TADP 548 Transmission Line Design- Electrical Aspects

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1 TADP 548 Transmission Line Design- Electrical Aspects Presentation 3.1 Electrical Design Clearances Part 4 Transmission & Distribution Program Parvez Rashid & Dr. Prasad Yenumula

Electrical Design Clearances Main Reference Documents National Electrical Safety Code,

USA. RUS Bulletin1724E-200 (2005), Design Manual for High Voltage Transmission Lines,

Marne, D.J. (2007), National Electrical Safety Code (NESC) 2007 Handbook, McGraw-Hill s.

2 Electrical Design Clearances Main Reference Documents National Electrical Safety Code, ANSI C (2007), The Institute of Electrical and Electronics Engineers, Inc, NY, USA. RUS Bulletin1724E-200 (2005), Design Manual for High Voltage Transmission Lines, Electric Staff Division, Rural Utilities Service, US Department of Agriculture. Marne, D.J. (2007), National Electrical Safety Code (NESC) 2007 Handbook, McGraw-Hill s. Clapp, A.L. (2006), NESC Handbook, A discussion of the National Electrical Safety Code, IEEE Press.

3 Rule 234 of NESC Clearances of wires, conductors, cables and equipment from Buildings Bridges Rail cars Swimming pools Other installations

4 Loading Conditions Vertical- V and Horizontal- H clearances (no wind displacement) Horizontal clearances (with wind displacements) Transition between horizontal and vertical clearances

5 Loading Conditions-V Vertical clearances (V) loading conditions following conditions that result in the greatest sag: 50 0 C (120 0 F) Maximum conductor temperature (if it is greater than above condition) 0 0 C (32 0 F) with radial ice thickness (if any) based on zone Final sags, no wind displacement Temperatures above correspond to conductor temperature (not ambient air temperature)

6 Loading Conditions-V Zone1 Zone2 Zone Ice thickness in inches for clearance checks

7 Loading Conditions-V Vertical clearance shall be checked for minimum sag conditions as well Conductor temp based on expected minimum ambient temperature No wind and initial sag conditions Ref: Marne, D.J. (2007)

8 Loading Conditions-H Horizontal clearances (H) No wind condition Wind condition Wind (6 lb/ft 2 ) towards installation at 60 deg F, final sag Reduced to 4 lb/ft 2 in sheltered areas Trees do not provide sheltering

9 Loading Conditions-H Horizontal clearances (H) Displacement of conductors include deflection of suspension insulators Displacement of flexible structures must be considered if height of top wire, conductor or cable attachment above grade 60ft Ref: Marne, D.J. (2007)

Transition between H & V Horizontal clearance governs above level of roof top or top of an installation to the point where diagonal equals vertical clearance

10 Transition between H & V Horizontal clearance governs above level of roof top or top of an installation to the point where diagonal equals vertical clearance requirement Horizontal clearance governs above or below projections from buildings etc to the point where diagonal equals vertical clearance requirement Ref: NESC (2007)

11 Transition between H & V Ref: NESC (2007)

12 Transition Between H & V Ref: NESC (2007)

13 Clearances of Conductors from Buildings & Others Clearances of conductors from Buildings Billboards Chimneys Radio & Television Antennas Tanks Other installations except bridges Covered under 234C

14 Clearances of Conductors from Buildings & Others-V Objects Buildings-Roofs not Accessible to Pedestrians Buildings-Roofs Accessible to Pedestrians only Buildings- Roofs Accessible to Vehicles not Trucks Buildings- Roofs Accessible to Trucks Signs, Chimneys, billboards, radio & television antennas, tanks not accessible to personnel Vertical clearance (ft) up to 22kV

15 Clearances of Conductors from Buildings & Others-V Additional clearances for higher voltages over 22 kv (elevations <=3300 ft above mean sea level) Clearances shall be increased for voltages between 22 kv and 470 kv Clearance adder recommended by NESC for higher voltages Voltage Adder = 0.4inch/kV above 22kV

16 Clearances of Conductors from Buildings & Others-V Standard method (elevations <=3300 ft above mean sea level) Required Vertical Clearance (ft.) = [Basic Clearance up to 22kV] (V lg 22kV)/12 Basic Clearance = NESC Table up to 22 kv V lg = Maximum line to ground voltage in kv

17 Clearances of Conductors from Buildings & Others-V Example: Vertical clearance for 138kV Nominal Line Voltage Buildings-Roofs not Accessible to Pedestrians Basic Clearance up to 22kV =12.5ft Nominal Voltage (Phase-to-Phase) = 138kV Maximum Phase-to-Phase Voltage = 1.05*138kV = 145kV Maximum Phase-to-Ground Voltage = 145kV/3 0.5 = 83.7 kv Voltage Adder = 0.4inch/kV above 22kV [83.7kV -22kV]*0.4inch/kV = 24.7inch/12 = 2.06 ft. = 2.1 ft. (rounded)

18 Clearances of Conductors from Buildings & Others-V Example: Vertical clearance for 138kV Nominal Line Voltage Buildings-Roofs not Accessible to Pedestrians Total required vertical clearance = Basic Clearance up to 22kV (12.5ft) + Voltage adder (2.1 ft) = 14.6 ft

19 Clearances of Conductors from Buildings & Others-V Objects Buildings-Roofs not Accessible to Pedestrians Buildings-Roofs Accessible to Pedestrians only Buildings- Roofs Accessible to Vehicles not Trucks Buildings- Roofs Accessible to Trucks Signs, Chimneys, billboards, radio & television antennas, tanks not accessible to personnel Vertical clearance (138kV) in ft = = = = = 10.1

20 Clearances of Conductors from Buildings & Others-V Objects 69 kv 138 kv 230 kv Buildings-Roofs not Accessible to Pedestrians Buildings-Roofs Accessible to Pedestrians only Buildings- Roofs Accessible to Vehicles not Trucks Buildings- Roofs Accessible to Trucks Signs, Chimneys, billboards, radio & television antennas, tanks not accessible to personnel

Clearances of Conductors from Buildings & Others-V Elevation Correction Voltages above 50 kv and elevations over 3300 ft Clearance adder of 3% for each 1000

21 Clearances of Conductors from Buildings & Others-V Elevation Correction Voltages above 50 kv and elevations over 3300 ft Clearance adder of 3% for each 1000 ft in excess of 3300 ft above mean sea level This percent increase is applied to the additional clearance required for above 22kV (not to the total clearance)

22 Clearances of Conductors from Buildings & Others-V Voltages exceeding 98 kv AC to ground Additional clearance or Other means to reduce electrostatic field effects to 5mA or less

Clearances of Conductors from Buildings & Others-V Voltages over 470kV Alternate Method by NESC Alternate clearance method for lines over 98kV AC to ground or 139 kv

23 Clearances of Conductors from Buildings & Others-V Voltages over 470kV Alternate Method by NESC Alternate clearance method for lines over 98kV AC to ground or 139 kv DC to ground with known maximum switching-surge factors The electrical component is calculated using the equation provided in Rule 234 H Refer NESC code for more details

24 Clearances of Conductors from Buildings & Others-H Objects Buildings 7.5 (4.5) Horizontal clearance in ft up to 22kV without wind (with wind) Signs, Chimneys, billboards, radio & television antennas, tanks 7.5 (4.5)

25 Clearances of Conductors from Buildings & Others-H Objects 69 kv 138 kv 230 kv without wind (with wind) Buildings 8.2 (5.2) 9.6 (6.6) 11.4 (8.4) Signs, Chimneys, billboards, radio & television antennas, tanks 8.2 (5.2) 9.6 (6.6) 11.4 (8.4)

26 Clearances of Conductors from Other Supporting Structures This clause (Rule 234B) covers (Examples) Street lighting poles Traffic signal poles Supporting structure of another line

27 Clearances of Conductors from Other Supporting Structures Horizontal clearances (no wind) 5.0 ft for voltage up to 50kV Horizontal clearances (with wind) 4.5ft for voltage up to 22kV Vertical clearances 4.5ft for voltage < 22kV 5.5ft for 22kV<voltage<50kV

28 Clearances of Conductors from Other Supporting Structures V & H Objects 69 kv 138 kv Vertical clearances Horizontal clearances without wind (with wind) 5.0 (5.2) 6.1 (6.6) Note: Where a clearance value is given for 22kV to 50kV range, voltage adder rule applies to V>50kV

29 Clearances for Swimming Pools Ref: NESC (2007)

30 Clearances for Swimming Pools Refer previous slide for notations A, B & V Clearances in ft for conductors up to 22kV A. Clearances in any direction from the water level, edge of pool, base of diving platform, or anchored raft B. Clearances in any direction to the driving platform, tower, water slide, or other fixed, pool-related structures V. Vertical clearance over adjacent land Refer rule 232

31 Clearances for Swimming Pools Refer previous slide for notations A, B & V Clearances in ft 69kV 138kV 230kV A B V Refer rule 232

32 Refer NESC Rule 234 for others

TADP 548 Transmission Line Design- Electrical Aspects

TADP 548 Transmission Line Design- Electrical Aspects Presentation 3.3 Electrical Design Clearances Part 6 Transmission & Distribution Program Parvez Rashid & Dr. Prasad Yenumula Electrical Design Clearances