Arc flash is a serious safety issue for electrical maintenance, and Schneider Electric is taking the initiative on this issue. Schneider says its Virtual Main Arc Flash Mitigation system is a new concept which reduces arc flash energy across the entire low-voltage switchgear, rather than just reducing energy levels for downstream equipment as largely seen in the past. It’s designed to improve worker safety, enhance electrical system reliability, and help organizations comply with new standards.
Extending to the low-voltage switchgear and switchboards has typically been more difficult to address. However users can be subjected to dangerous levels of arc flash incident energy when low-voltage switchgear is fed directly from a power transformer. The system reduces arc flash energy on low-voltage switchgear and switchboards, including the main incoming power distribution switchboard.
Components of the Virtual Main Arc Flash Mitigation System include:
- An engineering study to evaluate the optimum settings for the relays and circuit breakers in the unit substation. Optimizing the circuit breaker settings improves the reliability of service while assuring a reduced arc flash level at the substation. This is done by setting the virtual main relay to operate fast enough to reduce arc flash energy while operating slower than the downstream circuit breakers (circuit breakers closest to the fault).
- A switching device with fault interruption capability on the high-voltage side of the service transformer. If the high-voltage disconnecting device does not have fault interrupting capability, a circuit breaker or other vacuum interrupter can be retrofit in place. When the disconnecting means that is located on the high voltage side of the transformer trips, the entire low voltage equipment including the bussing at the incoming line section of the switchgear, is de-energized. This prevents the possibility of propagation of arcing fault within the switchgear.
- Three relaying class current transformers installed on the secondary side of the service transformer in the transformer compartment. The current transformers are installed in the transformer compartment (not the switchgear enclosure) to minimize the possibility of arc propagation beyond the current transformers.
- A self-contained relay package including a microprocessor-based relay and the necessary terminal blocks, pilot lights, and selector switches. The self-contained package is easy to install and connect. It is factory wired and tested, minimizing the required shutdown in the field.
The dangers of Arc Flash
The solution comes at a time when electrical safety and arc flash protection are increasingly top of mind for a wide range of organizations, including commercial buildings, industrial plants, data centers, and government and healthcare facilities.
When an electrical arc occurs, employees working on electrical equipment without adequate Personal Protective Equipment (PPE) risk serious injury or death. Even someone standing more than 10 feet from the fault source can be fatally burned. According to the American Society of Safety Engineers, more than 3,600 workers suffer disabling electrical contact injuries annually. Check out 10 Arc Flash Prediction and Prevention Myths for more information.
Schneider’s Virtual Main Arc Flash Mitigation System helps organizations comply with new standards from the Occupational Safety and Health Administration (OSHA) and the National Fire Protection Association (NFPA). Some of those rules were discussed in an Industry Perspectives column in September 2012. One of those new standards is NFPA 70E which requires organizations to implement arc flash protection boundaries.