Blade Sentry pyrometers are engine mounted to view the rotating gas turbine blades directly through a pressure-proof sight glass assembly.
The optical signal collected by the pyrometer is transmitted through a rugged, flexible, fiber optic light guide to a remote electronic signal conditioner.
The signal conditioner provides the following linear 4 to 20mA outputs for further analysis:
- Profile - a high speed signal sent to the data acquisition system for data logging
- Peak - the highest temperature on the blade array
- Average - the average temperature of the blade array
- Average Peak - the average of the highest temperature of each of the blades
A key phasor/power supply module (KP/PSU) provides power for each pyrometer and converts the gas turbine, once per revolution pulse (from the GT), into a trigger signal for use with Rotor Sentry data acquisition system. The KP/PSU also provides user connections to pyrometer outputs of peak rotor temperature, average rotor temperature and average peak rotor temperature outputs from the pyrometer.
In utility turbines it has been accepted practice to obtain turbine blade temperature by back-calculation from exhaust gas temperature readings. This method gives only a prediction of average blade row temperature, and uncertainties associated with this approach require the turbine to be operated below it's optimum efficiency. Turbine Sentry uses optical pyrometers to measure blade temperatures, giving significantly better accuracy than traditional methods and showing individual blades clearly.
Improved Engine Firing Rate
Using the close coupling between blade and inlet gas temperature, Turbine Sentry allows greater control of engine firing rate through accurate rotor temperature measurement.
- Elimination of uncertainty of rotor temperature allows increased firing temperature and rate, hence greater efficiency
- Each 0.1% increase in efficiency equates to an annual saving of approximately $20-40k.
Prevention of Blade Failure
Cooling integrity is critical - stress creep life has a strong correlation with blade temperature. Operation at overtemperature conditions can lead to damage or even catastrophic failure in the multi-million dollar range. Turbine Sentry provides early indication of conditions that could ultimately lead to blade failure. Detection of individual overheated blades gives early warning of potential failure, enabling corrective action to prevent costly engine damage and downtime.
Turbine Sentry detected an incorrectly cooled blade running on a large utility turbine: potential failure was avoided, saving an estimated $2M in repair and production costs (Source EPRI literature ref. IN-101150)
All gas turbine blades are coated, usually with an anticorrosion coating. Turbine Sentry can detect coating erosion, hence allowing the user improved planned maintenance. In modern turbine blade designs, increasing use is being made of thermal barrier coatings (TBCs). The relationship between blade temperature and the condition of the thermal barrier coating provides early warning of breakdown and subsequent loss of coating integrity.
Blade Life Management
By direct monitoring of individual blades, it is possible to refine blade lifepredictions and improve 'hot section' maintenance scheduling. Extending the period between replacing a row of blades by one year could save over $100,000: avoiding replacement could save far more.
Detecting of over-temperature blades
Modern turbine designs improve efficiency through higher inlet gas temperatures. The blades are exposed to temperatures well above their operating limit, made possible by the introduction of blade cooling. Unimpaired cooling of individual blades is critical for their protection. Traditional, generalized temperature monitoring cannot indicate localized blockages.
Turbine Sentry has shown that temperature can vary significantly from blade to blade. Detection of cooling channel blockages (e.g. by oxidation) are not detectable by traditional methods.