Copper Insulation Electrical isolation PVC / XLPE Filler Maintains round shape PVC / Polymer Banding Binds cores Polyester tape Inner Sheath Core protection LSHF compound Steel Wire Armour Mechanical protection Galvanized steel Outer Sheath Environmental protection LSHF / PVC
- 14. Cables Classification According toArmouring Types By eng. Ahmed Mahdy/ Khadija Academy
- 15. Armouring Types Type Advantages S.T.A(Steel Tape Armoured) S.T.A withstands mechanical stress more than SWA, that’s why it is used in underground cables. S.W.A (Steel Wire Armoured) S.W.A more flexible than S.T.A, It withstands high pull loads.
- 16. Cables Classification Accordingto Number of Cores and Cable Formation
- 17. Number of Cores Number ofCores Application Single Core Cable If CSA of each phase greater than 300mm2, used in riser of residential buildings, and as an earthing cable. Two Core Cable Used in low voltage single phase system, where only a phase and a neutral are needed, there is no earthing system [ L& N only ]. Three Core Cable Same application of two core but an additional core for earthing [L, N and E], also used in the medium voltage cable where only 3 phases are needed [R, S, and T]. Four Core Cable Used in the low voltage system where three phases are needed in addition to the neutral [R, S, T and N].
- 18. Cable Formation Cable FormationApplication Trefoil Formation • Same distance apart between which means the magnetic field and circulating currents are equivalent for each cable phase. • Trefoil phase formation is more commonly used for Low and Medium Voltage applications up to 132kV due to ease of installation and the reduction in space the formation has. ⚠️Heat Dissipation Limitation Because the cables are touching each other, the heat dissipation is restricted. This leads to higher cable temperature and therefore a lower current-carrying capacity compared to flat or spaced formations.
- 19. Cable Formation Cable FormationApplication Flat Formation What is Flat Formation? Flat formation is an arrangement where three single-core cables (phases R, Y, and B) are laid side-by-side in a straight line with equal spacing between them. 📏 Purpose: To provide better air circulation and heat dissipation, especially for high-current installations. Common in Medium and High Voltage (MV & HV) systems. Used where space is available — such as in trenches, ducts, or outdoor installations. Ideal for long horizontal runs (substations, feeders, transmission corridors). Since the cables are not symmetrically spaced, the magnetic field around each phase is unequal.
- 20. Derating factor • Deratingfactors or correction factors are the factors which makes a cable current carrying capacity less than the designed value. For example, ambient air temperature, soil temperature and laying method of the cable. • If a cable has derating factor of 0.8, this means that the cable can only provide 80% of it’s rated current capacity, so we need to select a higher current capacity cable to compensate for this drop. • Let’s say we have a cable with a current capacity of 100 Amps and the load is 100 Amps, this cable will not be able to satisfy load requirement due to derating factor, it will give only 80 Amps. • If we select a higher current cable of value = I/derating factor = 100/0.8 = 125 Amps and install this cable in the same conditions. This cable will provide 125*0.8 = 100 Amps, which is the required current.
- 22. Key Observations fromthe table Parameter Explanation Number of Circuits More circuits laid together cause greater mutual heating → lower derating factor. Formation Type Flat formation provides slightly better cooling than trefoil → higher derating factors. Spacing (L) Increasing spacing between circuits (e.g., from touching → 0.15 m → 0.30 m) improves heat dissipation → higher derating factors.
- 23. Typical Applications byNumber of Circuits Typical Applications by Number of Circuits 3️ 3️ ⃣ No. of Circuits How It’s Configured Where It’s Used Comment 1 Circuit One set of cables from source to load Apartment risers, DB feeders Typical small LV system 2 Circuits (Parallel) Two identical sets of cables in parallel Transformer → Main DB For medium loads or reduced voltage drop 3–4 Circuits (Parallel) Three or four identical runs Factory feeders, large commercial mains For high currents or long distances 5–6 Circuits (Parallel) Five or six identical cable sets Substation outputs, industrial distribution For high-capacity systems or redundancy
- 24. Selection of Neutraland Earthing Cable Cross Section Areas By eng. Ahmed Mahdy/ Khadija Academy
- 25. Neutral Conductor Cross Section Area •If the C.S.A of the phase conductor less than 35 𝑚𝑚2, then the neutral C.S.A will be the same as the C.S.A of any of the three phases. • If the C.S.A of the phase conductor greater than 35 𝑚𝑚2, then the neutral C.S.A will be half the C.S.A of any of the three phases.
- 26. Example Phase Conductor Size(mm²) Neutral Conductor Size (mm²) Rule Applied 10 mm² 10 mm² Equal (≤35 mm²) 25 mm² 25 mm² Equal (≤35 mm²) 35 mm² 35 mm² Equal (≤35 mm²) 50 mm² 25 mm² May be reduced (>35 mm²) 95 mm² 50 mm² May be reduced (>35 mm²) Example Table 4️ ⃣
- 27. Earthing Conductor Cross Section Area •If the C.S.A of the phase conductor less than 16 𝑚𝑚2, then the earthing C.S.A will be the same as the C.S.A of any of the three phases • If the C.S.A of the phase conductor 25 𝑚𝑚2 or 35 𝑚𝑚2 then the earthing C.S.A will be 16 𝑚𝑚2 • If the C.S.A of the phase conductor greater than 35 𝑚𝑚2, then the earthing C.S.A will be half the C.S.A of any of the three phases
- 28. Single or Multi Core Cable Powercables can be designed as: •Single-core cable → each phase (R, Y, B) has its own insulated conductor •Multi-core cable → all three phases and neutral (and sometimes earth) are contained in one outer sheath •Left diagram: Multi-core cable — all phases (R, C, T / N / E) under one sheath; compact, used for LV feeders. •Right diagram: Single-core cables — individual phase, neutral, and earth laid side by side or in trefoil; used for larger cross- sections or high current.
- 29. Cable Design –How To Select Cable Cross-Sectional Area? By eng. Ahmed Mahdy/ Khadija Academy
- 30. Find Rated Current ofThe Load and The CB Rating • I rated = 40∗74 6 3∗380∗0 .8 = 56.6 𝐴 • I CB = I rated * 1.25 = 56.6 *1.25 = 70.75 A. • I Cable = I CB Derating factor
- 31. Derating Factors - Catalog •Assume using PVC cable, the air temperature in the installation area is 50 °C, derating factor = 0.82. • The cable rating = 70.75 =86.28 A. 0.82 • Cable selected is (4x25)+16 mm2