On a 450/120V delta system where on windings A, B & C, 2.25, 2.4 & 2.2 kVA are connected respectively. What is the equivelant 3 phase kVA or kW that is seen. Based on these numbers, (3) 3kVA transformers were selected (loading not more than 80% of winding rating). Ratings of the single phase equipment connected to the transformer create this unbalance. The loads are connected to the transformer to provide the closest possible loading. Is it possible to sum single phase kVA loads and 3 phase kVA loads to acquire a system total kVA. The attempt is how to calculate the loading at the 450V panel supplying mulitple transformer delta loads.
Calculating Equivelant Power of 3 Phase Delta system
- Thread starter JLann
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The good thing about power is.....it's just power, plain and simple. If you're supplying 6.85 kVA total, it doesn't matter what configuration you're in. In a sense, there is no "3-phase equivalent power." It's just 6.85 kVA.
Now, as to that unbalance issue, you're about 5% out of balance, which isn't too terribly much. That kind of unbalance could conceivably damage 3-phase motor equipment or shorten its useful life, but since you're only supplying single phase loads, you should be ok from that end. A balanced 6.85 kVA system would be running line currents around 9 amps, but there's no substitute for a good clamp-on meter on the phases.
Now, as to that unbalance issue, you're about 5% out of balance, which isn't too terribly much. That kind of unbalance could conceivably damage 3-phase motor equipment or shorten its useful life, but since you're only supplying single phase loads, you should be ok from that end. A balanced 6.85 kVA system would be running line currents around 9 amps, but there's no substitute for a good clamp-on meter on the phases.
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- Lockport, IL
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- Semi-Retired Electrical Engineer
You first convert all loads to units of power. Take the current for each single phase 120 volt load and multiply each current by 120. If this were a 120/208 WYE system, and if you had single phase 208 volt loads, then multiply the current for each such load by 208. Finally, multiply each three phase load by the line-to-line voltage (in your delta case, that is 120 volts). Add everything up. To find the final line currents, divide the total by the line-to-line voltage, and divide again by the square root of three.
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