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Kamis, 01 Desember 2011

RUMUS PERHITUNGAN KABEL




I have given the way to calculate cable size based on my understanding from IEC.
Is this voltage drop calculation correct? Appreciate your comments.
__________________________________________
Cable Selected: 3 Core × 35 mm²
Cable Data:
Cable Resistance @ 20°C = 0.6270 Ω/km
Cable Reactance @ 50 Hz = 0.0860 Ω/km
Cable De-rated Current = 83.1 A
Cable Length = 0.200 km
Motor Full Load = 55 kW
Voltage = 440 V
Power Factor = 0.85
Efficiency = 0.89
Full Load Current = 1000 × kW / √3 × V × p.f. × effy.
= 1000 × 55 / 1.73 × 440 × 0.85 × 0.89 = 95.4 A
Minimum no. of cable runs required = 1.1 ie 2 runs
Volt Drop = √ 3 × IFL × L × ( R CosÆ + X SinÆ ) × 100 / n × V
= 1.73 × 95.4 × 0.2 ( 0.627 × 0.85 + 0.086 × 0.527 ) × 100 / 2 × 440
= 2.17 % Maximum Allowable Volt Drop 2.5% Feeder to Motor (Running)
Maximum Starting Current (Multiple of I FL) = 6
Starting Power Factor = 0.3
Locked Rotor Starting Current Ist= 6 x Full Load Current (Direct On Line)
= 6 x 95.4
= 572.4 A
Volt Drop (Starting) = √ 3 × IST × L × ( R CosÆST + X SinÆST ) × 100 / n × V
= 1.73 × 572.4 × 0.2 ( 0.627 × 0.3 + 0.086 × 0.954 ) × 100 / 2 × 440
= 6.09 %
Maximum Allowable Volt Drop 15% Feeder to Motor (Starting)
Therefore Recommended number of cables 2 Runs of 3C × 35 mm²

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