8. 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.
9. 1. Why Assess the Risk ?
Arc Flash Exposure Consequence
Arc Flash
Probability Minor Moderate Major Severe Critical
Moderate High Extreme Extreme Extreme
Most Likely
Moderate High High Extreme Extreme
More Likely
Low Moderate High High Extreme
Likely
Low Low Moderate High High
Unlikely
Low Low Low Moderate Moderate
Very Unlikely
10. 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.
13. 3. Assessment Tool Features
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
14. 3. Condition Assessment Audit Protocol
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%
17. 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”
23. 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
24. 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.
25. 3. Stage 1 ‐ Audit Protocol Agreed
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
26. 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.
30. 3. Stage 1 ‐ Audit Completed
What 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
32. 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
33. 5. Arc Flash Critical Learning’s
Critical 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
34. 6. Risk Assessment Outcomes
The 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
35. 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.
36. 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
37. 6. Risk Assessment Outcomes
Consequence
Probability Insignificant Minor Moderate Major Severe
Cat 0 Cat 1 Cat 2 Cat 3 Cat 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
40. Case Discussion
Was this an accident waiting to happen or “Just one of those things” ??
41. Case Discussion
• What have YOU done?
• What could YOU do on
your site?
42. Case Discussion
Poor Capability Poor Regulatory Compliance
Thermal and magnetic stresses Arc fault containment design
Containment of arcing fault Safety interlocks
Switchroom clearances
Poor Operability (User Safe working environment
Interface)
Manual racking and/or spring
charging Residual Risk Uncommunicated
Open panel access requirement Was arc flash energy considered ?
Was residual risk of containment
communicated ?
Poor Maintenance
Adequate PPE and signage
What went wrong and why ?
Procedures
Why was breaker fault not
discovered and repaired ?