- General electrical safety and risk assessment.
- Arc flash analysis.
- Arc blast calculations.
- General and principal recommendations to reduce energy exposure to personnel.
- Determine required Personal Protective Equipment (PPE) level
- Offshore surveys to determine if switchboards are arc-flash certified or arc-flash proof.
- Assessment of Internal Arc classification (IAC) of switchboards and electrical equipment.
- Verify electrical equipment arc flash energy levels against applicable IEC standards.
An arc flash hazard is a dangerous condition associated with the release of incident energy caused by an electric arc.
A Flash Hazard Analysis is “a method to determine the risk of personal injury as a result of exposure to incident energy from an electrical arc flash” according to the definition in IEEE 1584. It is conducted for the purpose of injury prevention and the determination of safe work practices and selection of appropriate levels of Personal Protection Equipment (PPE) according to NFPA 70E, article 100.
The basis for doing arc flash hazard analyses is short circuit current levels, protective device delay times and system information. Based upon this information the risk of personal injury is determined as a result of exposure to incident energy.
The arc flash incident energy is mainly influenced by 3 main factors: (many other factors have impact but with less significance)
- Short circuit current
- Fault interruption time
- Distance from the arc
Risk is considered as a combination of likeliness and consequence. The arc flash analysis calculates the consequence of an arc incident in 6 energy levels ranging from 0 to extreme incident energy. The arc analysis does not consider the likeliness of an arc happening.
The incident energy level is applicable when barriers like switchboard doors are opened (open barriers) or in case of personnel presence to non Internal Arc Classified (IAC) equipment and switchboards.
Electrical switchboard testing for internal arching faults is considered of great importance for personnel safety. This type of test is called Internal Arc Classification (IAC) and is considered important for incident energy hazard evaluation. The IAC classification offers a tested level of personnel protection against arc incident energy in case of closed barriers (as tested), i.e. switchgear in normal service condition. The IEC 62271 prevails for high voltage and IEC 61641 for low voltage.
Equipment internal arc fault testing (IAC) is carried out by manufacturers on switchboards or switchgear assemblies in order to establish switchgear arc test current (kA) and arc test current duration ratings (s). The outcome of the test is a short circuit current for which the switchgear is specified for permissible arc test current duration (for 0.1, 0.5, 1 or 3 seconds). The test is based on a series of criterion like correctly secured doors and covers do not open and indicators do not ignite etc. Different standards apply to high and low voltage switchgear. For HV switchgear the test acc. to IEC62271 is normative and for LV switchgear (IEC61641) this test is not a type test or a compulsory test, it is a special test subject to an agreement between manufacturer and user. As such, installing arc flash tested switchgear or switchboards is not mandatory.
Arc flash incident energy calculations are carried out by a consultant or engineering company in order to establish the level of flash hazard if a barrier is broken in Internal Arc Classified (IAC) switchboards, or if internal arc fault testing has not been carried out. Arc flash calculations are based on previously carried out short circuit and relay protection analysis.
The power distribution system is analyzed according to single line diagrams [referenced to as SL], short circuit levels [SC] and protective device operating times [PDC] in the reference section below. The number of locations to be studied will be determined by the incident energy levels found. The analysis will start at medium voltage level for example at 13.8 kV and 6kV and work its way through 690V down to 400/230 V distribution boards until PPE level 0 (no arc flash concern) is reached. No further calculations will be carried out below these points.
The incident energy hazard calculations will be completed for normal mode considering max / min bolted short circuit current levels. The incident energy is determined by the bolted fault level and the duration of the fault.
The Flash Hazard Analysis provides the following calculation results for each location:
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Incident energy in cal/cm2
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Hazard/risk categories (required personal protective equipment category, PPE class)
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Flash protection boundary
IEEE 1584 standard establishes nine key steps in the analysis process:
Step 1: Collect system and installation data
Step 2: Determine system modes of operation
Step 3: Determine bolted fault current
Step 4: Determine the arc fault current
Step 5: Find protective device characteristics and arc duration
Step 6: Document system voltages and equipment class
Step 7: Select the working distances
Step 8: Determine the incident energy
Step 9: Determine flash protection boundary
Steps 1-3 and 5-6 are done manually by scrutinising single line diagrams, operating strategy as well as short circuit and protective device coordination (PDC) studies performed earlier. Steps 4 and 7-9 are executed in the EDSA arc flash calculation module.