Gas Turbine Performance Monitoring at Coastal Power Plant

Case Study 1: Gas Turbine Performance Monitoring at Coastal Power Plant

Scenario A combined-cycle power plant located in Singapore (tropical maritime climate) upgraded its turbine inlet temperature (TIT) monitoring system to improve efficiency tracking and emissions compliance. The site experiences high ambient humidity and diurnal temperature swings (24–34 °C), making cold-junction compensation critical. Constraints included minimal downtime (<4 hours), legacy analog thermocouple wiring (Type K), and requirement to align with ISO 5725-1 repeatability criteria.

Given Data

• Thermocouple voltage reading: 28.4 mV
• Measured ambient temperature (cold-junction): 31.2 °C
• Reference ambient temperature (calibration lab baseline): 15.0 °C

Calculation The converter applies cold-junction compensation using the standard Type K thermocouple polynomial inversion (IEC 60584-1). First, the raw voltage is converted to temperature assuming a 0 °C reference: 28.4 mV → ≈ 702.3 °C (per NIST ITS-90 coefficients). Then, the ambient temperature offset is corrected by adding the equivalent voltage contribution of the difference between ambient and reference temperatures:

• Voltage equivalent of ambient (31.2 °C) = 1.234 mV
• Voltage equivalent of reference (15.0 °C) = 0.592 mV
• Compensation offset = 1.234 − 0.592 = +0.642 mV
• Corrected voltage = 28.4 + 0.642 = 29.042 mV
• Inverted to temperature: 29.042 mV → 718.6 °C (rounded to 718.6 °C)

Note: The tool internally performs this using embedded IEC 60584-1 polynomials — no manual lookup required.

Result and Decision The corrected turbine inlet temperature was 718.6 °C, 16.3 °C higher than the uncompensated value. This triggered a review of compressor fouling — subsequent borescope inspection confirmed 8% airflow restriction. The operations team scheduled offline water washing during the next maintenance window and adjusted fuel-air ratio setpoints to maintain NOₓ compliance without exceeding TIT limits.

Lesson Ambient temperature drift >10 °C from reference introduces >15 °C TIT error in Type K systems — always log ambient sensor readings synchronously with thermocouple scans; time-stamped dual-channel logging prevents misattribution of drift to turbine degradation.