Amps to kVA Formula [Single, Two, Three Phase Circuits]

Amps to kVA formula are used to calculate the apparent power from two known parameters: voltage and current.

Amps to kVA Formulas

Since power factor, and apparent power have no role in dc circuits. The term kVA has three formulas in case of single, two, and three-phase alternating current circuits. Single phase and three phase formulas are very commonly used in various calculations. While two and other six, four, phases are not used, their equations except two phase are excluded.

Calculation Examples

Calculations in single phase power systems

The single phase formula is a defined as voltage times current divided by the constant 1000.

kVA = (E * I)/1000 

Example # 1: The amps rating of a single phase 220 volts ac generator at a small station is recorded to be 20 A. Find the kVA rating of the generator.

kVA = 4.4 kVA

Calculations in single phase power systems

The twp phase formula is a defined as voltage time current into two divided by the constant 1000.

kVA = (E * I * 2)/1000 

Example # 2: The electrical current flowing through a 200 V circuit is recorded as 50 Amps. Find the kVA rating. Also, find the kVA rating from ampers for the same circuit when 100 and 25 A are passing through it. Comment the ratings for different amperage values.

  • For 50 A: 200 * 50 * 2 / 1000  = 20-kVA
  • For 100 A: 200 * 100 * 2/ 1000 = 40 kVA
  • For 25 A: 200 * 25 * 2/ 1000 = 10 KVA

One can easily understand that lower amount of current results in a lower rating of generator.

Calculations for three-phase power systems

The three-phase formula similar to the two-phase equation with the difference of multiplication factor which is 1.73 here. The number 1.73 itself is used for 3 ph systems where √3 is approximately equal to 1.73. One can use the square root of 3 or can directly put 1.73.

kVA = (E * I)/1000 

Example # 3: Repeat the example for same voltage rating for three phase. Compare the cases and generalize them.

Solution:

  • For 50 A: 200 * 50 * 1.73 / 1000  = 17.3-kVA
  • For 100 A: 200 * 100 * 1.73/ 1000 = 34.6 kVA
  • For 25 A: 200 * 25 * 1.73/ 1000 = 8,65 KVA

One can individually compare the results and can observe that for all the three cases the apparent power ratings are decreased.

Other useful formulas:

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