statistical evaluation of standardization in substation maintenance
TRANSCRIPT
Substation Equipment Maintenance APPLICATION OF STATISTICAL METHODSAMERICAN TRANSMISSION COMPANY
Does Standardization Improve Maintenance?
• American Transmission was formed when WI legislature prompted electric utilities to pool their facilities to form an independent transmission company.
• Transmission facilities consist of power lines, substation circuit breakers and transformers.
• Substation maintenance work is contracted back to the distribution companies which formed ATC.
• The same shops which performed substation maintenance when the equipment was owned by the distribution companies perform the work for ATC.
• Maintenance procedures are not currently standardized across ATC locations.
Travel Times Vary Greatly at Each LDC
• Looking at the relationship of travel times to distance covered, there is an expection of medium to strong correlation (0.5 to 1.0)
• This is not what was seen in reality: some sites actually had negative correlations.
LDC Shop Coefficient of Correlation
Alliant North -0.03
Alliant South 0.27
UPPCO Houghton 0.83
UPPCO Ishpeming 0.10
WE Fox Valley 0.60
WE Iron Range 0.48
WE Metro -0.36
WE North 0.65
WE South 0.40
WE West 0.40
WPSC Green Bay 0.04
WPSC Wausau 0.82
0.0
2.0
4.0
6.0
8.0
10.0
12.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0
TRAVELHOURS
TRAVEL DISTANCE
WPSC Wausau Travel Hours
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0.0 20.0 40.0 60.0 80.0 100.0 120.0
TRAVELHOURS
TRAVEL DISTANCE
Alliant North Travel Hours
Prediction Line: Travel Hours = 3.964 hrs - 0.003 hrs/mile x Travel Distance
BEFORE: wide variations in maintenance times
Procedure↓\ Parameter→ n µ σ n µ σ n µ σ n µ σ45 20 18 7
16.7 13.1 14.0 34.3
10.2 5.5 5.5 12.1
115 53 58 4
19.6 17.1 21.3 29.4
12.6 12.4 12.4 9.8
42 18 24
35.8 44.2 44.2
22.8 23.8 23.8
14 3 11
52.4 29.7 58.6
30.5 21.6 29.6
230 to 345 kV
Breaker Diagnostics
(SF6GasBreakers)
Breaker Diagnostics
(OilBreakers)
Breaker Major (OilBreakers)
Electric Test
(NonLTCTransformers)
All Voltages 069 kV 115 to 161 kV
AFTER: STANDARDIZATION SHOWS IMPROVEMENTS
After implementing standardized maintenance procedures, we see that variance has been greatly reduced and there is clearly more variation in the 2011 results versus 2012.
F-Test Two-Sample for Variances
OLD 115 to 161 kv (2011)
NEW 115 to 161 kv (2012)
Mean 21.27655172 36.37931034
Variance 156.7613458 18.45009074
Observations 58 58
df 57 57
F 8.496508119
F Critical one-tail 1.55175754