Excitation Controls Retrofit

MD&A’s Turbine and Generator Controls Division recently completed turnkey installation services for an excitation system retrofit at a power generation plant. The project entailed the replacement of several key components including the voltage regulator and interface to the control and protection systems. The team handled the entire project including design, component selection, installation, and unit tuning. The project concluded with a thorough checkout and commissioning process.

Before the retrofit, the power generation customer was experiencing voltage regulation issues. They understood the importance of determining the source of these problems and remediating them as quickly as possible. Failure to do so promptly could result in significant and costly damage caused by overheating of generators and motors. These issues can also lead to transmission losses or voltage collapse.

The customer attempted to resolve these problems on their own before asking MD&A for assistance. Unfortunately, they were no longer able to service and maintain the original voltage regulator due to its age. Ultimately, MD&A’s expert technicians were brought in to replace it. They selected and installed a digital excitation control system to ensure precise and consistent voltage moving forward. The voltage regulator interfaced with the plant’s distributed control system (DCS), the plant’s auto synchronization (25A) relay, and the existing generator lockout (86) relays.

To help ensure reliability and stability, the interface with the plant’s existing controls and protection equipment was also updated. To further help ensure safety and protection, the technicians also updated the generator protective relay interface, to make sure circuit breakers would trip if a fault is detected.

Once the new components were installed, MD&A’s experts conducted a thorough checkout and commissioning process. Offline commissioning began with the turbine not running. Prior to panel power up, wiring, power feeds, field switches, and instruments were carefully checked. Offline commissioning then continued with the turbine running at synchronous speed. This phase began with initial excitation startup and FCR gain tuning. It continued with saturation curve measurement, AVR gain tuning, offline OEL testing and setup of the exciter diode monitor.

Next MD&A’s technicians conducted synchronization commissioning. This started with an offline OEL and V/Hz review, by recording the settings and confirming they are correct for proper synchronization. Following, automatic synchronization was performed. Typically, the team will normally conduct manual synchronization first, but this was not possible due to some wiring issues that were discovered.

The team then commenced online commissioning with the unit running at 10% load. This phase consisted of AVR step tests, OEL gain tuning, UEL gain tuning, and power factor tuning. VAR control mode was conducted next.

The generator was brought up to full load and unity power factor. MD&A’s experts conducted AVR step tests and tuning. The unit was tested in all other control modes (manual, PF, and VAR) to confirm stable AVR operations.

The final commissioning phase consisted of setting up the data log, restart, and cleanup. Once completed, the unit was left to remain offline. The team provided the customer with a photographic documentation of the installation, a complete set of redline drawings, and the DECS-250N software configuration file. Further, they prepared a marked-up startup procedure checklist, to help ensure safe and successful future startups.

A report on further recommendations for system reliability was also produced by the MD&A team. It addressed two issues, one referring to a stop command, and the V/Hz limiter coming in frequently. Recommendations were made by the team on how to resolve each. Some instability issues were also experienced, and one of MD&A’s technicians worked with the plant’s I&C technician to adjust VAR PID settings to remedy the issue. As for the wiring issues that prevented manual unit synchronization, mentioned earlier, the team suggested that the customer correct the wiring on the voltage raise/lower switches to all for manual synchronization in the future. They also recommended that the customer test the field ground detection system at the next outage opportunity.

This project underscores MD&A’s ability to partner with in-house power plant service teams in a consulting capacity to resolve equipment issues before they grow into much bigger problems. MD&A’s Turbine and Generator Controls Division provided a turnkey solution, from equipment selection and installation, through testing and commissioning. Success stories such as this exemplify the professionalism and expertise that MD&A provides, and is the reason why MD&A is the go-to service company for power generation operators worldwide.

For any turbine or generator controls issue and to discuss creative resourceful solutions, call MD&A today at +1 (970) 224-2223 or use our contact form.

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