20150812AVU to Staff 50 Attachment G.pdf

2012 Wood Pole Management – Complete System Analysis
Background
Avista’s Wood Pole Management Department is tasked with overseeing the maintenance and repair of the wood poles
in Avista’s electric transmission and distribution systems. Part of the wood pole management program involves
inspecting all of the poles in the distribution system on a twenty year cycle and conducting maintenance as needed to
avoid future failures, which have the potential to cause an outages. Avista’s Asset Management Department has
conducted some analysis that looks very closely at the current twenty year inspection interval. The intent of this report
is to communicate the details of that analysis.
Model Assumptions
The following assumptions were made in the construction of the distribution system model
Poles
• The electric distribution system consists of 246,000 wood distribution poles
• Poles that fail will be replaced with another equivalent (45’) cedar wood pole
• Poles that do not meet code requirements are either reinforced with a steel stub or replaced with
another equivalent (45’) cedar wood pole
• The age of the poles is based on the age distribution of a representative sample
• The poles are inspected on a 20 year interval
Cross arms
• Each of the 246,000 poles has one cross arm
• The age of the cross arm is initially assumed to be the same as the age of the pole
Pin
• Each of the 246,000 poles has three pins
• The age of the pins is initially assumed to be the same as the age of the pole
Insulators
• Each of the 246,000 pole locations has three insulators
• The age of the pins is initially assumed to be the same as the age of the pole
Transformers
• There are approximately 118,000 transformers in the distribution system
• The age of the transformers is based on the age distribution of a representative sample
Lightning Arrestors
• Each transformer has one lightning arrestor
• The age of the lightning arrestor is initially based on the age of the transformer at each location
Wildlife Guards
• Each transformer has one wildlife guard
• The age of the wildlife guard is initially based on the age of the transformer at each location
Cutout
• Each transformer has one cutout
• The age of the cutout is initially based on the age of the transformer at each location
Ground Rod
• Each pole with a transformer has one ground rod
• The age of the ground rod is initially based on the age of the transformer at each location

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Model Assumptions (cont.)
Since the actual age of the distribution components is not exactly the same as the pole or transformer, the model’s
initial predictions don’t match the 2011 actual replacement quantities. The initial values and the errors can be seen in
Figure 1.

Figure 1
Error in initial calculations due to unknown age of components

It can be seen from the chart above that the model fairly closely predicts the number of replaced failed poles, stubbed
poles stubbed and transformers that are replaced (all highlighted green). The other components which have age profiles
based on either the poles or the transformers are not as accurate so the failure curves of each component were shifted
so that the predictions would more closely match the 2011 replacements. Figure 2 below, shows the actual failure data
points and the adjusted failure curve that is used by the software to calculate failures.

Figure 2
Offsetting Weibull Curve

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Analysis Results - 20 yr Inspection vs. No Inspection

The system was modeled to closely match the current scenario where each pole and its additional components are
inspected on a twenty year cycle. This case was compared to a hypothetical case where no inspection was completed.
Results from this comparison show that a twenty year inspection cycle has financial benefits to the customer. The results
can be seen tabulated in Figure 3 and graphically in Figure 4.

Figure 3
Comparison of Financial Data Between 20 yr inspection and no inspection
Figure 4
Cumulative Cost Comparison
Figure 5
20 yr Inspection vs. No Inspection - Labor Prediction Comparison
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Figure 6
20 yr Inspection vs. No Inspection – Effects Prediction Comparison
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Figure 7
20 yr Inspection vs. No Inspection - Equipment Prediction Comparison
Figure 8
20 yr vs. No Inspection - Spares Prediction Comparison

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Analysis Results - Inspection Interval Optimization

In addition to comparing our current inspection scenario to a case where no inspection is done, analysis was conducted
to see if a shorter or longer maintenance interval would be more cost effective. Five, ten, fifteen and twenty year
inspection intervals were compared. The results of this comparison show that increasing the frequency of the inspection
to approximately 10 yrs would yield financial advantages. A separate calculation was also done within Availability
Workbench to optimize the inspection interval. This calculation shows that there is a slight advantage to increasing the
inspection interval to approximately eight years. The results of this calculation can be seen in Figure 11. The charts and
figures below show the comparison between the current base case 20yr inspection interval with a 10yr inspection
interval as well as a comparison between the 10 year inspection interval and the no inspection case.

Figure 9
Figure 10
Figure 11
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Figure 12
Optimization of Inspection Interval

Figure 13
20 yr vs. 10 yr Inspection - Labor Prediction Comparison
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Figure 14
20 yr vs. 10 yr Inspection - Effects Prediction Comparison
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Figure 15
20 yr vs. 10 yr Inspection - Equipment Prediction Comparison
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Figure 16
20 yr vs. 10 yr Inspection - Spares Prediction Comparison

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Recommendations –

While the advantage is slight, all of the analysis indicates that increasing the frequency of inspection would yield
financial benefits to the customers. It may not be practical to immediately increase the inspection frequency to 10 years
but the goal should be to increase the inspection interval on a regular basis until such time as the number of yearly pole
replacements per year begins to stabilize. Although the budgetary requirements for increasing the inspection frequency
are considerably more than the current 20 year inspection frequency (See Figure 16) the increased costs will ultimately
yield financial advantages as few poles are replaced each year. (See Figure 17).

Figure 17

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