Impact of Proposed IEEE 1584 Empirical Model in Comparison to Existing Arc-Flash Hazard Assessment Calculation Methods

Transcription

1 Impact of Proposed IEEE 1584 Empirical Model in Comparison to Existing Arc-Flash Hazard Assessment Calculation Methods Justin McCann P.E., MidSouth Utility Consultants Inc. Joseph Johnson, MidSouth Utility Consultants Inc. David Bobbitt P.E., MidSouth Utility Consultants Inc.

2 History of Arc-Flash Hazard Safety Standards 1970 OSHA declares electrical arc flash a recognized hazard. Set-up requirements for proper PPE. Has been amended three times in 1974, 1990, and Ralph Lee publishes The other electrical hazard: electrical arc blast burns (Lee Method) NFPA 70E Standard for Electrical Safety in the Workplace. New and revised calculation methods to complement Lee Method. Revised in 2004, 2009, and 2012.

3 History of Arc-Flash Hazard Safety Standards 2002 IEEE publishes a new standard to provide an IEEE Guide for Performing Arc-Flash Hazard Calculations (IEEE 1584). IEEE 1584 amended in 2004 and ANSI/IEEE C2, NESC first detailed an arc-flash hazard assessment method. Revised in 2012.

4 Current Standard - IEEE 1584 The IEEE 1584 as amended includes: Empirical model for calculating arc-flash incident energy Theoretical model (Lee Method) Corrections to some text errors and updates the analysis process to include experience of industry professionals.

5 IEEE 1584 Empirical Method The empirical model detailed in the IEEE Std 1584 is applicable to systems meeting the following criteria: Voltages between 208 V-15,000 V, three phase. Frequency of Hz. Bolted Fault Current between 700 A-106,000 A. Grounding of all types and ungrounded systems. Equipment enclosures of commonly available sizes. Gaps between conductors between 13 mm-152 mm. Faults involving THREE PHASES.

6 IEEE 1584 Empirical Method Variables The variables in the equations for calculating available incident energy, arcing current (full arcing current), minimum arcing current, and flash protection boundary. The standard provides ranges for many but not all variables. Utilities must select/adjust: System Voltage Available Fault Current Arc Gap Working Distance Clearing Time System Voltage (kv) >1-5 >5-15 Equipment type Typical gap between conductors (mm) Distance x factor Open Air Switchgear MCC and Panels Cable Open Air Switchgear Cable Open Air Switchgear Cable Classes of Equipment Typical Working Distance a (mm) 15 kv switchgear kv switchgear 910 Low-voltage switchgear 610 Low-voltage MCC's and panelboards 455 Cable 455 Other To be determined in field a Typical working distance is the sum of the distance between the worker standing in front of the equipment, and from the front of the equipment to the potential arc source inside the equipment.

7 Existing Empirical Method The IEEE 1584 requires that two incident energy calculations be performed for each location. Full arcing current calculation and 85% of full arcing current calculation. The cases studied in this paper compare the existing and proposed standards based on the following typical distribution system conditions: kv L-L Arc gap = 2 Working distance = 18 Open configuration (no enclosure)

8 IEEE 1584 Full Arcing Current

9 IEEE % Arcing Current

10 Proposed IEEE 1584 (P1584/D2) Substantial amounts of research and testing to create new empirical models. The Proposed IEEE 1584 Draft 2 (P1584/D2) was released to the standards association for review in July 2017, including a new empirically derived model.

11 IEEE P1584/D2 Empirical Method Voltages between 208 V-15,000 V, three phase. Frequency of Hz. Bolted Fault Current 208 V-600 V: 500 A to 106,000 A 601 V- 15,000 V:200 A to 65,000 A Gaps between conductors: 208 V-600 V: 6.4 mm (0.25 in.) to 76 mm (3 in.) 601 V- 15,000 V: 19 mm (0.75 in.) to 254 mm (10 in.) Grounding of all types and ungrounded systems. Equipment enclosures tested at various sizes based on voltage level. Faults involving THREE PHASES.

12 IEEE P1584/D2 Proposed Empirical Method Variables Utilities must select/adjust the following: System Voltage Available Fault Current Arc Gap Working Distance Clearing Time Construction Configuration of Electrodes

13 Construction Configuration of Electrodes VCB VCBB HCB VOA HOA Vertical Electrodes, Cubic Metal Box Vertical Electrodes terminated in a Barrier, Cubic Metal Box Enclosure Horizontal Electrodes, Cubic Metal Box Vertical Electrodes, Open air Horizontal Electrodes, Open air HOA Construction Configuration VOA Construction Configuration

14 Proposed Empirical Method The IEEE P1584/D2 also requires that two incident energy calculations be performed for each location. Full arcing current calculation and a minimum arcing current calculation. System Voltage more prominent in the P1584/D2. Matrices of coefficients for each construction configuration for 4 voltage ranges: Less than 600V, 600V, 2,700V, and 14,300 V.

15 Proposed Empirical Method The cases studied in the paper comparing the existing and proposed standard are based on the following assumptions: kv L-L Arc Gap = 2 Working distance = 18 Open Configuration (no enclosure) HOA and VOA electrode configuration

16 IEEE P1584/D2 Full Arcing Current - HOA Insert Full Arcing Current HOA Calculation Graph

17 IEEE P1584/D2 Full Arcing Current - VOA

18 IEEE P1584/D2 Minimum Arcing Current - HOA

19 IEEE P1584/D2 Minimum Arcing Current - VOA

20 Comparison of IEEE 1584 and IEEE P1584/D2 Incident Energy Calculations The following graphs depict the percent difference for the following four cases: IEEE 1584 vs. IEEE P1584/D2 HOA (full arcing current) IEEE 1584 vs. IEEE P1584/D2 VOA (full arcing current) IEEE 1584 vs. IEEE P1584/D2 HOA (minimum arcing current) IEEE 1584 vs. IEEE P1584/D2 VOA (minimum arcing current)

21 Percent Difference of the IEEE Std to the IEEE P1584/D2 HOA Configuration (Full Arcing)

22 Percent Difference of the IEEE Std to the IEEE P1584/D2 VOA Configuration (Full Arcing)

23 Percent Difference of the IEEE Std to the IEEE P1584/D2 HOA Configuration (Min. Arcing)

24 Percent Difference of the IEEE Std to the IEEE P1584/D2 VOA Configuration (Min. Arcing)

25 Conclusions Proposed Standard P1584/D2 empirical model incident energy calculations could be higher than those using the existing IEEE 1584 for a distribution system Calculations outside of the range of the empirical model in the proposed standard and above 1 kv will no longer be supported by the Lee Method If the P1584/D2 obtains active status, utility management and engineering teams should reevaluate their system to incorporate the new calculation methods

26 Impact of Proposed IEEE P1584/D2 Empirical Model on Arc-Flash Hazard Calculations Questions? Contact Information Justin McCann, P.E. MidSouth Utility Consultants 9180 Crestwyn Hills Drive Memphis, TN Joseph Johnson, E.I.T. MidSouth Utility Consultants 9180 Crestwyn Hills Drive Memphis, TN David Bobbitt, P.E. MidSouth Utility Consultants 9180 Crestwyn Hills Drive Memphis, TN