Three phase star delta balanced load calculator

Keep line and phase labels distinct

Line-to-line voltage describes the supply between conductors. Phase voltage describes the voltage across one load branch. Their relationship changes with star and delta connection, which is why substituting one voltage for the other can create a square-root-of-three error.

The impedance input describes one phase branch, and all three branches are assumed identical. A measured total load impedance is not automatically the same quantity. Enter its magnitude, with power factor supplied separately.

The Transformer impedance voltage regulation calculator adds an approximate voltage-drop model using resistance, reactance and power-factor direction. The ideal balanced-load calculation here does not include those supply drops.

Apparent power and real power are different

The model calculates total apparent power from line quantities, then multiplies by displacement power factor to obtain real power. Reactive power is reported as a magnitude without assigning a leading or lagging sign.

The alternate expression three times phase voltage times phase current times power factor should give the same real power. Comparing those expressions is a useful independent check that the selected connection and quantity labels are consistent.

This is not a motor reconnection instruction

For the same per-phase impedance and supply voltage, the ideal delta line current is three times the star line current. That arithmetic does not establish whether an actual winding is rated for either connection or how a motor starter should be wired.

Unbalanced loads, harmonics, neutral current and startup transients are excluded. Cable and protection sizing need actual equipment and installation requirements, not just a steady-state current result from this educational model.

Work through the example

At 400 V line-to-line with 20 ohm per-phase impedance, star phase and line current are about 11.547 A. Delta phase current is 20 A and its line current is about 34.641 A.

Use the worked table to trace where each input enters. Then change one assumption and calculate again, leaving the others fixed. A comparison is easier to interpret when the change has one identifiable cause rather than a different set of measurements, dates and rates all at once.

What this model does not establish

Balanced identical sinusoidal phase loads only. No unbalance, harmonics, neutral current, motor efficiency, transient, wiring instructions or protection/cable approval.

Keep the input assumptions with any exported result. Illustrative values do not become observations merely because the output is precise. For a real purchase, financial reconciliation or technical decision, check the underlying records and applicable requirements before treating this scenario as a final answer.