International Conference on Large Electric Systems at high tension I-II. [antikvár]

11-01. PROGRESS REPORT OF STUDY COMMITTEE No. 17 (GENERATORS) T by G. RUELLE Secretary Asynchronous operation, Dielectric test. Excitation, Hydraulic generator, Insulation, Mechanical problem, Pumping station. Re-closing, Turbogenerator, Unbalanced load. The Committee met in Paris on the 13th June 1966, during the CIGRE biennial Session, and then in Rome a larger meeting was held from the 18th to the 20th September 1967. Several working groups of the Committee met at the beginning of 1967. During the meetings in Paris and in Rome, all the work of the Committee was reviewed, and was debated for a considerable time. A new working group comprising specialists on the particular problems of pumping stations was formed during the meeting in Paris, under the supervision of Mr. Jean Chatelain. The scope of the working groups entrusted with the examination of mechanical problems on large turbogenerators and hydraulic generators was definitely The other questions on the structure of the Committee and its future development were postponed while waiting for the nomination of a new Chairman in 1968. The meeting in Rome, excellently organised by the Italian National Committee, was called for the third time so as to coincide with a meeting of Sub-Committee 2 G of the IEC (synchronous machine constants). The programme included a combined visit to the nuclear power station at Latinia. A review of the work of the Committee and of its working groups will be found below. Three appendices drawn up by the working groups complete the information concerning preferential subjects for the Session in 1968 : the parameters for large turbogenerators, mechanical problems in large hydraulic generators, and pumping stations. The present work of the working group under the direction of Mr. G. Leroy has been concentrated on the method of test for stator insulation using very low-frequency alternating voltage, of the order of 0. 1 Hertz. Few definite results have been obtained, most countries being still engaged in the perfection of suitable test apparatus or in considering the actual value of this new method of test. The test at very low-frequency is sometimes considered as a rival and sometimes as a complement to the continuous voltage test. Like the test at continuous voltage, it can be used either as an acceptance dielectric test on a new machine, or as a non-destructive test for checking the state of the insulation on a machine which is in service. These two uses lead to different procedures and to different test apparatus. Mr. Leroy emphasised that the hit or miss dielectric test is of interest mainly to designers, while the check test when in service is the concern of the users. 1.1. Routine or acceptance dielectric test - Since there is no need to superpose several tests of this nature, the test at very low frequency is here a competitor of the continuous-current test, insofar as it is a substitute for the traditional test at industrial frequency. REPORT cleared up. 1. DIELECTRIC TESTS ON INSULATION APPENDIX I DESIRABLE SHAPES OF DISTANCE RELAY CHARACTERISTICS by J. LANDMARK BRÂTEN, SAMKJORINGEN, OSLO SUMMARY The main distance relay zones are considered and the desirable shapes of their characteristics are discussed from a theoretical point of view. The possibility of measuring additional impedances with an important reactive component and some other physical conditions in connection with the desirable shapes are treated in some detail. The report as discussed by the Study Group in Stresa, was more detailed. It also included a mathematical study of the additional impedances measured, alternatives to remote back-up etc. and information about practice and opinion in different countries concerning the use of distance relays and means to facilitate their setting. These matters as well as similar information given during the discussions in Stresa, cannot, due to lack of space, be included below. INTRODUCTION This study was started because it was believed to be in the interest of the users as well as the manufacturers to gather requirements and wishes concerning the desirable shapes of distance relay characteristics for the different zones and to gather also the reasons for such requirements and wishes. The study might also influence to some extent the work which is going on in many countries in order to improve the relays by means of new technical components in spite of the fact that many distance relays with commonly used characteristics operate satisfactorily in service. The desirable shapes of the characteristics and the reasons for and against certain shapes must be discussed under certain assumptions because the requirements may differ from case to case according to the network conditions. But a usual distance relay type cannot for technical and economic reasons satisfy all possible requirements and wishes. Some compromise is, therefore, necessary between desirable solutions and economically justified solutions and between theoretical advantages and practical disadvantages in case of complicated solutions. It is, therefore, for the time being not possible to state that a certain combination of characteristics is the only correct one in all cases. It may be, however, that the ideal shapes will be obtained in future distance relays with more ease and with a better economy than today - e.g.by a simple change in some components according to the requirements. This would be an advantage because the same relay can then be used for more purposes, and a certain relay can still be used even if conditions change. 1. GENERAL REQUIREMENTS FOR DISTANCE RELAY CHARACTERISTICS AND PERFORMANCE 1.1. The characteristic should cover the impedances in question with some margin because the impedance of the protected circuit cannot be stated exactly, because the line-impedance may vary along the line as well as from time to time and from phase-to-phase and because of moderate steady-state errors in measuring transformers and relays and practical limitations in the setting of relays. As such conditions are of no importance to the shapes of the characteristics, they are not treated in more detail in this report. 1.2. The characteristic should as far as possible ensure satisfactory operation in the presence of - Additional resistances in arcs, tower footings etc. measured in some cases as impedances with important reactive components. See section 3. - Small load impedances - even if of the same order of magnitude as the fault impedance. See 7.4 and 7.5.