Did you experience overload problems on your single phase reclosers this summer? Do you have recloser locations where the Peak Load Current exceeds 35% of the Minimum Fault Current you wish to detect? How can you provide uncompromising protection for larger Load Currents?
For example, consider the following single phase recloser location requirements:
System Voltage = 7200 / 12470 V
Peak Load Current = 60 Amps
Minimum Fault Current @ 40 ohms = 130 Amps
Maximum Fault Current = 3000 Amps
The following application rules apply:
1. The practical thermal limitation on the coil requires that the Peak Load Current not exceed 70% of the nominal coil size.
2. The Minimum Pickup Current equals 200% plus or minus 20% of the nominal coil size.
A type 'L' is an easy choice at this voltage and fault duty. But selecting the appropriate size presents some compromises. The table lists your choices.
Minimum Pickup 220% x Coil
Thermal Limit 70% x Coil
Short Circuit Rating 60 x Coil or 4000amps
Coil Size
50 amps 70 amps 100 amps 110 amps 154 amps 220 amps 35 amps 49 amps 70 amps 3000 amps 4000 amps 4000 amps
If you are concerned about detecting the Minimum Fault Current, then select the 50 amp coil with 110 amp Minimum Pickup but the compromise is that the 60 amp Peak Load Current exceeds the Thermal Limit of 35 amps. Overheating will definately occur.