Handbook of Electrical Engineering

266 HANDBOOK OF ELECTRICAL ENGINEERING are obtainable from within Europe and from other continents. The subject is complex and r ...

HAZARDOUS AREA CLASSIFICATION 267 9.Electrical safety in hazardous environments. IEE Conference 1 to 3 December 1982. Conference ...

11 Fault Calculations and Stability Studies 11.1 Introduction When a short circuit occurs in a power supply, larger than normal ...

270 HANDBOOK OF ELECTRICAL ENGINEERING Figure 11.1 One-line diagram of faulted high voltage system. Figure 11.2 Equivalent circu ...

FAULT CALCULATIONS AND STABILITY STUDIES 271 Table 11.1. Impedance data values Item R (ohms) X (ohms) R (pu) X (pu) at 100 MVA S ...

272 HANDBOOK OF ELECTRICAL ENGINEERING Figure 11.3 One-line diagram of faulted low voltage system. Figure 11.4 Equivalent circui ...

FAULT CALCULATIONS AND STABILITY STUDIES 273 for economic or technical reasons, a choice of MCC ratings may become critically de ...

274 HANDBOOK OF ELECTRICAL ENGINEERING The quadrature axis reactances are those that can be represented on an axis at right angl ...

FAULT CALCULATIONS AND STABILITY STUDIES 275 Figure 11.5 Equivalent circuits and the phasor diagram of a faulted synchronous gen ...

276 HANDBOOK OF ELECTRICAL ENGINEERING 11.5.2 Calculation of fault current – rms symmetrical values From sub-section 11.5.1 the ...

FAULT CALCULATIONS AND STABILITY STUDIES 277 centralised main switchboard. Mesh or looped systems such as those found in utility ...

278 HANDBOOK OF ELECTRICAL ENGINEERING Therefore, Sgen= ∑n i= 1 Sgi=KgSload WhereSgiis the rating of theithgenerator andKgis a m ...

FAULT CALCULATIONS AND STABILITY STUDIES 279 transformers is simply the arithmetic sum of their individual ratingsSti. Ste= ∑n i ...

280 HANDBOOK OF ELECTRICAL ENGINEERING It is customary to assume that all the generators are operating and that they are heavily ...

FAULT CALCULATIONS AND STABILITY STUDIES 281 The contribution from the lower voltage motors is found as follows. The average rat ...

282 HANDBOOK OF ELECTRICAL ENGINEERING Figure 11.7 Instantaneous current response in a series-connected R-L circuit that is fed ...

FAULT CALCULATIONS AND STABILITY STUDIES 283 The oscillating term reaches its first maximum value when wt+θ−φequals+π/2, or, tm ...

284 HANDBOOK OF ELECTRICAL ENGINEERING Table 11.4. Values of time corresponding to the currents in Table 11.3 X-to-R ratio T 1 ( ...

FAULT CALCULATIONS AND STABILITY STUDIES 285 The term in brackets is again called the ‘doubling factor’ but it is now less than ...

286 HANDBOOK OF ELECTRICAL ENGINEERING Figure 11.8 Short-circuit current waveform of a series connected R-L circuit that is fed ...