| Abstract: | Important characteristics of metal oxide surge arresters depend on the specified temporary overvoltage duty requirement due to the volt–ampere characteristics. However, there are few reports on the duty of surge arresters in noneffectively grounded systems. The temporary overvoltages of 1.43 pu proposed in effectively grounded systems is too low compared with nearly  pu in a line‐to‐ground fault. The overvoltages due to a combination of a line‐to‐ground and load rejection, where not only the main power circuits but also control systems such as AVRs participate, is rare but probably the severest case. Here the overvoltage duty of surger arresters is clarified for various residual voltage levels and system conditions. The severest condition is that in a system including a cable line because of operation of the UEL of the AVR. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 38–46, 1999 |
