Medium Voltage Calculators Online
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I wouldn't think voltage drop at 12 KV would be very much unless you are running a long, long, distance.
And in the case of a very long run, I would expect that the difference between shielded cable and conduit/wire might make a significant difference in voltage drop.
Steve
And in the case of a very long run, I would expect that the difference between shielded cable and conduit/wire might make a significant difference in voltage drop.
Steve
rcwilson
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Voltage is equal to current times cable impedance. Resistance of 600V or 15 kV cable is about the same but the inductance will be different.
Inductance varies with the phase spacing of the conductors. Most Vdrop calculators assume a conductor-conductor spacing based on typical insulation thickness with a fudge factor (20-30%) to account for random spacing of the wires in a conduit. (Three conductor cables have no fudge factor).
15kV insulation is thicker so the wire spacing and the impedance will be different.
Example: 600V, 250 kcmil XHHW, OD= 0.705". Assume spacing of 120% of OD = 0.846". From Okonite website, the impedance for this spacing is about 0.03 ohms/1000'.
250 kcmil, 15 kV insulation, OD= 1.39", assume spacing =120% = 1.67". Impedance is 0.05.
Assume the same resistance and calculate the impedance:
600V: Z= 0.054 +j 0.03 = 0.062 ohms/1000'
15 kV: Z= 0.054 +j 0.05 = 0.074 ohms/1000? a 20% increase in total impedance.
You can't just add 20% to the Vdrop tables since voltage drop depends on the load?s power factor.
Even if you did use the tables and multiplied by 20%, the end result is going to be negligible compared to 12.47 kV. Example - Assume a 2000 foot run, Z= 2 x 0.074 = 0.148 ohms. Assume 250A circuit amps, Vdrop per conductor is 250 x 0.148= 37 Volts or just 0.3% of the 12.47 kV. (These are very rough numbers, ignoring phase angle, phase-neutral voltages and other items.)
Unless you have an unusual circuit, voltage drop should not be a concern.
Inductance varies with the phase spacing of the conductors. Most Vdrop calculators assume a conductor-conductor spacing based on typical insulation thickness with a fudge factor (20-30%) to account for random spacing of the wires in a conduit. (Three conductor cables have no fudge factor).
15kV insulation is thicker so the wire spacing and the impedance will be different.
Example: 600V, 250 kcmil XHHW, OD= 0.705". Assume spacing of 120% of OD = 0.846". From Okonite website, the impedance for this spacing is about 0.03 ohms/1000'.
250 kcmil, 15 kV insulation, OD= 1.39", assume spacing =120% = 1.67". Impedance is 0.05.
Assume the same resistance and calculate the impedance:
600V: Z= 0.054 +j 0.03 = 0.062 ohms/1000'
15 kV: Z= 0.054 +j 0.05 = 0.074 ohms/1000? a 20% increase in total impedance.
You can't just add 20% to the Vdrop tables since voltage drop depends on the load?s power factor.
Even if you did use the tables and multiplied by 20%, the end result is going to be negligible compared to 12.47 kV. Example - Assume a 2000 foot run, Z= 2 x 0.074 = 0.148 ohms. Assume 250A circuit amps, Vdrop per conductor is 250 x 0.148= 37 Volts or just 0.3% of the 12.47 kV. (These are very rough numbers, ignoring phase angle, phase-neutral voltages and other items.)
Unless you have an unusual circuit, voltage drop should not be a concern.
Recommendation: get a copy of the Standard Handbook for Electrical Engineers. The inductance of a medium voltage system is usually MUCH higher than the resistance and has a much greater impact on the voltage drop. The handbook has impedances for common construction types to use for your voltage drop calculations.
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