Improving Efficiency at APS Cholla Power Plant Caleb

Improving Efficiency at APS Cholla Power Plant Caleb Breazeale , David Bruce, Joe Davidson College of Engineering and Natural Sciences Department of Electrical Engineering, Northern Arizona University, Flagstaff, AZ 86011; APS Cholla Power Plant Problem Statement To determine if it is economically viable for Cholla Power Plant to upgrade units 1, 2, and 3 from its current excitation system to a static type. Cholla Power Plant Specifications • Cholla Power Plant is located 90 miles East of Flagstaff, AZ. • There are four separate coal fired generators which produce electricity. Currently unit four is being upgraded to a static excitation system. Our task was to determine if it is cost effective to upgrade three existing units. • Unit One- 120 MW Westinghouse 1961, which utilizes a separate generator with collector rings and brushes. • Unit Two- 297 MW Siemens / Westinghouse 1978, which uses brushless Excitation. Analysis A MATLAB script was created to quickly calculate and plot the payback period when various parameters were changed. Three companies were suggested for the upgrade: Unit’s 2 and 3 will require more time to repay this investment because the reliability of the current system is good. The exact efficiency improvement is unknown because an efficiency analysis of units 2 and 3 was unavailable for our study. Some realistic estimates were used which can be seen below: These companies were contacted because they would provide equipment which would surpass our requirements for equipment quality and reliability: • Redundancy, including N+1 Power Bridges. • Oil Filled Transformers. • Installation of collector rings and brushes. • Power System Stabilizer(PSS). We were in touch with a sales representative from each company. Requirements were provided to the vendors to attain an estimate for the complete installation of the excitation systems. Total costs are summarized below: • Unit Three- 297 MW Siemens / Westinghouse 1980, which uses brushless Excitation. Conclusions We created an equation to calculate the payback period in years: What Is Excitation? Results The following graph shows the payback period for unit 1. With an improvement of one day per year, this investment will pay itself off in about 7. 33 years. The excitation system provides controlled power to the generator rotor, to establish a controllable rotating magnetic field. Unit 1 would benefit from the upgrade. Units 2 and 3 would require more time to pay back the cost of the upgrade. In the long term this upgrade would only benefit APS, for plant reliability, operator usability, and efficiency. Our calculation was very conservative. Other factors such as selling the old static excitation units, catastrophic failure of the current excitation units, which has occurred at other plants, were not considered in the model. If other factors like these are determined by APS to be of high relevance to the upgrade, then they can easily be integrated into the computer model. References • EPRI- Electrical Power Research Institute • Main Generator (#1011675) Model Parameters • Energy Value: $. 038 / k. Wh • Replacement Capacity Value: $100/k. W/year • Unit 1 Capacity: 122, 500 k. W • Units 2 & 3 Capacity: 290, 000 k. W • Unit 1 Installed Cost: $1, 327, 109 (average) • Units 2 & 3 Installed Cost: $2, 402, 109 (average) Excitation System Upgrade/Retrofit • Mr. John Demcko, P. E. Senior Consulting Engineer APS Acknowledgements We would like to thank Arizona Public Service for sponsoring our Capstone Project. In particular we would like thank Tim Vachon for taking time out of his busy schedule to attend our meetings and reply to our many emails.