Transformer No-Load Losses, Load Losses, and Impedance Voltage Calculation

By azhe July 6th, 2025 499 views

In power systems, transformers are key devices for energy transmission and distribution. To ensure efficient operation and minimize energy losses, understanding how to calculate no-load losses, load losses, and impedance voltage of transformers is particularly important. These parameters not only affect the efficiency of transformers but also relate to the overall performance of the grid.

1. No-Load Losses
No-load losses refer to the power consumed when rated voltage is applied to the primary side while the secondary side is open-circuited. It mainly includes two parts:

1. Core Losses (Hysteresis and Eddy Current Losses):

Core losses consist of hysteresis losses and eddy current losses, closely related to the quality of core materials.
The calculation formula is typically not directly provided but obtained from manufacturer data. For certain conditions, a simplified formula can be referenced:
PFe=k1×Bm2×f+k2×Bm2×f2
where $k_1$ and $k_2$ are constants, $B_m$ is the maximum flux density, and $f$ is frequency.

深色版本
where $k_1$ and $k_2$ are constants, $B_m$ is the maximum flux density, and $f$ is frequency.
2. Copper Losses (Cu Losses at No Load):

Under no-load conditions, due to extremely low current, copper losses are almost negligible.
Therefore, no-load losses primarily depend on core losses.

2. Load Losses
Load losses refer to the total losses beyond no-load losses when the transformer operates under rated load conditions. They mainly include:

1. Copper Losses:

When the transformer runs with a load, currents in the windings generate heat, leading to energy loss.
Copper losses can be approximated by the following formula:

where $I$ is the winding current, and $R$ is the winding resistance.
2. Stray Losses:

Including additional losses caused by leakage flux, etc., these losses are difficult to precisely calculate and usually require experimental measurement or empirical estimation.
3. Additional Losses:

Such as losses from the tank and cooling system, which are relatively small and may be neglected in some cases.
3. Impedance Voltage
Impedance voltage refers to the percentage of voltage required to be applied to the primary side to achieve rated current on the primary side during short-circuit testing. It is one of the important indicators for measuring the transformer's short-circuit resistance capability. Impedance voltage can be calculated through the following steps:

1. Short-Circuit Test:

Short-circuit the secondary side and gradually increase the voltage on the primary side until the secondary current reaches its rated value.
2. Calculation Formula:

be the voltage on the primary side at this point, then the impedance voltage percentage

where $U_n$ is the rated voltage on the primary side.
3. Consideration of Phase Factors:

For three-phase transformers, consideration must also be given to interactions between phases, with specific calculations adjusted according to actual conditions.

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