Glen Canyon Down-Ramp 

Rates and Automatic 

Generation Control

Presented by

Kirk LaGory

Argonne National Laboratory

September 7, 2001
Background

n Exceedances in 1500 cfs/hr down-ramp 

rate noted and attributed to effect of 

automatic generation control

n Definitions

n Area Control Error: instantaneous difference 

between scheduled generation and actual loa

n Automatic generation control (AGC):

automatic adjustments of releases to 

compensate for ACE
Background (Cont’d)

n Normally 80/20% split between Hoover 

and Glen Canyon Dams

n July 1998, target down-ramp rate 

reduced to 1450 cfs/hr and AGC switched 

entirely to Hoover during down-ramp 

periods to eliminate exceedances

n Concern regarding resource effects led to 

proposal to further evaluate issue
Analysis Questions

n What are the sources and causes of down-ramp 

exceedances?

n What are the frequency and magnitude of 

down-ramp exceedances?

n Are there temporal patterns in exceedance 

frequency?

n Do the measurements of releases correlate to 

flow data?

n To what level of accuracy can AGC comply with 

down-ramp rate targets?
Two Phases of Study

n Evaluation of existing SCADA data

n January 1993 to April 2000

n AGC experiments

n Glen Canyon gage re-established

n Accusonic data gathered

n September 2000 to July 2001
Phase I: Analysis of SCADA 

Data

n Only source of “historical” release data

n Analysis examined data from 1-93 to 

4-00

n Statistical analyses to determine:

n Frequency and magnitude of exceedance

n Temporal patterns (are exceedances more 

common during periods of high demand?)
Frequency of Down-Ramp 

Magnitudes: 1993 to 2000

0%

10%

20%

30%

40%

50%

60%

0-500

501-1000

1001-15001501-20002001-30003001-50005001-8000

> 8000

% Down-Ramp Hours
Percent of Exceedances of 

Different Magnitudes

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

1501-16001601-17001701-18001801-19001901-20002001-25002501-30003001-40004001-5000

> 5000

% Exceedances
Hour of Day Effect

χ2 = 1437.2

P < 0.001

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

0 2 4 6 8 10 12 14 16 18 20 22

Hour of Day

% Down Ramp Hours

 > 1500 cfs/hr
0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

1 2 3 4 5 6 7 8 9 10 11 12

Month

% Down-Ramp Hours

> 1500 cfs/hr

Month Effect

χ2 = 31.8

P < 0.001
0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

Sun Mon Tues Wed Thurs Fri Sat

% Down Ramp Hours 

> 1500 cfs/hr

Day Effect

χ2 = 56.6

P < 0.001
5.83%

0.57%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

w / AGCw /o AGC

% Down-Ramp Hours

ComplyExceed

“AGC” Effect

χ

2 = 327.6

P < 0.001
Conclusions: Phase I

n About 5% of down-ramp hours had 

ramp rates > 1500 cfs/hr

n Down-ramp exceedances most 

frequent during late evening downramp period and periods of high 

power demand
Conclusions: Phase I (Cont’d)

n Fewer than 1% of down-ramp hours 

had ramp rates > 1500 cfs/hr durin

the period when AGC was off Glen

n Effect of AGC not clear because it 

was confounded with reduction in 

target ramp rate during test period
Phase II: AGC Experiments

n Reduce the measurement period to get 

better understanding of AGC effect on 

flow variability

n Compare steady flow and fluctuating flow 

periods with AGC on and off

n Compare Glen Canyon gage, Accusonic, 

and SCADA data
0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Flow (cfs)

Accusonic

SCADA

Glen Canyon Gage

AGC on

AGC off

Steady Flow Test Period:

9/10 to 9/30/00
Variation in 5-minute Data: 

Steady Flows with AGC Off

n Accusonic

n Range: 8032 to 8279 cfs (247 cfs)

n CV: 0.23%

n Max difference between consecutive readings: 150 cfs

n Gage

n Range: 7971 to 8061 cfs (90 cfs)

n CV: 0.20%

n Max difference between consecutive readings: 45 cfs

n Stage

n Range: 31.42 to 31.46 ft (0.5 in)

n CV: 0.02%

n Max difference between consecutive readings: 0.02 ft 

(0.25 in)
Variation in 5-minute Data: 

Steady Flows with AGC On

n Accusonic

n Range: 6944 to 9497 cfs (2553 cfs)

n CV: 1.51%

n Max difference between consecutive readings: 1352 cf

n Gage

n Range: 7704 to 8472 cfs (768 cfs)

n CV: 0.94%

n Max difference between consecutive readings: 158 cfs

n Stage

n Range: 31.30 to 31.64 ft (4 in)

n CV: 0.11%

n Max difference between consecutive readings: 0.07 ft 

(0.8 in)
Hourly Flow Statistics during

Steady Flow Test Period

AGC Off

Mean Min Max CV

Accusonic 8210 8179 8246 0.17

SCADA 8035 7980 8110 0.32

Gage 8008 7973 8053 0.17

Stage 31.44 31.42 31.46 0.02

AGC On

Mean Min Max CV

Accusonic 8169 7861 8576 0.93

SCADA 7959 0 14580 9.75

Gage 8012 7817 8340 0.87

Stage 31.44 31.35 31.58 0.10
Fluctuating Flow Test Period: 

10/1/00 to 10/31/00

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Flow (cfs)

Accusonic

SCADA

Glen Canyon Gage

AGC on AGC on

AGC off
Hourly Flow Statistics during

Fluctuating Flow Test Period

AGC Off

Mean Min Max CV

Accusonic 9992 6870 12815 19.39

SCADA 9894 6770 12850 20.06

Gage 9717 6712 12395 18.62

Stage 32.15 30.84 33.26 2.41

AGC On

Mean Min Max CV

Accusonic 9884 6681 12908 20.15

SCADA 9834 6560 12900 20.66

Gage 9715 6553 12925 19.34

Stage 32.13 30.75 33.28 2.50
Down-Ramp Rate Values During 

Fluctuating Flow Test Period

AGC Off

Mean Min Max CV

Accusonic 558 0.1 1666 96

SCADA 588 10 1520 94

Gage 485 2.1 1559 91

Stage 0.2 0 0.7 91

AGC On

Mean Min Max CV

Accusonic 526 0.2 2413 102

SCADA 565 10 1990 96

Gage 477 0 1886 96

Stage 0.2 0 0.8 95
Exceedance as Measured by 

Different Methods During 

Fluctuating Flow Test Period

1.33 1.35 1.23

0

4.85

4.43

1.36

0.57

0

1

2

3

4

5

6

Accusonic SCADA Gage All

% Down-Ramp Hours > 1500 cfs/hr

AGC off

AGC on
Statistical Tests of AGC Effect on 

Down-Ramp Rate During 

Fluctuating Flow Test Period

Frequency of Exceedance (? 2)

Accusonic P = 0.17

SCADA P = 0.22

Gage P = 0.93

Magnitude of Ramp Rate (t-Test)

Accusonic P = 0.65

SCADA P = 0.75

Gage P = 0.88

Equality of Variances (F-test)

Accusonic P = 1.00

SCADA P = 0.80

Gage P = 0.77
Frequency of Down

Ramp Magnitudes 

as Measured by Different Methods: 

10/00 to 7/01

0%

10%

20%

30%

40%

50%

60%

0-500

501-1000

1001-15001501-16001601-17001701-18001801-19001901-20002001-30003001-40004001-5000

> 5000

% Down-Ramp Hours

Accusonic

SCADA

Gage
Exceedance Frequency as Measured 

by Different Methods: 10/00 to 7/01

5.4

7.3

3.1

1.7

11.0

1.0

0

2

4

6

8

10

12

Accusonic SCADA Gage Accusonic

& SCADA

Accusonic

or SCADA

All

% Down-Ramp Hours > 1500 cfs/hr
Example Down-Ramp Data

Accusonic SCADA Gage

1606 1590 1363

1059 1540 1204

1534 1300 1202

1520 1370 1208

1833 1360 1247
Comparison of Accusonic 

and SCADA Flow Data

0

5000

10000

15000

20000

25000

0 5000 10000 15000 20000 25000 30000

SCADA Flow (cfs)

Accusonic Flow (cfs)

Accusonic = 0.90 SCADA + 1149

R

2

 = 0.88
Comparison of Accusonic 

and Gage Flow Data

0

5000

10000

15000

20000

25000

30000

0 5000 10000 15000 20000 25000 30000

Gage Flow (cfs)

Accusonic Flow (cfs)

Accusonic = 1.00 Gage - 51.3

R

2

 = 0.96
Comparison of SCADA and 

Gage Flow Data

0

5000

10000

15000

20000

25000

0 5000 10000 15000 20000 25000

Gage Flow (cfs)

SCADA Flow (cfs)

SCADA = 1.04 Gage - 450.1

R

2

 = 0.94
Conclusions: Phase II

n Flow variation was greater with AGC on

n More apparent in short (5-min) time frame

n More apparent in Accusonic and SCADA data than in 

gage data (sensitivity? attenuation?)

n Accusonic and SCADA: frequency of exceedance 

higher with AGC on than off, but not significantl

n Gage: frequency of exceedance same with AGC 

on and off

n Down-ramp rate magnitude did not differ 

significantly between AGC periods
Conclusions: Phase II (Cont’d)

n Measurements using different methods 

strongly correlated, but variable

n Variability leads to difference in detected 

frequency of exceedance

n SCADA > Accusonic > Gage

n All 3 techniques seldom measured downramp rates > 1500 cfs/hr simultaneously 

(1% of the time)
Bottomline

n AGC increased variability in 

releases, but did not increase the 

frequency of down-ramps > 1500 

cfs/hr at the Glen Canyon gage