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<\/p>\nMechanical Dynamics & Analysis\u2019 Turbine and Generator Controls Division replaced an industrial co-gen turbine\u2019s original mechanical-hydraulic (MHC) controls with an electronic governor, electro-hydraulic trip system and self-contained control valve actuator.<\/p>\n
The primary drivers for the project were the operator\u2019s desire to increase the long-term maintainability and reliability by replacing the MHC components that had become more problematic as they reached their end of life. Secondary benefits of the retrofit were increased operability through enhanced remote control and on-line testing capabilities as well as the addition of automatic synchronization.<\/p>\n
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The MHC governor components in the turbine\u2019s front standard were removed and replaced with a Woodward\u00ae Governor 505D electronic governor, mounted in a stand-alone cabinet in the unit\u2019s control room.<\/p>\n
The turbine speed feedback to the governor is supplied by a toothed wheel mounted on the end of the generator shaft and electronic speed pick-ups mounted on the generator\u2019s collector assembly. The governor\u2019s load control and speed regulation software combine with set points from the plant DCS to provide a position signal for the control valve actuator governing the steam flow through the turbine.<\/p>\n
The low pressure hydraulic control valve actuator in the front standard has been removed and replaced with a REXA\u00ae high pressure, rotary electraulic™ actuator coupled directly to the control valve cam shaft. This rotary action and direct coupling eliminates lost motion and mechanical hysteresis inherent in the original system.<\/p>\n
The actuator\u2019s positioning electronics receive the desired position signal from the 505D governor and control the position of the rotary actuator. The electronic to hydraulic interface is provided by the REXA\u00ae skid mounted control module and accumulator assembly. The assemblies servo-motor, booster pump and motor, accumulator and trip solenoids provide control over the actuators normal motion, fast motion and trip closed functions respectively. The recommended maintenance cycle for the new actuator components is ten years.<\/p>\n
The unit\u2019s new electro-hydraulic trip system replaces the mechanical over speed device and trip system components that govern the operation of the unit\u2019s main steam stop valve. The MD&A trip manifold, which is mounted on the unit\u2019s front standard, has a two-out-of-three, de-energize to trip solenoid valve configuration which allows the manifold components to be fully testable with the turbine in operation.<\/p>\n
Trip and reset of the solenoid valves is governed by signals from a Woodward\u00ae ProTech TPS electronic protections system which is mounted in the control cabinet with the 505D governor. The TPS has speed pick-up, pressure switch and relay inputs to provide a single source for all of the turbine\u2019s protective functions including over speed, operational trips and generator protection trips.<\/p>\n
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The customer was satisfied and appreciative of this successful installation. The original installation plan was able to be modified \u201con the fly\u201d to facilitate easier access to turbine hardware during maintenance outages and utilize the customer\u2019s preferred pressure and temperature transmitter hardware.<\/p>\n
MD&A\u2019s Turbine and Generator Controls Division maintains a staff of OEM experienced field engineers who provide installation, technical support, advanced troubleshooting, training, and consulting services for gas and steam turbine controls, generator excitation, and auxiliary systems.<\/p>\n