Dissecting Power Plant Performance Guarantees
The contract of a new power plant or the upgraded power plant describes in detail the project scope of supply and the deliverables of the EPC contractor in charge of the building the new or upgraded power plant. The performance guarantees are part of this contract. This section describes the performance guarantees and the contractual obligations of each of the parties involved as well the guaranteed performance of the plant. The following is a description of the different components of the performance guarantees sections in a power plant performance contract.
PERFORMANCE GUARANTEES. – In this section, typically a table of values, there is a description of the performance parameters guaranteed by the EPC contractor to the owner of the plant. For example the most common performance guarantees are the electrical power output & power plant heat rate or power plant efficiency. However, depending of the project, could be additional guarantees such as steam exportation in the case of cogeneration power plants or maximum auxiliary electrical consumption or water consumption.
REFERENCE CONDITIONS. – As you already know, power plant performance is highly dependent on the ambient conditions and some operating parameters such as power factor or fuel heating values. In the power plant performance guarantees section, there will be a description of what are the reference conditions for the performance guarantees. In some contracts, it will say ISO conditions for ambient conditions or in others will be more specific to the design values of the plant. For example, in the performance guarantees section will say 850 MW and 7,200kJ/kWh and in the reference conditions section will say: Ambient temperature 21 C, 40% Relative Humidity, Ambient Pressure 1,040 mbar and for the operating parameters will say something like 0.85 power factor, 50 Hz. All this information, typically, is part of the same table of values together with the performance guarantees.
CORRECTION CURVES. – The performance guarantees section will include the contractual correction curves to use during the performance test. As we can’t control the ambient conditions and in most cases, neither the operating conditions of the plant; there is the need to have some way to translate the performance measured during the performance tests at whatever ambient conditions to the contractual reference conditions. For example, we will measure 834 MW of power plant output at 18 C of ambient and then we will apply the correction curves to translate this 834 MW to the reference ambient temperature. The same for all the guaranteed performance parameters and each of the reference conditions.
TEST UNCERTAINTY. – We know that there is not a perfect measurement. Each parameter is measured with a certain level of uncertainty. This test uncertainty depends of three main components. The accuracy of the instrument used to measure the parameter, the space in which the instrument is located and the variation of the parameter itself during the performance test. The Performance Testing Code ASME 19.1 describes in detail test uncertainty and the methodology to calculate it. The contract will say sometimes the expected level of uncertainty for the performance test. This uncertainty means that is the result of corrected power output is 835 MW and the uncertainty is +/- 0.6% then it means that the results of the test will need to take into account the uncertainty values.
TEST TOLERANCE. – There are contracts that call for a test tolerance for the performance test results. Meaning that the performance results are allowed to vary from the guaranteed values by a certain percentage. This test tolerance differs from the test uncertainty. Test uncertainty is a technical parameter and test tolerance is a contractual parameter.
TESTING CODES. – The performance guarantees section will describe the codes and standards to use during the performance test.
