Prospect No. 3 Hydroelectric Project FERC Project No. P-2337 Initial Study Report: Ramping May 2015

Transcription

1 Prospect No. 3 Hydroelectric Project FERC Project No. P-2337 Initial Study Report: Ramping May 2015 Prepared by: PacifiCorp Hydro Resources 925 South Grape Street Medford, OR For Public Review

2 TABLE OF CONTENTS 1.0 INTRODUCTION Background Project Area Operations-Related Ramping OBJECTIVES METHODS General Approach Desktop Analysis RESULTS Unit Trips Planned Outages Resuming Generation Following an Outage CONCLUSIONS REFERENCES Appendix A. Description of Pressure Relief Valve Appendix B. Ramping Events Appendix C. Rating, USGS Gaging Station No Initial Study Report: Ramping Page ii

3 LIST OF FIGURES Figure 1. Map of Project spill points and affected waters Figure 2. Ramp events in South Fork Bypass observed after a unit trip, WY 2010-WY Figure 3. Ramp events in South Fork Bypass observed after a planned outage, WY 2010-WY Figure 4. Ramp events in South Fork Bypass observed after the unit was brought online, WY 2010-WY LIST OF TABLES Table 1. Parameters and sampling techniques for the proposed study Table 2. Proposed ramp rates for South Fork Bypass Initial Study Report: Ramping Page iii

4 1.0 INTRODUCTION 1.1 Background PacifiCorp is in the process of relicensing the Prospect No. 3 Hydroelectric Project (Project), Federal Energy Regulatory Commission (FERC) Project Number P In accordance with FERC s Integrated Licensing Process (ILP), PacifiCorp has developed and implemented relevant resource management study plans, including a plan to analyze operations-related ramping in Project-affected waters. The current FERC license does not contain provisions that limit ramping. Ramping is an expression that describes changes in river stage. Ramp rates are typically expressed in fractions of a foot per hour or inches per hour. The term up-ramp refers to an increase in stage, whereas down-ramp is a decrease in stage. Because minimal information is available regarding ramping activities in Project-affected waters, PacifiCorp evaluated the relationship between Project operations and ramping to support the relicensing process. This study report describes the results of the ramping analysis. 1.2 Project Area The 7.2-megawatt Project operates in run-of-river mode with no significant storage capacity. The Project diverts up to 150 cubic feet per second (cfs) from South Fork Rogue River at South Fork diversion dam, located on river mile (RM) Water diverted from South Fork Rogue River (Project Water) is conveyed to a small forebay. A single penstock transports Project Water from the forebay to the generating unit. Water from the generating unit turbine discharges to a concrete tailrace structure, where Project water is then conveyed via sag pipe into Middle Fork Canal of the Prospect Nos. 1, 2, and 4 Hydroelectric Project (FERC Project No. P-2630). Project Water conveyed to Middle Fork Canal ultimately discharges to North Fork Reservoir, and Project Water is used for generation a second time, this time by the Prospect Nos. 1, 2, and 4 Hydroelectric Project. Under normal operations described above, Project Water does not discharge directly to a natural stream prior to confluence with the Middle Fork Canal. However, some events, including operational balancing, generating unit trips, and/or planned outages, may result in spill from Project facilities into adjacent waters. The points of spill and the affected waters include: (1) South Fork diversion dam, where water may be spilled into the bypassed reach of South Fork Rogue River (South Fork Bypass); (2) A spillway at the forebay and an overflow channel at the concrete tailrace structure, where waters of limited volume and duration may be spilled into Daniel Creek. Daniel Creek is a tributary of Middle Fork Rogue. Initial Study Report: Ramping Page 1

5 Spill events may cause ramping in any or all of these three water courses. A map of the spill points and affected waters is provided in Figure Operations-Related Ramping There are four general categories of circumstances during normal operations 1 that may result in ramping in affected waters: operational balancing, unit trips, planned outages, and resumed generation. The following list describes each circumstance. Operational Balancing Operational balancing refers to changes in powerhouse generation in response to available flows within the waterway. Operational balancing may result in spill of Project Water at the tailrace when the manual setting of the tailrace backwater gate does not match automated increases of flows through the generating unit and/or pressure-relief valve (PRV). PacifiCorp plans to automate tailrace backwater gate response to penstock flows, thereby eliminating spill at the tailrace overflow due to operational balancing. Unit trips Unit trips occur when the Project generating unit unexpectedly goes offline, closing the wicket gates and stopping Project Water flow through the unit, in response to natural, mechanical, or electrical disturbances. These events are typically beyond PacifiCorp s control. Subsequent upramps in Daniel Creek and Middle Fork Rogue River are generally not observed as a result of unit trips because of the PRV upstream of the generating unit. The PRV facilitates the flow of water through the conveyance system during a unit trip by bypassing the generating unit. In the past, the PRV was not incorporated into the Project s automatic control system, and the PRV stop nut position was manually set based on current flows 2. If diverted flows automatically increased in response to increased inflows to the Project, the previous manual setting of the PRV stop nut would have been insufficient to accept the full flow of the penstock during a unit trip, and Project Water would encounter a partial barrier to continuous flow, forcing Project Water in excess of the flow through the PRV to be spilled at the forebay and into Daniel Creek. To minimize ramping events in Daniel Creek caused by unit trips, PacifiCorp has automated the PRV. The necessary hardware and instrumentation were installed in August 2014, and software programming was completed in September Informal observations and finetuning of the system have been conducted since commissioning of the system, and a formal test will be conducted during the next planned outage in May Unit trips alone do not result in an increase in spill in South Fork Bypass below the diversion dam. The canal headgate is not automated to respond to the turbine wicket gates, and flows, if 1 These normal operations-related ramping events, do not include potential catastrophic events that could result in ramping events such as excess velocity valve closure as a result of penstock failure; concurrent mechanical failure of the turbine wicket gates and PRV; concurrent failure of the canal headgate at full open and the forebay backwater gate; or mechanical failure of the automated forebay trash rack rake concurrent with a plugged trash rack. 2 See Appendix A for additional details of the past and current operation of the PRV. Initial Study Report: Ramping Page 2

6 any, spilling over the dam and into South Fork Bypass at the time of a trip will remain consistent with the volume of inflows to the Project. Planned Outages Planned outages occur when the generating unit is intentionally taken offline and/or the Project waterway is dewatered for scheduled maintenance or repairs. The PRV allows for continued flow of Project Water through the Project waterway during planned outages of the generating unit, but ramping may occur when planned outages also result in dewatering of the Project waterway. During waterway outages, PacifiCorp is able to control the rate at which the unit is brought offline, and by extension, the resulting up-ramp in South Fork Bypass. Resumed Generation Resumed generation refers to the action of bringing the generator back online and/or refilling the waterway after a unit trip or planned outage. PacifiCorp is able to control the rate at which the unit is brought back online, and by extension, the resulting down-ramp in affected waters. In general, resumed generation does not result in observable ramping in receiving waters when the PRV provides a full bypass of Project Waters during the outage. However, if the PRV did not provide a full bypass of Project Waters during a generating unit outage, a down-ramp would be expected in South Fork Bypass, Daniel Creek, and/or Middle Fork Rogue River following resumption of generation as a result of cessation of spill into these watercourses and restoration of the flow of Project Water through the conveyance system. Automation of the PRV has largely eliminated the potential for spill in this scenario. Resumed generation may also cause a downramp to occur in South Fork Bypass when the Project waterway is refilled and the unit is brought back online after a waterway outage. Initial Study Report: Ramping Page 3

7 Figure 1. Map of Project spill points and affected waters. Initial Study Report: Ramping Page 4

8 2.0 OBJECTIVES As indicated in Section 1.3, ramping is a relatively rare occurrence in affected waters, and the majority of ramping issues in Daniel Creek and Middle Fork related to Project operations have been addressed by automation of the PRV. Accordingly, this ramping study was driven by the need for better information regarding (a) existing ramping, and (b) improvements that were provided by automation efforts. The primary objectives of the ramping study are to: (1) Determine the magnitude, duration, and frequency of ramping events; and (2) Provide a description and justification of a proposed ramp rate for South Fork Bypass. 3.0 METHODS 3.1 General Approach The study involved a desktop review and analysis of existing information associated with ramping in South Fork Bypass. A summary of the approach is provided in Table 1, and specific methodologies are described in the following subsections. Table 1. Parameters and sampling techniques for the proposed study. Parameter Technique Event Frequency, Duration, Periodicity Stage and Discharge Ramping Recommendation Reviewed log books from WY 2010 to WY Reviewed stage and discharge record at USGS gaging station during each identified outage between 2010 and Describe and justify proposed ramp rate(s) in South Fork Bypass. 3.2 Desktop Analysis Event Frequency, Duration, and Periodicity Analysis Outage frequency was identified by a review of the log books. A review of the 2010, 2011, 2012, and log books was conducted to identify (1) generator trips and planned outages that could result in spill (i.e., an up-ramp) at the forebay or diversion dam, and (2) events when 3 These dates differ from the Study Plan, which identified a date range of 2011 through During the writing of the Plan, PacifiCorp was concerned that operations prior to 2011 would not reflect current operations due to updates that occurred in 2011 to Project controls. However, the updates did not fundamentally change operations. PacifiCorp determined that a study period of 2010 through 2013 would provide satisfactory data for the ramping study. The period of 2010 through 2013 was preferred to 2011 through 2014, because the later period includes preliminary data from 2014, whereas the earlier period uses only published data. Initial Study Report: Ramping Page 5

9 generation was restored after an outage that could result in a down-ramp in South Fork Bypass, Daniel Creek, and Middle Fork Rogue River. The date, time, and cause of all recorded events were compiled. Stage and Discharge USGS gaging station number is located in South Fork Bypass, 0.25 miles below the diversion dam. The gage records for the years 2010 through 2013 were analyzed on dates corresponding with events identified in review of the log books. For each identified event, the up-ramp or down-ramp rates were calculated in inches per hour, and the duration of each ramping event was identified. Ramping Recommendation PacifiCorp proposes a ramping schedule that is based on the ramp rates and periods established by the Prospect Nos. 1, 2, and 4 license for the bypassed reaches of Red Blanket Creek and Middle Fork Rogue River 4. The ramp rates for these two streams were identified as protective of aquatic life, including sensitive life stages of native fish, based on a comprehensive ramping study (PacifiCorp, 2003). South Fork Rogue River is similar to Middle Fork Rogue River, in terms of discharge, hydrograph shape, and channel shape. The ramp rates were rounded to the nearest tenth of a foot to correlate compliance units with units of the gage (i.e., the compliance point) and reflect the level of operational control. PacifiCorp believes that the proposed rates, if adopted, will be protective of aquatic life in South Fork Bypass. The potential benefits of implementing the proposed ramping schedule were assessed by calculating the percent of controlled events (i.e. planned outages and resumed generation) during the study period that resulted in ramping that exceeded the proposed limits. The analysis assumed that the proposed ramp rates, if stipulated in the new license, would be consistently attained. Accordingly, the percentage of ramping exceedances observed during the study period is presented as the potential improvement that could be realized upon implementation of the proposed ramping schedule. Table 2. Proposed operational ramp rates for South Fork Bypass. Period Target Ramp Rate (in/hr) May 1 September 30 Not to exceed 0.2 feet per hour October 1 April 30 Not to exceed 0.3 feet per hour 4 May 1 through September 30, operational ramping should not exceed two inches per hour; October 1 through April 30, operational ramping should not exceed three inches per hour. Initial Study Report: Ramping Page 6

10 4.0 RESULTS 4.1 Unit Trips Thirty-four unit trips (i.e., unplanned outages) were observed during the study period, resulting in an average frequency of 8.5 trips per year. Unit trips occurred most frequently in March (nine trips) and January (seven trips). One to three unit trips were observed during the study period in all remaining months, except July. The unit never tripped offline in July. A list of unit trips is provided in Appendix B. Of the thirty-four unit trips, seven coincided with an observable, but non-operational, up-ramp in South Fork Bypass (Figure 2). Unit trips alone do not result in additional spill at the diversion dam since the canal headgate is not automated to respond to unit trips and the Project operates in run-of-river mode. Any ramping observed in South Fork Bypass at the time of unit trips is likely the result of storm events that concurrently resulted in a unit trip (e.g., trees toppled by wind may damage a transmission line resulting in a generating unit trip) and natural increases in river stage as a result of precipitation-driven storm flows. The seven recorded natural ramping events ranged in magnitude from 0.7 inches per hour to 7.4 inches per hour. The average ramp rate of all events was 4.9 inches per hour. Non-operational ramping events ranged in duration from 0.25 hours to two hours, with an average duration of 0.7 hours. The seven unit trips coincident with up-ramps were associated with higher flow events. The median bypass flow in South Fork Bypass during unit trips that were coincident with ramping was 87 cfs, and the average flow was 140 cfs. All other unit trips coincided with a median flow of 17 cfs and an average flow of 124 cfs in South Fork Bypass. Ramping in South Fork Bypass coincident with unit trips is almost always the result of natural flow increases upstream of the Project and is not the result of project operations. 5 PRV automation facilitates the continuous flow of water through the conveyance system during unit trips. This corrective action is expected to effectively eliminate ramping in Daniel Creek and Middle Fork Rogue River associated with unit trips. 4.2 Planned Outages Eleven planned outages were recorded in the operations log during the study period (Appendix B). Outages occured approximately quarterly over the study period, and are typically associated with annual maintenance, quarterly collector ring maintenance, and facility repairs. Five of the planned outages resulted in apparent up-ramps in South Fork Bypass, ranging in magnitude from 7.0 inches per hour to 11.3 inches per hour (Figure 3). The average ramp rate 5 Rare ramping events may occur in South Fork Bypass if the unit trips due to freezing conditions and ice formation on the trash rack that obstructs flow to the penstock. During the four-year study period, a unit trip associated with a frozen trash rack occurred only one time. Initial Study Report: Ramping Page 7

11 Figure 2. Non-operational ramp events in South Fork Bypass observed coincident with a unit trip, WY 2010-WY Flow Ramp Event 1, Q (cfs) Ramp (inches per hr) Initial Study Report: Ramping Page 8

12 Figure 3. Ramp events in South Fork Bypass observed after a planned outage, WY 2010-WY Flow Ramp Event 1, Q (cfs) Ramp (inches per hr) Initial Study Report: Ramping Page 9

13 of the five events was 8.8 inches per hour. Ramping events ranged in duration from 0.5 hours to one hour, with an average duration of 0.65 hours. The ramping limits proposed in Table 2 (above) will provide PacifiCorp with a compliance target for flow management while taking the unit offline. Of the eleven planned outages that occurred over the four-year study period, the proposed compliance target was not achieved on five occasions (Appendix B). 4.3 Resuming Generation Following an Outage The unit was brought back online after an outage (including unit trips and planned outages) forty-four times during the study period. A down-ramp was observed in South Fork Bypass on thirteen occasions after the unit was brought online (Figure 4). These ramping events were the result of increasing flows in the Project waterway. Event magnitude ranged from -0.8 inches per hour to -8.0 inches per hour, and the average magnitude was -3.7 inches per hour. Down-ramp events lasted between 0.25 hours to 1.75 hours, with an average duration of 0.8 hours. The proposed ramping limits will provide PacifiCorp with a compliance target for flow management during increases of Project Water in the waterway and resuming generation after an outage. Of the forty-four events when generation was restored following an outage over the four-year study period, the proposed compliance target was not achieved on six occasions (Appendix B). Initial Study Report: Ramping Page 10

14 Figure 4. Ramp events in South Fork Bypass observed after the unit was brought online, WY 2010-WY Flow Ramp Event 1, Q (cfs) Ramp (inches per hr) Initial Study Report: Ramping Page 11

15 5.0 CONCLUSIONS Unit trips do not result in ramping in South Fork Bypass. Canal intake headgate operation does not automatically respond to changes at the generating unit. Any ramping in the South Fork Bypass coincident to unit trips is the result of natural increases in stage from precipitation and resulting storm flows upstream of the diversion dam and not from Project operations. Prior to PRV automation, unit trips resulted in ramping in Daniel Creek and Middle Fork Rogue via the forebay overflow spillway, but this type of ramping has been eliminated by automation of the PRV. The PRV also eliminates the need to dewater the Project waterway during generating unit maintenance, thereby generally precluding the need to refill the waterway and subsequently ramp the South Fork Bypass down when the unit is brought back online. A total of eighteen ramping events (five planned outage up-ramps and thirteen return-to-service down-ramps) in South Fork Bypass as a result of Project operations were recorded during the four-year study period, resulting in an average of 4.5 operational ramping events per year. Eleven of the eighteen recorded operational ramping events resulted in ramp rates exceeding the proposed ramp rates (Table 2). The majority of planned outages (fifty-five percent) did not result in ramping in South Fork Bypass. When generation was resumed after an outage, ramping was avoided on seventy percent of all occasions. As described in Sections 1.3 and 3.3, Project operations only influence ramping in South Fork Bypass immediately before and after outages that require dewatering of the conveyance system. Planned replacement of the flowline and sag pipe will reduce the number of waterway outages due to wood-stave repairs during the new license term. PacifiCorp recommends that ramp rate compliance monitoring and reporting be limited to operation of the canal headgate before and after dewatering of the Project waterway. Implementation of the proposed ramp rates is expected to minimize the environmental effect of the occasions when ramping is required to dewater and/or fill the waterway. Initial Study Report: Ramping Page 12

16 6.0 REFERENCES PacifiCorp. (2003). Prospect Nos. 1, 2, and 4 Hydroelectric Project: Ramp Rate Study Technical Report. Portland. Initial Study Report: Ramping Page 13

17 Appendix A. Description of Pressure Relief Valve Ramping events related to generating unit trips are infrequent because the penstock is equipped with a pressure relief valve (PRV) upstream of the scroll case. The PRV actuator is mechanically linked to the turbine wicket gate actuator. The turbine wicket gate position is constantly adjusted by the control system based on available water and generating requirements. Conversely, the PRV has a manual adjustment or stop nut that allows periodic flow adjustment setting by operations personnel. In the past, the PRV stop nut position had to be manually set to activate based on current inflows and wicket gate opening. When the wicket gates close during a unit trip, the PRV opened according to its pre-set position by this stop nut. Once opened, the PRV diverts water around the unit and into the tailwater structure and subsequent sag pipe routing flows to the Middle Fork Canal of the Prospect Nos. 1, 2, and 4 Project. The uninterrupted flow of water through the conveyance system eliminates the need to spill excess Project Water at the forebay following a unit trip. In the past, approximately eight times per year, unit trips resulted in spill at the forebay. This spill was a result of the mismatch in wicket gate position and PRV stop nut position at the time of the trip, and was usually associated with natural circumstances, such as an inflow increases as a result of precipitation. The wicket gate position controls automatically adjusted in response to flow changes while the PRV stop nut adjustment did not. Operations personnel typically could not adjust the PRV activation threshold before this mismatch resulted in either spill at the forebay spillway, which discharges to Daniel Creek via an overflow channel, or unnecessary drafting of the forebay and penstock, which would cause a unit trip due to low forebay level alarms in the case of a PRV setting in excess of the available flows. The duration and magnitude of the events were dependent on flows in the canal and relative wicket gate openness at the time of the unit trip. To minimize ramping events in the spillway caused by unit trips, PacifiCorp automated the PRV stop nut adjustment so that the activation threshold will automatically change based on spacing between the stop nut and PRV bonnet while the unit is on-line. Automated bypassing of Project Water while the generating unit is off-line is determined by automatic stop nut adjustments in response to forebay elevation levels. Automation of the PRV was completed in August Post-automation, only catastrophic failures would result in ramping in Daniel Creek and the Middle Fork Rogue. The following four scenarios are considered catastrophic failures: (a) penstock failure causing the closure of the excess velocity valve at the top of the penstock; (b) simultaneous failure of turbine wicket gates and PRV; (c) simultaneous failure of canal headgate and backwater gate; or (d) failure of the trash rake that coincides with a debris-mobilization event that obstructs the trash rack. The occurrence of any of these scenarios is possible, but unlikely. Initial Study Report: Ramping Page 14

18 Appendix B. Ramping Events Initial Study Report: Ramping Page 15

19 Date and Time Cause (if known) Unit Trips and Ramping Maximum Up-Ramp, if applicable (in/hr) Exceeds Proposed Ramp (Y/N)* Duration (hr) 12/8/09 5:15 Ice on trash rack 4.08 Y /1/10 14:15 1/2/10 19:45 2/16/10 13:30 Communications failure 3/7/10 18:30 3/18/10 7:15 3/18/10 16:45 4/3/10 4:45 4/4/10 22:15 Low forebay 5/29/10 12:00 5/29/10 19:30 Bad fuses 6/3/10 7:45 8/12/10 11:30 9/19/10 6:30 9/24/10 10:00 9/28/10 13:00 Forebay level calibration 1.8 N /23/10 9:45 1/17/11 10:30 1/18/11 15:15 System disturbance 3/13/11 15:00 10/2/11 11:45 Low forebay 1/8/12 13:00 1/23/12 11:30 1/23/12 13:45 2/28/12 7:00 3/9/12 3:30 3/10/12 8:30 3/16/12 10:45 Hole in flow line 7.44 Y 0.5 4/23/12 17: N /1/12 15:45 System disturbance 9/4/12 19: Y 0.5 3/6/13 8: Y 2 3/28/13 22:45 6/3/13 17: Y 1 *Because unit trips are uncontrolled events, ramp rates are beyond the control of PacifiCorp s operations. Initial Study Report: Ramping Page 16

20 Date and Time Activity 1/28/10 10:00 Collector ring maintenance 4/11/10 15:00 Unknown 6/24/10 9:00 Collector ring maintenance Planned Outages and Ramping Maximum Up-Ramp (in/hr) Exceeds Proposed Ramp (Y/N) Duration (hr) 8/25/10 9:00 Biennial canal outage 6.96 Y 0.5 8/14/11 13:45 Repair penstock leaks Y 0.5 9/19/11 7:45 Annual maintenance 8.28 Y 1 1/26/12 9:30 Collector ring maintenance 6/21/12 8:00 Collector ring maintenance 11/5/12 8:00 Annual maintenance, automation 1/26/13 9:30 Collector ring maintenance 7.92 Y /25/13 10:00 Annual maintenance 9.36 Y 0.5 Initial Study Report: Ramping Page 17

21 Resuming Generation Following Outage and Ramping Date and Time Minimum Down-Ramp (in/hr) Duration (hr) Exceeds Proposed Ramp (Y/N) 12/8/09 15:15 1/1/10 15: N 1/2/10 21:30 1/28/10 14:15 2/16/10 14:15 3/7/10 20:00 3/18/10 8:30 3/18/10 20:30 4/3/10 6:45 4/5/10 9:00 4/18/10 15: N 5/29/10 18:15 5/30/10 3:30 6/3/10 9:45 6/24/10 15:00 8/12/10 12:45 9/1/10 12: Y 9/20/10 0:15 9/25/10 19:30 9/28/10 14: N 11/23/10 12:00 1/18/11 14:30 1/18/11 17:00 3/14/11 10:45 8/16/11 16: Y 9/23/11 15: Y 10/2/11 16:00 1/8/12 15:00 1/23/12 13:00 1/23/12 15:45 1/26/12 12:30 3/1/12 13:45 3/9/12 14:45 3/13/12 12:15 3/19/12 9: N 4/24/12 8: N Initial Study Report: Ramping Page 18

22 Date and Time Minimum Down-Ramp (in/hr) Duration (hr) Exceeds Proposed Ramp (Y/N) 6/1/12 17:15 6/21/12 10:15 9/5/12 9: Y 1/25/13 11: N 1/26/13 11: N 3/6/13 13: Y 3/29/13 12:00 6/4/13 8: Y Initial Study Report: Ramping Page 19

23 Appendix C. Rating, USGS Gaging Station No Initial Study Report: Ramping Page 20

24 Initial Study Report: Ramping Page 21

25 Initial Study Report: Ramping Page 22