This practice has allowed the customer to optimize their unit’s operational availability while reducing their maintenance costs. The predictive approach allows savings to be realized by avoiding unnecessary periodic maintenance while assuring component integrity, thereby avoiding episodic maintenance due to in-service failures which often result in forced outages. This service is available for all types of steam turbine servo controlled actuators on fossil-fired, industrial, and combined cycle units.

Currently, no regulatory maintenance practices or intervals have been specified in the United States for non-nuclear steam turbine valves and actuators. Typically, we have seen OEM’s, Non-OEM’s and other industry organizations recommend minimum maintenance intervals for steam turbine valve inspection and repairs every three (3) to five (5) years. Some say these inspections and repairs should occur, as a minimum, every 25,000 Effective Operating Hours (EOH).

Adopting a data-driven approach to condition analysis will produce the following beneficial results when compared to strictly periodic maintenance:

• Understanding of, and insight into, the asset’s current operating performance

• Awareness of life expectancy predictions for individual system components

• The time and confidence to plan and optimize downtime

• The ability to focus on and manage costly repairs before they are required

To further describe the steam turbine valve actuator diagnostics service performed, we started off by recording valve motion data from each of the customer’s Control Valves, Main Stop Valves, and Intercept Valves. Each of these valves had servo modulated position control capabilities and were opened and closed at a rate of 3% per second. Data was gathered for servo coil voltage and demodulated position feedback voltage.

Individual valve hysteresis test results for each valve were then graphed.  There were no concerns of mechanical problems with the hydraulic cylinders on the control valves and intercept valves.  As shown in the graph for one of the main stop valves below, observations made by MD&A’s controls engineer indicated that the measured servo coil voltage ramp rate showed anomalies. The slope changes indicate the actuator cylinder is either leaking or sticking.

Our recommendations included further investigation of main stop valve 2 within the next year, and the hysteresis test should be performed again to confirm the anomaly is repeatable.

The cost savings associated with this type of predictive analysis can be substantial. Maintenance on a high-pressure positioning actuator typically ranges from $20,000 to $30,000, including removal and re-installation costs. If the actuators on an averaged size turbine are found to be in good condition as a result of the analysis, savings could be well over $200,000.

MD&A’s 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. Call our MD&A Turbine and Generator Controls Division today at +1 (970) 224-2223 or use our Contact form.

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The post Steam Turbine Valve Actuator Diagnostics for Predictive Maintenance appeared first on MDA Turbines.

The customer’s EX2100e static exciter’s bus bolt was heavily corroded and damaged which caused overheating of the bus bar and bolt. The overheating melted nearby materials in the exciter and had already broken the bus connectors.  Further damage would have eventually caused an equipment short.

A new busbar was fabricated during the outage and was lightly coated with dielectric grease to impede oxidation, increase current efficiency, and reduce temperature rise. Additionally, several other fasteners needed to be retorqued to ensure similar issues did not occur in the future.

Our expert also discovered oil and grease in the collector housing which was already causing field ground alarms. If left uncorrected this would have caused damage to the rotor. After cleaning and reenergizing, MD&A experts were able to eliminate the condition in the short term. However, this emphasizes the need for properly functioning auxiliary systems, such as the oil system.

Additionally, the aux contacts on the exciter output contactor were binding when the main contactor was in the closed position. Over time this can break the contact assemblies. Once the aux contact plungers were readjusted, the contacts operated smoothly.

Even with spotless conditions, regular inspections are recommended to deter outage and trip situations. Several actions are recommended for this equipment:

• Periodic thermal imaging inspection of the bus bar and rectifier bridge. The thermal imaging operations should be kept to less than a minute due to airflow over the bridge. Visual inspection of bolt torque marks should also be performed.
• Consistent cleaning of the cabinets of the exciter, linear reactor, and the PPT.
• Correction of the oil misting at the collector end of the generator. During future outages, removal, cleaning, and remounting of the collector rings may be required if this condition is not corrected.

Thorough inspections are crucial in maintaining high voltage equipment. MD&A experts will conduct these operations resulting in a reduction in unplanned outages and increased reliability.

MD&A’s 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.

Call our MD&A Turbine and Generator Controls Division today at +1 (970) 224-2223 or use our Contact form.

The post Regular Inspections Key to Efficient Operations with an EX2100e Static Exciter appeared first on MDA Turbines.