Improving Reliability for High-Profile Customers

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1 Improving Reliability for High-Profile Customers By Mark Kimbell Chief Engineer at Murfreesboro Electric Department How important are commercial customers to an electric utility? Are you doing everything that you can to be sure your high profile customers have the most reliable power possible? Can you cost justify installing distribution automation that will help keep power on to the local hospital or the local convention center? What are the costs to customers when the power is off? These questions do not always have simple answers. Sometimes the solutions can be very expensive, then it becomes a question of how much money to spend or how much protection to provide. Distribution Automation (DA) has advanced to the point where you should not ignore the improvement in service that you can provide your most important customer by having fewer and shorter outages. The growth of Murfreesboro, Tennessee, presented Murfreesboro Electric Department (MED), a medium-sized municipal of 50,000 customers, with a unique opportunity. In 2005, the city constructed a new gateway from the interstate into the center of Murfreesboro. This new four mile road corridor started at Interstate I-24 and continued into the city. The road was built on farm land that included over 1000 acres of green-fields. Many new businesses were constructed along the new road, with the major player being a new 200+ bed hospital. The road was named Medical Center Parkway. After the hospital announced that they were purchasing land along the corridor, a new Embassy Suites Hotel with an attached 4000 person convention center was planned to be built at the new I-24 interchange. A new 100-acre outdoor lifestyle mall was built beside the new Embassy Hotel. Many other medical offices, shopping venues and restaurants have been added along this new gateway into Murfreesboro. To enhance the community and the area around Medical Center Parkway, city leaders determined that this area should be served by underground facilities. The city installed duct banks for MED to use to supply the area with electricity. The challenge had been issued to keep as much equipment below grade as possible. MED had never installed underground feeders that served more than 400 amps. Much electrical system planning would need to be done before the first building was constructed. Multiple 800 ampere feeder circuits would be needed to feed this area. The major questions to answer were what routes and wire size could MED use to serve this new load, what protection equipment could MED use to make the electric feed into the Medical Center Parkway area as reliable as possible, and how do you cost justify the decisions to purchase this protection equipment. MED decided to go with parallel runs of Okoguard EPR 500 Cu 15kV primary wire for the main feeders of underground electric service. Each feeder would supply approximately 800 amps of capacity. In 2006 there were three feeders and two substations available to supply the Medical Center Parkway corridor. The exponential growth that occurred has dictated feeds from several different substations. To date there are now four circuits that feed this area with plans for three more circuits and a new substation. A new 161/12.47kV substation has been planned along a Tennessee Valley Authority transmission line that crosses the center of this development area. The substation will supply load growth in the area for several years to come. With the load questions answered, MED then turned to the question of protection. Since the city leaders wanted to keep as much equipment below grade as possible, we investigated equipment that could accomplish the edict. We found out that below-grade equipment at the 800 to 900 ampere range was not readily available. Only a few vendors were able to provide the required switching equipment. MED decided to use S&C Vista equipment that could be installed below grade, inside a vault with spring loaded lids. The Vista switchgear is submersible and rated for 900 amps. The CDR vaults were large enough to accommodate Vista equipment with up to six switches or fused sections. When the lid tops are opened, you can treat the equipment as open air. This avoided all the rules and regulations for providing forced air for confined spaces. MED decided to look at the possibility of distribution automation for the 1042-R119

2 Medical Center Parkway area. S&C showed MED what some of the possibilities were and how reliability could be improved. Keeping the power on is becoming more critical to all customers, but the commercial and industrial customers are affected more monetarily. MED has a General Mills plant in the city that can potentially lose over $30,000 of product if there is an electrical outage lasting more than 30 minutes. This does not count lost production time, that increases the damage cost of an outage. You can see how improved reliability with automation equipment begins to pay for itself quickly. Power outages at hospitals are a matter of life and death. The new Middle Tennessee Medical Center (MTMC) had MED install a dual underground feed from two directions and two different circuits with automated Vista switchgear to ensure that their outage time is minimal. They shared the cost of this dual feed with MED due to the nature and importance of the healthcare business. Can you imagine what an outage of one hour would do to a shopping mall? Murfreesboro has three major shopping areas and a Super Wal-Mart within the automation area. Many restaurants are located around the malls and the convention center. While not life critical, all of these commercial businesses would have to consider closing if power was not restored quickly. The decision to automate distribution is both hard and easy. The quantitative justification is difficult, but the qualitative improvements to the customers and the community are significant. The biggest deterrent is how do you cost justify the equipment? Since one automated Vista switch can be over $100,000, the question becomes what is the payback? Monetary savings of kwh sold in outage times will not come close to justifying the cost of a Vista switch or an automated overhead switch. Lost revenue from a 30 minute outage of a 500 ampere load on a primary circuit would end up being around $100 for one outage. As you can see, it would take many outages to justify one piece of automated equipment if lost revenue was the only factor, but what about the customers on that circuit? What is the cost of their lost production for a 30 minute outage? That lost production number can be significant. If a circuit this size has 150 commercial customers and each customer losses $100 in revenue during the 30 minute event, then that event has caused an outage where the community lost $15,000 in revenue. The correct lost revenue cost is most likely much higher than $15,000. These numbers come much closer to cost justification for automation. Payback for a $100,000 piece of Vista gear is probably close to four to five events. Payback for a $25,000 overhead ScadaMate or IntelliRupter switch could end up being one or two events. The benefits of improved reliability are hard to measure, even when reliability can be measured. MED tracks SAIDI (System Average Interruption Duration Index) and CAIDI (Customer Average Interruption Duration Index) reliability numbers to see how we compare to the national average. These numbers help you track progress, but do not tell you how much automation is worth to your system. What is it worth to avoid an operation at a hospital? How much damage do you do to your own equipment (station transformers, distribution transformers, switch contacts, connections, etc.) by avoiding operations? What kind of safety factor can you consider when you prevent traffic chaos by keeping power on to traffic signals? What benefit does automation provide electric operations staff if an outage is minimized to a small part of a circuit versus the whole circuit being out? Does the community benefit from a small section of the city having automation? MED management can see the value of automating circuits to protect high profile customers. By installing DA equipment, MED believes that we have improved the quality of life in our community. How do you measure quality of life? DA can be used as an economic development tool. When potential commercial and industrial prospects discover that the local electric utility has distribution automation experience, you are guaranteed to make an immediate positive impression, and that is a recruiting plus. Many new businesses are placing a premium on electric reliability, which goes up with the use of distribution automation. Multiple feeds and automation are a necessity for a new hospital, call center or data center. Underground distribution protection is different than overhead distribution protection. When an outage occurs on overhead lines you can generally find the problem by sight. With underground lines, you have to rely on equipment that will isolate the problem to a smaller area and then take sections at a time to open equipment and test the underground wire. Fault detectors 2

3 can help locate the fault, but unless there are sectionalizing devices in the line, underground outages can take hours to locate, where overhead faults can be located in minutes. Automation helps the fault location process by sectionalizing the line automatically, which is exponentially more important with underground distribution because of the time involved; and less fault location time in turn improves reliability index numbers. With DA, underground feeders can possibly isolate with a minimum amount of outage time, allowing crews to pinpoint the outage, repair the outage during regular hours, and re-energized the feeder without any further interruption of service to any customers. Murfreesboro Chooses Automation The decision was made to begin to automate the area around the hospital. Once MED decided to go this route an initial plan was made for five Vista switchgear locations along Medical Center Parkway. CDR Vista vaults were installed at critical locations and a Vista 642 (six bays, four switches, two fault-interrupting bays) and Vista 633 (six bays, three switches, three fault-interrupting bays) were ordered from S&C. Plans were also made to install five overhead ScadaMate switches and one pad-mount switch with motor operators in the surrounding area to work in conjunction with the Vista equipment. Five breakers at two different substations were equipped with S&C Universal Interface Modules (UIMs), that allowed the breakers to talk to the other DA switches and work together to create automation zones of protection on the distribution system. All this equipment included S&C 5800 Series Automatic Switch Controls with IntelliTEAM II Automatic Restoration System software. The communications medium was Landis & Gyr spread-spectrum UtiliNet Radios that hopped communications from one radio to another. Each switch location communicates with its neighbors to form a mesh network, so that each switch knows what that next switch in the zone is doing. 3

4 Initial Murfreesboro Electric Distribution Automation Plan - October 2007 As additional customers continue to be added to the electric system in the Medical Center Parkway area, MED has added to the automation system. Murfreesboro has been one of the fastest growing cities in the nation the last 10 years. The growth in this Medical Center Parkway area of the city has reflected this growth. What was open land a few short years ago is now a thriving commercial center. Within the automation zone MED has installed six Vista switches, two IntelliRupter switches, six overhead ScadaMate switches, two pad-mount switches, and eight UIMs at the substation breakers. MED currently has two more Vista switches and one more IntelliRupter to install at key locations within the area and plans to expand the automation to additional circuits and customers. Some of the locations along Medical Center Parkway were pre-planned, but an automation system almost has a natural growth progression. The more area that is covered, the easier it is to see where the next piece of automated switchgear could be placed. MED will look at each circuit and try to break the load up into automation teams of 100 amps each. This will split each circuit up into five or six sections. If the customer, such as the new hospital, is large enough or is high profile enough, that customer would be in a zone of their own. Communications continues to be a key part of the DA technology. MED has gone through one complete change to newer, faster S&C SpeedNet radios. These new radios helped speed up communications exponentially, which is important to the speed of response of the DA equipment. Plans are being made to replace some of the radios with Ethernet fiber ports that will make communications almost instantaneous. All the radios report back to a head-end radio at MED s Primary Substation that is connected to MED s main office with fiber. This connection, in turn, supplies information to a Proxy Server that collects all the current switch data and reports it to MED s Advanced Control Systems (ACS) SCADA system. MED Operations staff can observe, record and operate all the automatic switches from the Operations Center at the MED main office through the ACS SCADA system. Engineers or Operations staff can also access the equipment remotely using the configuration and diagnostic software. This is a valuable engineering tool for maintenance and troubleshooting. 4

5 Current Murfreesboro Electric Distribution Automation Layout - December 2010 Lessons Learned To date there have been five automation events where portions of the distribution feeder were reconfigured to keep the power on to customers. Two of the events occurred when two separate tornadoes came through the city. All of the events to date have been weather related on the overhead distribution system. The largest automation event occurred this past summer in August when a violent lightning storm came through the city. MED s Primary and Blackman Substations are the two current substations that feed into the Medical Center Parkway area. Primary Sub has three breakers that feed into the automation area and Blackman has one breaker that feeds into the area. The storm caused an event that tripped the whole yard at Primary Sub, including Tennessee Valley Authority s 161kV switchyard. This means that MED lost three feeds into the automation area, which is about the worst case scenario. The one circuit feeder that was left picked up almost 60% of the circuits that were out in less than two minutes. The outage to the substation was over 45 minutes long. The process worked as planned. As another section energized, the system kept up with how much new load was being added. When the Blackman feeder got to around 760 amps the automatic switching stopped because there was no more capacity left. The automation logic looks at available spare capacity when making restoration decisions, so that the alternate feeder will not overload. Without automation this event would have left the new MTMC hospital in the dark. Since the automation was in place, the hospital was only out of power for less than a minute. MED was lucky that this event occurred on a reasonably mild summer day when the circuits were not heavily loaded. The lesson learned is that when you automate, feeder capacity is very important. You need to have excess capacity and feeders out there that can supply the automation zone. A month before the August event occurred, another lightning storm caused the same type event where the Primary Substation and TVA switchyard were tripped out. All the automation 5

6 switches opened on the Primary circuits, but the backfeed operation failed due to a bad battery on the motor operator at the OPEN point between Primary Substation and Blackman Substation. Battery maintenance and replacement are critical to keeping the automation system ready to operate at a moment s notice. Equipment continues to evolve where battery tests are now performed automatically, which would have prevented this failure. There have been lessons learned where the equipment has not worked as planned due to operator error. April 10, 2009 the weather was volatile all day. Early in the morning a small thunderstorm rolled through the city. The wind was very strong and caused an outage on one of the automated circuits served out of MED s Primary Sub. An open wire secondary streetlight circuit broke and was wrapped up in the primary line above. The automation worked almost to perfection and isolated the section where the fault occurred, but the backfeed to one section of the Primary Sub circuit did not operate due to a settings issue at the OPEN point between the circuits. This switch location is the open point between the Primary and Blackman substations. The settings and status of the switches at OPEN points in the automation scheme are critical to the proper operation of the system. Since the complete event did not operate correctly, snapshots of all the controls involved were taken back to the main office and careful analysis was done until the wrong setting was discovered. Reports of an impending weather front began to filter in before lunch that same day. With that knowledge, MED staff was encouraged to go to lunch early. The plan was to correct the automation settings at the OPEN point switch after lunch. At 12:32 pm an F4 tornado touched down and cut a 22-mile path across Murfreesboro. The tornado went through the first automation team at the Blackman Substation and locked out that circuit. The automation switches on that circuit all opened properly, but since the OPEN point switch between the Primary and Blackman substation had an incorrect setting, the automation backfeed could not be completed. MED lost over a third of the total electric system due to the tornado. It would have been great if the automation had worked correctly. The automation would have probably re-energized a mall and the new convention center if the setting had been corrected before lunch. 6 Murfreesboro Good Friday F4 Tornado April 10, 2009 Knowing what is happening in the automation zone is of utmost importance. If automation teams are not READY to switch, then automatic operations will not take place.

7 When crews are working on sections of line in the automation zone, automation will have to be shut down, but care must be taken to get the automation teams back to READY after the crew work is complete so that the switches are prepared for an automation event. Without SCADA information or network connection or both, keeping up with the status of the automation system can be difficult. Personnel would need to connect by radio or physically go to each switch location to check on the system to make sure the system was READY to operate. With SCADA you receive alarms that let you know when problems are present. Connecting through a radio is cumbersome at best due to network settings that will need to be changed to communicate with other automation radios. A network connection with a head-end radio is a much smoother way to look at each switch. It allows personnel to easily update and change settings from the main office at any PC on the network. The only real barriers on the network were radio settings issues and IT firewall issues allowing the correct IP addresses to punch through. The scale and experience with automation continues to grow at MED. The capabilities of the DA equipment, the software and the communications continue to improve. The IntelliRupter technology allows an electric system to drastically improve the operations and blinks that customers will see and to minimize the stress of fault current put on the electric system. Automation is about to reach the point where one section will isolate, the source side distribution will not operate and the load side portions of the circuit will backfeed with the closing of one switch if capacity is available. MED s distribution truly is a self-healing distribution system that improves reliability for all customers within the Automation Zone. 7