delectric123
Senior Member
- Location
- South Dakota
I have a 25 KVA 480 to 240 1 ph. step-down transformer. under no load the input current is 3.8 amps. any idea what the power factor would be so I can calculate the standby losses?
I have a 25 KVA 480 to 240 1 ph. step-down transformer. under no load the input current is 3.8 amps. any idea what the power factor would be so I can calculate the standby losses?
140211-2119 EST
I don't know for your size, but my guess is below 0.1 and probably lower.
On a 175 W transformer I measured 0.18 . A larger transformer should have a lower PF. Also the core material, and transformer design will have a considerable influence. Excitation voltage vs design voltage is a major factor.
See http://www.csemag.com/single-articl...oncerns/478c06eebfe849e4db9cbec2f3969fe7.html
If we assume 3% loss at 35% load and that 50% of the loss at 35% load is no load loss, then for your 25 kVA unit we get 0.03 * 0.35 * 0.5 * 25,000 = 131 W. This would be a PF of 0.005 .
Using older design criteria the result is PF = 0.03 * 0.5 = 0.015 . Both seem low. But I don't have a 25 kVA to test. A 2 kVA at the shop, no load, runs too hot to touch. Is 3% loss a valid criteria at 100% load in an older design?
Check the specification for your particular transformer.
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KW/H is almost always something to sneeze at. Or at least cough politely. The proper unit is just kW.
Tapatalk!
If the transformer is reasonably new, then loss data should be available from the supplier.
In the case of an old unit, the only reliable way to determine losses is by measurement, either use a true watt meter, or a utility type KWH meter for a known time.
Note that the off load losses are virtualy the same no matter which way round the transformer is connected.
It might be easier to energise the lower voltage side for test purposes, for example if you have a 240 volt KWH meter to hand but do not have a 480 volt unit.
I have no problem at all with kWh/h. It is just kW/h (rate of increase of energy usage?) that bugs me.
Your usage makes perfect sense. But it could also be simplified as average kW.
I have no problem at all with kWh/h. It is just kW/h (rate of increase of energy usage?) that bugs me.
Your usage makes perfect sense. But it could also be simplified as average kW.
Tapatalk!
I have no problem at all with kWh/h. It is just kW/h (rate of increase of energy usage?) that bugs me.
Your usage makes perfect sense. But it could also be simplified as average kW.
Tapatalk!
I have a 25 KVA 480 to 240 1 ph. step-down transformer. under no load the input current is 3.8 amps. any idea what the power factor would be so I can calculate the standby losses?