ARC FLASH PROTECTION
What is Arc Flash?
Simply put, ‘arc flash’ is a phenomenon where a flashover of electric current leaves its intended path and travels through the air from one conductor to another, or to ground. The results are often violent and when a human is in close proximity to the arc flash, serious injury and even death can occur.
According to NFPA 70E (the relevant standard from the National Fire Protection Association), Arc Flash is a “dangerous condition associated with the release of energy caused by an electrical arc.” It is measured in terms of arc flash incident energy E (AFIE), which is used to determine the level of Personal Protective Equipment (PPE), and in terms of an arc flash protection boundary (FPB). Arc Flash Hazard is the term used to define the danger to people working on live parts.
Arc Flash Hazard Analysis defines the procedures which limit the damage of electrical arcs on personnel and, by measuring the released energy, defines the risk areas and determines the relevant level of the personal protective equipment (PPE).
An electrical arc occurs whenever there is a loss of insulation between two conductive objects at sufficient potential (voltage). Near high power electrical equipment, such as transformers, service entrance switchgear or generators, the short-circuit power available is high and consequently so is the energy associated with the electrical arc in case of a fault. The energy released by the arc due to a fault creates a rise in the temperature and pressure in the surrounding area. This causes mechanical and thermal stress to nearby equipment and creates the potential for serious injuries in the vicinity.
The physical effects of an arc flash are:
- Pressure wave in the environment where the arc is generated
- Heating of the materials coming into touch with the arc flash
- Potentially harmful light and sound.
Personnel hazards due to the release of energy generated by an arc event may include:
- Injuries due to ejection of materials
- Damage to hearing and to eye-sight
- Inhalation of toxic gases
The high temperature levels of the gases produced by the electrical arc and the expulsion of incandescent metal particles may result in severe burns. Flames can cause all types of burns, up to carbonization; the red-hot solid metal fragments can cause third degree burns, superheated steam causes burns similar to hot liquids and the radiant heat generally causes less severe burns.
- Injuries due to ejected materials
The ejection of metal particles or other loose items caused by the electric arc can result in severe injuries to the most sensitive parts of the human body, like the eyes. The materials expelled due to the explosion produced by the arc may penetrate the cornea. The extent of the lesions depends on the characteristics and kinetic energy of these objects. Also, the eye area can sustain injuries to the mucosa, such as the cornea or retina, because of the gases released by the arc and the emission of ultraviolet and infrared rays.
As already mentioned, the electric arc is a true explosion, whose sound may cause permanent hearing loss.
- Inhalation of toxic gases
The fumes produced by burnt insulating materials and molten or vaporized metals can be toxic. These fumes are caused by incomplete burning and are formed by carbon particles and by other solid substances suspended in the air.
- Referenced Global Codes and Standards Addressing Arc Flash Analysis & Protection
The Standards dealing with prevention of arc flash and its effects are:
- OSHA 29 Code of Federal Regulations (CFR) Part 1910 Subpart S,
- NFPA 70-2008 National Electrical Code,
- NFPA 70E-2009 Standard for Electrical Safety Requirements for Employee Workplaces,
- IEEE Standard 1584-2008 Guide for Performing Arc Flash Hazard Calculations.
The standards give the following guidelines:
- Defining a safety program with clear responsibilities
- Procedures for arc flash hazard assessment
- Defining appropriate personal protective equipment (PPE) to be provided for the employees;
- Training program to sensitize employees regarding arc flash hazards
- Choosing suitable tools for a safe workplace
- Labeling equipment; labels shall be placed on the equipment by the plant owner and not by the manufacturer. The labels shall indicate the minimum protective distance, the energy level which can be released and required personal protective equipment (PPE).
- How to Minimize Arc Flash Hazards to ALARP*
The standards state that before working on electrical equipment, the equipment must be de-energized. This solution eliminates arc flash hazard but is sometimes difficult to apply. To minimize the arc flash effects, it is necessary to limit the energy released so that personnel are not in harm’s way.
Measures may be divided into passive measures and active measures. Passive measures limit the effects of the incident energy, such as distance and barriers. Active measures limit the incident energy level.
- Passive measures
Passive measures can be barriers or procedures as enumerated below:
- Arc-proof switchgear: designed to direct the arc energy to vent out the top of the switchgear, and limit the energy directed to the front
- Remote control operation of protection and switching devices: keep personnel at a safe distance from the equipment
- Closed door racking-in/out of the withdrawable circuit breakers: Most OEMs for circuit breakers allow closed door operations and have their primary connections isolated by shutters
- Remote or longer operating mechanisms so that racking-in/out operations can be carried out at a safe distance
- Barriers between personnel and equipment during racking-in/out or opening/closing operations
- Reduction of the short-circuit current by disconnection of unnecessary power supply sources; for example, disconnecting parallel transformers and opening bus ties
- Remote control devices for racking-in/out of the circuit breaker at a safe distance.
- Active Measures
To reduce incident energy level and increase the level of protection to personnel and equipment, GIL does the following in the design phase of our switchgear line;
- Arc-Flash Hazard Analysis: The arc flash hazard analysis is the process to determine the risk category, the level of the PPE required and to define all the measures for minimizing personnel exposure to hazardous conditions. This analysis requires knowledge of the short-circuit currents and the clearing time of the protective devices used or to be used.
- Flash Protection Boundary Calculations: this involves a mathematical approach to determine the distance from the live equipment from which the personnel can only be affected by a curable, second degree burn (NFPA 70E 130.3(A))
- Detailed Protection & Coordination Studies: this involves the development or deployment of a protection scheme with timely response to fault-clearing. The time-selectivity and definition of protection zones must be fastidiously carried out.
One of the most important measures we take at GIL Automations in delivering high quality, and safely operable systems ‘that work’, is to partner only with OEMs with global footprint and relevance, with high quality standards. We can always bank on their support to deliver according to global standards. Our Engineering teams are also second to none; as we pride ourselves in giving 100% customer satisfaction. Below are pictures of some of our switchgears (2000A Low-Voltage Switchgear), both in design and in-operation states;
Design phase of 2000 Amps Switchgear
Design phase of 2000 Amps Switchgear
2000 Amps Switchgear in operation
Our type-tested assemblies are rugged, designed to meet even the strictest of standards; both locally and on the global scene.
At GIL Automations, we pride ourselves at being the forefront of technology deployment and innovations around the globe; and as such, possess a world-class facility for the design, building, maintenance and/or upgrade of MV and LV Switchgears. In addition to Arc-Flash studies, we also carry out studies (Load-Flow, Short-circuit, Protection & coordination studies, Electrical System Audits and so on) to improve Electrical Systems. Our clientele spans the upstream and downstream sector of the Oil & Gas Industry, Manufacturing, and Power/Energy Industries.
GIL Automations as a premier systems integrator, in partnership with many world-leading Original Equipment Manufacturers (OEM’s), remains committed to providing support to all our clients on the implementation of innovative systems that work.