Overhaul or Upgrade: Legacy Control Systems One Hundred Years Later

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Overhaul or Upgrade: Legacy Control Systems One Hundred Years Later

DATE:

May 9, 2022

BY:

Matt Roberts, Director, Renewable Projects, Emerson

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Overhaul or Upgrade: Legacy Control Systems One Hundred Years Later

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Mechanical governors have been the stalwart hydroelectric control system for over a century. The reliability and longevity of these governors have inspired confidence in generations of hydro maintenance crews. Thousands of these mechanical governors remain in service today around the world.

Governors built in the early 1900s can meet the vigorous regulations of today even as governor technology has long since moved into the digital age. As the years go on, utility owners often wonder: Should I maintain my existing governors or upgrade them?

Through most of the 20th century, governor upgrades were low on most owners’ priority list. The original equipment governors worked well and were extremely reliable; maintenance crews understood how they worked and knew how to service them; spare parts were either on-hand or readily available; and the major original equipment manufacturers (OEMs) continued to provide good support. There was no reason to upgrade.

All that changed by the year 2000. Governor-only OEMs had either gone out of business or been acquired by other firms. Parts were increasingly expensive and lead times were long. Power plant crews found creative ways to get parts: they bought them locally, borrowed from other plants, or simply made the parts themselves. With little to be gained in terms of unit efficiency and concerns about computer technology, digital upgrades remained a low priority.

Yet, governor technology had long since evolved into digital control, and governor OEMs made a business decision to cut off support for their legacy governors. When customers requested parts, they were told that their governors were obsolete and, although some parts were still available, support would end. Plants were encouraged to begin planning for digital upgrades, sending a shock wave through the hydro industry.

Today, there are myriad options available for owners of ‘orphaned’ governors. Parts, service, and training are available from non-OEM providers, and digital upgrades are no longer mandatory. With the immediate urgency of “no support available” removed, owners and operators can make a reasoned decision whether or not to upgrade their governors.

Reasons to Upgrade to Digital Controls:

  1. Relicensing-driven control upgrades
  2. Market-driven enhancements
  3. Personnel-driven operations changes

Reasons to Maintain Your Legacy Controls:

  1. Parts and repair services are available.
  2. Tailored training is available.
  3. Readily available retrofit kits improve performance.
  4. Product life cycle of digital products is short.

Emerson has a comprehensive portfolio of support for legacy mechanical and new digital governors alike, and our Governor Decision Matrix, and governor experts, can help you prioritize the factors to consider before making a decision about the future of your plant or fleet.

Contact us for your own copy of the Governor Decision Matrix.

Reasons to Upgrade

Legacy governors were designed primarily to provide speed and frequency control; however, new functions were added in the mid-20th century in response to customer operational needs. Remote control, megawatt control, level control, and bypass valve control were all achieved by adding auxiliary devices to the basic governor mechanisms.

With only electrical and mechanical technology to work with, implementation of these control modes tended to be imprecise. Remote control originally referred to being able to control the governors from the Main Control Room. In the 1970s, Supervisory Control and Data Acquisition (SCADA) joined the lexicon of utility vocabulary. Remote control now referred to remote computer control, from tens or hundreds of miles away.

The only way to change governor setpoint was pulsing the DC motors in the governor cabinet, and early SCADA systems struggled with controlling the unit using this method. Due to gear lash and overtravel, there was no fixed correlation between pulse length and resultant unit output. Complicated methods were devised using variable pulse lengths and time delays. Some utilities devised governor shaft braking systems to prevent overtravel after a motor was pulsed. These workarounds proved acceptable until relicensing, which is when wholesale control improvements were typically required.

Relicensing-Driven Control Upgrades

During the relicensing process, utilities are often required to improve the operation of their plants. They may have to guarantee stable river flows, with or without the generating units, and they may have to adhere to strict limits on the rate of change of downstream flows. These requirements are valid reasons to upgrade the governors, especially when myriad stakeholders can monitor USGS stream flows online. Penalties for violating flow requirements can be very severe.

New functionality driven by relicensing includes:

▪ Better downstream flow control

▪ Time-of-day water releases

▪ Automatic flow ramping, within prescribed limits

▪ Better coordination of turbine and bypass valve or spillway gates

Market-Driven Enhancements

Today, utilities are constrained by rising energy prices, end-user demands for cheap, reliable power and shareholder demands for profitability. To succeed in an environment of deregulated markets and spot pricing structures, some utilities invest heavily in unit and plant automation.

For example, to capture the best price for power, a utility Dispatch Center may need to start a unit hundreds of miles away and ramp it up to load in just ten or fifteen minutes. All the remote, automatic systems must work; the power market makes no allowance for delays due to balky relay logic, slow communications, or worn governor equipment, and there’s not enough time to dispatch a crew to manually start and synchronize the unit. If power is not delivered to the grid at the agreed-upon time, the utility can be penalized. To avoid this, utilities invest in unit automation systems that can include the following governor enhancements:

▪ Remote auto-start

▪ Automatic sequencing of auxiliaries

▪ Automatic synchronizing

▪ Faster on-line load ramping

▪ High-level SCADA interface (Ethernet/RS485/set point control)

During unit automation projects, utilities may also try to improve efficiency:

▪ Improved 3D cam control (Kaplan turbines)

▪ Improved needle sequencing (Impulse turbines)

▪ Smart unit dispatching (Replaces joint load control)

New vs. Old: Technology and O&M Staffs

Many utilities have already reduced their operations and maintenance (O&M) staff and converted, or plan to convert, their plants to unattended operation. With a generation of senior plant mechanics and electricians approaching retirement, the average age of O&M crews is getting younger. More familiar with digital technology, new-generation O&M crews view the benefits of digital upgrades in terms of:

▪ Intuitive, informative governor interface (color touchscreen replaces meters)

▪ Improved governor diagnostics

▪ Simplified maintenance procedures

▪ Extended maintenance interval

Reasons to Maintain

Now that you’re ready to upgrade, let’s take a step back and consider some of the reasons you will want to hold on to your existing mechanical governors.

1.Parts and service are available: Mechanical governors were designed to last 100 years or more with regular overhauls. Although many experienced governor specialists and field service engineers are no longer working for the OEM doesn’t mean they left the industry.

Third-party vendors hired many of them, and they continue to provide support for legacy governors. Without the physical overhead and ideological baggage of an OEM, these vendors offer world-class governor parts, service, and training at economical rates.

2. Legacy governor training available: Professional training is also available from third-party vendors, at your site or in their classroom. Whether for a new crop of apprentices or a group of seasoned mechanics or electricians, periodic site training is the best way to keep your staff up to speed on legacy governor technology. The more you know about your legacy governor, the less intimidating it is to work on, and the more work you can complete in-house.

3. Retrofit kits improve performance: Retrofit kits are available to eliminate weak spots in your legacy governor system. These kits may be all you need to extend the useful life of a legacy governor. Modern-technology kits can replace:

    •  Obsolete 3D cam controllers
    • Selsyn transmitters and receivers
    • Mechanical overspeed switches
    • ‘Snap-action’ pump pilot valves

If you like the reliability of your mechanical governor but want to incorporate some modern control and communications features, a digital governor interface kit may be right for you. Small and inexpensive, the kit includes a PLC controller that provides a bridge between your mechanical or analog governor and your SCADA system. It preserves everything you like about your legacy governor, including auxiliary valve control and adds enhancements like remote setpoint control, fast on-line ramp rates, governor out-of-calibration alarms, and digital communication. To the rest of your system, your legacy governor will look like a digital governor.

4. Product life cycle of digital governors is relatively short: Whether proprietary or off-the-shelf, the product life cycle of modern digital controls and hydraulic components is poor compared to a mechanical governor. This is due to the rapid development of newer technology. The result is that spare parts can be difficult to find and expensive to purchase just ten years from installation. Software and the computers that can run it become obsolete. We call this the “digital treadmill.” Some customers have remarked to us that their newest governors are the most difficult and expensive to support and maintain.

Maintain or Upgrade?

At this point you may be thoroughly confused. “If the governor upgrade I thought was inevitable is once again optional, what should I do?” This section describes a method for analyzing and evaluating all the pros and cons.

You will prioritize the things that are important to you, grade your current situation, and in the end, arrive at a score for each unit and powerplant.

Let’s begin by answering a few preliminary questions:

  1. Has your governor been reliable?
  2. Are spare parts available at reasonable prices for your governor?
  3. Is technical support available at reasonable prices for your governor?
  4. Are field service engineers readily available at reasonable prices?
  5. Are training classes available for your governor?
  6. Can your governor provide the control features you need now?

If your answer to all of the above questions is “yes,” then a governor upgrade is not necessary.

If you answered “no” to question 6, and the new functionality you require cannot be obtained through minor modifications (retrofit kits or digital governor interface), then a governor upgrade is necessary.

Learn more and make the best-informed decision with our Governor Decision Matrix.

Conclusion

Digital governor upgrades are no longer mandatory. The decision to maintain or upgrade your legacy governors should be made based on sound analysis, not emotion or fashion. Application of the evaluation criteria and our Governor Decision Matrix will enable owners to make sensible choices, saving time and money in the process.

Contact us for your own copy of the Governor Decision Matrix.