An arc flash evaluation that Rozel performed identified a high arc flash hazard. After analysis, we were able to recommend a simple setting change which ultimately saved the day and likely prevented a great amount of damage.
You can see in the one line drawing below that the main breaker and the gear itself had an arc flash value greater than 90 cal/cm^2 @ 18" (many additional breakers on this gear are not shown). You can also see that MDP2 K1 is a power factor correction capacitor installed directly connected to the bus with no protective device mounted to MDP2.
Our recommendation was to change the Instantaneous setting on MDP2 - MAIN from "7" (28000A) to "3" (12000A). In order to make this recommendation we first looked at the TCC (time current characteristic) of the main breaker and all of it's downstream overcurrent protective devices (breakers and fuses). This TCC does show the additional breakers on MDP2 which were not shown on the one line drawing above. Here is what we saw:
By dialing the Instantaneous down to a 3, we achieved the following results:
The factory followed our recommendation, which was very simple. A turn of a screwdriver implemented this.
Once work was complete, the power was reapplied... and the main breaker had an instantaneous trip.
The install went as planned however the new capacitor was faulty. This bad unit caused a bolted fault directly on the MDP2 bus, this in turn caused the main breaker to trip.
The damage was minimal and isolated to the faulty capacitor. The people in the room while the gear was energized were not injured. Prior to the Instantaneous setting change however, this same fault could have caused injuries to people over 20ft away. Additionally a fault at the previous arc flash level would have most definitely destroyed electrical equipment and brought long downtime to the factory.
It is impossible to tell if your equipment is at it's safest arc flash hazard without an evaluation. Your employees must be trained to recognize these hazards and understand how to work around them safely. Rozel can help with both. Contact us today.