Energy & Power Generation Consulting,
Engineering & Management Services



Allen-Bradley PLC-5/40C with a ControlNet 1.25 network

PROJECT: State Prison Solar Turbines (2) Maintenance Services

This State Prison was a facility that has two 3.0 MW Centaur 40 Solar Turbines with each turbine exhausting heat into its own Heat Recovery Steam Generator (HRSG). Steam produced from the HRSG was used for facility heating, laundry cleaning, kitchen dish washing, and food preparation. The facility has a central power house that also serves as the electrical distribution hub for switchgear control between the two gas turbine/generators, local utility power, and four additional high voltage load feeder breakers.

Three years prior (at the end of 2004), The State completed a major turbine, turbine controls, and facility control system upgrade. The goal of the 2004 project was to fully automate the dispatching of the two gas turbine/generators based on facility loads such that the local utility power consumption was held at a fixed operator set point of approximately 300 kW. The operator would select the lead/lag assignment between the two turbines and the automatic controls would start/stop the lag turbine based on the facilities change in load demand always attempting to maintain 300 kW of "import" power from the local utility power source.

Engineering services were required to resolve instabilities resulting from the automatic controls not correctly controlling the gas turbines. The State was unsuccessful at forcing the original contractor to resolve final commissioning instabilities in the 2004 upgrade project.

The primary load and switchgear breaker control system logic was performed in PLC style controllers supplied by ENCORP. The Solar Turbine logic was resident in Allen-Bradley PLC-5's and obtained direct on/off digital commands and an analog kW set point from the ENCORP PLC's.

The engineering services successfully diagnosed numerous tedious logic errors, incorrect tuning values, and design flaws that all contributed to, at times, very severe load instabilities. Prior to these improvements, the units always ran in manual with the operator performing all load changes through 15 minute periodic inspections of the facility load requirements. Now the units run in full automatic and the site operators have stated they have never seen this good a performance in the machines since their original commissioning.


• Completed a full assessment of the multiple control systems used to attempt to automate load dispatch of gas turbin/generators, facility loads, and utility supplemental power. Completed work through use of breaking down site documentation.

• Reversed engineered the Allen-Bradley PLC-5 ladder logic used to convert the kW set point to the eventual fuel valve demand signal to the gas turbine into simple block diagram format. Includes speed control, over-rides, and closed loop feedback.