With more than 4,000 pole miles of distribution lines, Memphis Light, Gas and Water (MLGW; Memphis, Tennessee) has had its share of weather-related damage. On Feb. 5, 2008, however, Mother Nature was relentless as she unleashed a series of tornados across Tennessee.

MLGW, the nation's largest three-service municipal utility serving more than 429,000 customers, has more than 60 electric substations spread over a service territory of 755 sq miles across Shelby County.

For the first time in the utility's 70-year history, MLGW experienced extensive damage to an electric substation that could not be quickly resolved by isolating the troubled area and re-routing power around it through the substation. Additionally, MLGW had two transmission towers collapse.

Eye of the Storm

Around 5:30 p.m. central standard time, a supercell thunderstorm produced a tornado in Southaven, Mississippi. The tornado quickly tracked across the Mississippi-Tennessee state line and into southeastern portions of Memphis.

This tornado produced a wide path of extensive damage over residential and commercial areas. The National Weather Service office in Memphis rated the tornado an EF2. In the Memphis area alone, three people died and many were injured. The event was later labeled the “2008 Super Tuesday Tornado Outbreak.”

One of the tornados that roared through the region unleashed a storm of debris into substation 71. This sub-station provides power to the Hickory Hill area, which is located in the southeast region of Memphis and has 63,000 residents.

Path of Destruction

Some customers complained because the substation could not be re-energized immediately. They did not understand the tornado was not like an atomic bomb that made the substation disappear. Instead, the high winds acted more like a grenade that forcefully cast debris like shrapnel into the substation.

Flying debris from the shattered warehouse damaged conduits, power cables, insulators, breakers and other equipment throughout the entire substation. All the equipment had to be inspected, tested and wiped down before being re-energized. Some of the equipment also had to be replaced or repaired first.

The substation did not incur any substantial mechanical damage or electrical arc damage. This suggests the substation was de-energized as a result of the transmission line relays tripping before the storm reached the substation and hit it with all the debris.

In the substation, supervisory control and data acquisition (SCADA) communication was lost because of damaged coax on the antenna, and two breakers were out of service because of damaged conduit, cables and jumpers. In addition, two sets of switches were bent and damaged, and the roof on the control house was damaged and leaking. The fence around the substation was down on three sides and two lightning protection poles were bent. The buss to the capacitor banks was damaged, metal cable tray covers at junction points were missing, and various buss supports, arrestors, jumpers and insulators were damaged.

On the transmission line feeding the substation, two adjacent towers fell, causing MLGW to lose four circuits, including one of the two circuits feeding the substation. The other transmission feed to the station was lost because of damage to 36 insulators and 200 feet of conductor.

Call to Action

MLGW relied on not only all of its linemen to handle the electric distribution outages, but also a full crew of substation electricians to restore the damaged substation.

The company's experienced and hard-working substation crews restored the substation as quickly as possible. Through coordinated efforts and working together, MLGW substation crews restored the substation within three days. Distribution support restored one of the transmission line feeds, which allowed five feeders to be energized.

At one time, as many as 59 employees were working within the substation to clean up, wipe down equipment, make repairs and test equipment. With this many employees working in such a limited space, and added pressure on them to work quickly, one would expect an increased possibility of an injury. However, there were no safety incidents in the process of restoring the substation. The only injury occurred when an employee hurt his back repairing distribution services.

Additionally, MLGW restored the other transmission feed into the substation six days after the event so that the substation was no longer single-ended. The second feed was restored by building temporary transmission towers and restoring two of the four transmission circuits previously lost. A couple of months later, the temporary transmission structures were replaced with permanent structures.

About 64,000 customers lost power at some point during the storm, and the damage totaled about $4 million. The tornados inflicted damage to 22 distribution and five transmission circuits, 146 distribution poles, two transmission towers, an electric substation, distribution and transmission line wire, insulators and other equipment. Despite this destruction, all of the electric service to the customers was restored in just five days.

While Mother Nature unleashed all of her fury on MLGW and its substations, transmission system and electrical distribution, the crews pulled together to restore power and ultimately get all the equipment back online. The utility successfully recovered from the tornado outbreak but hopes that Mother Nature decides not to test the company again anytime soon.

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Michael Ray Russell (mrussell@mlgw.org) is the manager of electric substation engineering and operations for Memphis Light, Gas and Water.

List of Tornados in the “2008 Super Tuesday Tornado Outbreak”

Confirmed	Confirmed	Confirmed	Confirmed	Confirmed	Confirmed	Confirmed
Total	EF0	EF1	EF2	EF3	EF4	EF5
87	31	30	16	5	5	0

TIPS ON RESPONDING TO AN EMERGENCY SITUATION

After the tornado outbreak, MLGW met with management and field employees to discuss what went well and what needed improvement. As a result of those meetings, the company learned the following lessons in relation to substation work.

Employees

• Substation employees need to be notified, organized and on standby (should not immediately send a large number of employees into the substation).
• Situation must be made and confirmed safe before work starts.
• Problems must be evaluated and prioritized first (it typically takes two to 24 hours to access damage).
• After being made safe, employees can help with damage assessment and clean up until work can be prioritized and assigned.

Tailgate meetings

• Crews should have a tailgate meeting every morning with the leadership to discuss the plans for the day and any related issues or items from the day before.
• Next, there should be a tailgate meeting at the job site with all employees working at the site before work starts to discuss safety as well as plans for the day.
• If working 16-hour days, hold a mid-shift tailgate meeting at the job site by the leadership to discuss the status of the plans for the day and any related issues.

In-charge person

• If the damage is known to be isolated to one location, immediately assign a foreman to be in charge of the job site.
• If the extent of the damage is unknown or covers several locations, immediately assign crew leaders by seniority to be in charge of the job site.
• If after a couple of days the other locations where damaged occurred are resolved, or damage is confirmed and limited to one site, transfer responsible charge from the crew leader to a foreman.
• Communicate clearly to the group, including all employees during tailgate meetings, who the person is in charge of the job site.

Work shifts

• It works best to do the 16 hours on/8 hours off for all employees as opposed to staggered shifts if there is plenty of work and room. If not possible or not enough room, then stagger the shifts to maintain 24-hour work on the project.
• Every so often, evaluate the need for employees at the site. Remove employees who are not needed.
• Reduce employees during re-energizing for safety, but keep a few on hand in case there is a problem.

Work breaks

• Variety in type of food and location is important (make arrangements for direct charge to company and clearly communicate limits of expenditure per employee).
• Half/half staggered lunch instead of all at once works best (this eliminates the appearance to the public that no one is working to resolve the problem).

Communication

• This is the most important item and contributes to safety as well.

Hold orders

• Must be clearly defined, clearly stating what is a part of the order and what is at the discretion of the person with the order. You must clearly communicate if and what grounds are not at discretion and the actual status of equipment both when order is obtained and released.
• One person per substation location with order representing the group at the site works best. Hold order in conjunction with distribution to create a double order on anything coming in or going out (feeders and transmission lines).

System operations/control center

• Need to have or be able to provide a person at control center to handle substation orders - dedicated and same person for all sites to maintain safe communications.

Materials

• Internal metal shop is a great asset to be able to modify and fabricate special items if needed.
• Buying an extra one of something special or unique is helpful.
• Need asset management tool for material both installed and stored and know where all the spares are located.

Lights

• Leased lighting worked well to allow work at night and doubled as a source of power (came with generator output).
• Own a couple of sets of lights/generator combos with 120/240 V (208 V).
• Generators are also used to keep batteries charged and charge/wind up tripping springs in breakers.

Contracting

• The people who design it, build it and maintain it are the best at fixing it if they have enough resources.
• Only use contractors in substations if resources are not available in-house.