arc flash study update - jodi bullinger

Arc Flash Assessment Using WindMil

Presented by: Jodi Bullinger

Cass County Electric Cooperative Fargo, North Dakota

Arc Flash Assessment Outline •  Requirements

–  NESC –  OSHA

•  Methodology •  Results

–  Primary 15 kV –  Primary 25 kV

•  Effective January 1st, 2009 – Employer shall ensure that an assessment is performed to determine potential exposure to an electric arc for employees who work on or near energized parts or equipment.

•  Employer shall provide training to all employees who work in the vicinity of exposed energized lines and parts.

NESC Requirements – Section 410

•  Exposure greater than 2 cal/cm2

–  Perform an arc hazard analysis or use the NESC table.

–  The employer shall require employees to wear clothing that has an effective arc rating not less than the anticipated level of arc energy.

NESC Requirements – Section 410

•  NEW for 2012 - low voltage (50V-1000V) arc rated clothing table.

–  Based on equipment type. –  Independent of fault current. –  Nominal Voltage Range. –  Clothing arc rating cal/cm2

–  18 inch distance from arc to employee. –  Industry testing demonstrated that voltages between

50 V and 250 V will not sustain arcs for more than 2. cycles, limiting exposure to less than 4 cal/cm2

–  Look at footnotes.

NESC Requirements – Table 410-1

•  Old Table 410-1 in 2007 NESC code book Medium Voltage (1.1 kV-46 kV). –  Nominal Voltage Range. –  Fault current (kA). –  Maximum Clearing Times (cycles). –  Clothing arc rating (cal/cm2 ). –  15 inch distance from arc to employee. –  Based on open air phase-ground arc. –  Not intended for phase-to-phase arcs or

enclosed arcs.

NESC Requirements – Table 410-2

•  1910.335(a)(1)(i) “ Employees working in areas where there are potential electrical hazards shall be provided with, and shall use, electrical protective equipment that is appropriate for the specific parts of the body to be protected and for the work to be performed.”

OSHA 1910

•  IEEE 1584 – Guide for Performing Arc-Flash Hazard Calculations –  Empirically derived model for voltages from 208v to 15 kV 3-

phase AC. •  Milsoft WindMil Arc Flash Report and Calculator

–  Uses IEEE 1584 for voltages 208 V to 15 kV and fault currents greater than 700 amps.

–  Lee method used for voltages over 15 kV and fault current less than 700 amps.

•  Milsoft Light Table •  Microsoft Excel •  ARCPRO

Tools for Determining Arc Flash Energy

•  System Voltage •  Fault Current •  Arc Fault Current •  Clearing time of upline protective device •  Arc Gap Length •  Is Arc in box or Open Air •  Working Distance

–  NESC Table 410-2 based on 15 inches.

Data determining Arc Flash

WindMil Model Requirements •  Accurate model

–  Connectivity –  Source impedances –  Updated Device definitions

•  Make sure Devices link to Light Table. •  Add transformer fusing if analyzing secondary voltages.

Create Arc Flash Project

Arc Flash Analysis Manager - Colors

Arc Flash Analysis Manager - Settings

Arc Flash Preferences

15 kV Substation Result

Hazard Level 3 Analysis

Arc Flash Calculator •  Utilities – Arc Flash

Calculator •  Voltage = 5 kV •  Fault Current < 700 A •  Clearing time: 4.2 sec

Enter Working Distance

Change fuse: faster clearing time

Reports

Global Editor Query

• Base kV >1 • Hazard Level >2 • Arc flash energy > 8 cal/cm2

•  Reviewed all 5kV and 15 kV substations. •  Reviewed areas with incident energy greater than 8 cal/cm2 or Hazard Level 3

and above. •  Compared those areas with NESC 410-2.

–  Clearing time less the 46.5 cycles at 5kA of fault current. •  Lee method used for areas where fault current less than 700 amps.

–  Not empirically derived. –  Results are conservative.

•  IEEE Method used for fault currents greater than 700 amps. •  85 % of Arc Fault used to retrieve conservative device clearing time •  Working Distance of 15 inches used initially.

Primary 5 & 15 kV Results

25 kV Substation Fault Current

25 kV Arc Flash Results – Fast Curves Off

25 kV Arc Flash Results – Hot Line Tag

25 kV Arc Flash Results *Change Working Distance = 36 inches

Primary 25kV Results •  Lee Method Used. •  Initial clearing time based on substation slow curves. •  Utilize Hot Line Tag or Non-reclose when working.

–  This can be set remotely via SCADA. –  Energized Switching done with Hot Line Stick –Increased

Working Distance. •  Setting the breaker to one FAST operation will cause

coordination issues down-line.

Conclusions •  WindMil results more conservative as compared with the

2012 NESC tables. •  Utilizing WindMil to change devices and settings to obtain

required clearing is very easy. •  IF transformer fusing not modeled inside of WindMil.

–  Use WindMil utilities to bring in fusing. –  Use NESC table 410-1. –  Create excel spreadsheet.

Contact Information

Jodi Bullinger Cass County Electric Cooperative

4100 32nd Avenue South Fargo, ND 58104

701-356-4475 jbullinger@kwh.com