2-11 What are the advantages and disadvantages of HVDC?
A: Advantages:
1) the line cost is low, the annual energy loss is small;
2) there is no system stability problem;
3) limit the short-circuit current.
4) fast adjustment, reliable operation;
5) No capacitor charging current.
6) save the line corridor.
Disadvantages:
1) the commutation device is more expensive;
2) the consumption of reactive power and more;
3) produce harmonic effect;
4) the lack of DC switch;
5) The transformer can not be used to change the voltage level.
3-1 What is the significance of heating the conductor and the electrical equipment? What are the characteristics of long-term fever and short-term fever?
A: The current will produce loss, these losses will be converted into heat and so the temperature of electrical equipment. Heat impact of electrical equipment contains following drawbacks: to reduce the performance of insulating materials; to reduce the mechanical strength of metal materials; the conductor contact resistance increases.Conductor short circuit, although the duration is not long, but the short-circuit current is high that produce a lot of heat.This heat is not easy to shed in a suitable time, so the conductor temperature rapidly increased. At the same time, the conductor is also subject to the electric power exceeding the allowable value that will make the conductor deformation or damage. thus Visible, fever and electric power is the electrical equipment operation must pay attention to the problem. Long-term heating is generated by the normal operating current; short-term heating is caused by short-circuit current fault.
