Calc Power for 3 phase power supply
Calc Power for 3 phase power supply
(OP)
I am trying to calculate the efficiency of a 3-phase 480V power supply that outputs 10.5 volts DC at 840 amps. The purpose is to see how much we can save in electricity by using a newer more efficient power supply. We are not charged for power factor by our electric utility. I've got a Fluke quality analyzer logging the inputs, which are:
Volts1 = 480.9
Amps1 = 17.29
Volts2 = 473.5
Amps2 = 17.4
Volts3 = 477.0
Amps3 = 14.6
Power Factor = .72
I want see how efficient the P/S is by comparing the input watts to the output watts. I wasn't sure if I needed to take into account power factor. I calculated:
Input KW = ((V1*A1) + (V2*A2) + (V3*A3))/1000 = 23.56KW
Output KW = (10.5 VDC x 840 Amps) / 1000 = 8.82 KW
The efficiency would then be 8.82/23.56 = 37%. This means that 63% or 14.7KW would have to be turned into heat, sound and vibration by the power supply. That sounds like way too much wasted energy. This power supply is about the size of a full server rack and it gets warm, of course, but not that hot. Am I missing something?
Volts1 = 480.9
Amps1 = 17.29
Volts2 = 473.5
Amps2 = 17.4
Volts3 = 477.0
Amps3 = 14.6
Power Factor = .72
I want see how efficient the P/S is by comparing the input watts to the output watts. I wasn't sure if I needed to take into account power factor. I calculated:
Input KW = ((V1*A1) + (V2*A2) + (V3*A3))/1000 = 23.56KW
Output KW = (10.5 VDC x 840 Amps) / 1000 = 8.82 KW
The efficiency would then be 8.82/23.56 = 37%. This means that 63% or 14.7KW would have to be turned into heat, sound and vibration by the power supply. That sounds like way too much wasted energy. This power supply is about the size of a full server rack and it gets warm, of course, but not that hot. Am I missing something?






RE: Calc Power for 3 phase power supply
RE: Calc Power for 3 phase power supply
I suggest you rent one or buy a watthour meter then divide by the time.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Calc Power for 3 phase power supply
RE: Calc Power for 3 phase power supply
Doesn't that Fluke have a POWER setting? Do not just multiply the voltage with the current as you will get garbage. Internally that meter will multiply the the instantaneous voltage with the instantaneous current and supply the actual watts.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Calc Power for 3 phase power supply
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RE: Calc Power for 3 phase power supply
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RE: Calc Power for 3 phase power supply
RE: Calc Power for 3 phase power supply
Even as you heed other folk'd advice here, there is basic error in you formulas.
The KVA power of 23.56kVA is incorrect. For your method of adding power in each phase, you need to use per phase (phase to neutral) voltage, which is 277V or (Line to line voltage)/sqrt of 3. 480V is the line to line voltage.
or in other words you input kVA will be 23.56/1.732 =13.6kVA.
If your pf of 0.72 is correct then the input kW will be 13.6*0.72=9.8 kW. Now recalculate our efficiency!
RE: Calc Power for 3 phase power supply
thread238-246755: 3Ø Amps Per Ø
RE: Calc Power for 3 phase power supply
RE: Calc Power for 3 phase power supply
--Scott
RE: Calc Power for 3 phase power supply
Rafiq Bulsara
http://www.srengineersct.com