20 V 1 kHz C= 0.47µF R = 400 Ω Figure 10-2

An emergency power supply is required to provide a three-phase sinusoi- dal voltage source of 208 V (L-L) at a frequency of 400 Hz. The power is to be obtained from a battery consisting of cells in series, each cell hav- ing an internal voltage of 2.2 V and an internal resistance of 0.006 m. The load on the three-phase, 400-Hz system requires a fundamental fre- quency apparent power of 7.2 kVA at 0.9 power factor lagging. The in- ductance of the load is such that harmonic currents are negligible. How many cells should be connected in series to provide the required output? The switches may be regarded as ideal.

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