Three-C Electrical Company, Inc.

Three-C Restores Power After Switchgear Explosion

Three-C Electrical recently responded to an emergency call from a light industrial company. They had suffered an explosion in their Main 5kV switchgear and were without power to their entire site. Our initial investigation found that one of their 5kV switches had experienced an arc fault and subsequently went to ground. The resulting arcing and fire had compromised the rest of the switchgear, the medium voltage cables, site padmount transformer, and several low voltage switchboards. In addition, the three single phase utility transformers had overheated and were damaged by the event. The company's entire power system was destroyed.

Action Required: 3C responded immediately.  While one crew was assessing the damage and developing a plan to restore normal power, a second crew began the work of providing temporary power to the site. We quickly sourced and installed large temporary generators that were connected at the secondary side of each transformer. One location required power at 600 volts. This was handled by providing a 480 volt to 600 volt transformer along with the generator.  In total, five generators and one transformer were installed within 24 hours of the initial power outage. This was a total of almost 3 MVA of supplied capacity. The customer was operating with temporary power for almost 3 weeks.

Recommendations: 3C’s Engineers and Project Managers were busy putting together a plan to restore the normal power feed. We quickly determined that the existing switchgear would need to be completely replaced. Because of the short time frame we were working with, new switchgear was not an option. We located a suitable replacement for the customer on the used market. This switchgear was completely re-furbished, reconfigured to the new specifications, and shipped to the site within 9 days. Once on site, 3C engineered the new power system including the metering transformers, fuses and ground grid required by electrical code and the utility standards for protection and utility grade metering.

Site Work: While the replacement switchgear was being re-worked, the site was prepared to receive it. Our crew was able to remove the old switchgear and the old concrete pad, replace the ground grid, install underground conduits (all cables had been direct buried previously), and re-pour a new pad prior to arrival of the new switchgear.

3C also needed to test all of the affected switchgear during the reconstruction. Our testing included the five transformers, 6 cable circuits, 8 switchboards, and a large number of circuit breakers to ensure that these critical components were not compromised by the event. We determined that one transformer, four of the six cables circuits, and numerous circuit breakers all needed to be replaced. Within 6 days, we completed the testing and required replacement of components before the new switchgear arrived. This was quite a feat considering that one of these components was a 500kVA padmount transformer that had to be sourced, shipped, tested and the old one removed prior to installation.

Results: The new switchgear arrived and was placed on the new concrete pad by crane. 3C connected cables and the control circuits to the switchgear and completed the acceptance tesing. Total time between our first arrival on-site and restoring power was 21 days. This would be quite an accomplishment any time of year but even more so considering this was done over the Christmas and New Year's holiday.