David Sweeting

Arcing faults in electrical equipment

Electrical incidents that result in significant injuries to people are often the result of substantially unconstrained free-burning arcing-fault currents within electrical equipment. It is necessary to understand the nature of these arcs and be able to quantify the parameters before it is possible to really comprehend what is actually happening inside arcing faults and how they cause injuries to personnel in the immediate vicinity. This requires an understanding of the energy dissipation and the energy transfers in the vicinity of these uncontrolled arcs. This paper sets out to describe the physics of arcing faults and uses this to describe the energy transfers within an arcing fault. This provides a basis for describing the potential energy transfers to personnel in the vicinity of an arcing fault. This includes arc-root movements on humans and the transfer of the arc out of the body, which occurs in milliseconds. This has a significant impact on ventricular fibrillation and personal protective equipment for high-voltage workers.

Energy transfers within arcing faults in electrical equipment

An arcing fault often develops from an insulation failure within electrical equipment. Arcing faults are substantially unconstrained free-burning arcs within electrical equipment. In order to assess the hazards of arcing faults to personnel in the immediate vicinity of the fault it is necessary to understand their nature and be able to quantify the hazards. This involves an understanding of the energy dissipation and the energy transfers in the near vicinity of these uncontrolled arcs. This paper sets out to describe the physics of arcing faults and uses this to describe the energy transfers within an arcing fault. This is the basis for describing the potential energy transfers to personnel in the vicinity of an arcing fault.

Applying IEC 60909, Fault Current Calculations

Rather than the short-circuit current that would occur in a specific instance, International Electrotechnical Commission 60909 derives the maximum and minimum prospective short-circuit currents in a system for each specific location and time. This is reported using a series of parameters which relate to the rated short-circuit current of equipment and the tests required on equipment to prove that rating. The influence of arc voltage on short-circuit currents is then discussed.

Testing PPE for Arc-Hazard Protection IEC 61482-1 Test-Rig Evaluation Including Proposed Changes

The IEC Standard 61482–1 describes procedures for measuring the thermal performance of fabrics and garments intended for use in clothing for workers exposed to electric arcs. This paper demonstrates that the tests in this standard fail to produce controlled laboratory conditions. The dominant magnetic and thermal buoyancy forces have been minimised leaving two undefined and uncontrolled forces to randomly dominate arc motion, plasma flow and thermal stress. The tests also produce hazards significantly different to those facing victims in real situations. The velocity of the plasma impinging on a victim is incorrect. The color of the radiation is incorrect. The molten metal droplets impinging on the victim are incorrect. The tests only consider clothing stretched over a surface whereas loose and un-backed cloth suffers considerably more stress. In order to emulate real arcing faults, it will be necessary to use parallel copper and aluminium electrodes. In addition for high voltage personnel a “pop-out” test needs to be developed because a fault current that starts by entering and exiting the body becomes an arc inside the clothing.

Protecting your staff from arcing hazards

The characteristics and components of an arcing fault are described and the hazards caused by arcing faults are then listed in order of severity. Hazard control measures are then discussed in the order described in Table 1 of ANSI Z10. Designing the system to fail safely and separating the person from the energy are treated under the heading of eliminating the hazard. Installing arc contained switchgear, retiring old equipment and designing the system to be maintainable are considered under substituting less hazardous equipment. The engineering controls considered include; Displaying measured values remotely and taking into account the probability of the event. The main engineering control is carrying out the correct protection studies by calculating maximum and minimum fault currents for single-phase, two-phase-and-earth and three phase faults. It is necessary to ensure the protection works with arcing fault currents. The need for precision on warning and information labels is emphasized. Under administrative controls hazard assessments and the need to consider live work are discussed together with access control, work procedures and training. Finally PPE requirements are discussed..

Arcing Faults in Electrical Equipment

Electrical incidents that result in significant injuries to people are often the result of substantially unconstrained free-burning arcing fault currents within electrical equipment. It is necessary to understand the nature of these arcs and be able to quantify the parameters before it is possible to really comprehend what is actually happening inside arcing faults and how they cause injuries to personnel in the immediate vicinity. This requires an understanding of the energy dissipation and the energy transfers in the near vicinity of these uncontrolled arcs. This paper sets out to describe the physics of arcing faults and uses this to describe the energy transfers within an arcing fault. This provides a basis for describing the potential energy transfers to personnel in the vicinity of an arcing fault.

Testing PPE for arc hazard protection IEC 61482–1 test rig evaluation including proposed changes

The IEC Standard 61482–1 describes procedures for measuring the thermal performance of fabrics and garments intended for use in clothing for workers exposed to electric arcs. This paper demonstrates that the tests in this standard fail to produce controlled laboratory conditions. The dominant magnetic and thermal buoyancy forces have been minimised leaving two undefined and uncontrolled forces to randomly dominate arc motion, plasma flow and thermal stress. The tests also produce hazards significantly different to those facing victims in real situations. The velocity of the plasma impinging on a victim is incorrect. The color of the radiation is incorrect. The molten metal droplets impinging on the victim are incorrect. The tests only consider clothing stretched over a surface whereas loose and un-backed cloth suffers considerably more stress. In order to emulate real arcing faults, it will be necessary to use parallel copper and aluminium electrodes. In addition for high voltage personnel a “pop-out” test needs to be developed because a fault current that starts by entering and exiting the body becomes an arc inside the clothing.