Enter your Phase Type, Primary Voltage, Secondary Voltage, Load Current, and Power Factor into the Auto-Transformer Calculator to find your required Transformer kVA Rating, along with the Primary Current, Turns Ratio, and Voltage Regulation for your auto-transformer design.
Transformer kVA Rating
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Primary Current
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Turns Ratio
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Voltage Regulation
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An auto-transformer is a type of electrical transformer with only one winding that acts as both primary and secondary. It provides voltage transformation with higher efficiency and lower cost compared to conventional two-winding transformers.
kVA (kilovolt-amperes) is the apparent power rating of a transformer. It represents the product of voltage and current, indicating the transformer's capacity to handle electrical load without considering power factor.
For single-phase: kVA = (Volts × Amps) ÷ 1000. For three-phase: kVA = (Volts × Amps × 1.732) ÷ 1000, where 1.732 is the square root of 3.
Single-phase transformers use one alternating voltage, while three-phase transformers use three alternating voltages 120° apart. Three-phase systems are more efficient for high-power applications and provide more balanced power delivery.
Turns ratio is the ratio of primary voltage to secondary voltage, which equals the ratio of primary turns to secondary turns. It determines how much the voltage is stepped up or down by the transformer.
Power factor affects the actual power (kW) delivered by the transformer. While kVA rating remains constant, a lower power factor means less useful power is delivered, requiring consideration for proper transformer sizing.
Auto-transformers offer higher efficiency (95-98%), smaller size, lower cost, and better voltage regulation compared to conventional transformers. They are ideal for applications requiring moderate voltage transformation ratios.