A transformer’s rating is always expressed in kilovolt-amperes (kVA). Find & calculate the power rating of a single phase or three phase transformer with the help of the two simple formulas that are shown below.
In any condition, the voltage as well as the currents should be derived from a single side, either the primary (or) the secondary side, respectively (for example, primary voltage (Volts) x primary current (Amps) or secondary voltage (Volts) x secondary current (Amps)). To determine the appropriate structural size of a transformer for a necessary domestic device, need to determine the supply voltage in volts & secondary load current measured in amperes.
Calculating the Size of a Single Phase Transformer
Transformer with a single phase has the following ratings:
P = V x I
Where:
V – Primary (or) Secondary Voltage
I – Primary (or) Secondary Current
P – Power in VA
The kilovolt-ampere rating of a transformer with a single phase
kVA= (V x I) / 1000
Calculating the Size of a Three Phase Transformer
Transformer with a three phase has the following ratings:
P = √3 x V x I
Where:
V – Primary (or) Secondary Voltage
I – Primary (or) Secondary Current
P – Power in VA
The kilovolt-ampere rating of a transformer with a three phase
kVA= (√3 x V x I ) / 1000
kVA= (1.732 x V x I ) / 1000
Where:
√3 – 1.732
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