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
1. Why Assess the Risk ? 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 ? 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
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.
2. Condition Assessment OverviewApprox 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 recordedOther methodologies could be equally valid.
3. Assessment Tool FeaturesMajor 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)
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
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%
3. Assessment Tool Features Toolkit Sample Checksheet.pdf
3. Assessment Tool Features Toolkit Sample Criteria Review.pdf
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”
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.
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
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 CompletedTotal of 174 HV & LV switchboards inspectedCombined ranking assessment: Qualification data incorporated in spreadsheet; Spreadsheet data sorted by: SKM Final Ranking order (Qualitative); Plant Productivity Priority (Criticality); Assessment Score (Quantitative).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 ResultsPrincipal 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 HVSorted 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’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
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
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 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
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 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 ?