The purpose of this paper is to discuss the factor.docx

1、The purpose of this paper is to discuss the factorThe purpose of this paper is to discuss the factors and options that should be considered in proposals to develop and apply consistent ambient weather de-rates to the Qualifying Capacity (QC) of thermal generating units. This paper was developed by a

2、n ad hoc working group made up of representatives from SCE, Dynegy, Calpine, CAISO and the CPUC. The initial white paper is not intended to convey a recommendation on whether and how ambient weather de-rates should be applied, but is intended to frame issues to facilitate ambient weather de-rate pro

3、posals from other parties. The de-rates discussed here are not short-term de-rates that unit owners sometimes apply to their units weeks or days ahead of operation, but instead are systematic de-rates that would be applied via QC rules to all relevant generators months or more in advance when the NQ

4、C list is published. In general, the proposed process for establishing ambient de-rates would be:1.Determine to which types of thermal generating units ambient temperature de-rates should apply. 2.Key inputs and factors: the cause of ambient weather de-ratesWork group discussion and options: The gro

5、up agreed that the two most affecting weather variables are temperature and humidity. The thermal generation technology most affected by temperature and humidity is combustion turbines. Combustion turbines output depends on air density, which is significantly affected by air temperature. The group d

6、id not believe that steam turbine capability is significantly affected by ambient weather conditions. The working group concluded that ambient de-rates should be applied to (1) combustion turbines, and (2) plants which integrate combustion turbines into their total delivery, such as combined cycle g

7、as turbine facilities. Possible Affects of Ambient Conditions on thermal resources other than gas turbinesAmbient temperature affects all thermal generating units, although the effect with traditional thermal units is usually less than that found with gas turbine technology.Traditional thermal units

8、 or Rankine Cycle Units usually involve a boiler, steam turbine generator and some type of condenser and cooling water system. Both the boiler and condenser may be limited by ambient weather conditions. For the boiler, the size of the FD (forced draft) fans or ID (Induced draft) fans may be a limiti

9、ng factor for a units capacity. The boiler requires air to be mixed with the fuel. The FD and ID fans provide this air. Fans have a CFM (cubic feet per minute) rating. If the boilers fuel system requires the maximum CFM from a fan to reach capacity, the boiler is fan limited. The actual heat input t

10、o a boiler may still vary with ambient temperature in a fan limited boiler. Density of the air is a function of ambient temperature. The higher the ambient temperature, the lower the air density and hence the less air is available to mix with the fuel. The fuel flow may need to be reduced due to the

11、 creation of pollutants in an oxygen deficient atmosphere which is exacerbated at higher ambient temperature.The resource may also be constrained due to increased cooling water temperature. To generate useful power, a steam turbine requires a condenser to remove heat from the steam. The condenser is

12、 cooled using cooling water or it may be an air cooled condenser. Either configuration will be adversely affected by increased temperature. As with a fan, a pump has a maximum GPM (gallon per minute) rating. Once the pump is at maximum GPM flow, the only way cooling may be changed is that the conden

13、ser is subjected to higher or lower temperature cooling water. The temperature of the cooling water may be affected by the volume of water within a closed looped system or the depth of a water source for once through cooling. If cooling water temperature limits a units output, the unit is said to be

14、 “back pressure” limited.It is possible that the maximum output of a Rankine Cycle unit will not vary with ambient temperature. Instead, a boiler may be fuel limited. In fuel limited operation, the maximum flow of fuel has occurred before the unit becomes fan, back pressure or limited by other means

15、 such as permit restrictions or other equipment. In this case, the boiler has adequate fan and cooling water, but may not generate beyond a given capacity due to fuel input restrictions. Ambient temperature will not significantly affect a unit that is fuel limited. It is also possible that a unit ma

16、y be fuel limited up to a point, then become limited by another parameter.Due to these variabilitys, a Rankine Cycle unit should perform a capacity test as may be required of gas turbine technology units.Effect of Ambient Temperature on Duct FiringDuct firing causes a combined cycle unit to operate

17、in a manner similar to that of a boiler unit and may be subject to the same constraints as a boiler unit. The FD fan is replaced by the compressor of the CT. Sufficient air is available downstream of the CT combustion system to allow the duct burners to have sufficient oxygen to combust with the duc

18、t burner fuel. The fuel input from the duct burners is usually small as compared to the fuel input into a CT. Steam turbine constraints are similar to those explained above.3.Determine the maximum capability (MW) of a thermal generating unit through a performance test under known, measurable conditi

19、ons. 4.Key inputs and factors: using plant instrumentation calibrated to applicable standardsusing “standard” operating practices during the test. the frequency of the performance testsWork group discussion and options: The work groups discussion focused on the need to establish the “baseline” capab

20、ility of the unit through a performance test conducted under known and standard conditions. The performance test should be conducted in a way that did not overstate the units capability under normal operating conditions. During the performance test, the unit must be operated using only the controls

21、normally available to the operator, and must not be temporarily and specifically modified just for the test or operated in a way that could not be easily reproduced. The performance test should be conducted over a reasonable period of time (several hours) to ensure that the unit can sustain its maxi

22、mum output for that reasonable period of time and the maximum capability reported is not a transient value that can be only produced for a very short period of time. The group also discussed the importance of using instrumentation calibrated to applicable standards to ensure that all measurements ob

23、tained during the performance test are accurate and verifiable. The work group discussed that, given the expense involved in such performance tests, the tests should be conducted only periodically perhaps every few years, and following a major overhaul. While operating experience gained over time co

24、uld help plant personnel understand how the units capability varied with the weather, the group still felt that it was essential to periodically conduct a performance test to establish the “baseline” capability of the unit. Recognizing that the CAISO currently has authority to do certain testing und

25、er the Participating Generator Agreement and CAISO Tariff section 40 the group felt that one option would be for the CAISO to conduct the tests as part of the Reliability Requirements detailed in Section 5.1.3.2 of the CAISOs Business Practices Manual, and CAISO MRTU Tariff Sections 40.4.3, 40.4.4,

26、which provide for the CAISOs authority to conduct physical tests to validate Pmax limits. The CAISO has not agreed to perform this testing function but for purposes of discussing possible options is willing to consider what would be required. At the current time there is limited tariff authority to

27、require tests to be conducted for NQC adjustments but the tariff does not list any specified intervals nor any specific conditions under which these tests would be conducted. In addition, the process associated with implementing an NQC testing program, as referenced in the BPM and tariff sections ab

28、ove, is not developed. If the CAISO were to take on this testing process for ambient temperature adjustments there would be a need for a stakeholder process and possible filing of tariff language with the FERC. The CAISO is going through a stakeholder process for the Standard Capacity Product, which

29、 is looking at performance standards, but to date the topic of ambient de-rates has not been included in these discussions. The test should be conducted in accordance with Accepted Electrical Practices and the provisions of Performance Test Code ASME PTC-46-1996 (Combined Cycle Generating unit) or P

30、erformance Test Code ASME PTC-22-1997 for gas turbine power plants (Simple Cycle Generating Unit). See Attachment A for sample testing procedures.5.Project the ambient weather conditions at the units location consistent with the weather assumed in determining RA requirements for the same period. 6.K

31、ey inputs and factors: establishing the relationship between ambient weather conditions at the plant location and a weather station that has provided a reasonable history of dataprojecting the ambient weather conditions at associated weather stations consistent with the weather assumed in developing

32、 the RA requirements whether unit qualifying capacity values should be different for system and local RA requirements, which are determined based on different assumed weather conditions.Work group discussion and options: The purpose of ambient de-rates is to determine the maximum output of a generating unit under the weather conditions that will be in place during the time of system peak demand. Californias system RA requirements are based on 1-in-2 year peak demands, while local RA requirements are base