Stray current – A big data issueDavid Stuart Smith and Josh Symonds

Outline

1.What is Stray Current?2.Why so much data?3.Taming the data4.What might be hiding in the

data?5.Conclusions© Arup

What is stray current?

Measuring stray current interference on utility assets

What a raw recording looks like

The magnitude of the data gathering

• Ten’s of buried utility assets• Pre and post construction• Post energisation• Recording the potential on each for at least 24hrs at 5s intervals

What we want to know pre-energisation• Are there pre-existing non-

compliant interference potentials?

• Where are they coming from?

• Have we successfully resolved the pre-existing interference?

What we want to know post-energisation

• Is the light rail causing non-compliant interference potentials?

• If so why? Where’s the leak?• Have we successfully fixed it?• Are we sure that there is not a new

external source of interference?

Without a powerful tool to manage the data, the answers to these questions are not going to come easily

What do we need to do in order to understand what is happening with stray current interference on utility assets?

• Record the data• Import the data into the database• Display and analyse the data

Recording the data

This should be the simple bit…..• Clock incorrectly set• Wrong scale factor• Poor connection – missing data• Different data file formats

Stray Current Visualiser – Overview

• Project setup• Adding in and managing assets• Importing and managing series data• Displaying the data and derived quantities as a time-series• Annotate and “revise” the data• Display as a “heat map”

Project setup

Adding in assets

Importing series data

Displaying the data as a time-series

Interrogating the data as a time-series

Displaying the data and derived quantities as a time-series

Heat map

Annotate and “revise” the data

Why compare different series?

• The voltage along the rails varies from point to point – highly correlated interference measurements probably indicate a single source of the interfering potential.

• If the interference on nearby assets is quite different then asking why is probably useful.

Why calculate average anodic and average cathodicshifts from quiescent?

• The average anodic shift is what drives the possible corrosion of the utility asset.

• The average cathodic shift is relevant for coated assets and lead assets.

Correlations

• Post energisation correlation with rail to reference can establish the possibility of causality – no correlation, no causality.

• Average anodic shift relates to the magnitude of the impact

Traps and avoiding them• Aliasing – if the logger does

not have an appropriate anti-aliasing filter 50Hz interference can look like something varying over seconds or 10’s of seconds, much like traction current!

• Reference ½ cell location – as close as possible to the utility asset and in exactly the same place for repeatability –photograph the location!

Sources of non-traction interference• Tides• CP systems• Industrial processes• Natural geo phenomena

(“telluric” current)

Conclusions

• Recognising this early as a “big data” situation will potentially save much frustration and re-tracing of ones steps

• Having the right tool to manage the data will make life much easier

Questions?