IEEE C50.12-2005 IEEE Standard for Salient-Pole 50 Hz and 60 Hz Synchronous Generators and Generator/Motors for Hydraulic Turbine Applications Rated 5 MVA and Above.
Reasons for the limits summarized in Figure 1 are described in the following list: a) As the operating point moves away from rated values of voltage and frequency, the temperature rise or total temperatures of components may progressively increase. Continuous operation near certain parts of the boundary of the shaded area in Figure 1 at outputs near the limits of the generator’ s reactive capability curve may cause insulation to age thermally at approximately two times to six times its normal rate. b) Generators will also be capable of operation within the confines of their reactive capability curves within the ranges of +5% in voltage and +3%/- -5% in frequency as defined by the outer boundary of Figure 1 with further reduction of insulation life. c) To minimize the reduction of the generator’s lifetime due to the effects of temperature and temperature differentials, operation outside the shaded area should be limited in extent, duration, and frequency of occurrence. The output should be reduced or other corrective measures taken as soon as practicable. d) The boundaries of Figure 1 result in the magnetic circuits of the generator to be overfluxed or underfluxed by no more than 5%。The sloped boundaries in Figure 1 correspond to constant voltz per hertz. e) The machine may be unstable or margins of stability may be reduced under some of the operating conditions shown in Figure 1. Excitation margins may also be reduced under some of the operating conditions shown in Figure 1. f) As the operating frequency moves away from the rated frequency, effects outside the generator may become important and need to be considered. As examples, the turbine manufacturer will specify ranges of frequency and corresponding periods during which the turbine can operate, and the ability of the auxiliary equipment to operate over a range of voltage and frequency should be considered. g) Operation over a still wider range of voltage and frequency, if required, should be subject to agreement between the purchaser and the manufacturer.
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