Additional Control Retrofit Considerations
These issues are often overlooked, but tend to impact the long term success of a turbine controls upgrade. They are provided for the benefit of plant engineers, technicians and management in writing specifications and making retrofit decisions.
(A) Parts Obsolescence Issues
Many mechanical and hydraulic parts of older original equipment turbine governor and valve actuator systems become more and more difficult to find as time passes. While mechanical pieces remain in production for new orders, spares are easy to come by, but once abandoned for new orders their procurement becomes much more tenuous. This is not presented as criticism of the turbine OEMs. When production levels drop below a feasible level, mechanical parts fabrication is subcontracted out to job shops. The quality of the replacement mechanical part may be fine, but the delivery lead times grow and the price escalates. When a new pilot valve spool for an old hydraulic servomotor costs as much as an entire replacement electric actuator we know the cost of continuing the old system's operation is prohibitive.
The caution to "Look before you leap" also applies for parts obsolescence of the target new system. The designer of modern turbine control electronics has a choice of a wide range of processors on which to base the design. A danger exists, however, in specifying "trendy" processors which although very high performance for the time, will soon be discontinued by their manufacturer and replaced with ever-changing "improvements". Most of us have experienced this in the purchase of personal computers. It's common to purchase a "state-of-the-art" computer, then find out that six months later it is out of production and one year later service parts are difficult to find. When trendy electronics are used in turbine governor design the constituent parts can and do soon fall out of production and jeopardize spares availability. For this reason Lovejoy Controls has been diligent to specify automotive-type application micro controllers as the basis for all of its governor designs. Because the automotive designs have committed production guarantees of over twenty years and production volumes are enormous, continued availability for spare parts is assured.
(B) Supplier Service Issues
LCC is an independent turbine control system manufacturer which is not aligned with any turbine OEM nor controlled by any foreign conglomerate. This formula has provided stability and continued ready access of qualified engineers for service, spare parts, and immediate support to our customers for the past thirty one years. LCC customers have the opportunity to directly contact system design engineers. This cannot be said of others offering retrofit turbine controls. A close look at company histories finds many discontinued product lines following new corporate owners, often foreign, resulting in new larger companies but actually having fewer turbine controls engineers and a lot more talking heads. While we may be impressed with large multi-national corporations with frequently visiting cheerful sales people, the fact remains that eventually you're going to need to talk to someone that:
1. You can understand.
2. Understands YOUR turbine, YOUR control system, and can quickly answer questions of immediate concern.
3. Can trouble-shoot YOUR problem and make it THEIR PROBLEM.
4. Will be available in years to come
So far the large multinational conglomerates have excelled at a strong sales presence, but qualified technical support is scarce and costly. If you are operating a major power plant you can probably get the support you need, but if you are a smaller process or municipal plant you may find that your service is a low priority to the multinationals.
(C) Hydraulic Valve Operator Issues (M-H Actuators)
If existing hydraulic valve operators are to be retained and positioned by the new Governor it is recommended that the performance of the devices be verified and the operators be refurbished or replaced if sub par prior to the post-modification start up. A poorly performing valve operator will negate the advantages of a modern turbine Governor retrofit since all control commands must be processed through to the steam admission valves. As a minimum, the following specifications should be met for hydraulic operators of steam turbine governor valves:
C1. Less than 6% hysterisis on directional change at mid-strokes, less than 8% at travel limits.
C2. Less than 3% maximum non-linearity over full stroke in one direction for both open and close directions with no sudden discontinuities.
If a hydraulic operator fails to meet the basis performance specifications the pilot valve, pilot valve bushing, feedback linkage, pivot bushings, and follow-up spring should all be inspected and replaced if out of design tolerance. Excessive performance issues should be addressed by electric actuator replacements.
If the retained valve operators are in good serviceable condition LCC can fit a variety of simplex or redundant Low Pressure EHC (LPEHC) actuation systems to replace the existing high maintenance hardware. However, for best long term reliability and the least future maintenance LCC recommends electric actuators.
(D) High Pressure (EHC) Valve Operator and Self-Contained Actuator Issues
Several manufacturers and independent suppliers have offered synthetic fluid, segregated delivery oil systems and high pressure valve actuators generically termed "EHC". These systems were first available in the 1970's and are still marketed in various forms. EHC designs generally improved performance due to higher working pressures (2000 PSI typical), but introduced new problems such as:
D1. Toxic Material Handling Issues (fluid handling and disposal difficulties)
D2. Vulnerable Exposed Long High Pressure Piping Runs
D3. Extreme (5-micron) Fluid Filtering Requirements
D4. High Cost EH Converter Rebuilds
Good in 1970, OK in 1990, high pressure retrofits have become too complicated and expensive to consider over electric actuators.
To avoid the cost of a full EHC centralized skid and piping, self-contained actuators were marketed for retrofits in the 1980's and 1990's. With self-contained actuators each valve operator had a reservoir, filter system, and pump dedicated to move the one valve. Performance was not quite as good as EHC, but cost was less. The high component counts proved high maintenance, however, and few such systems are available today. Again, the electric actuator upgrade is the best plan.
(E) Spare Parts Inventory
When planning a turbine controls retrofit it is prudent to arrange delivery of a full set of spare parts to arrive with the new systems. Although modern systems are very reliable and require far fewer parts change-outs than older mechanical systems, incidents such as accidental damage or area fire can demand the immediate need for spares. Having the replacement component on site greatly shortens the outage period to restore operation.
What is not obvious and what is often a large surprise is what a full set of spares costs from some vendors. Be sure to include these in any competitive system price comparisons.
(F) Coordinated Turbine Supervisory System Upgrade
If the turbine under controls upgrade is running an old supervisory instrument system with replacement parts issues and aging components, consider a coordinated TSI Upgrade at the same time from LCC. This approach has a number of cost savings advantages:
○ The TSI data can be transmitted within the LCCNET control networks, greatly reducing plant cable runs compared to "stand alone" systems
○ The TSI data can be transferred to plant computers and operator alarm panels within the control system components, eliminating duplications.
○ Any TSI sensor can be integrated into the upgrade package.
(G) Cyber Security Issues
A great deal of concern has been placed on the security of program code in operating power plants. All LCC designs place program code within OTP (One Time Programmable) PROM chips installed in the system modules. The program code cannot be molested nor changed by any outside means. In contrast, hard drive loaded code can be altered upon hacked access to the drive. Thus, LCC 200-Series and Series-2 platform turbine control systems share cyber security by design architecture and do not require elaborate defense barriers that hard drive resident code systems must use.
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