TRENDS IN TURBOMACHINERY CONTROLS

PERFORMANCE, SAFETY, INTEGRATION, CLOUD COMPUTING AND DIGITIZATION

LEAD THE PACK

By Drew Robb

The controls sector is one of the most vibrant areas of turbomachinery innovation. Vendors such as Compressor Controls Corp., Schneider Electric, Turbine Diagnostic Services, Tri-Sen, Woodward, GE, ABB and Siemens are among the leaders. These vendors explained how they were addressing trends related to performance, safety, integration, cloud computing, digitization and plant versus turbomachinery systems.

Woodward

Eric Freitag, Customer Account Manager at Woodward Industrial Turbine Systems, expressed concern for the growing deployment of low-cost control system hardware and the utilization of integrators to program these systems who are not turbine control experts. Programmable logic controller (PLC) integrators, he said, are reverse-engineering control system algorithms from OEM purpose-built systems. They are selling the expectation of providing the same control system performance the OEM control system provided.

“General purpose PLC control system hardware is not capable of meeting the control system performance requirements turbine packagers are providing as original equipment,” said Freitag. “Many PLCs do not have a magnetic pick-up (MPU) input module, as the MPU signal is a specialty input signal typically not used in a traditional PLC application.”

Instead, PLC providers are developing or applying signal convertors to convert a turbine MPU signal to a pulse signal the PLC can read on a counter module. In this conversion, high-speed sampling, filter and derivative calculations specified in the OEM control are no longer being met. One outcome of this, said Freitag, is the inability of the controls system to meet system dynamics performance of grid stability and load-response performance.

End users should talk to other users about their experiences with various controls as well as investigating the historical track record of the product lifecycle management of the control system hardware and software, he said. This should include the track record for addressing parts obsolescence. Lack of due diligence could lead to spiraling costs over the lifespan of the control system.

Woodward’s MicroNet Plus control system, he said, is designed to meet stringent aeroderivative OEM performance requirements. The MicroNet Plus speed input module operates at a 100 microsecond recursion rate to provide the signal sampling speed derivative calculations required to meet the transient performance expected by users and grid authorities. Additionally, its redundant processor and failover performance is designed for bump-less failover between the processor in control and the back-up processor. This is accomplished without freezing control parameters during the failover (Figure 1).

Figure 1: Example of a Woodward Mark VI 90-70 controls upgrade

Tri-Sen

During the last 18 months, Michael Montesinos, Product Manager at Tri-Sen, has seen significant interest from end users and operators with respect to turbine safety focusing on the turbine trip interface. This interest appears to be driven, in large measure, by API 612 and 670 revisions specifying redundancy and performance requirements (trip speed) necessary to maintain compliance with API standards.

“As end-users become more informed, they will demand cost-effective, trip-interface solutions that are fast-acting, predictably reliable and continuously available,” said Montesinos. “The Tri-Sen TetraSentry is a parallel, dual-redundant hydraulic trip interface that’s fast-acting, on-line testable, and on-line repairable.” (Figure 2). In addition, Tri-Sen launched an on-line performance tool for turbine trip systems that can be used to calculate turbine over-speed.

Figure 2: Tri-Sen TetraSentry parallel, dual-redundant hydraulic trip interface

CCC

One of the biggest ongoing trends in turbomachinery controls is that capital projects often go over-schedule and over-budget, said Pietro Gaiaschi, Product Manager at Compressor Controls Corp. (CCC). The controls piece is only a small portion of the total cost of the turbomachinery project, but is often placed on the critical path of the project schedule.

“Even small delays and issues in the execution of these projects can end up costing end users in the excess of ten times the original project value,” he said. “As a lot of jobs have been lost and many workers in the industry have retired or are about to retire, there is a definite loss of knowledge and expertise. This is particularly true for turbomachinery controls projects where the expertise and knowledge are highly specialized.”

As a result, end users should approach capital projects in a different way. The old school way of having several review cycles for documentation, and leaving the detailed engineering to be figured out at the Factory Acceptance Test (FAT) or during site installation may no longer be sustainable. Project engineering should be executed as early as possible to maximize the opportunity for change when it is the least expensive, said Gaiaschi. “Having design reviews just a few weeks before FAT is too risky. Changes at this time are the most expensive and can end up impacting the production schedule and the overall profitability and performance of the business.”

To reduce the cost of project engineering, CCC has developed software engineering tools. One such toolset is RapidState. It allows its engineers to correctly identify the best solution to user problems, capture the knowledge that the customer had lost, and then execute and document the project.

“The RapidStat engineering toolset makes it easy and fast to specify and engineer a project from the first face-to-face meeting, and enhances our engineers’ capability to capture end user knowledge, and retain it evergreen and up-to-date,” said Gaiaschi. “It functions as a project lifecycle management software package.”

Scheinder Electric

Schneider Electric noted how the increasing change in the availability and reliability of assets was affecting users. “With the changes of feed stock, some processes have to adapt to properly handle the new procedures,” said Tim Pieszchala, Application Consultant at Scheinder Electric. “Controls that can manage these changes, such as steam turbines, compressors and variable speed drives help to keep profitability up with agile requirements” he said. “Users should ensure that their assets are capable handling the possible changes required within their processes with controls, condition monitoring, performance monitoring, variable speed drives and partnering.”

Schneider Electric’s Triconex controller for rotating equipment allows flexible programming of various process scenarios. It manages driven equipment and does it on a fault-tolerant control platform. In the 1970s, with the advent of the microprocessor, things were always limited by the transportation media, speed and storage of the information, said Pieszchala. While steady progress was made through the years, storage problems remained. And without the amount of data needed it was not possible to predict the overall operation of turbomachinery assets and how they fit into the process.

“Now the storage issue is resolved with the arrival of the cloud and the promise of unlimited data at the speed of the internet, allowing us to analyze with an eye on assets holistically,” said Pieszchala. “We can now see the turbine as a piece of equipment in the process as opposed to a stand-alone item.”

As a stand-alone asset, it was not possible to determine that a valve needed adjustment or to correlate vibration and temperature to determine when maintenance cycles needed to occur. However, by taking a more holistic view, it is possible to look at the production throughput, determine the best operating performance for a particular process, and optimize the asset to handle production factors along with the maintenance aspects for increased profitability.

Turbine Diagnostic Services

Many plants are looking to upgrade governor and unit-control functions, auto and manual synchronization, voltage regulation, turbine and generator protection, and supervisory monitoring, said Ron Rubrecht, President of Turbine Diagnostic Services (TDS). This allows for an older analog system or early digital system to be replaced along with all of the old exciter hardware and electro- mechanical protection components, he said. Some users want to abandon the mechanical over-speed trip mechanism in favor of a triple-redundant, over-speed monitor with electronic back-up.

“Many have elected to implement a standalone Woodward Protech TMR Overspeed Monitor, adding it to other systems, which may or may not have been upgraded, or in conjunction with a standalone governor, PLC and vibration monitor,” he said.

TDS provides standalone governor and over-speed monitor retrofits, as well as an integrated control system known as the TurboNet DASH 1 DCS-structured Turbine Generator Control System. These control system upgrades generally include an integrated exciter upgrade. As TDS is an authorized Basler retrofitter, it can integrate the operation of the new exciter into the TurboNet. This can be accomplished with a digital front-end on many old rectifier bridges which need controller upgrades. New multi-function relays for electronic generator protection are often implemented during such an upgrade to provide a lockout and interface to TurboNet.

TDS has options for a new triple redundant trip manifold, which if implemented with TurboNet TMR backup overspeed protection, would allow for each electronic channel and one of three interlocking hydraulic manifolds to trip and verifying the action of the electronic channels and the trip solenoid valves.

GE Oil & Gas

GE Oil & Gas sees the rapid performance increase of turbomachinery controls systems due to advances in microprocessor and software technology as the biggest trend. This allows local and cloud-based related computation to become more capable, available and cost effective, said Homero Endara, Control Solutions O&G Product Line Leader at GE Oil & Gas Digital Solutions.

The implications of this advance include: The ability to digitize and embed algorithms in turbomachinery control systems based on machine knowledge acquired over decades of servicing equipment; the creation of digital models that can emulate operating conditions and embed this knowledge in the turbomachinery control system itself or make it available thorough secured cloud computing; and the reduction of unplanned downtime and operating costs.

“Users should adopt lifecycle postures for turbomachinery control systems that can benefit from evolving computing technology to increase machine availability and reliability, while also seeking a reduction in operating costs through the latest automation and control technology,” said Endara.

He called attention to enhancement modules for GE’s OpFlex software, which are said to improve reliability, provide system diagnostics, prevent trips and increase productivity. Four new packages feature 20 modules to complement the Mark VIe control system. The Start-Up Reliability Package, for example, provides a collection of control software enhancements to ensure on-time, reliable plant start-up. This includes Pre-Start System Check tests to confirm the availability, operability and reliability of auxiliary and accessory systems. In addition, the Expanded Alarm Help module tells operators about a signal driving an alarm, the alarm description, possible causes, associated hardware and recommended actions.

Siemens

The seamless integration of turbine control products into the plant control system was highlighted by Martin Wismath, Product Management SPPA-T3000 at Siemens. This provides additional value by optimizing turbomachinery in terms of emissions and flexibility of operations. “Solutions like data collection for machinery learning have to be made cost efficient as an enabler for next generation turbine control products,” said Wismath. “Total cost of ownership should be considered by evaluating the benefits of next generation turbine control products.”

Siemens recently released SPPA-T3000 Cue to integrate process and machinery diagnostics and its optimization. This allows power plant operators to simplify day-to-day operations and enables quicker reaction in critical situations to increase power plant performance.

ABB

During the last few years, the turbomachinery control industry has seen an increased focus on the dynamic response and overall performance requirements of the control system, said Camilo Lopez, Turbine Control Product Manager and Conventional Segment Manager at ABB. “The ability to react quickly, cycle load frequently and operate at any load level have become mandatory characteristics of the standard turbine control system for steam and gas turbines.”

One of the main drivers behind this trend, he said, is the need to adjust to grid fluctuations as a result of the growing presence of renewable energy sources. Another driver is the high penetration of GTs in the market, bringing along their traditional strict response time requirements for governor control and compressor surge protection. The final driver would be “competitive evolution”, where DCS vendors are introducing the technologies to increase reliability and safety aspects.

Users, therefore, should demand automation solutions that demonstrate dynamic, reliable and safer governor control operating in under 20 msecs, as measured from speed pulse input to servo-controller current output. This provides enhanced safety and frequency response capability. “Ensure that turbine control system vendors take responsibility not just for supplying an integrated solution, but also for ensuring that each of the components and their in-between communications are fully tested and optimized,” said Lopez. “The vendor should guarantee compatibility and performance throughout its lifecycle.”

The ABB Symphony Plus turbine control solution has high-end processors, along with tools for protection, valve positioning, auto-synchronization and condition monitoring. It has been designed as a single technology platform.