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ASME PTC 42-1988 (2004) — Wind Turbines
🍃 ASME/ANSI PTC 42-1988 (2004) is the ASME Performance Test Code for field testing of wind turbines (WT), issued in 1988 and reaffirmed in 2004. Its primary objective (para. 1.1) is to compare the net amount of electrical energy produced by the WT during a given period with the predicted test energy for the same period and the same wind speed histogram. The procedures and practices were compiled specifically for WTs of 100 kW or more, but are applicable to all sizes. As an early benchmark for power-curve and annual-energy acceptance testing, it laid the methodological foundation later refined by IEC 61400-12 for power performance measurement.
💡 The logical core of PTC 42 is “wind resource in, electrical energy out”: the measured power-versus-wind-speed curve replaces the reference curve, and annual energy output is computed on the same annual wind speed histogram, evaluating turbine performance in energy terms.
1. Primary and Secondary Objectives 📌
The primary objective (para. 1.1) is to compare the net electrical energy produced by the WT during a given period with the predicted test energy for the same period and the same wind speed histogram. Secondary objectives (para. 1.2) include:
- comparing the test power-versus-wind-speed curve with the reference power-versus-wind-speed curve;
- comparing the annual energy output calculated with the test curve versus the reference curve, for the same annual wind speed histogram;
- determining the effects on WT performance of changes to subsystems and components, or changes in operation methods, for specified conditions at a given site;
- comparing the performance of the WT with the established performance of other WTs at the same or different sites.
⚠️ Applicability boundary: the Code is not intended to govern general or specialized research, or the development of subsystems and components. Nevertheless, when such testing is performed and results are intended for publication, testing and reporting should proceed as nearly as practical in harmony with this Code.
2. Test Methods and Instrumentation 🔧
The Code specifies methods, procedures, and instrumentation for field testing: wind speed measurement position and height, net electrical energy measurement (generation minus parasitic consumption), data acquisition and time-interval subdivision, average power statistics per wind-speed bin, and power-curve fitting and correction. Particular emphasis is placed on the statistical representativeness of the wind speed histogram: the wind-resource distribution during the test should span the turbine’s operating range, and predicted test energy must be computed on the same histogram basis as the measured energy.
| Test Element | Requirement | Purpose |
|---|---|---|
| Wind speed measurement | Representative position/height, calibrated | Establish wind-speed/power relationship |
| Net energy measurement | Generation minus parasitic load | Compare net output energy |
| Wind-speed binning | Average power per bin | Construct power curve |
| Wind speed histogram | Cover the operating range | Basis for annual-energy extrapolation |
| Data screening | Remove shutdown, curtailment, anomalies | Representative normal operation |
3. Power Curve and Annual Energy Output 📈
The power-versus-wind-speed curve is the central characterization of WT performance: between cut-in and cut-out wind speeds, output power varies with wind speed. The difference between the test curve and the reference (guarantee) curve indicates whether the turbine meets contractual performance. Annual energy output (AEO) is computed by convolving the test power curve with a selected annual wind speed histogram — summing power × hours over each speed interval. The Code requires both curves to be evaluated on the same histogram so that wind-resource differences do not distort the comparison.
💡 Operational significance: a 5% power-curve shortfall can mean millions of kilowatt-hours lost over a 20-year life. Periodic re-measurement of the power curve per PTC 42 is a quantitative way to detect blade soiling, pitch misalignment, yaw error, and gearbox losses.
4. Engineering Practice Essentials 🛠️
- 🔍 Acceptance testing: after commissioning new or retrofitted turbines, run power-curve and energy acceptance tests; the statistical method for comparing results with guarantees must be agreed in advance.
- 🔧 Component-change evaluation: after blade replacement, control-strategy upgrades, or pitch-system changes, use objective 1.2(c) to assess the performance gain and guide investment.
- 📊 Site comparability: performance comparison across sites must account for air density, turbulence intensity, and wind shear; the Code requires normalizing these environmental factors.
- 📋 Data quality: simultaneity and completeness of wind data are critical — calibrate anemometers, log shutdown codes, and establish data-screening rules.
🚨 The silent killer in wind testing is data bias: wind-speed data contaminated by trees, nacelle turbulence, or mast installation errors shifts the power curve systematically. Keeping the met mast clear of the wake and at a sound distance from the turbine is the first principle of site layout.
5. Frequently Asked Questions ❓
❓ Q: How does PTC 42 relate to IEC 61400-12?
A: PTC 42 is the early (1988) wind turbine performance code; the IEC 61400-12 series continues and refines power performance measurement including uncertainty assessment. They share methodology; modern acceptance follows IEC, while historical machines and literature often cite PTC 42.
A: PTC 42 is the early (1988) wind turbine performance code; the IEC 61400-12 series continues and refines power performance measurement including uncertainty assessment. They share methodology; modern acceptance follows IEC, while historical machines and literature often cite PTC 42.
❓ Q: Why “net” energy rather than total generation?
A: Net energy = generation minus parasitic consumption (yaw, heating, controls). Parasitic loads differ significantly between designs; only net energy fairly compares wind-to-electric conversion efficiency.
A: Net energy = generation minus parasitic consumption (yaw, heating, controls). Parasitic loads differ significantly between designs; only net energy fairly compares wind-to-electric conversion efficiency.
❓ Q: What if the wind resource during the test is not ideal?
A: The Code allows accumulating test data over extended periods to span a wider speed range; if high-wind data are insufficient, extrapolate with the reference curve and declare the associated uncertainty.
A: The Code allows accumulating test data over extended periods to span a wider speed range; if high-wind data are insufficient, extrapolate with the reference curve and declare the associated uncertainty.
❓ Q: How do I decide whether a power-curve difference is significant?
A: Apply the measurement uncertainties (anemometer calibration, bin sample sizes) in a statistical judgement; a difference smaller than the uncertainty band does not establish performance degradation.
A: Apply the measurement uncertainties (anemometer calibration, bin sample sizes) in a statistical judgement; a difference smaller than the uncertainty band does not establish performance degradation.
