An arrester disconnector as seen in Figure 1 is a device connected in series with an arrester that separates the ground lead from the bottom of the arrester if the arrester has overloaded and failed. It is also known as a ground lead disconnector (GLD) or Isolator.

The GLD only operates if power frequency fault current flows through the device during a failure. It will not operate from surge current. Basis of Operation Commonly used designs available today include a heating element, steady state bypass element and a separation element. Electrically it is represented by Figure 2.There are several variations of this design,
but all fundamentally operate the same way.During steady state operation the arresterleakage current is conducted around the
heating element and separation element.The separation element is generally a small explosive device that is heat activated.
During lightning surges, the heat generated in the disconnector is not adequate to ignite the separation element. The separation element is designed such that it only operates when fault current flows through the device.
Note: The standard arrester disconnector is not an interrupting device. It may break the fault current upon operation but only under ideal conditions such as low fault currents. Since the disconnector does not interrupt fault current, an over-current device will be required to operate when an arrester is overloaded and fails.System Conditions relevant to proper
use of a disconnector As stated in the last section, the GLD is only activated from power frequency fault current. Because of this operation requirement ungrounded systems and impedance grounded systems may not operate a GLD if the arrester fails. Some disconnector designs do have sensitivity in the 1 amp fault current range but most do not.

Coordination with 0ver—current devices If an over—current device is upstream of an arrester with a disconnector, it is possible for the Over-Current to be faster than disconnector ignition capability.
Time Current Curve Each disconnector has a time current characteristic curve represented either graphically or tabular as shown in Figure 3. As stated earlier, since the disconnector is not a fault breaking or clearing device, the only curve that can be properly displayed is a disconnection initiation curve. Disconnection initiation is defined as the first sign of external arc voltage across the device during its disconnection operation arrester with a disconnector to coordinate the disconnector initial disconnection curve with the minimum melt curve ofthe over-current device. It can be generally assumed that if the over-current device is slower than a typical 20K fuse link curve, then coordination with the disconnector is attained.

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