Loss tests under no-load conditions are crucial for understanding and enhancing the energy efficiency of transformers. Discover how these tests unveil valuable information about losses in the equipment and learn how to maximize its energy performance.
What are no-load loss tests?
No-load loss tests are conducted on transformers to measure the losses that occur when the equipment is powered with nominal voltage and frequency at one terminal while the other terminal remains open, i.e., without load.
These tests provide essential information about the transformer's performance and efficiency under no-load conditions.
During the test, it's possible to determine the energy losses that occur when the transformer is operational but without load, and these losses are known as no-load losses. These losses are of great importance as they provide insights related to the transformer core and its energization.
Composition of no-load losses:
No-load losses consist of two main categories: losses in the core iron and losses in the transformer windings. These losses occur due to various physical phenomena such as Foucault currents and magnetic hysteresis.
1. Core iron losses:
Core iron losses are primarily caused by two physical phenomena: magnetic hysteresis and Foucault currents. These losses occur due to the variation of magnetic flux in the transformer core.
1.1. Magnetic hysteresis:
When the magnetic flux in the core varies, the magnetic particles of the core material undergo a magnetization reversal. This process of magnetization and demagnetization results in energy losses in the form of heat due to the material's resistance to the change in magnetic field direction. Hysteresis losses are proportional to the frequency of the magnetic flux variation.
Figure 1: Saturation Curve
Figure 2: Hysteresis Loop and Sinusoidal AC Current Waveform
1.2. Foucault currents:
When the magnetic flux varies in the transformer core, electric currents called Foucault currents are induced in the conductive materials present in the core. These currents circulate in closed paths, creating electrical circuits that dissipate energy in the form of heat. Foucault current losses are proportional to the square of the frequency of the magnetic flux variation and the electrical resistance of the core's conductive materials.
2. Winding losses:
Transformer winding losses are primarily caused by the electrical resistance of the conductor wires used in the primary and secondary windings. These losses occur when there is a current flowing through the conductor wires.
2.1 Wire resistance:
Conductor wires have an associated electrical resistance. When a current passes through the wires, there is a dissipation of energy in the form of heat due to this resistance. Winding losses are proportional to the square of the current flowing through the wires and the electrical resistance of the wires.
Additionally, winding losses can be influenced by parasitic currents or stray currents circulating between the different winding conductors. These parasitic currents can be caused by the physical proximity of the conductor wires or the winding geometry.
It is important to note that both core iron losses and winding losses contribute to the total losses of a transformer. During the no-load loss test, core iron losses are determined separately from winding losses, allowing for a more precise analysis of total losses and the evaluation of transformer efficiency.
Nonlinear behavior of magnetization current
Due to saturation occurring in the transformer core, both magnetic flux and reluctance vary nonlinearly. This results in a non-purely sinusoidal behavior of the magnetization current. The relationship between power and no-load current, therefore, exhibits a nonlinear character and a not perfectly defined relation.
Importance of nominal voltage and excitation current
To obtain reliable results in no-load loss tests, it is fundamental to choose the analysis point corresponding to the normal operation of the transformer. Therefore, it is necessary to supply the transformer with the nominal voltage at the low-voltage terminals. Additionally, when using low-voltage terminals, there is a lower demand on the power supply.
During the no-load test, the test current is, in fact, the excitation current of the transformer. This current is measured along with the no-load losses, and it is important to measure it properly, considering its non-purely sinusoidal behavior.
Achieve energy excellence based on the obtained results
Through no-load loss tests, you will have valuable data on the performance and efficiency of your transformer under no-load conditions. Our state-of-the-art laboratories are designed to provide accuracy, reliability, and unparalleled insights into transformer performance under no-load conditions.
Equipped with cutting-edge technology and advanced instrumentation, our laboratories provide a controlled, safe environment for operators and high precision to conduct no-load loss tests according to the highest industry standards and technical norms. Our highly qualified experts ensure the precise execution of tests, following rigorous protocols and ensuring the reliability of the obtained results. Come talk to our experts to find the ideal solution for optimizing your transformer test performance. We are confident that we can help you with our expertise and solutions!