Transformer Design Calculators – kVA, FLC, Efficiency
CircuitSecrets Transformer Calculators
Professional Electrical Engineering Tools for Design & Analysis
IEEE C57 | IEC 60076 | BS EN StandardsTransformer kVA Rating Calculator
Calculate apparent power rating from voltage and current measurements
About Transformer kVA Rating
The kVA (kilovolt-ampere) rating represents the apparent power capacity of a transformer. This rating determines the maximum load the transformer can supply continuously without exceeding temperature limits specified in IEC 60076-2.
- Single Phase: S = V × I (in VA)
- Three Phase: S = √3 × VL × IL (in VA)
- The √3 factor (≈1.732) accounts for the phase relationship in three-phase systems
Transformer Full Load Current Calculator
Calculate primary and secondary full load currents from transformer rating
About Full Load Current
Full Load Current (FLC) is the maximum current a transformer can deliver continuously at rated voltage without exceeding temperature rise limits per IEC 60076-2 and IEEE C57.12.00.
- Single Phase: IFL = S / V
- Three Phase: IFL = S / (√3 × VL)
- HV current is typically lower than LV current (inverse of voltage ratio)
- Used for sizing cables, circuit breakers, and protection devices
Transformer Turns Ratio Calculator
Calculate turns ratio and voltage ratio from primary and secondary voltages
About Turns Ratio
The turns ratio is the ratio of primary to secondary winding turns, which directly determines the voltage transformation ratio in an ideal transformer per Faraday's law of electromagnetic induction.
- Step-Down: Ratio > 1 (VP > VS) - reduces voltage
- Step-Up: Ratio < 1 (VP < VS) - increases voltage
- Isolation: Ratio = 1 (VP = VS) - galvanic isolation
- IEC 60076-1 tolerance: typically ±0.5% of declared ratio
Transformer Efficiency Calculator
Calculate transformer efficiency from output power and losses
About Transformer Efficiency
Transformer efficiency is the ratio of output power to input power, with losses occurring in the core (iron losses) and windings (copper losses). Modern distribution transformers typically achieve 95-99% efficiency per IEC 60076-1.
- Iron/Core Losses (Pi): Hysteresis and eddy current losses, constant regardless of load
- Copper Losses (Pcu): I²R losses in windings, varies with square of load current
- Maximum Efficiency: Occurs when iron loss = copper loss (typically 50-70% load)
- Efficiency classes: IEC 60076-20 defines Tier 1 and Tier 2 requirements
Transformer Voltage Regulation Calculator
Calculate voltage regulation from impedance and power factor
About Voltage Regulation
Voltage regulation indicates the percentage change in secondary voltage from no-load to full-load condition. Lower regulation means more stable output voltage under varying loads, which is critical for sensitive equipment.
- Lagging PF: VR% = %R·cos(φ) + %X·sin(φ) (positive regulation)
- Leading PF: VR% = %R·cos(φ) - %X·sin(φ) (may be negative)
- Typical Values: Distribution transformers: 2-5%, Power transformers: 5-10%
- %Z = √(%R² + %X²), where %X is typically much larger than %R
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