Lightning Detection – Strategies for Monitoring & Integrating Into a Blade Maintenance Program

Ben RiceSandia 2016 Wind Turbine Blade WorkshopAugust, 2016

Pattern Energy Introduction

Current Operating Capacity: 3,300 MWNumber of Turbines: 1,550Turbine Manufacturers in Fleet: Siemens (65%), Mitsubishi (10%), GE (25%)

Agenda

§ Starting Early: The In-Warranty Force Majeure Paradox§ Budgeting for Lightning§ Lightning Monitoring Strategy§ Proactive Targeted Inspections§ Periodic Sampling Inspections§ Damage Categorization & Tracking

The In-Warranty Force Majeure Paradox

Warranty Period à Lower Risk to the owner

The In-Warranty Force Majeure Paradox

Warranty Period à Lower Risk to the owner

AND…

Lower Risk à More hands-off approach with little to no self-perform maintenance strategy

The In-Warranty Force Majeure Paradox

Warranty Period à Lower Risk to the owner

AND…

Lower Risk à More hands-off approach with little to no self-perform maintenance strategy

BUT…

A Force Majeure event is not a warranty claim and is a risk ONLY to the owner

The In-Warranty Force Majeure Paradox

Warranty Period à Lower Risk to the owner

AND…

Lower Risk à More hands-off approach with little to no self-perform maintenance strategy

BUT…

A Force Majeure event is not a warranty claim and is a risk ONLY to the owner

SO…

The owner must have a maintenance strategy to identify and mitigate the effects of force majeure events as well as be able to differentiate force majeure from

turbine deficiencies and manufacturing defects

Force Majeure à Lightning Damage

Force Majeure à Lightning Damage

Lightning Damage EventsIn most regions of the U.S., lightning is an inevitability, with high probability of strikes to turbines.

Lightning Protection Systems are designed to capture the majority of lightning events and pass to ground, with the threshold for testing at 98%.

For manufacturers, lightning damage that occurs to a blade is a force majeure claim automatically, since the LPS is expected to safely pass to ground any strikes within design specifications.

Force Majeure à Lightning Damage

Lightning Damage EventsIn most regions of the U.S., lightning is an inevitability, with high probability of strikes to turbines.

Lightning Protection Systems are designed to capture the majority of lightning events and pass to ground, with the threshold for testing at 98%.

For manufacturers, lightning damage that occurs to a blade is a force majeure claim automatically, since the LPS is expected to safely pass to ground any strikes within design specifications.

Particularly for older turbines, there is no remote indication of a strike occurring, and the manufacturer has little incentive to monitor for damage that is outside the scope of the warranty

So…the owner is placed in the position of monitoring for damage at an early stage before it moves from a lower cost repair situation, to a full replacement requirement.

Budgeting for Lightning Spending

OnemonthoflightninginWestTexas!

Budgeting for Lightning Spending

Before building a project, it is useful to do a lightning risk profile making basic assumptions about:

§ Estimated strikes per turbine per year

§ Number of inspections required

§ Cost per inspection

§ LPS effectiveness rate (and therefore number of expected damages)

§ Cost per repair and replacement

Budgeting for Lightning Spending

Example (all numbers are hypothetical):

§ Number of turbines = 100

§ Estimated strikes per turbine per year = 5

§ Number of inspections required = 20

§ Cost per inspection = $500

§ LPS effectiveness rate = 99%

§ Cost per repair and replacement = $10,000 (repair) / $150,000 (replace)

Total annual budget for lightning & inspections = ~$60,000 – $150,000

Retrieving Lightning Data

Lightning Data available through Vaisala’s National Lightning Detection Network (NLDN)

§ Accessible via Vaisala directly or third party applications

§ Allows for historical lightning data with recorded metrics:

– Lat/Long coordinates of strike

– Confidence of strike location accuracy

– Max amplitude of the strike’s current (kAmps)

§ Metrics needed but missing:

– Total energy transferred by the lightning strike (Joules)

– The rise time (in seconds) from zero to peak current

Lightning Monitoring Strategy

Options Available

§ Proactive Targeted Turbine Inspections

– Identify high risk turbines for one-off inspections after major storms and weather events

– Too resource intensive to check all turbines!

§ Annual/Periodic Sample Inspections

– Intended for those turbines missed by proactive inspections

– Internal or contracted 3rd party

– Goal is to inspect a subset of the turbine population each cycle so that the full fleet is covered by the Nth cycle

Proactive Targeted Inspections

WTG 1 WTG 3WTG 2

Strike 1

Strike 2

99% Confidence Ellipse

150m

Proactive Targeted Inspections

Proactive Targeted Inspections

HighestLowestLikelihood of Damage

Lightning Monitoring Strategy

Options Available

§ Proactive Targeted Turbine Inspections

– Identify high risk turbines for one-off inspections after major storms and weather events

– Too resource intensive to check all turbines!

§ Annual/Periodic Sample Inspections

– Intended for those turbines missed by proactive inspections

– Internal or contracted 3rd party

– Ground-based, on ropes/platform, or drone

– Goal is to inspect a subset of the turbine population each cycle so that the full fleet is covered by the Nth cycle

Periodic Sampling Inspections

Periodic Inspections

Year 1 – 33% Sample Inspection (WTGs 2 & 6) --- Fleet 33% Complete

2

6

Periodic Sampling Inspections

Periodic Inspections

Year 2 – 33% Sample Inspection (WTGs 1 & 4) --- Fleet 66% Complete

1

4

Periodic Sampling Inspections

Periodic Inspections

Year 3 – 33% Sample Inspection (WTGs 3 & 5) --- Fleet 100% Complete

35

Damage Categorization & Tracking

Sample Damage Scale Categorization

Ultimately, the goal is to catch damages while they are still cost-effectively repairable, and to compile a list of turbines that need to be monitored and revisited to ensure that damage has not progressed. Both a periodic and a proactive maintenance strategy aim to achieve this goal.

No Damage Identified

WTG Taken Offline for Repair/Replacement

1 5Decreasing intervals of re-inspection for damage progression

Re-inspect in 6 months

Re-inspect in 3 months

Re-inspect in 1 month

Damage Categorization & Tracking

Periodic & Targeted Inspections

Historical Inspection Database – Tracking Results and Follow-Up Requirements

OK

OK

OK

Re-inspect6-months Re-inspect

3-months RepairBlade A

Summary

§ Lightning typically qualifies as a non-warrantable damage condition, so vigilance is important to avoid full replacement situations

§ Lightning data is available for quantifying lightning risk profiles and storm-specific analyses

§ With large turbine populations, full site inspections are impractical, so a combination of targeted proactive and sampling periodic inspections is useful in capturing damages and avoiding larger repair/replacement costs

§ Damage categorization is important in standardizing and executing re-inspection and repair work scheduling

Thank You…Questions?

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