10.5KV high-voltage line is about10.5 km long, and the conductor used is steel-cored aluminum stranded wire (old line), with the first 500 meters and 50 square millimeters. Others use 35 square millimeters of steel-core aluminum stranded wire. There are two transformers at the end of the line, one with a capacity of 500KVA and the other with a capacity of 160KVA. Because it is a dedicated line, the user requires us to have a high-voltage control cabinet in our station to control this line. Vacuum circuit breaker is used for control and protection, and current quick-break protection and time-limited overcurrent protection are used. Now I'm going to set it as follows:

Line length:1.5km.

Line material: the first 500 meters are 50 square mm steel-core aluminum stranded wire, and the rest are 35 square mm steel-core aluminum stranded wire.

Total transformer capacity: 660KVA

Rated primary current of transformer: 660 kva/1.732/10kv = 38.1a.

Transformation ratio of current transformer: 100/5=20 times.

The setting of current quick-break secondary current is calculated according to the closing impulse current that can avoid the transformer (38. 1AX8 = 8 times the rated current of 304A transformer): 38.1x8/20 =15.24a.

The secondary current setting of time-limited overcurrent is verified by 2 times the rated current: 38.1x 2/20 = 3.81a.

Overcurrent time limit: 1 sec