If you are concerned about maintaining the integrity of the recloser and not exceeding the Thermal Limit, then select the 100 amp coil with a 70 amp Thermal Limit but the compromise is the liability of the 220 amp Minimum Pickup exceeding the Minimum Fault Current of 130 amps.


Most engineers probably would select the 70 amp coil as the best compromise. The Minimum Pickup can be made 'acceptable' by assuming a 30 ohm fault resistance. The Thermal Limit is only exceeded during summer peaks. Unfortunately, a recloser coil does not have a large heat capacity and achieves maximum temperature in approximately one hour for any given load current. Simply stated, one summer afternoon peak will overheat a recloser coil burning out the inner winding insulation. This partial winding failure degrades the magnetic force of the coil elevating the Minimum Pickup and/or altering the Current vs. Time relationship. Coordination problems will occur, if not immediately, over time.


How can we solve this problem?


Why not design a better coil? Introducing the Oil Cooled Recloser Coil. A coil designed to be electrically and mechanically interchangeable with present designs but implementing oil cooling ducts, similar to a transformer coil, to transfer the heat generated in the coil to the oil in the tank.


The electrical ratings of the Oil Cooled Reclosers Coils are listed in the following table:




Note that the Thermal Limit now equals the Minimum Pickup. For all practical purposes, the Oil Cooled Coil has eliminated the application restriction of the Thermal Limit. Now the only consideration is the Minimum Pickup!
Returning to our example, the solution to the requirements of a Peak Load of 60 amps and a Minimum Pickup less than the Minimum Fault Current of 130 amps is to select the 60 amp Oil Cooled Coil. Oil cooled coils are available for Types 'L', 'E' Form 2 and '4E' reclosers. 

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