13.2kv feeder sizing
13.2kv feeder sizing
(OP)
Is sizing a Medium voltage feeder like sizing low voltage?
When sizing a 13.2kv feeder off a 175A fuse, should I multiply the 175A fuse by 125% and figure for the feeder size or should I just compare against the 175A fuse size?
Eg..
1.25 * 175A fuse = 219A and compare aginst 310.77 detail 3 = #350 kcmil
or 175A compared against 310.77 detail 3 = #4/0
When sizing a 13.2kv feeder off a 175A fuse, should I multiply the 175A fuse by 125% and figure for the feeder size or should I just compare against the 175A fuse size?
Eg..
1.25 * 175A fuse = 219A and compare aginst 310.77 detail 3 = #350 kcmil
or 175A compared against 310.77 detail 3 = #4/0






RE: 13.2kv feeder sizing
RE: 13.2kv feeder sizing
See thread238-106115.
RE: 13.2kv feeder sizing
RE: 13.2kv feeder sizing
Though the settings may be above the cable ratings as you mentioned, the NEC requires overcurrent protection of all conductors, including MV, per Art. 240.100.
RE: 13.2kv feeder sizing
RE: 13.2kv feeder sizing
RE: 13.2kv feeder sizing
davidbeach is correct and also see the thread I posted. MV protection feeder protection is not meant for 'overload' but just short circuits.
Also review characterisitcs of E-rated MV fuses, they are desined to open at 200% or E-rating at 5 min. Under that they may not even open or take very long time.
Overload is protected by "design" or the secondary protection device of the transformer in your case. Also see IEEE Buff bood for more info, which recommends sizing MV tramfomer fuses closer to its FLA rating, mainly to assit in coordination with other protective devices.
A 175E fuse for 2500KVA xfmr is oversized imho, a 125E for 100% rating and 150E for fan-rating (33%more) would be more appropriate. Larger fuse will more likely will not coordinate with upstream protection, you need to verify that.
RE: 13.2kv feeder sizing
Often MV cable size is upsized just for this reason. Again a smaller fuse will permit use of smaller conductor too, as long as it meets load rating.
RE: 13.2kv feeder sizing
RE: 13.2kv feeder sizing
The same combination of cable impedance and current will give 6.24 Volts drop, regardless of the circuit voltage.
On 13,800 volts, a drop of 6.24 volts is only 0.045%.
Put another way, you can run a circuit (13,800/208=66) times farther at 13,800 volts than at 208 volts for the same percentage voltage drop.
respectfully
RE: 13.2kv feeder sizing