Page 38 - Occupational Health & Safety, June 2017

ELECTRICAL SAFETY
service transformer, can reduce the arc flash energy on the entire switchgear, including the main incoming section. The system is de- signed to trip an existing upstream fault breaking device, often a medium-voltage circuit breaker or other vacuum interrupter. Ad- ditional features that help further reduce energy or maintain selec- tive coordination may be added, such as:
1) A maintenance selector switch, which temporarily lowers the instantaneous short circuit current setting. The maintenance setting lowers the available arc flash incident energy and temporar- ily forfeits selective coordination.
2) Zone-selective interlocking with downstream branch circuit breakers in the switchgear eliminates the need for the maintenance selector switch. Arc flash energies can be permanently reduced with zone-selective interlocking.
Removing Workers From Harm’s Way
De-energizing equipment does not absolve the facility from the responsibility of performing an arc flash analysis or providing the necessary personal protective equipment (PPE). OSHA and NFPA have rules that prohibit energized work. In order to establish that a circuit is de-energized, the circuit must be approached to verify that it has been de-energized. Until then, the circuit must be con- sidered energized per NFPA 70E and the worker who performs the verification test must wear full PPE. Hiring contractors to per- form electrical work does not absolve the facility from performing the calculations and providing the arc flash exposure levels to the
contractor’s workers. The following arc flash mitigation solutions remove workers from the location of exposed energized parts or place a barrier between them and energized parts.
Infrared Viewing Windows
Having infrared (IR) windows permanently installed into electri- cal equipment enables IR scans to be performed without removing equipment covers, potentially saving the worker from exposure to hazardous energy.
Online Temperature Monitoring
Online temperature monitoring, via wireless sensors, provides continual access to critical connection points where traditional thermography cannot be used. The sensors are installed during a planned outage and can be used in equipment with high arc flash ratings without a risk of danger to personnel or equipment.
Remote Racking System
A remote racking system (RRS) allows circuit breaker racking op- erations to be performed via a control panel located away from the cell, removing the operator from manual contact with the circuit breaker. If the operator controlling the RRS is located outside the arc flash boundary, the need for PPE is eliminated.
Antony C. Parsons, Ph.D., P.E., is a Senior Staff Engineer for Schnei- der Electric specializing in electrical power distribution systems.
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