Server upgrades, migration of historical data

At Dogwood Energy Facility, a 2 × 1 combined cycle in Pleasant Hill, Mo, powered by 501FD2 gas turbines, historical data provide Plant Manager Steve Hilger and his team valuable insights and often are used to troubleshoot existing issues as well as to identify new ones. The facility is owned by Dogwood Energy Management and operated by NAES Corp.

While historians store a massive amount of data, some of that information may be left behind when systems are replaced with new technology. As plants upgrade, add equipment, and change configurations, historical data can be forgotten, easily—until needed.

One of Dogwood Energy’s challenges was how to move archival data from four different control systems into a secondary historian to allow evaluation of that information. Installing a new control system offered an additional challenge as personnel looked for the best way to identify and resolve communications issues with the third-party controls. Plants often experience a loss of data transfer to the historians—sometimes even a complete loss of data from those third-party systems.

Dogwood’s OSI PI historian was commissioned after the plant was completed in 2001. At that time, the active control systems were WDPF/Ovation, Teleperm, Tosmap, and Allen Bradley. PI’s flexible architecture and OSIsoft LLC’s willingness to work with users to improve its product enabled the plant to capture historical data from all four systems up to 50,000 exceptions per second.

Since 2001, Dogwood has been upgraded PI three times. With the historical data transfer, the plant has used only half the available archive space. In addition to capturing data, PI also provides interfaces—such as PI ProcessBook and Excel PI DataLink—that allow data extraction and trending. These capabilities are readily available to both plant staff and offsite owners.

Having a secondary plant historian is nothing new; it pays dividends when installing a new control system/historian. Dogwood completed a total DCS change-over in fall 2013, moving to a single T3000 platform for plant controls. To maintain continuity of data through the plant sale and DCS change-out, staff maintained the PI historian and lost no data.

The impact on end-users was minimized by remapping all historical points to the new control system and to PI. Plant personnel pulled the hard drives and native tape back-ups of obsolete systems and kept them on hand—just in case.

Dogwood currently is working to alleviate third-party interface issues by moving non-critical interfaces out of the plant’s control system and directly into the PI historian through multiple OPC and separate Modbus interfaces. These changes have improved the reliability of the Allen Bradley interface and allowed staff to gather additional data points. The plant continues to migrate and expand the interfaces into the PI server. The PI hard drives were upgraded to solid-state drives and switches from 10/100 to a gigabit Ethernet.

Improvements to the historical operating-data archive system provide the opportunity to sample and perform analyses on over 500,000 data points in less than 30 seconds, give plant personnel access to all available information, while enabling them to create pages in ProcessBook that provide read-only, real-time data displays from any computer in the plant. The fact that PI supports all versions of OSI’s software and is backwards compatible only sweetens the value of the system.

Flux probes enable predictive maintenance

Monitoring the condition of in-service electric generators is a challenge for the plant O&M staff. Based on some known issues with partial discharge (PD) and spark erosion (SE) in the generators married to Dogwood Energy’s gas turbines, the plant embraced online PD technology and offline borescope inspection over the last several years to assess stator condition.

This helps plant personnel predict when maintenance is required to mitigate the effects of PD and SE, and to protect against a ground fault. An unplanned outage to repair such a fault would be very costly and highly undesirable.

The lack of predictive-maintenance tools to evaluate generator rotor health raised these questions:

• What were the most cost-effective tools Dogwood could use to predict when generator rotor maintenance is required—without taking units off-line.

• How could these tools help provide early identification of potential rotor problems and reduce the risk of “surprise” events?

Based on this investigation—and considering that Dogwood historically has been a cycling facility—staff determined that air-gap magnetic flux probe technology was a cost-effective tool for monitoring the condition of rotor windings, without impacting availability.

Analysis of air-gap flux probe data can pinpoint the number and location (pole and coil) of rotor-winding shorted turns with the unit online. The effects of shorted turns in rotor windings can cause operating conditions that may limit net plant output—or in severe cases, an extended forced outage. While PD detection technology historically has provided a level of predictive monitoring, it doesn’t come close to providing this level of precision.

During a stator rewind in 2014, Dogwood elected to install a flux probe in the generator air gap. The flux-probe cable is routed from the stator core, through the stator end-windings, and out to the generator casing. A gland that provides a gas-tight penetration for the flux-probe cable, is welded to the outside of the generator casing. The analysis system is connected to the casing gland using coaxial cable, allowing the collection outside the generator while the unit is running.

Assessment. The flux-probe supplier collected the first data from this system in summer 2015 to establish a baseline on rotor shorted turns. The flux-probe waveforms were strong, noise-free, and repeatable, with excellent rotor coil slot-peak definition. This indicated proper operation of the flux probe.

Personnel varied the load during testing from minimum to 90% of the rated generator load, providing an acceptable data set for detecting single-turn shorts in all rotor coils. Analysis of the information showed no indication of turn shorts in any of the eight rotor coils.

Based on the information provided by this first test and the predictive-maintenance value confirmed by the test results, management decided to install flux probes on the remaining generators at the site.

Engineering Manager Chuck Berg said the information gathered and analyzed with these tools allows staff to provide stakeholders with timely, well-informed recommendations on when to perform generator maintenance, while minimizing the risk of “surprise” events that could reduce plant performance and availability.

New cabinet streamlines LOTO system

Dogwood Energy Facility’s lock-out/tag-out program continually meets requirements by use of LOTO forms, energy control isolation procedures, lock boxes, individually keyed locking devices, and a padlock board to account for the locks. While the LOTO program seemed to work well during small outages, plant personnel found it challenging to manage during outages with expanded work scopes.

Despite meeting LOTO requirements, the plant had no dedicated area to store lock boxes and associated paperwork. They were kept in a three-shelf multi-use cabinet in the control room, which also was used for the plant radios and their charging stations, handheld air monitors, etc.

Space restrictions created inefficiencies and LOTO boxes and associated paperwork would migrate to various places around the control room. The temporary solution was to bring in two folding tables to organize the LOTOs, but this arrangement took up more floor space than desired.

With NERC requirements restricting control-room access, plant management believed the LOTO work station should be mobile, allowing the safety program to be administered in the lobby or other designated areas, when necessary.

To streamline the process of getting contractors signed on and off LOTOs, Mike Davis, an O&M technician, took responsibility for working with a reputable local shop to design and build a mobile cabinet allowing better organization and providing separate cubbies for LOTO boxes and paperwork. The cabinet is 42 in. high, an ergonomic working height for most standing individuals.

Dogwood used the new lock-box cabinet during its 2015 fall outage, and it was well-received by plant staff and contractors. Feedback from several contractors that previously had worked Dogwood outages: The new system flows better, reduces confusion, and allows workers to quickly return to work. The ability to easily locate the desired lock box and associated paperwork has significantly improved time management and reduced frustrations that often arise during an outage.