Transformer kVA Calculator

Transformer kVA Calculator supports engineering calculations with transparent assumptions, practical result interpretation, and links to next-step technical resources.

Transformer Loading Visualizer

Formula

S = √3 × VLL × I

I = S / (√3 × VLL)

V = S / (√3 × I)

Isc ≈ Ifl × (100 / Z%)

Balanced operation and nominal impedance approximation are assumed.

Simplified Transformer Block

Load vs Current Curve

Enter required values to render load-current curve.

Inputs & Outputs

Phase System

Voltage Reference

Transformer Rating (calculated)

Rated Voltage (required)

Rated Current (required)

Power Factor (optional)

Load Factor (optional %)

Transformer Impedance (optional %Z)

Transformer Rating—

Rated Current—

Operating Current—

Line-Line Voltage—

Line-Neutral Voltage—

Power Composition

Apparent Power (S)—

Real Power (P)Set PF to solve

Reactive Power (Q)Set PF to solve

Operating Apparent Power—

Impedance-Based Fault Estimate

Enter % impedance to estimate prospective secondary short-circuit current.

Transformer Sizing Fundamentals

Transformer loading is primarily specified in kVA. Real power draw and reactive demand depend on operating power factor, while fault duty is heavily influenced by transformer impedance.

kVA Rating Logic

kVA determines thermal loading envelope of transformer windings.

Current and voltage trade directly inside the same kVA rating.

Impedance Impact

Lower impedance increases prospective fault current.

Protection coordination should be verified against calculated fault level.

Equation Matrix

Core equations for converting between voltage, current, and transformer apparent power.

System	Base Equation	Solve for Current	Solve for Voltage
Three-phase	S(kVA) = √3 × VLL × I / 1000	I = S × 1000 / (√3 × VLL)	VLL = S × 1000 / (√3 × I)
Single-phase	S(kVA) = V × I / 1000	I = S × 1000 / V	V = S × 1000 / I
Fault estimate	Isc ≈ Ifl × (100 / Z%)	Lower %Z yields higher fault current	Use with protection coordination checks

Selection Matrix

Connect calculator outputs to transformer capacity planning and protection workflow decisions.

Scenario	Objective	Recommendation	Critical Checks
Panel feeder transformer selection	Match load kVA and running current with adequate margin	Calculate full-load current first, then apply planned load factor and design reserve before selecting standard rating.	Ambient temperature, harmonic content, duty profile
Secondary protection coordination	Estimate prospective fault duty and protection stress	Use impedance-based short-circuit estimate as first-pass reference before detailed study.	Breaker interrupting capacity, cable withstand, clearing time
Power quality budgeting	Separate real and reactive contribution at expected PF	Include PF to map kVA to kW and kvar for upstream source planning.	PF correction strategy, source loading, thermal losses