The Impact of Ice

1
The Impact of Ice
Nebraska Public Power District2006-2007
2
Christmas Storm Outcome

• 10 transmission lines out made temporary
  repairs to 8 2 remained out of service
• 4 telecommunications fibers inoperable no
  telecommunications west of Holdrege
• 2,500 retail customers impacted
• 21 NPPD technicians assist Dawson PPD
• 1.0 Million in damages (approximate)

3
New Years Storm Timeline

• Friday December 29
• Rain, freezing rain, icing, wind
• Saturday December 30
• Severe icing conditions and wind
• Widespread, extensive damage
• Crews respond to numerous outages
• Sunday December 31
• Major effort to assess damage and restore power

4
Back-to-Back Storms
Christmas Storm
New Years Storm
5
Normal NPPDTransmission System
Grand Island
Lexington
Kearney
Hastings
Holdrege
6
System Condition January 1
7
System Condition January 4
8
Kearney Area Damage Assessment


-Wood Structures
-Steel Towers
-Shield Wire Miles

63
2
42
314
125
2
18
10
43
54
5
1
10
34
52
53
109
1
9
Early Priorities

• Kearney
• Lost 4 of 5 transmission feeds
• Priority restoration of second feed
• Rolling blackouts during initial restoration
• Holdrege
• Lost all 3 transmission feeds
• Mobile generation located within the community
• Key Messages
• Energy conservation
• Fragile system
• Safety

10
System Status March 2, 2007

• Initial Current
• Miles assessed 2,650
• Customers without power
• NPPD Retail (service restored 1/6/07)
  11,612 0
• Wholesale customers 31,000 0
• (service restored 1/19/07)
• Transmission System (approx, 71 repaired)
• Number of line segments out 37
  7
• Transmission miles out-of-service
  1,053 184
• Number of substations out 18 0
• Miles of conductor down 301
  86
• Number of structures damaged 1,136
  473
• GGS east flow limitation
  224 MW 990 MW
• Communities on Mobile Generators
  14 0
• More than a dozen public power utilities impacted
  by storm
• Contractors on site throughout reconstruction 260
  - 320

Up to
Up to
These MW will depend on transmission system
status, loading conditions and regional
transmission system conditions.
11
FEMA Disaster Declaration FEMA-1674-DR
12
Ice on a guy wire
13
Engineering Design Criteria

• National Electrical Safety Code 1997
• Heavy combined ice and wind loading, ½ inch
  radial ice, 40 mph wind, 0F
• National Electrical Safety Code 2007
• Heavy combined ice and wind loading, ½ inch
  radial ice, 60 mph wind, 15F
• New Years storm
• 2 inch radial ice, winds averaging 21 mph, gusts
  up to 40 mph, temperatures hovering around
  freezing

14
Effect of Ice on Power Lines

• Typical weight of conductors without ice ½ to 1
  pound per foot
• Weight of lines with ice can increase by 4 - 8
  pounds per foot
• Weight on structures increased up to 8 - 10 times
  after ice storm
• Example 115kV structure load went from 3,000
  pounds to 26,000 pounds (2-inch radial ice)

15
(No Transcript)
16
Size of ice one week after storm
17
The ice mangled 345-kilovolt structures like
twist-ties
18
More than 40, 345-kilovolt structures were
destroyed
19
The storm snapped H-frame structures like twigs
20
More than 300 miles of line and 1,137 structures
were damaged
21
Ice on Substation near Holdrege, Neb.
22
Emergency Restoration
23
Initial Response

• Public Safety
• Cleared roadways
• Public Service Announcements
• Coordinated Emergency Personnel
• Coordinated with Governors Office
• Coordinated with Nebraska Emergency Management
  Agency (NEMA) and Federal Emergency Management
  Agency (FEMA)
• Employee/Contractor Industrial Safety
• Reinforced NPPD Safety policies
• Cognizant of portable generators

24
Initial Response

• Assessed damage to transmission infrastructure
• Surveyed more than 1,900 miles of line using
  helicopters from Air National Guard, Nebraska
  Highway Patrol and a private flying service
• Ensured Nebraskans had power
• Needed to energize 115kV substations
• Restore transmission feeds to hardest hit
  communities which lost multiple transmission
  feeds
• Energize distribution system to end-use customers
  
• Site mobile generation (NPPD, NEMA, FEMA)
• Assist other utilities as resources permit
• Restore telecommunications capability

25
Emergency mobile generation was brought in for 14
communities
26
Mutual aid near Elgin, Neb.
27
Day-after-day diligence for more than 30 days.
The last community on emergency generation was
restored line service on Jan. 29, 2007.
28
Reconstruction
29
Reconstruction Strategy

• Reconnect Nebraska electrically west to east
• Secure contracts and labor resources to safely
  expedite rebuilding transmission system network
• Align reconstruction contractors based on
  capability, line criticality and proven
  performance
• Align contractors, mutual aid workers and
  District employees with performance expectations

30
Restore Transmission System

• Material procurement and delivery
• Focus on primary reconstruction efforts
• Hire and assign contractors
• Parallel efforts (Customer Service Priorities)
• System Network Priorities
• Watch the weather
• Ensure equipment functions

31
(No Transcript)
32
More than 3,000 wood poles ordered.
33
Unloading conductor at NPPDs York Operations
Center for 400 miles of line
34
Contractors Reconstructing South of Holdrege, Neb.
35
Restoration efforts near Prosser, Neb.
36
Questions?
37
Long-Term Challenges

• Maintaining electric grid reliability with
  weakened high-voltage transmission system
• Reconstructing during winter months (possibility
  for additional storms)
• Repairing electric grid in time for irrigation
  season and peak summer electric load
• Ensuring timely material deliveries managing
  multiple, concurrent projects
• Restoring normal generation output from Gerald
  Gentleman Station

38
Major Impacts

• Over 200 Union Pacific trains stopped due to
  downed lines across rails and loss of power to
  central signal control
• Multiple Fiber Breaks
• Hildreth to Holdrege
• Holdrege J2
• Axtell Holdrege
• Crooked Creek Riverdale
• Riverdale - GI

39
New Years Ice Storm Area
Transmission Lines Out-of-Service
39
40
Generators at Holdrege
41
Loads on Line Supports
Transverse
Tension
Tension
TOP VIEW
Typical Failure Point
Force
42

• (This storm) was the greatest catastrophe to
  ever hit a Nebraska utility. It will be
  remembered and talked about for lifetimes.
• Comment describing March 29,1976 ice storm from
  NPPD commemorative booklet.