15 kV Medium Voltage Switch Gear

[PE (always learning)]

Hey everyone,

Hope you are doing well. Currently I am helping out a PE with a power systems study project and we are hired as the third party to look at other engineers design work. I am looking at medium voltage switchgear and I had a question about the fuse sizes. To put some perspective into the project I will offer a description of the switchgear in question. The switchgear is 600 amp, 15 kV and has a main section and a distribution section with load interrupting switches and fuses. The main section uses (3) Eaton RBA 250E fuses which feeds the distribution section that has four load interrupting switches that each connect to (3) CL-14 200E fuses. I guess im confused on why the main section has a 250A fuse and feeds a distribution section with four 200A fusible switches. Is this common for equipment with higher voltages to have the main sized so close to the distribution components? Please let me know what you think.

Best Regards,
Engineer in training

 

[Ingenieur]

without knowing
the connected loads
the source

can't guess

suppose each switch feeds a 2 mva load ( fmr, motor, etc), 80 a
running load 60 a
and only 3 run concurrently
so 250 is fine

 

[rian0201]

I agree.. So can also see in the fuse TCC about the characteristics of the fuse.. E rated i think doesnt start to meet that their rated value example 250A.

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