Clearance questions

[TRAMPLINEMAN]

Can someone please tell me what the standard is for phase to ground clearance on 345KV. Also, what is phase to phase clearance on 345KV?

[compression]

8' 6" to ground and 16' 8" phase to phase.

It changes with altitude and surge caculations which I have never seen, I did see a formula for it somewhere tho,..... maybe ieee.org - prolly search for the ieee 516 standard and find it.

[CPOPE]

Line-to-ground clearances dictate maximum line-loading levels, usually post-contingency, in many operating situations. Since measuring them all is not possible in real time, utilities must rely on predictions of this important operation condition. But how good are the predictors?

Conductor clearance above ground is a complex and uncertain function of variables concerning when the conductor and line were built, what mechanical and electrical loadings the line has endured, and even the pre- and post-contingency weather and line loading. Lines that may be loaded to a level that might compromise required ground clearances are critically analyzed to ensure clearance is not an issue. If clearance is an issue, one of several real-time thermal-rating systems can be deployed to manage the phase-to-ground clearance.

Typical overhead line thermalrating systems are based on measurements of tension, sag, temperature or weather and circuit load. In the last instance, the data are used to predict a conductor temperature that tracks changes in sag. These measurements or predictions may not be good enough to address all the relevant uncertainties, especially since some conductor properties change during high-temperature operation. Many utilities and specialty manufacturers of rating systems have lingering concerns about how well any given system actually predicts conductor clearance.

http://tdworld.com/overhead_transmission/power_accurate_line_clearance/

The conductor clearance requirements of Rule 235 of the National Electrical Safety Code (NESC) are what generally govern the clearance.

http://books.google.com/books?id=A0rEoBGVr10C&pg=PA227&lpg=PA227&dq=NESC+clearance+requirements&source=bl&ots=NEipOL4ccB&sig=lxRFy6-qZXHgkiTUIEzkrsRtFT8&hl=en&ei=nbYTSpSJLaCW8wTrm-z-Aw&sa=X&oi=book_result&ct=result&resnum=4

http://www.usda.gov/rus/electric/pubs/1724e-200.pdf

http://www.usda.gov/rus/electric/pubs/1724e203/1724e203.pdf

[CPOPE]

8' 6" to ground and 16' 8" phase to phase.


Careful, 8'6" over the ground ain't right. It's more like a minimum of 25ft over grade worst case condition.

Line conditions under which the NESC states vertical clearances shall be met (Calculations are based on Maximum Operating Voltage):
- 32°F, no wind, with radial thickness of ice, if any, specified in Rule 250B of the NESC for the loading district concerned.
- Maximum conductor temperature for which the line is designed to operate, with no horizontal displacement
http://www.usda.gov/rus/electric/pubs/1724e-200.pdf

[ratbastard101]

Careful, 8'6" over the ground ain't right. It's more like a minimum of 25ft over grade worst case condition.

Line conditions under which the NESC states vertical clearances shall be met (Calculations are based on Maximum Operating Voltage):
- 32°F, no wind, with radial thickness of ice, if any, specified in Rule 250B of the NESC for the loading district concerned.
- Maximum conductor temperature for which the line is designed to operate, with no horizontal displacement
http://www.usda.gov/rus/electric/pubs/1724e-200.pdf

I believe tramp is refering to the other ground.....As in what is the clearance required between an energized phase and a grounded object (ie. not the ground we walk on) and between two seperate phases.

[CPOPE]

I believe tramp is refering to the other ground.....As in what is the clearance required between an energized phase and a grounded object (ie. not the ground we walk on) and between two seperate phases.

Cool, I guess I'm slow on the uptake.
Follow the link please and tell me if I'm reading this wrong.http://www.usda.gov/rus/electric/pubs/1724e-200.pdf

TABLE 6-1
RUS RECOMMENDED VERTICAL SEPARATION IN FEET BETWEEN PHASES
OF THE SAME OR DIFFERENT CIRCUITS ATTACHED TO THE SAME STRUCTURE

Nominal voltage, Line-to-Line Voltage in kV 230
Minimum Vertical Separation at Support

1. Phases of the same circuit (Note A) 9.6feet
(Based on NESC Table 235-5)

2. Phases of different circuits (Notes B & D) 10.8feet
(Based on NESC Table 235-5,footnote 7 &8)

3. Phase conductors and overhead ground 6.4feet
wires (Based on NESC 235C and 233C3)

That all said the flippin table only goes up to 230KV
I opened up nesc table 235-5—Vertical clearance between conductors at supports and is a ***** to decifer.

I'll let someone else confirm what clearance should be. 8 ft 6 in or 7 ft 3 in.
The calculation should be performed, documented and explained by the engineer who stamped the plan not me.

Good Luck,