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Superior Tray Systems Inc.: Introduction to the Technical and Safety Aspects of Cable Bus
- 2. Introduction to the Technical and Safety Aspects of Cable Bus
- 4. • Power distribution system • Parallel conductors braced inside rigid enclosure • Capacity up to 10,000 A and 218kV and higher
- 9. • Cable bracing prevents displacement in short circuit • Every cable protected by shock absorber • Prevents insulation damage in short circuit event • Non magnetic and non metallic support system
- 10. Safety
- 11. • Fully insulated power cables (protection to workers) • No issues with sprinklers, water leaks, or moisture • No splice joints • Materials are fire retardant and UV resistant
- 13. • Ethylene Propylene Rubber (EPR) preferred insulation • EPR has advantages over Cross Linked Polyethylene (XLPE) • XLPE is victim to "water-treeing“ • EPR insulation is far more flexible and easier to install
- 14. Installation
- 16. • Does not need precise alignment with transformer bus bars • Custom fittings accommodate frost heave, thermal expansion, and custom angles
- 17. • Easily adapted to unforeseen changes (can be cut to fit on site)
- 18. Short Circuit
- 19. • In a balanced system a short circuit is carried evenly by all conductors. • In short circuit event, a balanced system has a greatly reduced maximum magnetic force due to opposing magnetic forces that cancel out.
- 20. System Balance
- 21. • Ampacity: Most phasing arrangements provide inter-phase balance of the currents due to the load impedance, but only specific arrangements provide an intra-phase current balance. • Properly balanced systems ensure that the ampacity balance is within 3% between all conductors.
- 22. • Impedance: A balanced impedance ensures a similar load per each conductor. This allows cables to be run at their full rated capacity rather than one particular conductor limiting the capacity of the entire system. • Magnetic Field: An unbalanced system has higher risk of cable insulation damage due to higher magnetic forces.
- 23. Current Density Flux Lorentz Force Current Density Flux Lorentz Force Balanced Phasing Unbalanced Phasing
- 25. • Cable rated to 90°C Low Voltage, and 105°C Medium Voltage • Switchgear rated to 75°C • Much myth and confusion surrounds temperature rating of switchgear and equipment
- 26. Ampacity Rating
- 27. • Ampacity is calculated according to the Ampacity Standards as dictated by the International Conductor Engineers Association (ICEA) found in both the NEC and the CEC • Table 310.17, 310.19, and 310.69 in the NEC. • Table 1, and 3 in the CEC
- 28. Voltage Drop
- 29. • All systems designed to achieve the required voltage drop • Measured in percentage drop (2% to 3% at best) • Voltage drop is a function of conductor sizing • Voltage drop is proportional to distance • More conducting material for a given ampacity, the lower the voltage drop
- 31. • Cables available with FT4 or FT1 rating • Required flame test rating will depend on local and national building code • Both tests relate to the smoke development classification and the flame spread rating of the cable
- 34. According to NBC Article 3.2.2.30 any cable installed into a building constructed of non combustible materials (any building of storey area greater than 4800 square meters) must have at least the FT4 rating FT1 cables can be used in combustible buildings. Determination of non-combustibility as per NBC Article 1.1.1.3.2. Many cables with XLPE insulation are only available in FT1.
- 36. • Safer (several times lower short circuit forces) • Lower cost • Longer service life • Less maintenance
- 37. • Field adaptable • Lower KAIC • Lower impedance and lower voltage drop • No need for heater strips or forced air ventilation
- 38. Advantages Over Wire in Conduit
- 39. • Conduit has no phase balancing or free air rating • Cables generally need to be de-rated • One of the most difficult systems to install • High cost of material
- 41. • Cable tray has no short circuit rating • No current balance • Every section of cable tray must be cut on site
- 42. Superior Tray Systems Inc. #12 – 13025 84th Avenue Surrey, BC V3W 1B3 Tel: 604.572.4419 Email: info@superiortray.com Web: www.superiortray.com
- 43. Copyright 2016 Superior Tray Systems Inc.