Gorge 2nd Tunnel

Appendix K: Load Rejection Test Technical Memorandum

Date

Client logos Aligned right

Stacked

Prepared by:

Jacobs Associates 1109 First Avenue, Suite 501

Seattle, WA 98101

May 22, 2009 Revised December 10, 2010

MEMORANDUM

TO: Gregg Davidson, PE; Bob Fuchs, PE FROM: Drake Hughes, PE; David Elwood, EIT CC: Stephen Spain, PE; David Summers, PE; SUBJECT: Gorge Load Rejection Test

In December of 2008, Devine Tarbell and Associates (Now HDR|DTA) was contracted by Jacobs Associates and their client Seattle City Light to perform hydraulic analysis as part of the design of a second tunnel at the Gorge Powerhouse. In support of its hydraulic transient analysis, HDR|DTA collected field data during partial load rejection testing of Unit 24 conducted by Seattle City Light personnel.

HDR|DTA provided pressure transducers and other instrumentation as listed in the table below to collect data on the scroll case pressure, unit speed, and surge tank level during the load rejections. This data can be used to help calibrate a numerical hydraulic transient model of the existing Gorge system to be used in the design of the second tunnel. Tests were conducted on May 12th and 13th 2009 and data was collected during two load rejections of Unit 24 from 38MW and 60MW load respectively (see attached excerpt from plant logbook).

The 200 MW Gorge powerhouse lies on the Skagit River in the town of Newhalem, Washington. The powerhouse contains three 38 MW Francis units (Units 21, 22, and 23) and one 100 MW unit (Unit 24). The powerhouse characteristics are given in the following table.

Parameter Value Units Powerhouse Characteristics

Reservoir Elevation (max) 875 Ft Reservoir Elevation (min) 825 Ft Runner Centerline

Unit 21, 22, and 23 500 Ft Unit 24 497 Ft

Tail Water Level (max discharge)

494 Ft

The parameters recorded to calibrate the hydraulic model are given in the following table.

Parameter Instrument Location * Unit 24 Speed Frequency Input Signal Conditioning

Module Analog Devices 5B45-01D

Connected to AC Kilovolts gauge on main control board

* Unit 24 Wicket Gate Position

Ametek/Rayelco P-20A Wicket Gate Servomotor

* Unit 24 Pressure Druck PTX7217 Scroll Case pressure taps * Unit 23 Pressure Druck PTX7217 Scroll Case pressure taps * Unit 22 Pressure Druck PTX7217 Scroll Case pressure taps * Unit 21 Pressure Druck PTX7217 Scroll Case pressure taps * Key Phasor Bently Nevada 3500 Bently Nevada 3500 Front Panel Surge Tank Level RBR DR-1050P Surge Tank * These parameters recorded by IMPULS3 Data Acquisition System

Test Procedure

Unit 24 operated at steady state with prescribed target load of either 37 MW or 60 MW.

Units 21 and 22 operated at steady state with approximately 10 MW.

Data collection started approximately 30 seconds before Load Rejection.

Unit 24 load rejection initiated.

Data collection continued until Unit 24 speed reached zero.

Unit 24 38MW Load Rejection

The Unit 24 38MW load rejection was initiated by the following procedure:

Attempted to reject Unit 24 using 86E breaker. Unit failed to reject.

Opened Unit 24 breaker manually. Overspeed of Unit caused governor to begin closing wicket gates.

Manually began closing the Unit 24 shut-off valve.

Approximately one minute after opening breaker manually hit Unit 24 stop button. Wicket gates pinched shut.

As a result of the failure of the Unit to reject using the 86E breaker the Unit had to be shut down manually. There was a one minute delay between opening the Unit 24 breaker and hitting the stop button. During this time the wicket gates closed but did not squeeze. The pertinent data from this test are provided in the following Table and plots.

Table 1. Conditions Prior to 38MW Load Rejection

Unit Initial Conditions

Time Pressure (psi) Flow (cfs) Power (MW) Speed (RPM)

Unit 21 21:26 151 429 10.8 257

Unit 22 21:26 151 418 10.5 257

Unit 23 21:26 152 25 0 0

Unit 24 21:26 151 1554 38.1 163

Plant Total 2426 59.4

Tailrace/Lake Level

Time Level

Tailrace 21:10 491.9 Feet

Lake 21:10 870.9 Feet

Table 2: Transient Penstock Pressures after 38MW Load Rejection

Maximum Pressure Long Pressure Wave

Maximum Pressure

Time After Rejection

Maximum Pressure

Minimum Pressure

Period

psi Seconds psi psi Minutes

Unit 23 167 2 165 145 5.75

Unit 24 180 1.5 n/a* n/a* n/a*

* Turbine Shut-off Butterfly Valve was closed.

Table 3: Wicket Gate Timing after 38MW Load Rejection

Initial Position 34 %

Time to Close from 34% to 10% Open 3.6 Seconds

Time to Close from 10% Open to 0% 5 Seconds

Total Time to Close 8.6 Seconds

Table 4: Unit 24 Overspeed after 38MW Load Rejection

Maximum Overspeed 189 RPM

Time After Rejection 4.5 Seconds

Table 5: Surge Tank Response after 38MW Load Rejection

Time from Rejection to Crest of First Wave 3.75 Minutes

Maximum Rise in Surge Tank 28 Feet

Wave Period 5.5 Minutes

Lag between Surge Tank and Penstock Pressure Waves 2 Minutes

0

5

10

15

20

25

30

35

40

45

150

155

160

165

170

175

180

185

190

195

‐0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0

Wicket G

ate Po

sitio

n (%

 of Full G

ate)

Pressure (P

SI), Unit S

peed

 (RPM

)

Time from Unit Trip (sec) 

Unit 24Wicket Gate Position, Pressure and Speed Response after 38MW Load Rejection

Unit 24 Pressure

Unit 24 Speed

Wicket Gate Position

0

5

10

15

20

25

30

35

40

45

0

20

40

60

80

100

120

140

160

180

200

21:31:06 21:32:33 21:33:59 21:35:25 21:36:52 21:38:18 21:39:45 21:41:11

Wicket G

ate Po

sition

 (% of Full G

ate)

Pressure (P

SI), Unit S

peed

 (RPM

)

Time on 5/12/2009

Transient Hydraulic Response after 38MW Load Rejection of Unit 24

Surge Tank Pressure (relative to Unit 24 CL)

Unit 24 Pressure

Unit 23 Pressure

Unit 24 Speed

Wicket Gate Position

0

5

10

15

20

25

30

35

40

45

120

130

140

150

160

170

180

190

200

‐5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0 70.0 75.0

Wicket G

ate Po

sitio

n (%

 of Full G

ate)

Pressure (P

SI), Unit S

peed

 (RPM

)

Time from Unit Trip (sec) 

Transient Pressure and Speed Response after 38MW Load Rejection

Unit 24 Pressure

Unit 24 Speed

Wicket Gate Position

140

145

150

155

160

165

170

175

180

21:31:06 21:32:33 21:33:59 21:35:25 21:36:52 21:38:18 21:39:45 21:41:11

Pressure (P

SI)

Time on 5/12/2009

Pressure Wave Generated in Tunnel after 38MW Load Rejection

Surge Tank Pressure (relative to Unit 24 CL)

Unit 23 Pressure

850

855

860

865

870

875

880

885

890

895

900

905

21:07:12 21:36:00 22:04:48 22:33:36 23:02:24 23:31:12 0:00:00

Elevation of Free Su

rface (feet)

Time on 5/12/2009

Surge Tank Response after 38MW Load Rejection of Unit 24

Unit 24 60MW Load Rejection

The Unit 24 60MW load rejection was initiated by the following procedure:

Opened Unit 24 breaker manually. Overspeed of Unit caused governor to begin closing wicket gates.

Immediately after opening breaker hit Unit 24 stop button.

Manually began closing the Unit 24 shut-off valve.

After completing the 60MW load rejection HDR|DTA personnel attempted to retrieve the RBR DR-1050P pressure transducer from the surge tank. Unfortunately the retrieval line for the pressure transducer had become fouled during the test and the transducer could not be recovered. The pressure transducer was later recovered by Jacobs Associates staff during a dewatered inspection of the tunnel in October, 2010. The pressure data was retrieved from the transducer and post-processed. During the post-processing of the data it became clear that the transducer’s retrieval line had become fouled during installation of the device. As a result, the precise elevation of the transducer during the load rejection is unknown. The approximate elevation of the transducer during the test was estimated using a measurement of the elevation of the water in the surge tank just before transducer installation and by comparing the absolute pressure measurements from the device just before and just after being lowered into the surge tank. The difference between the pressures measured just prior to installation and just after installation was assumed to be due to the amount of submergence below the water surface in the surge tank. The pertinent data from this test are provided in the following Table and plots.

Table 6: Initial Conditions Prior to 60MW Load Rejection

Unit Initial Conditions

Time Pressure

(psi) Flow (cfs) Power (MW) Speed (RPM)

Unit 21 21:10  149  424  10.7  257 

Unit 22 21:10  149  414  10.4  257 

Unit 23 21:10  149  25  0  0 

Unit 24 21:10  147  2300  61  163 

Plant Total    3163  82.1    

Tailrace/Lake Level

Time Level

Tailrace 21:10  491.9  Feet

Lake 21:10  870.9  Feet

Table 7: Transient Penstock Pressures after 60MW Load Rejection

   Maximum Pressure Long Pressure Wave

  Maximum Pressure

Time After Rejection

Maximum Pressure

Minimum Pressure

Period

   lb/in^2 Seconds lb/in^2 lb/in^2 Minutes

Unit 23 170 33 170 141 5.5

Unit 24 185 2 n/a n/a n/a

* Turbine Shut-off Butterfly Valve was closed.

Table 8: Wicket Gate Timing after 61MW Load Rejection

Initial Position 50 %

Time to Close from 50% to 10% Open 6 Seconds

Time to Close from 10% Open to 0% 5 Seconds

Total Time to Close 11 Seconds

Table 9: Unit 24 Overspeed after 61MW Load Rejection

Maximum Overspeed 214 RPM

Time After Rejection 6 Seconds

Table 10: Surge Tank Response after 60MW Load Rejection

Time from Rejection to Crest of First Wave 3 Minutes

Maximum Rise in Surge Tank 45.5 Feet

Wave Period 5.5 Minutes

Lag between Surge Tank and Penstock Pressure Waves 1 Minute

0

10

20

30

40

50

60

70

80

90

100

0

50

100

150

200

250

21:30 22:00 22:30 23:00 23:30 24:00 24:30 25:00 25:30 26:00 26:30 27:00 27:30 28:00 28:30 29:00 29:30

Wick Ga

te Position (%

 Ope

n)

Pressure (P

SI), Unit S

peed

 (RPM

)

Time after 2100 (min:sec)

Transient Hydraulic Response after 60MW Load Rejection of Unit 24

Unit 24 Speed

Unit 24 Pressure

Unit 23 Pressure

Wicket Gate Position

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

55.0

60.0

65.0

70.0

145

150

155

160

165

170

175

180

185

190

195

200

205

210

215

‐0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

10.5

11.0

Pressure (P

SI), Unit S

peed

 (RPM

)

Time from Unit Trip

Unit 24Wicket Gate Position, Pressure and SpeedResponse after 60MW Load Rejection

Unit 24  Pressure

Speed

Wicket Gate 

145

150

155

160

165

170

175

180

185

190

‐0.50 0.50 1.50 2.50 3.50 4.50 5.50 6.50 7.50 8.50 9.50 10.50 11.50 12.50

Pressure (PSI)

Time from Unit Trip (sec)

Unit Pressures after 60MW Load Rejection of Unit 24

Unit 24  Pressure

Unit 23  Pressure

Unit 22  Pressure

Unit 21  Pressure

135

145

155

165

175

185

0 500 1,000 1,500 2,000 2,500 3,000 3,500

Pressure (PSI)

Time from Unit trip (sec.) 

Pressure after 60MW Load Rejection of Unit 24

Unit 23 Penstock

Surge Tank (Relative Unit 23)

No data for this time period Restart of Unit 24

840.0

850.0

860.0

870.0

880.0

890.0

900.0

910.0

920.0

21:00:00 22:00:00 23:00:00 0:00:00

Elevation of Free Su

rface (feet)

Time on 5/13/2009

Surge Tank Response after 60MW Load Rejection of Unit 24