Method for detecting a failed ZnO disk in a surge arrester network
First Claim
1. In a varistor network comprising M≧
- 2 parallel-coupled stacks of varistors, each stack containing a plurality of disks, a method of detecting a defective disk in one of the M stacks, the method comprising the following steps;
(a) measuring a difference in stack surge current flowing through each pair of stacks comprising said M stacks;
(b) measuring total current (I) through said M stacks;
(c) comparing stack surge current differences measured in step (a) for each pair of stacks with total current I divided by M to detect whether stack surge current flowing through any one of said M stacks exceeds a fixed fraction of total surge current flowing through said varistor network;
wherein a said stack detected in step (c) as conducting such excessive stack surge current is identified as containing at least one defective disk.
1 Assignment
0 Petitions
Accused Products
Abstract
A method of detecting failed disks in power-system surge arresters comprising a network of at least two parallel-coupled stacks of series-coupled ZnO varistors includes measuring differential current flow through each pair of stacks during surge voltage conditions, and comparing the current so measured with a fixed fraction of the total current carried by the arrester. Because each stack contains a like number of substantially identical varistors, current flow through the stack containing a failed disk will measurably exceed current flow through each non-defective stack. If the measured current flow through a stack is excessive relative to current flow through the remaining stacks, the excessive current flow stack is presumed to contain a defective disk. In today'"'"'s technology, precision Rogowski coils or fiber-optic current sensors provide the high-bandwidth, high dynamic-range transducers necessary for the measurement of both total and differential current.
23 Citations
11 Claims
-
1. In a varistor network comprising M≧
- 2 parallel-coupled stacks of varistors, each stack containing a plurality of disks, a method of detecting a defective disk in one of the M stacks, the method comprising the following steps;
(a) measuring a difference in stack surge current flowing through each pair of stacks comprising said M stacks; (b) measuring total current (I) through said M stacks; (c) comparing stack surge current differences measured in step (a) for each pair of stacks with total current I divided by M to detect whether stack surge current flowing through any one of said M stacks exceeds a fixed fraction of total surge current flowing through said varistor network; wherein a said stack detected in step (c) as conducting such excessive stack surge current is identified as containing at least one defective disk. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
- 2 parallel-coupled stacks of varistors, each stack containing a plurality of disks, a method of detecting a defective disk in one of the M stacks, the method comprising the following steps;
Specification