RISK MITIGATION for ELECTRICAL WORK. Feb 2013 San Diego CA

Transcription

1 RISK MITIGATION for ELECTRICAL WORK Feb 2013 San Diego CA

2 Agenda I. RISK Define the Risks Arc Flash Review II. MITIGATION 3 Easy Steps New Designs Vs. Existing Systems III. DUKE UNIVERSITY EXAMPLE

3 I. Risk Shock Arc Flash - Arc Blast Equipment Damage Unplanned Outage

4 II. Mitigation Understand the Hazard Have a Plan Know your System / Equipment

5 A. Arc Flash - Review IE = Incident Energy Variables: Fault Current & Time Overcurrent Detection Devices are typically Inverse More Current = Faster Operation Lower Currents = SLOW Operation Time is a much greater influence on Arc Flash Therefore - Lower Fault Current = Higher Arc Flash Hazard!

6 A. Calculated IE Example Available Primary Fault Current =12,000A Available Primary Fault Current = 13,700A %Z = 6.36 Secondary Fault Current = 22,700A Identical Settings %Z = 6.21 Secondary Fault Current = 24,400a Incident Energy = 580 cal/cm 2 Extremely Dangerous Motor Contribution = 3,300A Motor Contribution = 3,000A 480V Switchgear Incident Energy = 16 cal/cm 2 Workable with Adequate PPE

7 A. Trip Times Example CURRENT IN AMPERES 85% Arcing Current 11,030 Amps 100% Arcing Current 12,976 Amps Breaker Trips in 15.9s IE = 580 cal/cm CURRENT IN AMPERES 85% Arcing Current 11,739 Amps 100% Arcing Current 13,810 Ampus XAM - Phase TIME IN SECONDS XBM - Phase TIME IN SECONDS Breaker Trips in 0.33s IE = 16 cal/cm A A K 10K 100K 48XAM.tcc Ref. Voltage: 480V Current in Amps x K 10K 100K 48XBM.tcc Ref. Voltage: 480V Current in Amps x 1

8 B. Safety Plan 1) NFPA 70E & or NESC: a) Require a Task Hazard Assessment b) Require Arc Flash Analysis c) Require Interpretation

9 B. Interpretation Selection of Personal Protective Equipment When Required for Various Tasks. Where selected in lieu of the incident energy analysis of 130.5(B)(1), Table 130.7(C)(15)(a) and Table 130.7(C)(15)(b) shall be used to determine the hazard/risk category and requirements for use of rubber insulating gloves and insulated and insulating hand tools for a task. The assumed maximum short-circuit current capacities and maximum fault clearing times for various tasks are listed in Table 130.7(C)(15)(a). For tasks not listed, or for power systems with greater than the assumed maximum short-circuit current capacity or with longer than the assumed maximum fault clearing times, an incident energy analysis shall be required in accordance with

10 B. Interpretation Choose Wisely: The collective experience of the task group is that, in most cases, closed doors do not provide enough protection to eliminate the need for PPE for instances where the state of the equipment is known to readily change (for example, doors open or closed, rack in or rack out). It is the collective experience of the Technical Committee on Electrical Safety in the Workplace that normal operation of enclosed electrical equipment, operating at 600 volts or less, that has been properly installed and maintained by qualified persons is not likely to expose the employee to an electrical hazard.

11 B. Interpretation Relationships with Contractors (Outside Service Personnel, and So Forth). (A) Host Employer Responsibilities. (1) The host employer shall inform contract employers of the following: a. Known hazards that are covered by this standard, that are related to the contract employer s work, and that might not be recognized by the contract employer or its employees b. Information about the employer s installation that the contract employer needs to make the assessments required by Chapter 1

12 B. Interpretation Parallel Sources vs. Closed Transition 100mS or Less AHJ determination N E

13 C. Know Your System 1. Up to Date Documentation User friendly Accurate Accessible 2. Existing Conditions Age / Condition Factor Interpret the Standards Asses Existing Conditions

14 C. Know Your System 27MW Combustion Turbine Generator Multiple Sources On-Line LOTO / Isolation Emergency Only 2.5MW Emergency Generator Designed to Keep the Power On

15 C. Documentation User Friendly / Accessible / Accurate IF REQUIRED IF REQUIRED SUBSTATION EQUIPMENT - BUILDING - LETTER NUMERIC NUMBER DESCRIPTOR NUMBER IDENTIFIER IDENTIFIER 1,2,3,4,5, EXAMPLES TX, SW, PMH, ,7549, - A,B,C, 1,2,3, 1 TX A 1 F A 3 1 PMH B

16 C. Existing Conditions Interlocking No Instantaneous Function Longer Clearing Times Ventilated Enclosures Adequate PM?

17 C. Pad Transformer Door Interlock ANSI C57.12

18 C. Existing Equipment

19 III. Duke University Comprehensive Safety Plan Excellent Documentation Thorough Analysis

20 The End Conclusions Understand the Hazards = Assessment & Studies Have a Plan = Adopt & Interpret Know your System = User Friendly, Accurate, Accessible Documentation Questions? Comments? Constructive Criticism?