The above method relies on remembering a few simple principals and manipulating the problem to give the answer. Phase current I (A) is the single phase apparent power divided by the phase to neutral voltage (and given V LN= V LL / √3): Using Formulasīalanced three phase system with total power P (W), power factor pf and line to line voltage V LL
Of course if you do have some super ability at remembering formula, you can always keep to this approach. My advice would be to always try remember the method and not simply memorize formula. When I try to remember formulae I always forget them soon or become unsure if I am remembering them correctly. For a three phase system multiply by three to get the total power.Īs a rule I remember the method (not formulae) and rework it every time I do the calculation. To find the power given current, multiply by the voltage and then the power factor to convert to W. Now simply follow the above single phase methodĮasy enough. Three phase power is 36 kW, single phase power = 36/3 = 12 kW The line to neutral (phase) voltage V LN = 400/√3 = 230 V To convert a three phase problem to a single phase problem take the total kW (or kVA) and divide by three.Īs an example, consider a balanced three phase load consuming 36 kW at a power factor of 0.86 and line to line voltage of 400 V (V LL) : Similarly a transformer (with three windings, each identical) supplying a given kVA will have each winding supplying a third of the total power. The kW per winding (single phase) has to be the total divided by 3. Take a three phase motor (with three windings, each identical) consuming a given kW. To me the easiest way to solve three phase problems is to convert them to a single phase problem. To better understand this or gain more insight, you can read the Introduction to Three Phase Electric Power post
In a three phase system we have the line to line voltage (V LL) and the phase voltage (V LN), related by: Three phase system - The main difference between a three phase system and a single phase system is the voltage. To convert from VA to kVA just divide by 1000. Note: you can do these equations in either VA, V and A or kVA, kV and kA depending on the magnitude of the parameters you are dealing with. As an example, consider a load consuming 23 kW of power at 230 V and a power factor of 0.86: The current is simply the kVA divided by the voltage. Given the kW and power factor the kVA can be easily worked out. Single phase system - this is the easiest to deal with. The relationship between kVA and kW is the power factor (pf): The product of the voltage and current is the apparent power and measured in VA (or kVA). The power taken by a circuit (single or three phase) is measured in watts W (or kW).
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