Translated Abstract
Arrester with air gap in parallel is one of the most common methods for ungrounded transformer neutral-point protection of 110kV electric system in our nation. However, when lightning stroke happens, the misoperation of air gap can cause the action of relay protection device, lead to the extention of failure, result in severe damage to power system.
To solve the misoperation of air gap, find an effective method for transformer neutral-point protection, firstly, the overvoltage occuring on the ungrounded neutral points of the 110kV solidly grounded systems is analyzed with PSCAD in this paper then, experimental study of breakdown characteristics of arrester with rod-rod gap in parallel stressed by standard and nonstandard lightning impulses is made in laboratory at last, certain suggestions are given to improve the protection of 110kV transformer neutral-point insulation.
According to the equivalent model of transformer windings under lightning impulse voltage,
the overvoltage occuring on the ungrounded neutral points caused by lightning stroke is simulated, find that: there are obvious differences between the overvoltage and standard lightning impulse, for example, the rise time of the overvoltage is much longer than the standard lightning impulse.
Through the experimental study of breakdown characteristics of arrester with rod-rod gap in parallel stressed by standard lightning impulse, find that, the intersection of arrester’s V-S characteristics and air gap’s locates in the rise time area of the lightning overvoltage, which occurs on the ungrounded neutral point, is the basic reason for the misoperation of air gap caused by lightning stroke. The clamping voltage of arrester is higher than the lightning impulse breakdown voltage of air gap, is an other reason for the misoperation of air gap.
Through the experimental study of breakdown characteristics of rod-rod gap stressed by nonstandard lightning impulses, the rise time of which are varied from 1.2µs to 70µs, find that the breakdown characteristics is closely related to the rise time of the lightning impulse used. Thus, it is necessary to verify the breakdown characteristics of the gap under nonstandard lightning impulses before used.
Corresponding authors email
