In order to identify the specific arc flash hazard at a given piece of equipment within a given facility, an arc flash study must be performed.
Outcome of Arc flash Study?
- Identify the Arc Flash Protection Boundary (this is the closest approach allowed before PPE must be worn).
- arc flash equipment labeling
- Fault current and coordination analysis
- recommendations for PPEs
- Arc Flash Incident Energy Mitigation Strategies
How Arc flash Study carried out?
There are
several software packages available, similarly to short circuit study and
coordination study software packages, to facilitate this analysis by a qualified professional electrical engineer.
Following seven steps to be carried out to done complete Arc flash study of the facility.
1.Gathering all as built documentation of the facility
The starting point of study is to accumulate all documentation like Electrical and earthing drawing etc.
If the old drawing not found than sinle-line diagram to be made of the system.
2.Field verification as per documentation
Before loading the data from the electrical drawings into the Arc
Flash Analysis software, the drawings must be field verified. This requires a
survey of each site to verify one-line documentation and document any missing
information in order to generate an encompassing and accurate one-line.
3.Acquire load information
Before loading the data from the electrical drawings into the Arc
Flash Analysis software, the drawings must be field verified. This requires a
survey of each site to verify one-line documentation and document any missing
information in order to generate an encompassing and accurate one-line.
Equipment covers need to
come off so we can visually inspect and acquire PD (protective device)
manufacturer/types/sizes/settings, cable type/lengths, transformer impedance
values, and KVA sizes. Look below for types of equipment surveyed.
After the field survey is complete and the information on the drawings
has been verified, this information is then loaded into our software package
(Example:SKM Power Tools) to run the Short Circuit, Coordination, and Arc Flash analysis
4.Run a short-circuit study
Once the data has been loaded into software, we review the L-L-L-E and L-E line to ground fault currents against the protective device
“duty rating” to ensure the device can clear the fault.
If a fault occurs at
any given protective device, the value of the duty rating is the amount of
fault current the device can handle and clear the fault in what we call a
“bolted fault”.
In other words, if the available fault current
is less than the duty rating of the device, the device will do what it is
intended and manufactured to do (clear it).
If the fault currents are
more than the duty rating, the device will likely fail and cause an arc flash
incident.
In a properly coordinated system, the nearest protective device upstream
of the fault will clear the fault without affecting protective devices further
upstream. This will limit the impact of a fault on the overall electrical
distribution only to where the fault is located.
In order to be assured that all over current protection devices
are coordinated, it is necessary to look at the time vs. current
characteristics of each device and compare it to the characteristics of any upstream
devices.
6.Evaluate Equipment
When applicable, we provide recommendations to lower the incident energy levels including maximizing coordination.
How we do this and as mentioned in section 5 above, for those protective
devices that have the option of making setting adjustments, we can adjust for
both; good coordination and lowering of “incident energy levels”.
7.Arc flash study conclusion
Completing the Arc Flash study includes:
- Generating and applying the Arc
Flash labels
- Training of the electrical
staff
- PPEs rating and usage
- Arc flash labeling
- Training to the asset facing people
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