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How to convert VA to Watts and KVA to Kilowatts
Basics
Since watts is volts times amps, what is VA? VA (or volt-amps) is
also volts times amps, the concept however has been extended to AC power. For DC current
VA = Watts (DC current).
In AC if the volts and amps are in phase (for example a resistive
load) then the equation is also
VA=Watts (resistive load)
where V is the RMS voltage and A the RMS amperage.
In AC the volts and amps are not always in phase (meaning that
the peak of the voltage curve is does not happen at the peak of the current curve). So in AC, if the volts and amps are not
precisely in phase you have to calculate the watts by multiplying the volts times the amps at each moment in time and take the
average over time. The ratio between the VA (i.e. rms volts time rms amps) and Watts is called the power factor PF.
VA·PF = Watts (any load, including
inductive loads)
In other words, volt-amps x power factor = watts. Similarly, KVA*PF = KW,
Or
kilovolt-amps times power factor equals kilowatts.
When you want to know how much the electricity is costing you,
you use watts. When you are specifying equipment loads, fuses, and wiring sizes you use the VA, or the rms voltage and rms
amperage. This is because VA considers the peak of both current and voltage, without taking into account if they happen at the
same time or not
Finding the Power Factor
How do you find the power factor? This isn’t easy. The idea
is that you multiply the amps times the volts for every increment of time and take the sum and average. You then divide this by
the power you would have calculated if the amps and volts are exactly in phase. Since the voltage and current can be out of
phase (which is the whole point of power factor) the power factor can be anywhere between zero and one. For computer power
supplies and other supplies that are power factor corrected the power factor is usually over 90%. For high power motors
under heavy load the power factor can be as low as 35%.
Industry standard rule-of-thumb is that you plan for a power
factor of 60%, which somebody came up with as a kind of average conservative power factor. Converting VA to
Amps
How to convert VA to amps? Use the following formula: A = (Va *
Pf)/V
Where A stands for the RMS amps, VA stands for volt-amps, V
stands for RMS volts and PF stands for the power factor.
Converting VA to Volts
How to convert VA to volts? Use the following formula:
V=(Va*Pf)/A
Where V stands for RMS volts, A stands for the RMS amps, VA
stands for volt-amps, and PF stands for the power factor.
What is KVA?
KVA is just kilovolt-amps, or volts times amps divided by
1000:
KVA·PF = KW (any load, including inductive
loads)
Where KVA stands for kilovolt-amps, KW stands for kilowatts, and
PF stands for the power factor.
Keep the factor of 1000 straight when dealing with mixed units:
KVA·PF = W/1000 (any load, including
inductive loads)
VA·PF = 1000·KW (Kilowatts to
VA)
The Following equations can be used to convert beween amps, volts, and VA. To convert between
kilovolt-amps, kilowatts, and kiloamps, keep track of the factor of 1000.
Convert VA to Amps (at a fixed voltage)
Convert KVA to KW (kilovolt-amps to kilowatts)
Convert KVA to Amps (at a fixed voltage)
Converting Watts to KVA (watts to kilovolt-amps)
Convert Amps to VA (at a fixed voltage)
Convert VA to Volts (at a fixed current)
Convert Volts to VA (at a fixed current)
Convert Volts to Amps (at a fixed VA)
Convert
Amps to Volts (at a fixed VA)
Converting VA to Amps (voltage fixed)
The conversion of VA to Amps is governed by the equation Amps = VA·PF/Volts)
For
example 12 VA·0.6/(12 volts) = 0.6 amp
Converting KVA to KW
(Kilovolt-amps to Kilowatts)
The conversion of KVA to KW is governed by the equation KVA = KW/PF)
For example, if the
power factor is 0.6
120 KVA·0.6 = 72 Kilowatts
Converting Watts to KVA (watts to kilovolt-amps)
The conversion of W to KVA is governed by the equation KVA=W/(1000*PF)
For example
1500W/(1000*0.83) = 1.8 kVA (assuming a power factor of 0.83)
F
Converting Amps to VA (voltage
fixed)
The conversion of Amps to VA is governed by the equation VA = Amps · Volts/PF
For
example 1 amp * 110 volts/0.6 = 183 VA
Converting Amps to
KVA (voltage fixed)
The conversion of Amps to KVA is governed by the equation KVA = Amps ·
Volts/(1000·PF)
For example 100 amp * 110 volts/(1000*0.6) = 18.3 KVA
Converting VA to Volts (current fixed)
The conversion of VA to Volts is governed by the equation Volts = VA·PF/Amps
For
example 100 VA · 0.6/10 amps = 6 volts
Converting Volts to VA
(current fixed)
The conversion of Volts to VA is governed by the equation VA = Amps · Volts/PF
For
example 1.5 amps * 12 volts/0.6 = 30 VA
Converting
Volts to Amps at fixed VA
The conversion of Volts to Amps is governed by the equation Amps = VA·PF/Volts
For
example 120 VA* 0.6 /110 volts = 0.65 amps
Converting Amps to Volts at fixed VA
The conversion of Amps to Volts is governed by the equation Volts = VA·PF/Amps
For Example,
48 VA · 0.6 / 12 Amps = 2.4 Volts
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