The wavelet transform is introduced a s a method for analyzing electromagnetic transients associated with power system faults and switching. This method, like the Fourier transform, provides information related to the frequency composition of a waveform, but it is more appropriate than the familiar Fourier methods for the non-periodic, wide-band signals associated with electromagnetic transients. It appears that the frequency domain data produced by the wavelet transform may be useful for analyzing the sources of transients through manual ,or. automated feature detection schemes. The basic principles o i wavelet analysis are set forth, and examples showing the application of the wavelet transform to actual power system transients are presented. INTRO D U C T I 0 NThe analysis of electromagnetic transients associated with an abnormal condition in a power system has always been fundamental to explaining and then correcting the cause of the condition. It is for this reason that well instrumented substations have transient event recorders. 'The recent conversion to digital transient recording (even by computer-based relays) has made much more data rspidly available to the engineer.In digital form, the transient information is amenable to automated analysis. Present efforts for characterizing transients such as liglitiiiiig and switching surges use parameters such as crest value, front time or time to crest, and time to half value. Standards have been established for obtaining these parameters graphically from recorded waveforms [l], and recently several methods have been proposed for extracting these data from digital recordings using curve fitting techniques [a, 31.The volume of data necessary to capture valuable high-frequency information while retaining the dynamic response of the power system, if only for a fraction of a second, requires massive data storage and handling systems. Presently, taking full advantage of information about power system viability from transient responses is not practical. Even if rule-based analysis had been fully developed, the vast amount of data that has to be transferred to a central site for correlation with transient data collected at other points in the system would overwhelm communication channels. Until on-site, automated analysis becomes available, human evaluation of the data fur-95 SM 391-3 PWRD A paper recommended and approved by the IEEE Transmission and Distribution Committee of the IEEE Power Engineering Society for presentation at

Self-excitation of induction generators or small synchronous generators connected to distribution feeders is analyzed during the transient period following the islanding of a generator on the feeder. The relationship of feeder load after separation and the occurrence of ferroresonance with an isolated induction, synchronous or single-phase generator are developed. The results indicate that an isolated distribution system generator (DSG) can theoretically support as much as three times the generator's rated power output in a ferroresonant mode provided the prime mover has the needed inertia or torque available at the abnormal isolated speed. The abnormal voltage and frequency operation during separation modifies load, generator, and prime mover characteristics and may result in an energy balance, although such balance is not obvious before separation. INTRODUCTIONThe resurgence of interest in the application of induction generators in power systems has been driven by the PURPA legislation of 1978. Induction generation has been viewed as an attractive option for the small power producer because it is a seemingly simple device which is relatively inexpensive and easy to maintain. Under normal steady-state conditions this assessment is largely true. However, when switching operations are required on the feeder to which such generation is interconnected the transient response may be far from simple. Under specific feeder conditions the damage that can be sustained by the feeder or the unit during these transient periods can eliminate any savings in first cost or operating cost.The 1935 paper by Bassett and Potter is one of the earliest papers to treat the subject of self-excited operation of the induction generator.1 Their steady-state analysis promoted the concept that stand-alone operation of induction generators was plausible using carefully sized capacitors to provide the source of excitation. In a 1939 paper, Dr. Wagner first analyzed the problem of accidental separation of an induction motor with terminal connected power factor correcting capacitors.2 His quasisteady-state analysis clearly demonstrated that high overvoltage could be produced by high inertia shaft loads or "...applications are known in which gas or gasoline motors are connected to the samne shaft with the induction motor and the utilization device, so that, in the event of the removal of the electric power source, the armature can actually increase in speed and remain at the increased speed until manual readjustments are made." Wagner's work was the first to show that any overspeed during a separation transient will be in the direction to aggravate the overvoltage problem. His paper also gave evidence that a machine will self-excite under load "very nicely" during isolated operation.in more eloquent mathematical form.3 Barkle and Ferguson introduced the use of the induction machine circle diagram to predict overvoltages and the range of parameters that would produce overvoltage operation. However, their analysis was also a quasi-steady-state appr...

No abstract

No abstract

No abstract