Manhole explosions due to arcing faults on underground secondary distribution cables in ducts

Abstract

Arcing faults on low-voltage insulated conductors are widely considered to be selfextinguishing and consequently not very hazardous to people or property. Nevertheless, a number of arcing faults recently occurred on Hydro-Qu6bec's underground secondary 120/240-V and 347/600-V systems and caused manhole explosions in downtown Montrdal. To trace the probable cause, a series of staged tests was performed in IREQ's high-power laboratory. The results obtained prove that in wet, dirty ducts an arcing fault can take the form of an interrupted arc which is difficult if not impossible for common overcurrent protections systems to detect. However, any such fault that has a long duration produces a significant amount of gaseous by-products which escape to the ends of the duct where they can ignite or form explosive concentrations. Kewords:arcing fault, secondary distribution, underground distribution, manhole explosion.

High impedance fault detection in low voltage networks

“…Presumably as the soil dries out completely, fault current will go to zero. This result is similar to that observed in [2], that faults will occur and persist at low voltages in the presence of moisture. Figure 4 shows the typical wavefonn of arcing fault current.…”

“…These staged faults are simulations of phase to ground faults. Phase to phase faults, or cable to cable faults, can be expected to produce far higher currents and more dramatic thermal effects at the point of the fault, as reported in [2]. Resource limitations prevented accurate staging of these types of faults during this project.…”

“…These faults can have current well below the current limiter sizes. If not cleared promptly, they can cause fires that spread along the conduit tubing and damage vault equipment, [2] and present a safety hazard to the operator of the digging equipment. These consequences motivate the study of HIF characteristics and dewtion algorithms for these systems.…”

Multidimensional Risk Management for Underground Electricity Networks

“…see Koch and Carpentier, 1992;Walsh and Black, 2005). Aging of an underground grid, lack of appropriate maintenance and interference from other underground systems have generated many accidental events, thus putting human life in danger, and generating consequences for society, the local distribution company and third parties (e.g.…”

“…Aging of an underground grid, lack of appropriate maintenance and interference from other underground systems have generated many accidental events, thus putting human life in danger, and generating consequences for society, the local distribution company and third parties (e.g. see Koch and Carpentier, 1992;Walsh and Black, 2005). For example, in New York, hundreds of accident events in vaults occur every year, such as fires, explosions, smoke, etc.…”