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Learning from Hurricane Keith

Learning from Hurricane Keith. Learning from Hurricane Keith.

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Learning from Hurricane Keith

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  1. Learning from Hurricane Keith

  2. Learning from Hurricane Keith • Hurricane Keith affected the eastern part of Belize from September 30, 2000 to October 2, 2000. The hurricane started as a depression about 60 miles Northeast of Cape a Dios, Honduras on September 28, 2000 and rapidly intensified to a Category IV storm on September 30, 2000.

  3. Learning from Hurricane Keith • The hurricane affected primarily the area North of Belize City with winds of up to 135 mph and estimated maximum gusts of 150 mph. The eye of the hurricane passed twice over San Pedro and as close as 45 miles from Belize City. The areas hardest hit were San Pedro, Caye Caulker and Belize City. Caye Caulker electrical system was totally destroyed and most of the San Pedro system was damaged.

  4. Learning from Hurricane Keith

  5. Learning from Hurricane Keith • A line withstand is a function of velocity • The design velocity is the wind velocity that has a 0.02 annual probability of occurrence or the 50-year return • F = 0.0025 V2

  6. Learning from Hurricane Keith • The Safir-Simpson scale below classifies Hurricane force winds.

  7. Learning from Hurricane Keith Number of Customers - affected

  8. Learning from Hurricane Keith Cost of Damages

  9. Learning from Hurricane Keith Recommendations to Minimize Future Problems ·Change all rotten and underclass poles and reinforce all footing to include concrete base to prevent movement ·In Cayes (islands) where there is sandy soil or in swampy areas, ensure that all poles in future are installed in a drum and concreted in place. This is due to inundation and washing away of foundation ·Consider changing the 10% plus 2 feet rule to 10% plus 4 feet.

  10. Learning from Hurricane Keith Recommendations to Minimize Future Problems ·Utilize baulking boards as much as possible ·Install storm guys on lines where practical. Use stainless steel guy grips and use correct sandy or swamp anchors with adequate holding strength ·Always install transformers on one pole class HIGHER

  11. ULTIMATE WIND SPEED WITHOUT TRANSFORMERS (8000 psi poles Azusa Conductors) MPH SPAN (ft) H-1 Pole C-1 Pole C-2 Pole C-3 Pole 100 189 175 161 146 125 178 165 151 137 150 168 156 143 129 175 160 149 135 122 200 153 142 129 116 225 147 136 124 111 250 141 131 119 107 300 132 122 111 100 Learning from Hurricane Keith Design Issues ·How do we choose a design speed? Note that a Category V storm has wind speed greater than 155 mph ·The force is proportional to the wind velocity squared. 130 mph to 155 mph means an extra force of 1.42.

  12. Learning from Hurricane Keith Recommended Design Values and Issues ·Not cost effective to design beyond 143 mph. Note even at this value there must be an overload factor of 1.33 (NESC Rules 260 C and 250 C) ·Design for Category III or IV. Limits spans to 225 feet. Can go as high as 250 feet in housing areas because of shielding. But for pole heights above 45 feet must do detailed design. ·Use Class 2 poles and Class 1 for transformer poles. ·Seek to eliminate joint use.

  13. Learning from Hurricane Keith Other Issues ·Do tree trimming before the start of the season and eliminate overhangs ·Consider changing transformer attachment to pole ·Verify the integrity of insulator pins ·Eliminate the use of lugs for underground terminations ·Install anti-split bolts on pole heads ·Under-building can reduce line withstand by as much as 30 mph

  14. Learning from Hurricane Keith Other Issues … cont’d ·Eliminate use of soft-drawn aluminum tie wire ·Do proper soil analysis BEFORE line design ·Use heavy duty swing angle brackets ·Do a proper anchor study and pole setting depth for EACH installation

  15. Learning from Hurricane Keith Generally the issue is one of pole strength and the number of attachments. A detailed designed using a 50 feet pole, using Canton conductor, 69 kV, Class 1 pole concluded that the maximum allowable span is 271 feet, for a line that is NOT on the coast.

  16. Planning for the next Hurricane Planning ·Do tree trimming before the start of the season and eliminate overhangs ·Must have adequate poles, transformers and connectors ·Must have adequate small generators and gas driven tools ·Eliminate poorly tensioned lines

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