open-flame arc[¦ō·pən ¦flām ′ärk]
an electric arc that burns freely in air and is not subjected to any special action that speeds up the process of its extinction. The energy balance of an open-flame arc depends primarily on the natural heat exchange between the arc path and the environment. The fundamental characteristics of both DC and AC open-flame arcs are the static current-voltage characteristic (for AC, the amplitude current-voltage characteristic), the length of the arc, and the burning time. An open-flame arc is extinguished spontaneously when its length increases—and the current magnitude decreases—to critical values, such that the energy balance in the path of the arc becomes negative.
An open-flame arc occurs when low currents are cut off by switching apparatus that has no arc arresters (for example, by circuit breakers in high-voltage installations), and also in cases of short circuits on power switchboards and aerial power lines. When low currents are cut off in low-voltage and high-voltage circuits, the open-flame arc is extinguished spontaneously. In case of a short circuit, an open-flame arc is usually extinguished spontaneously only when one phase of a power line in a system having an insulated neutral is short-circuited to ground. In other cases, the open-flame arc is extinguished by disconnecting the site of the short circuit from the source of power, often in combination with an automatic reclosing.
M. A. ARONOV