经济翻译

C. Discussion of Measurement Time The measurement time in the new method is dependent upon the response time of the three-phase active power meter is about 0.5s [8]. On the other hand,the measurement time of the conventional method is determined by the sampling time of the FFT analyzer . A typical sampling time of a digital power meter with FFT analyzer function is about 1s [9]. Therefore, the measurement time in the new method is one-half as short as that of the conventional one.However ,the measurement time is not a critical factor because calculation of harmonic power in both methods can be completed within a few milliseconds when a high-performance DSP is used .To hunt unknown harmonic sources in actual distribution feeders, the transition of harmonic power over a long period ,for example one day or week, must be investigated [2], [3] . Thus, simplicity and precision rather than fast measurement time are required for detecting harmonic active power. Ⅳ . SEARCH FOR DOMINANT HARMONNIC SOURCE In this section, harmonic power flow of a system with two harmonic sources is investigated to demonstrate an application of the new method to search dominant harmonic sources . Fig. 3 shows a circuit configuration including two thyristor converters, one of which has an LC filter for harmonic compensation and the other has no LC filter .Table V shows circuit constants for the three transformers in Fig.3. Fig. 4 shows simulation waveforms for Fig.3. Although the thyristor converter Rec.1 has an LC filter connected in parallel ,.the source current is still contains harmonic currents. Harmonic interference problems such as burnout of the LC filter may occur, if we can not find another harmonic source besides Rec.1. Table VI is obtained by calculating the harmonic active power of (6) at each node. Clearly , the harmonic active power dissipated by the LC filter , is larger than , which is generated by Rec.1. Next, the harmonic active power PS1h at the terminal downstream of the transformer Tr1 is calculated from vT1 and is1. The positive value of indicated that the LC filter receives some harmonic active power from the source side in FIG.3. On the other hand , the harmonic active power between and is at the receiving terminal is-17W, so the harmonic power is flowing into the source vs from the downstream system .Therefore, it is concluded that an unidentified harmonic source , for which no harmonic compensator has been installed , is on the downstream side and that harmonic currents generated by this harmonic source are flowing into the LC filter . We now investigate the harmonic active power on the other branch . Thus, the harmonic power between and at the receiving terminal is calculated as = -26W . This indicates that an unidentified harmonic source such as a thyristor converter is on the down stream of . We can conclude that the harmonic power generated by Rec.2 flows into the LC filter and is dissipated there. Therefore, it is recommended that a harmonic compensator such as shunt passive or active filter be installed close to Rec.2.