Bracelet is more than a fashion statement
Specialists from Hydro-Quebec’s IREQ division have developed a lowcost device for quick detection of defective synthetic insulators. The detector is constructed in the shape of a bracelet and consists of two nickel plated steel half-circles, around which a warning flag is wound. The bracelet is attached as tiffany closely as possible to the upper end of the extension rod, which connects the insulator to the support structure so that it hugs the rod once it has been closed and forms a magnetic circuit with an air gap.
The bracelet operates as follows: in a power leakage, a current surge flows through the rod (i.e., inside the bracelet) creating a magnetic pull that is capable of reducing the air gap to almost zero. As soon as the power leakage reaches 1000 A, the bracelet is unlatched and the warning flag attached to the device becomes visible. The warning flag allows the defective insulator to be rapidly located.
The device was designed for 735-kV transmission lines so that it triggers more silver bracelets quickly than protection relays (i.e., at less than two cycles). However, the device can be modified to meet the requirements of systems operating at lower voltages.
Hydro-Quebec installed 50 devices on its 765-kV transmission system in 1996-97. The devices have performed as expected and there have been no false alarms. Other utilities that have expressed interest in the device include Electricite de France, New Brunswick’s electric utility and Florida Power & Light.
Circle 180 on Reader Service Card
Tags: silver bracelets
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