Three Phase - Technical Notes
Three phase transformers are used throughout industry to change values of three phase voltage and current. Since three phase power is the most common way in which power is produced, transmitted, an used, an understanding of how three phase transformer connections are made is essential. In this section it will discuss different types of three phase transformers connections, and present examples of how values of voltage and current for these connections are computed.
Three Phase Transformer Construction:
A three phase transformer is constructed by winding three single phase transformers on a single core.
Three-Phase Transformer Connections:
Delta to Delta - use: industrial applications 3Phase to 3Phase (NO Neutral)
Delta to Star - use : most common; commercial and industrial 3Phase to 3P+Neutral
How to convert VA to Watts and KVA to Kilowatts
Basic
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).
VA TO WATT
This depends on the Power factor which If unknown, use a power factor of 60%
It can vary from 35 to 90%
Typically
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%.
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
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.
Requied mains supply per phase
VA divide by input volts the X 1.73
30kva / 415v = 72.28Amps divid by 1.73 = 42Amps