【正文】
lements of a power system. Reactive power is swapping twice per voltage cycle between capacitive elements and inductive elements. When capacitive elements are absorbing reactive power, inductive elements must be releasing reactive power, and vise versa. The capacities of these capacitive/inductive elements are not always constant. The amount of reactive power that is related to line charging is proportional , w hile that related to series reactance is proportional. Reactive power pensation can be made at different levels: distribution, transmission and generation. For a vertically integrated utility, the costs of reactive power pensation might be included into distribution cost or transmission cost depending on w here the pensation devices are installed. The costs of reactive power supplied by generators might not be listed separately, or even the reactive power capacities of generators are not considered as the costs of reactive power. When utilities are doing reactive power planning, different utilities might have different considerations. No matter how utilities treat the costs of reactive power pensation or how they carry out the planning, the electricity price always reflects this part of costs. In the deregulated power industry, several questions that were not seriously discussed in regulated era are raised, such as: who is responsible for the reactive power pensation, are the providers of reactive power services, do consumers need to pay for the required reactive power loads, w hat roles should generation panies play in reactive power pensation, etc. Under deregulation circumstance, power system security faces more threats than ever. Due to the potential dynamic power trading, the reactive power requirements are also dynamically changing. Some generation units are inefficient in generating real power and are not petitive on power market. However, they are necessary to stay online in order to maintain system voltage. This type of mustrun units causes few arguments in the regulated power industry. Not all mustrun