Maquoketa Valley Electric Cooperative uses SCADA and AMI data to proactively reduce SAIDI by 30% over 10 years.
In today's world, most consumers consider a blink almost the same as a prolonged outage. Minimizing blinks on a rural power system historically has been a reactive approach, but with the implementation of advanced technology, a proactive plan can be put into place.
Maquoketa Valley Electric Cooperative (Anamosa, Iowa, U.S.) began implementing a technology plan in 1998 with the installation of a supervisory control and data acquisition (SCADA) system and digitizing system maps. SCADA was installed at each of MVEC's 37 substations and records valuable engineering and operational data, including information on every fault that occurs on the distribution system. Along with the SCADA installation, a geographic information system (GIS) from ESRI was developed to enable the creation of a detailed engineering model.
WindMil software from Milsoft Utility Solutions allows MVEC to accurately model and predict the performance of the distribution system, which has resulted in significant infrastructure upgrades over the past 10 years. In 2004, MVEC added an outage management system (OMS) from dataVoice International to its stable of engineering software, and most recently, the cooperative completed the installation of an advanced metering infrastructure (AMI) from Cooper Power Systems' Cannon Technologies.
Operating a rural electric distribution grid of 3300 miles (5311 km) of line, where 95% of the line is overhead, creates numerous opportunities for momentary and sustained outages that require the constant use of data provided from the different technologies MVEC employs.
Pinpoint Maintenance Areas
Momentary interruptions are a nuisance, but not many member-consumers complain until the problem becomes repetitive. A high priority has been made to use the technology available to be proactive about blinks and to correct the problem before any member-consumers call to make MVEC aware of the issue.
The SCADA system from Survalent Technologies provides MVEC with detailed information about each fault that occurs on the system. A two-year study compared the fault current values from known outages with the assumed fault current provided from the engineering model. As a result of the study, it was determined that almost every fault that led to an outage on Maquoketa Valley's system had an impedance value near zero ohms.
Discovering this was helpful in attempting to determine where a fault occurred on the system, because location accuracy decreases with increasing fault impedance. From this data, trends can be recognized in the fault current values as reported by a substation, feeder, and phase, which can then help pinpoint the area in which crews need to increase their attention.
System fault currents are then analyzed on a daily basis in an effort to identify problem areas prior to their becoming a major nuisance to the member-consumers. A report is generated at the end of each month showing the number of faults not associated with an outage. This report helps determine if any fault trends were missed during the month or shows other maintenance issues that need to be addressed.
An example of a maintenance issue that needs to be addressed would be when a tree grows too close to the line but only makes contact with the overhead conductor when there is a strong wind from one direction. The tree is a given distance from the substation and results in a similar fault current each time it makes contact. Using the similar fault current value and the engineering model, an estimate fault location can be determined.
Outside contractors are used as needed to clear-cut trees to prevent momentary or sustained outages from occurring. These areas are picked by either recommendation from the crew assigned to the area or by looking at historical outage data in conjunction with a drive-by survey to determine the need. The number of unknown momentary outages where the fault current matches the area also plays a major role in determining areas in which to focus maintenance efforts.
In addition to vegetation issues, MVEC has used fault analysis to identify floating conductors, faulty lightning arresters, bad insulators and areas prone to small animals. By finding these issues early, MVEC reduces permanent outages and improves the reliability of service provided to its membership.
From an operational standpoint, adding AMI would help provide clarity to outages before sending trucks to the area. Therefore, the next logical step for MVEC to take was installation of Cooper Power Systems' power-line carrier solution for the 16,000 meters on the system. Because the benefits of an AMI system cannot be fully realized until 100% of the system is installed, MVEC took an aggressive approach to system implementation and had the Cannon infrastructure installed and operating systemwide within 16 months. While SCADA provides information at the substation level, AMI takes data to the next level by interrogating meters and providing valuable information on what is occurring outside the substation fence.
When a fault indication is read by SCADA, the probable fault location can quickly be obtained through engineering software. Next, the meters can be pinged through the OMS by selecting a specific line section to help determine the extent of the outage. By being able to select a specific line section or device from which to start pinging meters — instead of selecting all the devices on the substation or feeder — results are displayed much more quickly. In many instances, this process allows MVEC to have crews headed toward the outage before the member-consumer reports the outage. In some cases, outages are restored without ever having been reported.
There are times when a fault current matches with multiple line sections on the same substation, circuit and phase. In these instances, an individual meter can be interrogated for the time stamp and duration of the last six outages the meter experienced. This data can then be matched up with the data captured through the SCADA system to determine which device operated in the field to clear the fault. A report can be run to see if there is a trend in the data that was reported and maintenance efforts can be focused in the appropriate area.
Notifications of Outages
Equipment failures happen. Outages occur. How quickly the engineering and operations staff becomes aware of the problem is critical to keeping reliability numbers as low as possible. Maquoketa Valley does not staff its operation center 24/7; rather, it has a contract with Cooperative Response Center (CRC) to handle outage calls and dispatch crews after normal business hours.
CRC only becomes aware of the extent of an outage after member-consumers begin calling in to report a loss of power. At that point, CRC contacts the on-call crew to handle the problem, and if enough outage calls come in, CRC contacts the on-call supervisor, as well. There needed to be a way for SCADA, OMS or AMI to notify the appropriate person when a major problem occurred before the calls were received. MVEC decided text message alerts were the solution.
When a power-supply outage occurs at a substation, a text message is sent through the SCADA system. The person in charge of handling major outages then uses a secure VPN to connect to the SCADA system from home to determine the extent of the outage. All non-electronic substation reclosers have motor-operated actuators — NASAT MC by Tyco Electronics — connected to them, enabling remote operation of the open/close and one-shot handles. Major three-phase tie lines also have motor-operated switches installed at the normal open point between substations. The combination of these devices allows circuits to be remotely switched through SCADA instead of having crews in place to do the switching manually. By transferring load through SCADA, MVEC can reduce the outage durations for power-supplier-caused outages, which historically have accounted for 30% of the total outage hours.
Alarm points have been set up on each substation recloser, so when an open status is seen, a text message is sent notifying the appropriate people. This allows crews to be dispatched without having to wait for any reported power outages. A probable fault location also can be determined, so the crew can begin looking for the cause of an outage and eliminate the need to patrol long sections of line. Once the crew has the problem resolved, they can then call to have the substation recloser closed in remotely, so they do not have to travel back to the substation, which helps decrease outage durations, as well.
Voltage abnormalities at the substation level are also checked by SCADA. If the voltage stays outside of the tolerance for a given amount of time, a text message is sent warning of the problem. One instance triggering this type of alarm would be a fault occurring that is cleared by the high-side fuse of the power transformer. Another instance would be if a voltage regulator or load tap changer failed and was allowing the voltage leaving the substation to be too high or too low.
Down-line meters can be set up to notify staff by text message when the voltage seen by the member-consumer is too high or too low. The first meter per phase beyond every voltage regulator is set to report back its voltage every five minutes to ensure proper operation. If the voltage is outside the acceptable limits, a message is sent warning of a possible malfunction of the voltage regulator or regulator control. Voltage profile data from the previous five days can then be downloaded to verify the results.
In the first year and a half since this type of notification has been in place, messages have been sent out four times, and the problem was corrected before any complaints were received.
End-of-line meters predicted to have the lowest voltage from the engineering model are also set up to report their voltage back to the office. These values help verify the models used for system planning are accurate and that all problems are accounted for prior to proceeding with construction.
Wealth of Data
The installation of an AMI has opened up a wealth of data and prompted the creation of ways to sift through to find the important data. A mixture of pre-made and custom reports have been created to pull data out that should be looked at on a daily, weekly or monthly basis. These include reports comparing the peak energy demand (kilowatts) to the rating of the transformer, the analysis of blink counts recorded on the meters, and the minimum and maximum voltage readings on the meters. These reports have helped MVEC correct problems during normal work hours instead of having to respond urgently after hours.
Data can also be used to help with cost-of-service studies. Historically, load profile data was gathered from a few meters and applied to a group of like meters. AMI now makes it possible to gather actual load data from each meter to help determine how and when electricity is used by each group and enables an accurate allocation of costs.
The addition of technology systems at MVEC has had a significant impact on not only the performance of the distribution system, but how the system is monitored and operated on a daily basis. This has resulted in a significant amount of information available for MVEC to better serve its member-consumers on a daily basis.
MVEC's reliability numbers have also improved significantly over the last five years. The number of outages (system average interruption frequency index) has decreased 6.8% and the annual average outage duration (customer average interruption duration index) has decreased 19.7%, resulting in a 29.9% overall decrease in the annual average outage time (system average interruption duration index) for MVEC member-consumers.
Mark Scheibe (firstname.lastname@example.org) is currently distribution engineer at Maquoketa Valley Electric Cooperative and has been in that position since he graduated in 2005 from Iowa State University with a BSEE degree. His responsibilities include system planning and design, managing the SCADA and AMI systems, and analyzing data provided through the SCADA, AMI, OMS and ESRI systems.
Jeremy Richert (email@example.com) has worked at Maquoketa Valley Electric Cooperative since 2000 and currently serves as the director of engineering. He graduated in 2000 from Iowa State University with a BSEE and is a licensed professional engineer in the state of Iowa.
Editor's note: This is the first feature article T&D World has obtained from the social networking service Twitter. Technology Editor Vito Longo (@Uncle_Vito) received the article proposal via a tweet from author Mark Scheibe (@mas1683).
Companies mentioned in this article:
Cooper Power Systems www.cooperpowersystems.com
Cooperative Response Center www.crc.coop
dataVoice International www.datavoiceint.com
Maquoketa Valley Electric Cooperative www.mvec.com
Milsoft Utility Solutions milsoft.com
Survalent Technologies www.survalent.com
Tyco Electronics www.tycoelectronics.com