3-2 Why should the provisions of the conductor and electrical equipment to allow heat temperature? Short-term heat to allow temperature and long-term heat to allow the same temperature, and why?
A: conductor connection part and the conductor itself is a resistance (that causes the power loss); the surrounding metal part forms the magnetic field, the formation of eddy current and hysteresis loss; insulation materials in the electric field under the action of loss, such as: tg value measurement
Current-carrying conductor heat: long-term heating effect: refers to the normal working current caused by heat while Short-term heating effect refers to the heating effect caused short circuit current.
The effect of heat on insulation
Insulation material is effected by temperature and electric field. The influence of heating on the contact part of conductor Temperature is too high because of the surface oxidation resistance increases the IR vicious circle.
3-3 What is the permissible current for a conductor to be heated for a long period of time? What should be done to increase the allowable current?
A: Its answer is based on the stability of the conductor to determine the temperature rise. In order to carry high capacity currents, it is appropriate to use materials with low resistivity, such as aluminum and aluminum alloy; Conductor shape is also an effecting variable, the cross-sectional area of circular conductor surface area should be smaller, and rectangular and trough surface area should be larger. Conductor layout should be used the best way of cooling effect.
3-4 Why calculate the maximum temperature of the conductor short-term heat? How to calculate?
A: The purpose of heat calculation of short-circuit current-carrying conductor is to determine the short-circuit current when the maximum temperature should not exceed the specified short-circuit current with the heat in allowable temperature range. When this condition is satisfied, it is considered that the conductor is thermally stable when short-circuited.
3-5 What is the meaning of the equivalent time What is the equivalent time law used for?
A: Equivalent time method calculation is simple because it has a certain accuracy and still it is most widely used. However, the curve is based on the capacity of 500MW of generator, according to the short-circuit current cycle component of the average attenuation curve produced for larger capacity generators, is bound to produce errors. In this case, it is preferable to use other methods.
