1、中文 1970字 Reactive Power Planning and Operating in the Deregulated Power Utilities . INTRODUCTION The purposes of this paper are to review the current strategy of reactive power management and search for proper reactive power strategy, which is expected to result in a more efficient and economic way
2、in reactive power management. These goals are actually consistent with the spirit of the deregulation of power industry. Reactive power affects system voltages, energy loss as well as system security. As power system deregulation has been widely accepted by power industry, the philosophy of reactive
3、 power management and power system operation is expected to be much different in order to meet the spirit of deregulation and the security requirements. In a vertically integrated utility, reactive power facilities are owned and operated by the same utility. The costs and contribution of reactive po
4、wer supply are not precisely evaluated. Under deregulation circumstance, the obligations and rights of the owners of reactiv e power facilities become an essential issue that affects not only the investment returns of power industry but also the power system security. This situation is even more com
5、plicated for the interconnection of several self -supported systems. Reactive power is always required during power delivery in an AC system even there are no reactive power loads. However, unlike real power, reactive power is not consumed by any elements of a power system. Reactive power is swappin
6、g 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 react
7、ive power that is related to line charging is proportional , while that related to series reactance is proportional. Reactive power compensation can be made at different levels: distribution, transmission and generation. For a vertically integrated utility, the costs of reactive power compensation m
8、ight be included into distribution cost or transmission cost depending on where the compensation 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 p
9、ower. When utilities are doing reactive power planning, different utilities might have different considerations. No matter how utilities treat the costs of reactive power compensation or how they carry out the planning, the electricity price always reflects this part of costs. In the deregulated pow
10、er industry, several questions that were not seriously discussed in regulated era are raised, such as: who is responsible for the reactive power compensation, are the providers of reactive power services, do consumers need to pay for the required reactive power loads, what roles should generation co
11、mpanies play in reactive power compensation, 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 p
12、ower and are not competitive on power market. However, they are necessary to stay online in order to maintain system voltage. This type of must-run units causes few arguments in the regulated power industry. Not all must-run units must be on-line all the time. Depending load and operating conditions
13、, some of them can be off-line but must be standby and some of them must be on-line only under certain conditions. Most generators have a limitation of minimum real power output and can not simply operate as synchronous condensers. Their operating costs should include real power cost. .REACTIVE POWE
14、R COMPENSATION ATDISTRIBUTION LEVEL Main purposes of reactive power compensation at load sites are to reduce long distance transmission of reactive power and reduce the reactive power flow within distribution network, thus reduce MW loss and voltage dip. Reactive power itself is sort of energy swapp
15、ing between reactive element and capacitive element and is not consumed for pure reactive and capacitive elements. If most of reactive power load can be supplied at load sites, the amount of reactive power flow in either transmission network or distribution network can be reduced. Fig. 1 is a 12-bus
16、 sample system which is a small piece of distribution network of New York City. The loads and shunt compensations shown in the figure are three phase total. Balanced three-phase load is assumed in the calculation. Four compensation cases are presented to illustrate the effects on MW loss and voltage
17、 dip. All four cases are under same load conditions as shown in Fig. 1 except that the reactive power compensations are different: Case 1 : Without reactive power compensation. Case 2: Reactive power compensations are shown in Fig. 1. Case 3: Total reactive power compensation of case 2(1380 KVAR) is
18、 made at Bus # 1 Case4: Reactive power compensation at Bus #1 is increased to obtain unity power factor. Similar situation can be found from bus voltages. Compensation method of case 2 is most effective in voltage improvement among those cases. Case 3 and case 4 have no direct effects on bus voltage
19、s of distribution network. .REACTIVE POWER COMPENSATION IN TRANSMISSION NETWORK For normal operation the compensation should be sufficient to keep the voltages of feeders within an acceptable range. For emergency operation the compensation should be able to keep the voltages within a wider acceptabl
20、e range with the reactive power support from generation companies. Fig. 2 is a small system of 110 buses, 136 branches including 71 transformers and 33 generators. System load is about 400 MW. Individual bus loads are not shown in the figure. The first case is base case. In the base case power facto
21、rs of generators are not necessary the same and, similarly, power factors of load buses are not necessary the same either. In the second case, load conditions are the same as base case, including 3 shunt compensations, but with the generators operating near unity power factor. The last four cases, g
22、enerators are operating near unity power factor and the power factor of all load buses is assumed 1.0, 0.95, 0.9 and 0.85, respectively. .REACTIVE POWER RESREVE OF GENERATORS The proposed reactive power management scheme assumes that generators are not responsible for reactive power supply under normal operation conditions. The generators, however, have to have sufficient reactive power reserve for contingencies. An important issue is how much reserve is necessary for each
