Fig. 1.9. Worked example of a Hawk IR Sightglass heat-flux calculation based on existing test data;

Background

Hawk IR Sightglass is tested on a host piece of Arc-Resistant equipment in accordance with C37.20.7-2001.

Nominal Minimum Voltage – 7.2kV

Maintained Fault Current – 40kA

Approximate phase-to-phase Arc-Gap – 5”

Distance of IR Sightglass optic from Arc – 17.75”

Arc Data (Calculated)*

Arc Column Area – 143.4421 sq. inches

Arc Diameter – 9.13187 inches

Arc Power in Watts – 5937500 Watts

Arc Power in Calories per Second – 1418469

Heat Flux on Surface of Arc – 1533.146 cal/cm2 –sec

Heat Flux on Sightglass – 86.52 cal/cm2 –sec

Total Calories per Sq. Cm. at Sightglass -  43.2 cal/cm2 –sec

THIS EQUATES TO A NFPA70E LEVEL 4  HAZARD/RISK CATEGORY

*data aquired using Duke Power Heat-Flux calculator