1994 Volume 114 Issue 7-8 Pages 814-820
A sodium current limiter, which has been developed and applied for low voltage use, is not a current limiting fuse but a new type of reusable current limiting device which utilizes metallic sodium as a fusible element. The excellent current limiting performance and the quick self-rehealing properties of the sodium limiter allowed highly reliable electric power systems to be obtained economically and compactly.
In this paper we experimentally examine the rehealing properties of the sodium limiter after current limiting operation and discuss the over current coordination of the sodium limiter for a low voltage distribution system. The results are summarized below. (1) The resistance of the sodium limiter, being between about one thousand and several thousand times its normal resistance ro at room temperature during a current limiting operation of short circuit fault currents, changes abruptly to 30 to 40 times its ro value just after the disappearance of the fault current and falls steadily to r_??_.
(2) The sodium limiter can recover current carrying capability for a over load current even imme-diately after a current limiting operation and maintain its capability for the following normal load current. The upper limit of the recovery of the sodium limiter is given by its over current against the time characteristics under the normal condition.
(3) The self-rehealing characteristics of the sodium limiter presented here give the ability to design a low voltage motor control center using the sodium limiter which maintains maximum service continuity up to high fault currents.