Preparing for a hurricane may seem like an overwhelming task and an exercise in futility. However, the time taken to plan is well worth the effort. Preparation includes material and personnel logistics, but the greatest benefit comes from the protection of assets.
Almost 15 years ago, Dominion Virginia Power (Richmond, Virginia, U.S.) developed a plan to protect substation and transmission equipment. Over the years, the plan has grown and matured as new experiences have been encountered. However, the most important planning that must be done pertains to substation flooding.
Prediction & Preparation
The water damage from flooding can completely render a substation control house unusable. The question is how much floodwater can you expect? Years ago, the National Oceanic & Atmospheric Administration (NOAA) developed a hurricane storm surge prediction tool called Sea Lake Overland Surge Height (SLOSH). By imputing the expected storm magnitude, speed and direction of movement into the program, a flood height can be calculated based on height above sea level and the expected tide height.
Dominion developed a database with flood heights for each possible condition. Based on the height above sea level, many substations were shown to be unaffected by a hurricane tidal surge. This database is now the starting point for each hurricane preparation plan. Different station flood heights require different actions. Radical action is required for a storm surge of 5 ft (1.5 m) or greater.
Preparation must take place a minimum of 24 to 48 hours ahead of time to ensure safety for personnel. Transportation before the storm can be difficult, especially if mandatory evacuations have been issued. Gridlock can and will occur at some point, so routes to and from the substations must be planned. When sending employees out even 48 hours before the storm, make sure they have adequate water, food and toiletries in case they are stuck and cannot return. During 1989's Hurricane Hugo, one utility sent its employees to turn the breaker reclosing off at a substation and ended up having them stuck for three days because of fallen trees.
Planning and Prevention
The planning process should begin by targeting substations with paralleled transformers. If the entire load can be transferred to one transformer, then the other can be de-energized and prepared for the floodwaters. The strategy is to protect critical infrastructure by eliminating the number of potential through faults to substation transformers, which can lead to transformer failures. It is devastating to service restoration efforts if too many transformers are damaged while in service and replacement units are unavailable.
Motor operators for high side switches should be removed or sealed to prevent water contamination. LTC or control cabinets should be sealed with watertight duct seal or silicone room temperature vulcanizing (RTV). Typically, transformer protection panels can be de-energized by pulling group fuses for both dc and ac. De-energized panels should have relays removed.
Relays should be removed and taken to a safe location. This may be complicated if the relays are digital electronic instead of electromechanical. If you know storm flood heights, consider locating the relays at a greater floor height during the design stage.
Breakers are hard to seal and most likely will need to be replaced if the floodwater reaches the control or mechanism cabinet. This was the experience after 1996's Hurricane Fran, when Dominion's Tarboro substation flooded to almost 8 ft (2.4 m) of water, which required that all breakers be replaced.
Panels that remain in service may be destroyed by the galvanic corrosion from salt and brackish water. Depending on the height of the battery cabinets, all lead acid cells that are below the expected flood height should be prepared. Vent caps should be removed, and duct seal should be applied. If salt water contaminates the electrolyte, the cell jars must be replaced.
Make sure all substation drawings and prints are stored in a location that will remain dry. All spare fuses and equipment stored inside the control house should be relocated or placed above floodwaters.
Unplug all stationary phones and place in a safe location or take with you. The loss of communications during restoration is more than a nuisance. After 2003's Hurricane Isabel, cell phones worked sporadically.
If the flood height is expected to be less than 3 ft (0.9 m), then sand bagging and sump pumps are effective at keeping the control house dry. This method worked during Hurricane Isabel where all but one substation was kept dry. In that case, the storm surge water was higher than anticipated due to rain run off. This information was updated in the flood height database for future use.
Inspect the substation yard for material that may blow in to an energized bus such as aluminum drums or cable trays. Wood poles should be tied down so they cannot float away and damage the control house or surrounding equipment. Securing the area around substations can be difficult as many of them are in industrial areas where objects outside of the fence can potentially cause damage. Look outside the station and negotiate with neighbors if necessary to remove or secure potentially harmful objects.
Transmission and distribution reclosing should be turned off in a planned method. Some utilities have the capability to perform this remotely while others may do this manually. Make sure that the plan is reviewed by both operations and planning groups.
Switching or disconnecting systems into islands is a good risk strategy to protect the infrastructure. This can result in possible voltage problems with customers so gauge the risk benefit. Protecting your equipment can trade days of outage time for hours.
Strategies should be formulated based on expected wind speeds and tower construction. Switch transmission lines out of service unless they are critically needed. Repairing transmission lines is quicker and easier when splicing is not required because of annealed, burned down conductor.
The best advice is to plan ahead for a hurricane and do not wait until the last minute to put the plan into action. Practice the plan and make sure every one knows what is required. A utility's success in working the plan and taking the preventative measures suggested will influence the extent of the damage and how quickly service can be restored.
Mark McVey has worked 19 years for Dominion Virginia Power in system protection as an operations supervisor. Currently, McVey is an Engineer 3 in the substation electrical equipment group. He is a member of the IEEE Capacitor Subcommittee as well as various IEEE standards working groups. McVey received a BSEE degree from Virginia Tech in 1982.
|Substations*||District||0 ft||1 ft||2 ft||3 ft|
|Substation water heights for pre-storm normal tides (tide height). |
*6.0/4.2-kV distribution substations