A Practical Arc Flash Risk Assessment Strategy
8th August 2012
Part 1: A Practical Arc Flash Risk Assessment Strategy
Overview
1. Why Assess the Risk ?
2.Condition Assessment Overview
3. Assessment Tool Features
4. Risk Assessment Outcomes
1. Why Assess the Risk ?
1. Why Assess the Risk ?Where should I spend the money and effort ? PPE quick and easy but may not be effective for all faults
New switchboards effective but costly, time consuming to install
Remote switching good but racking/charging still a danger
Protection mods improve detection but degrade security supply
Protection mods still require fast and capable circuit breakers
Arc faults present significant danger to man and machine
OHS Regulations require risk assessment
Aust Stds require arc flash consideration in design
Available procedures target consequence and PPE
1. Why Assess the Risk ?
Any assessment of risk must include both ‘likelihood’ and ‘consequence’ factors
Arc Flash Evaluation provides a measure for ‘consequence’ of arcing faults
A physical condition assessment of the switchgear can provide a measure of ‘likelihood’ of arcing faults occurring
Combining arc flash evaluation and physical condition assessment can help determine overall risk.
1. Why Assess the Risk ?
1. Why Assess the Risk ?
Arc Flash Probability
Arc Flash Exposure Consequence
Minor Moderate Major Severe Critical
Most Likely Moderate High Extreme Extreme Extreme
More Likely Moderate High High Extreme Extreme
Likely Low Moderate High High Extreme
Unlikely Low Low Moderate High High
Very Unlikely Low Low Low Moderate Moderate
2. Condition Assessment Overview
SKM currently use a simple methodology for condition assessment of multiple SwBds:
visual inspection of the switchboard and environment, Review of operating history, maintenance records &
drawings Interview of responsible site personnel
Allows multiple SwBds to be assessed and ranked quickly.
Approx 50 criteria elements evaluated for each swbd installation.
This is a Fault Exposure Likelihood assessment tool, NOT a maintenance tool Does NOT use statistical methods BUT operational/maintenance issues are recorded
Other methodologies could be equally valid.
2. Condition Assessment Overview
3. Assessment Tool Features
Major Switchboard Consideration Groups (affecting safety & condition):
Age & Fault Rating (Considered most Critical) Environment (Affecting SwBd Deterioration) Design and Installation (Capability & Design Safety) Service History (Maintenance/Documentation) Operational History (Loading/Switching/Failures) Protection Systems (Type/Condition)
Desirable Protocol Considerations: Must allow for visual inspection only
Simple identifiable checklist items
Minimal interpretation confusion
Easy criteria evaluation
Simplified item scoring
Score to include weighting for important items/elements.
Note: This is Not an exact science. Can be Tailored
3. Assessment Tool Features
Criteria Scoring– Three level process:
1. Criteria Element compliance score: 0, 1, 2; (best to worst)2. Criteria Element weighting multiplier: 0% to 100%;3. Weighted compliance score totalled for each switchboard;
– Possible scoring range: 0 to 200.
Example Critical weighting criteria:• Age 15%• System/Design Fault 15%• Failure History 10%• Loading 5%• Spares Availability 5%• Balance 54 Elements 50%
3. Condition Assessment Audit Protocol
Toolkit Sample Checksheet.pdf
3. Assessment Tool Features
Toolkit Sample Criteria Review.pdf
3. Assessment Tool Features
4. Risk Assessment Outcomes SwBd condition “Likelihood” now quantified as a numerical
value
Multiple SwBd condition values can now be compared and ranked for attention.
Condition “Likelihood” and arc flash “Consequence” can now be combined into a Risk Matrix for mitigation planning.
The actual task can now also be considered vs the “risk”
Exposure Risk Assessment Matrix Example.pdf
4. Risk Assessment Outcomes
Questions and Discussion
Part 2: Recent WA Case Study
Introduction1. Hazard Recognition
2. Management Resolve
3. Protocol Agreed
4. Condition Assessed
5. Arc Flash Assessed
6. Critical Learnings
1. Management Hazard Recognition
Aging switchboards
Rising fault levels
Deterioration in mechanisms
Higher maintenance costs & delays
Operator concerns
Occurrence of actual arc faults
Personnel injury from new switchboards
2. Management Decision
Progressive replacement or upgrade of all suspect swbds.
Highest risk boards to be identified for schedule & finance
Safety & Condition Assessments to be undertaken• Stage 1 ‐ Physical condition assessment (Likelihood)• Stage 2 ‐ Arc Flash assessment (Consequences)
Assess for condition/safety/reliability NOT life extension
3. Stage 1 ‐ Audit Protocol Agreed Criteria and Checklists developed based on:
Past experience of switchgear and minerals processing Recent condition audits for similar process site Knowledge of client requirements
Main Protocol Considerations: 150+ switchboards, 12 week time frame Multiple rotating inspection teams Must allow for visual inspection only Simple identifiable checklist items Minimal interpretation confusion Easy criteria evaluation with simplified scoring Weighted scoring for critical items/elements.
This matched the capability of the in‐house Assessment model
Minor Changes made:
Check Lists were refined to suit client preferences
Plant Criticality factor included
Priority Ranking for Condition Assessment modified
3. Stage 1 ‐ Audit Protocol Agreed
3. Stage 1 ‐ Audit Protocol Agreed
Client Preferred Condition Priority Ranking
• Group A – Unacceptable safety/commercial issues – replacement 0‐2yrs.
• Group B – Major commercial/safety risk issues – replacement 2‐5yrs.
• Group C – Minor commercial/safety risk issues – replacement 5yrs +.
• Group D – Safe to operate, but not arc fault contained. Address by risk mitigation.
• Group E – Safe to operate, no upgrade works required.
3. Stage 1 ‐ Audit Protocol Agreed
Switchgear Condition Assesment Checksheet Rev 6_SKM Logo.pdf
3. Stage 1 ‐ Audit Protocol Agreed
Condition Assessment Checksheet Rev 6_wer.pdf
3. Stage 1 ‐ Audit Completed
Qualification data incorporated in spreadsheet;
Spreadsheet data sorted by: SKM Final Ranking order
(Qualitative);
Plant Productivity Priority (Criticality);
Assessment Score (Quantitative).
Total of 174 HV & LV switchboards inspected
Combined ranking assessment:
Upgrade Order & Summary Overview.pdf Detailed Ranking Assessment Logo.pdf
3. Stage 1 ‐ Audit CompletedWhat did we find ?
Condition Assessment Summary:– Switchboards inspected 174– Priority group A 0‐2yrs 37– Priority group B 2‐5yrs 58– Priority group C 5+ yrs 56– Priority group D mitigation 22– Priority group E safe 0– Non grouped decomm 1
– High Thermally loaded >80% 3– High Fault level >90% 32– High Fault level >100% 17
4. Stage 2 ‐ Arc Flash Evaluation Results
Principal Findings of Arc Flash Assessment – 173 swbds
No definable relationship between voltage and arc flash “consequences”were observed but Very High (Cat4+) more common at HV
Sorted by Voltage
Seven (7) switchboards initially required higher than Category 4 PPE (40 cal) at 0.5m – Reduced by modifying settings
4. Stage 2 ‐ Arc Flash Evaluation Results
Safe working distance without PPE 6.0 m for 92% of switchboards
13 Switchboards unsafe to approach at more than 10m without PPE. (probable accuracy limitations)
Note 1: Assumes primary protection operates correctly
(Otherwise Double Jeopardy Rating Applies)
Note 2: Assumes live bus work or power terminals are exposed.
Note 3: IEEE 1584 has accuracy limitations
5. Arc Flash Critical Learning’sCritical Learning from Arc Flash studies for PPE Consideration:
Category 3 (25 Cal) PPE adequate for approximately 80% of all switchboards at 500mm.
Specified ratings for some swbds assume normal operating configuration. (but care required)
Most common personnel injury due to Arc Flash is to face, arms and hands.
LV arc faults are just as dangerous as HV faults
6. Risk Assessment OutcomesThe following outcomes have been achieved to date:
All Client swbds audited for condition & arc flash hazards.
Prioritised upgrade list prepared for funding & scheduling.
Dedicated Switchboards Project Team established
Several high risk switchboards already replaced
Others in process
Five year plan in place with forward funding
6. Risk Assessment Outcomes
Short term mitigation for 11 Cat 4+ swbds implemented to reduce arcing time or current:
Enabled/adjusted high set element (instantaneous element) to trip for the calculated Arcing current
Changed out relays in some instances with relays having a ‘hi‐set’element.
Modified system configuration to reduce parallel feeds
Note: Protection setting mods for max arc flash protection can reduce reliability of supply by limiting grading.
6. Risk Assessment Outcomes Action profile raised with workforce.
Increase control of unauthorised access
Flame Resistant clothing trialled by volunteers
PPE Workshops undertaken • Cat 2 FR clothing made standard for all EW’s• Arc flash records to be strictly maintained• Short form records to be located in subs• Isolations to be implemented in accordance to risk• Preferred signage for swbds agreed• Training program was developed
6. Risk Assessment Outcomes
ProbabilityConsequence
InsignificantCat 0
MinorCat 1
ModerateCat 2
MajorCat 3
SevereCat 4
Group A (0-2 Yrs) Moderate High Extreme Extreme Extreme
Group B (2-5 Yrs) Moderate High High Extreme Extreme
Group C (5+ Yrs) Low Moderate High High Extreme
Group D (Mitigate) Low Low Moderate High High
Group E (Safe) Low Low Low Moderate Moderate
6. Risk Assessment Outcomes
Switchboard Sticker Layout _2_.pdf
WHERE TO FROM HERE ??
Case Discussion
Was this an accident waiting to happen or “Just one of those things” ??
Case Discussion
• What have YOU done?• What could YOU do on
your site?
Case Discussion Poor Capability
Thermal and magnetic stresses
Containment of arcing fault
Poor Operability (User Interface) Manual racking and/or spring
charging
Open panel access requirement
Poor Maintenance What went wrong and why ?
Why was breaker fault not discovered and repaired ?
Poor Regulatory Compliance Arc fault containment design
Safety interlocks
Switchroom clearances
Safe working environment
Residual Risk Uncommunicated Was arc flash energy considered ?
Was residual risk of containment communicated ?
Adequate PPE and signage
Procedures
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