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225 Kvar

The document discusses sizing circuit breakers, contactors, and fuses for a 225 kvar capacitor bank. It determines that a 700 amp circuit breaker, contactors rated for 45, 35 and 25 amps, and fuses rated for 50, 40 and 25 amps would be required for the 10 steps of 20 kvar, 1 step of 15 kvar, and 1 step of 10 kvar capacitors, respectively. Safety and overload factors are applied in the calculations.

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Khaled Kamel
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294 views2 pages

225 Kvar

The document discusses sizing circuit breakers, contactors, and fuses for a 225 kvar capacitor bank. It determines that a 700 amp circuit breaker, contactors rated for 45, 35 and 25 amps, and fuses rated for 50, 40 and 25 amps would be required for the 10 steps of 20 kvar, 1 step of 15 kvar, and 1 step of 10 kvar capacitors, respectively. Safety and overload factors are applied in the calculations.

Uploaded by

Khaled Kamel
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOC, PDF, TXT or read online on Scribd
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‫ فار‬.

‫ ك‬225 ‫محطة مياة‬

1-Circuit breaker sizing for capacitor bank

Assuming Q = 225 kvar , voltage V= 400 v


Power factor CosФ = 0.8
Current I = Q/(√3хVх Sin Ф)
= 225 х 1000 /(√3 х 400 х 0.6)
= 541 Amp
Circuit breaker Amp required = Current ( I ) х Safety factor
= 541 х 1.25
= 676 Amp
≈ 700 Amp

2-Contactors sizing for capacitor switching

For 225 kvar, 12 steps ( 10 steps х 20 kvar + 1 step х 15 kvar + 1 step х 10 kvar )

Nominal current In = Q х 1000 / (√3 х V )


= Q х 1000 / (√3 х 400 )
= 1.443 х Q
Thermal current It = 1.5 х In
= 1.5 х 1.443 х Q
= 2.16 х Q

Thermal current for 20 kvar capacitor = 2.16 х 20 = 43.2 ≈ 45 Amp


Thermal current for 15 kvar capacitor = 2.16 х 15 = 32.4 ≈ 35 Amp
Thermal current for 10 kvar capacitor = 2.16 х 10 = 21.6 ≈ 25 Amp

3- gG fuses sizing for capacitors

Fuse rating Amp for capacitor = 1.7 х In


= 1.7 х 1.443 х Q
= 2.45 х Q

Fuse rating Amp for 20 kvar capacitor = 2.45 х 20 = 49 ≈ 50 Amp


Fuse rating Amp for 15 kvar capacitor = 2.45 х 15 = 36.8 ≈ 40 Amp
Fuse rating Amp for 10 kvar capacitor = 2.45 х 10 = 24.5≈ 25 Amp

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