| Summary: | 碩士 === 國立清華大學 === 電機工程學系 === 92 === This thesis presents the methodologies, tailored to the Taipower system, for calculating the maximum and the minimum three-phase short-circuit currents (SCC). By referring to the Korea、the Kyushu and the Kansai electric utilities, which have systems similar to Taipower, we compare the calculation rules of these three power utilities with the rules of Taipower and test all rules numerically on the same Taipower system data. Based on the numerical results, the thesis suggests revisions to the Taipower calculation rules.
With respect to the maximum SCC, the thesis compares Taipower’s calculation rules with the IEC and IEEE as well as with the draft document(ER G74) proposed by the British power industry. The comparison accounts for all the influential factors on the calculation of the maximum SCC, such as decaying dc, decaying ac, the contact parting time for circuit breaker, voltage factor etc.. According to the numerical test results, the calculation formula for the decaying dc, adopted presently by Taipower, is acceptably close to that by the IEEE standard. The numerical comparison of Taipower rules with those of the above three power utilities further demonstrates the necessity of revising Taipower rules for a reduction on the maximum SCC values.
As to the calculation for the minimum SCC, the thesis suggests the use of system SCC corresponding to the cumulative probability at 5% for the system hourly load distribution, as the minimum SCC for the year under evaluation. For comparison, the thesis also calculates the SCC on basis of Taipower’s present rules which accounts for the disconnection of system generators and transmission lines and transformers. The numerical comparison of Taipower rules with those of Korea、Kyushu and Kansai reveals that the SCC values resulted from Taipower rules, are among the highest of the four power utilities. Thus the thesis suggests Taipower revise the present rules by adopting the aforementioned SCC calculation approach which is based on the 5% probability for the system hourly load distribution throughout the year for calculation of the yearly minimum SCC. Before making this suggestion, we had surveyed the hourly SCC distribution throughout the year and denoted the SCC corresponding to the cumulative probability at 5% for the distribution as ISC,5%. The above suggestion has been made after comparing the ISC,5% with the SCC calculated on basis of the minimum(5%) load.
In addition to the primary transmission, this thesis also presents the results of numerical analysis on the calculation of minimum SCC for the secondary transmission system. On basis of the results, we then make suggestions on the present Taipower rules for the minimum SCC calculation for the secondary transmission system.
|
|---|
