1
1ManRiot
Scenario:
3 phase DNO with 100A fuses into a control unit feeding 2x 5kVA txs with combined load of 40A.
We're adding 2 more 5kVA txs, one with 14A, the other 21A.
What I've come up with so far:
63A fuse consumer side will need replacing with an 80A BS 88-2 (gG) fuse (max Z[SUB]s[/SUB] 0.57Ω).
Existing 70mm[SUP]2[/SUP] 3-core using reference method D has a current carrying capacity of 173A with an existing load of 40.3A and an estimated 55A in-rush current.
Points 20A
Load 14A
Protection 20A C-Type BS 60898 providing a required Z[SUB]s[/SUB] of 1.15Ω
Cable 144m of 16mm[SUP]2[/SUP] 3-core at 2.30mΩ/m = 144 x 2.3x10[SUP]-3[/SUP] = 0.3312Ω which satisfies the protection Z[SUB]s[/SUB]
Volt-Drop VD = 2.4mV x 14A x 144m = 4.8384V
230V - 4.8384V = 225.1616V (230V – 5% = 218.5V)
Points 20B
Load 21.2A
Protection 25A C-Type BS 60898 providing a required Z[SUB]s[/SUB] of 0.92Ω
Cable 100m of 16mm[SUP]2[/SUP] 3-core at 2.30mΩ/m = 100 x 2.3x10[SUP]-3[/SUP] = 0.23Ω which satisfies the protection Z[SUB]s[/SUB]
Volt-Drop VD = 2.4mV x 21.2A x 100m = 5.088V
230V – 5.088V = 224.912V (230V – 5% = 218.5V)
Does this look ok so far? I know 16mm2 is massive overkill but that's what has been specified by the powers that be.
I'm a little confused at the Zs aspect of it though, in how does the Zs of each circuit tie in with the entire system Zs? Is it a case that so long as the Ib <= In <= Iz < = It) is correctly calculated for each stage, with sufficient discrimination applied at each level, Zs will be correct throughout the system?
If that doesn't make much sense it's because I'm still new to this and could have worded it incorrectly!
(Before the "don't know what you're doing" brigade chip in, someone far more experienced will be going over this in its entirety, I'm merely trying to learn for myself)
3 phase DNO with 100A fuses into a control unit feeding 2x 5kVA txs with combined load of 40A.
We're adding 2 more 5kVA txs, one with 14A, the other 21A.
What I've come up with so far:
63A fuse consumer side will need replacing with an 80A BS 88-2 (gG) fuse (max Z[SUB]s[/SUB] 0.57Ω).
Existing 70mm[SUP]2[/SUP] 3-core using reference method D has a current carrying capacity of 173A with an existing load of 40.3A and an estimated 55A in-rush current.
Points 20A
Load 14A
Protection 20A C-Type BS 60898 providing a required Z[SUB]s[/SUB] of 1.15Ω
Cable 144m of 16mm[SUP]2[/SUP] 3-core at 2.30mΩ/m = 144 x 2.3x10[SUP]-3[/SUP] = 0.3312Ω which satisfies the protection Z[SUB]s[/SUB]
Volt-Drop VD = 2.4mV x 14A x 144m = 4.8384V
230V - 4.8384V = 225.1616V (230V – 5% = 218.5V)
Points 20B
Load 21.2A
Protection 25A C-Type BS 60898 providing a required Z[SUB]s[/SUB] of 0.92Ω
Cable 100m of 16mm[SUP]2[/SUP] 3-core at 2.30mΩ/m = 100 x 2.3x10[SUP]-3[/SUP] = 0.23Ω which satisfies the protection Z[SUB]s[/SUB]
Volt-Drop VD = 2.4mV x 21.2A x 100m = 5.088V
230V – 5.088V = 224.912V (230V – 5% = 218.5V)
Does this look ok so far? I know 16mm2 is massive overkill but that's what has been specified by the powers that be.
I'm a little confused at the Zs aspect of it though, in how does the Zs of each circuit tie in with the entire system Zs? Is it a case that so long as the Ib <= In <= Iz < = It) is correctly calculated for each stage, with sufficient discrimination applied at each level, Zs will be correct throughout the system?
If that doesn't make much sense it's because I'm still new to this and could have worded it incorrectly!
(Before the "don't know what you're doing" brigade chip in, someone far more experienced will be going over this in its entirety, I'm merely trying to learn for myself)
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