Copper Loss vs Core Loss of Power Transformers | Complete Guide

          Published by: JINSHANMEN TECHNOLOGY CO., LTD      

          Company Profile: JINSHANMEN TECHNOLOGY CO., LTD mainly produces oil immersed power transformers, dry-type power transformers, oil immersed three-dimensional coiled power transformers, dry-type three-dimensional coiled power transformers, mining explosion-proof dry-type transformers, mining explosion-proof mobile substations, amorphous alloy power transformers, on load capacity regulating power transformers, locomotive dry-type transformers, as well as prefabricated substations, modular substations, wind energy box type substations, high and low voltage switchgear and other transmission and distribution equipment. The company supplies customized distribution transformers for global industrial and municipal power projects.

Ⅰ. Introduction

          All electrical power equipment generates energy loss during long-term operation, and power transformers are no exception. Transformer energy loss is divided into two core categories: copper loss (load loss) and core loss (no-load loss). For power grid operation, factory maintenance and equipment selection, distinguishing these two losses helps users optimize operation efficiency, reduce power consumption, and select qualified 500 kva 3 phase transformer and durable oil filled distribution transformers for commercial and industrial power distribution scenarios.

Ⅱ. Copper Loss (Load Loss)

1. Definition & Working Principle

          Copper loss refers to the thermal energy loss generated by current flowing through copper windings inside transformers, also defined as variable load loss. Most conventional distribution transformers adopt high-purity copper windings to stabilize conductivity. Based on Joule's law, current passing through winding resistance generates heat loss. Copper loss is proportional to the square of operating current, irrelevant to operating voltage. It changes dynamically with load current, so it belongs to variable loss, and accounts for the largest proportion of operating loss for loaded transformers. When a 500 kva 3 phase transformer runs under full load, its copper loss will reach the rated design value.

2. Key Influencing Factors

• Operating Current: The decisive factor of copper loss; higher current brings exponentially increased copper loss.
• Winding Resistance: Larger winding resistance leads to higher copper loss; winding material and wire size determine resistance value.
• Coil Layers: More coil layers extend current flow path, increase overall winding resistance and raise copper loss.
• Switching Frequency: For conventional 50/60Hz grid-grade distribution transformers working at power frequency, copper loss is dominated by DC winding resistance loss (I²R loss), and the influence of operating frequency on copper loss is negligible and can be ignored in daily loss calculation. Frequency-related copper variation only occurs in high-frequency special transformers, not common distribution transformers.
• Operating Temperature: High temperature increases copper resistivity; load leakage flux also causes winding eddy current loss and external metal stray loss to raise total copper loss.

3. Calculation Formulas

          Formula 1 (Rated Copper Loss Power Calculation): Copper Loss Power (kW) = I² × Rc I = Rated operating current, Rc = Single-side copper winding resistance. This formula calculates real-time power loss, which has no connection with operating time. Total copper consumption energy needs to multiply operating time additionally.

          Formula 2 (Rated load copper loss calculation): Copper Loss = I² × R Total copper resistance R = (R1+R2)/2, R1=Primary side resistance, R2=Secondary side resistance

4. Practical Methods to Reduce Copper Loss

• Enlarge winding conductor cross-sectional area to lower inherent conductor resistance
• Adopt high-conductivity materials such as copper foil and high-purity aluminum foil for windings
• Optimize power distribution scheduling to reduce long-term light-load operation of on-site power distribution transformers

Ⅲ. Core Loss (No-load Loss)

1. Definition & Working Principle

          Core loss, also named no-load loss, is fixed loss generated by transformer iron core, independent of load current, winding current and load capacity. It exists constantly as long as the transformer is energized, no matter under no-load or full-load status. Core loss will slightly decrease when internal electric field intensity drops. Different from variable copper loss, core loss is a fixed operating cost for all distribution transformers, including standard oil filled distribution transformers.

2. Two Classifications of Core Loss

2.1 Hysteresis Loss

          Transformers work on electromagnetic induction principle. Alternating magnetic flux circulates inside the iron core, and core magnetic resistance hinders flux circulation. Repeated magnetization and demagnetization of core magnetic molecules generate friction heat, forming hysteresis loss. High-grade silicon steel core can effectively cut down hysteresis loss.

2.2 Eddy Current Loss

          The iron core is conductive metal material. Alternating flux induces potential on core cross-section, forming closed circulating eddy current and heat loss. Manufacturers adopt laminated thin core sheets to increase core resistance, restrain eddy current and reduce eddy current loss, which is a standard manufacturing process for qualified medium-capacity power transformers.

3. Key Influencing Factors

• Voltage & Frequency: Determine core magnetic flux density and magnetization cycle, directly affecting total core loss
• Core Material: Low hysteresis alloy and amorphous alloy core deliver lower core loss than ordinary iron core
• Manufacturing Process: Core lamination mode, inter-sheet insulation treatment and assembly precision affect eddy current loss value

4. Calculation Formulas

          Formula 1 (Classification Core Loss Calculation): Core Loss = P + P P = Hysteresis Loss, P = Eddy Current Loss (Standard academic symbol for transformer core loss composition)

          Formula 2 (Industry universal formula): Pcore = Kf × Bm² × f Kf = Core loss constant, Bm = Maximum magnetic flux density, f = Operating frequency

5. Practical Methods to Reduce Core Loss

• Adopt low-loss amorphous alloy or high-grade silicon steel core for transformer production
• Upgrade core insulation and lamination process to weaken internal eddy current
• Optimize electromagnetic structure design at the design stage to match rated voltage of mainstream grid distribution transformers

Ⅳ. Core Difference Between Copper Loss & Core Loss

Ⅴ. Conclusion

          To sum up, copper loss changes with load current while core loss keeps stable after energization. For global power grid investors and engineering buyers, choosing loss-optimized transformers can cut long-term power operation cost. JINSHANMEN TECHNOLOGY CO., LTD provides energy-saving customized 500 kva 3 phase transformer, standard anti-corrosion oil filled distribution transformers and full-series transmission and distribution equipment, meeting low-loss power distribution demands for industrial, commercial, wind power and mining projects worldwide.