Transformer KVA Sizing — AutoCAD 2024 Utility

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🔋 Transformer KVA Sizing Calculator

Calculate required KVA from load data, or find primary/secondary currents from a known KVA rating. Always select the next standard size up from calculated KVA.

Phase

Primary Voltage (V)

Secondary Voltage (V)

Load Method

Secondary Load Current (A) Full load amps on secondary side

Demand Factor (%) Apply if not all loads run simultaneously

Future Growth (%) Typical: 20–25% for new installations

Phase

Transformer KVA

Primary Voltage (V)

Secondary Voltage (V)

Standard Transformer KVA Ratings

Always select the next standard size above your calculated requirement. Apply demand and diversity factors where appropriate. Add 20–25% for future load growth on new installations per good engineering practice.

KVA Rating	1Φ Primary A @ 480V	1Φ Secondary A @ 240V	3Φ Primary A @ 480V	3Φ Secondary A @ 208V	Typical Application

Transformer Formulas

KVA Calculations

Single Phase: kVA = (V × I) / 1000
Three Phase: kVA = (V × I × √3) / 1000 = (V × I × 1.7321) / 1000

Primary Current (1Φ): I_pri = (kVA × 1000) / V_pri
Primary Current (3Φ): I_pri = (kVA × 1000) / (V_pri × 1.7321)

From kW with Power Factor: kVA = kW / PF
Turns Ratio: N = V_pri / V_sec
Current Ratio: I_sec / I_pri = V_pri / V_sec

Utility Distribution Transformer Reference

Type	Voltage Class	Typical KVA Range	Mounting	Common Use
Single-Phase Overhead	5kV–35kV primary	5–167 kVA	Pole-mounted	Residential, small commercial
Three-Phase Overhead	5kV–35kV primary	45–500 kVA	Pole bank or platform	Commercial, small industrial
Padmount (1Φ)	5kV–35kV primary	10–167 kVA	Ground pad	Residential URD, subdivisions
Padmount (3Φ)	5kV–35kV primary	75–2500 kVA	Ground pad	Commercial, industrial, campus
Substation (3Φ)	35kV–345kV primary	1–50 MVA	Substation	Distribution substation T&D
Dry-Type (1Φ/3Φ)	600V primary	1–1000 kVA	Indoor panel/wall	Building feeders, switchgear