Technical innovation Power equipment heating phenomenon analysis Xu Jianke 1 Fan Zhennan 12 (1 State Grid Neijiang Electric Power Bureau Production Technology Department 2 State Grid Sichuan Electric Power Company Training Center), in recent years, China's power industry has made great achievements. At the same time, however, the problem of temperature rise and heat generation of various types of power equipment has also become increasingly prominent. In order to improve the operation and maintenance level of the power system, it is necessary to seriously investigate the loss and heat generation of the power system.
1 Power equipment heat source classification The common heat sources of power equipment are as follows.
Conductor Joule loss. There are often a large number of conductor windings in power equipment. When there is current passing through, there is a loss due to the presence of resistance. This loss is usually called Joule loss.
The formula can be expressed as follows: ferromagnetic loss. In electrical equipment, the alternating current in the winding will produce an alternating magnetic field. Under this action, ferromagnetic loss will be generated in the ferromagnetic material. The instantaneous bulk density is: f is the frequency, which is the core conductivity; k is the additional loss. Coefficient; k is the core lamination in one cycle T, the average bulk density of the core loss is: Therefore, the total core loss can be calculated by the following formula: dielectric loss. The dielectric is under the action of an alternating electric field of the electric device, and energy can be generated to cause the thermal breakdown of the dielectric to cause thermal breakdown. Corresponding losses can be divided into relaxation loss, resonance loss and conductance loss.
When the alternating electric field frequency is reached, the relaxation loss has a maximum value. Where T is the relaxation time of the polar molecules and thermionic ions constituting the medium. For the resonance loss, when the electric field frequency reaches the natural frequency of the dielectric vibrator, the loss is the largest. The conductance loss is related to the material current and conductance.
Harmonic loss. Due to the existence of harmonic voltage and current in the power system, the core loss and copper consumption of electrical equipment such as transformers and capacitors will increase, and the skin effect will be aggravated, so that the loss distribution will be more concentrated. It constitutes a heat source for electrical equipment. Some of the heat will be dissipated by conduction and convection, and the rest of the heat will be absorbed by the power equipment, causing the temperature of the equipment to rise, bringing the following types of hazards.
Causes deterioration of the material. Excessive temperature rise will cause the organic insulating material to become brittle, the insulation performance will be degraded, and even the breakdown will affect the inorganic materials. It is also possible that the semiconductor element is thermally broken down, the performance is deteriorated, and even the wire is broken to form an open circuit.
Fire accidents. When the temperature rise of the power equipment is too high, it will cause a dielectric breakdown to induce a serious short circuit accident, and a huge short-circuit current will cause a great short-circuit thermal effect to cause combustion. In addition, if the power equipment is poorly dissipated, it will cause local high temperature and ignite surrounding flammable materials to cause fire.
Increase power loss. Whether it is the heating of the conductor or the skin effect, the resistance will inevitably increase, and the power loss and loss will be further increased, resulting in a vicious cycle, which will damage the equipment.
Countermeasures To reduce the risk of heat loss from electrical equipment, the following measures may be taken.
The core uses a high magnetic permeability material to enhance the insulation between the laminations, and uses advanced technology to reduce ferromagnetic losses.
Use winding or wire transposition technology to reduce the winding current loss of the winding conductor.
Use harmonic suppression technology to improve power quality.
Improve equipment ventilation and heat dissipation conditions, and suppress equipment temperature rise.
Conclusion Correctly understand the principle and hazard of heating of power equipment, and take reliable measures to suppress the loss of heat and improve the safety and reliability of power system operation.
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