How to prevent transformer magnetic saturation

As an indispensable and important equipment in power system, the stability of transformer operation directly affects the safety and efficiency of the whole power grid. During the normal operation of the transformer, the magnetic flux in the iron core should be within the range allowed by the design; However, when the magnetic flux density exceeds the saturation magnetic density of iron core materials (usually silicon steel sheets), magnetic saturation will occur. Magnetic saturation will not only lead to the increase of transformer loss and temperature rise, but also lead to harmonics and current distortion, and may even cause protection misoperation or equipment damage. Therefore, it is of great significance to take effective measures to prevent transformer from magnetic saturation.

First, the reason analysis of transformer magnetic saturation

Transformer magnetic saturation is mainly caused by the following reasons:

1. Overvoltage operation: When the transformer operates at a voltage higher than the rated voltage, the main magnetic flux increases, exceeding the saturation point of the core material, resulting in magnetic saturation.

2. Frequency reduction: According to the basic voltage formula of transformer $ U = 4.44 f N B A $,when the frequency $ f $ decreases, the magnetic flux density $ B $ will increase under the condition of constant voltage, which is easy to cause saturation.

3. Excitation inrush current: The excitation inrush current generated during no-load closing will cause the iron core to be temporarily saturated, resulting in a large transient current and electromagnetic force.
　　. Improper design or aging of the iron core: If the cross-sectional area of the iron core is too small, the lamination is loose or the material is aging, etc., the iron core will be close to saturation under normal operating conditions.

Second, the main measures to prevent transformer magnetic saturation

In order to prevent the transformer from magnetic saturation, we can start from the following aspects:
　　 (1) Reasonable design of transformer parameters
　　In the design stage of transformer, the operating conditions should be fully considered, and the appropriate core material and cross-sectional area should be selected to ensure that the magnetic flux density is within a safe range under rated operating conditions. At the same time, set the turns ratio and voltage level reasonably to avoid approaching the saturation point during normal operation.

# (2) Over-excitation protection device is installed

Modern transformers are often equipped with over-excitation protection function, which judges whether over-excitation occurs by detecting the ratio of voltage to frequency (V/f). When the V/f exceeds the set value, the protection device can give an alarm or cut off the power supply, effectively preventing the continuous development of magnetic saturation.

# (3) Adopt proper operation mode

During operation, the operator should strictly control the working voltage and frequency of the transformer to avoid long-term operation under overvoltage or low frequency conditions. Especially when the frequency of power system fluctuates greatly, the monitoring of transformer operation state should be strengthened.

# (4) Use high saturation magnetic density materials

In special applications, such as traction transformers or some industrial transformers, core materials with higher saturation magnetic density, such as amorphous alloy or ultra-thin silicon steel sheet, can be selected to improve the anti-saturation ability.

# (5) Reasonable control of closing operation

In order to prevent magnetic saturation caused by inrush current, circuit breakers with closing resistance or synchronous closing technology can be used to reduce the sudden change of magnetic flux at the moment of closing, thus reducing the risk of core saturation.

Third, summary

Magnetic saturation of transformer is an engineering problem that can not be ignored, which not only affects the normal operation of transformer, but also may cause adverse consequences to the whole power system. Through scientific design, reasonable operation management and advanced protection technology, magnetic saturation can be effectively prevented and controlled. With the development of power electronics technology and smart grid, the protection measures of transformer magnetic saturation will be more intelligent and automatic in the future, which will provide a stronger guarantee for the safe and stable operation of power system.