Comprehensive Problems
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Comprehensive Problems
- 13.93 A four-winding transformer (Fig. 13.146) is often used in equipment (e.g., PCs, VCRs) that may be operated from either 110 or 220 V. This makes the equipment suitable for both domestic and foreign use. Show which connections are necessary to provide:
- (a) an output of 14 V with an input of 110 V, (b) an output of 50 V with an input of 220 V.
Figure 13.146
For Prob. 13.93.
*13.94 A 440β110-V ideal transformer can be connected to become a 550β440-V ideal autotransformer. There
are four possible connections, two of which are wrong. Find the output voltage of:
- (a) a wrong connection,
- (b) the right connection.
- 13.95 Ten bulbs in parallel are supplied by a 7,200β120-V transformer as shown in Fig. 13.147, where the bulbs are modeled by the 144-Ξ© resistors. Find:
- (a) the turns ratio n,
- (b) the current through the primary winding.
For Prob. 13.95.
*13.96 Some modern power transmission systems now have major high-voltage DC transmission segments. There are a lot of good reasons for doing this but we will not go into them here. To go from the AC to DC, power electronics are used. We start with three-phase AC and then rectify it (using a full-wave rectifier). It was found that using a delta to wye and delta combination connected secondary would give us a much smaller ripple after the full-wave rectifier. How is this accomplished? Remember that these are real devices and are wound on common cores.
Hint: Use Figs. 13.47 and 13.49, and the fact that each coil of the wye connected secondary and each coil of the delta connected secondary are wound around the same core of each coil of the delta connected primary so the voltage of each of the corresponding coils are in phase. When the output leads of both secondaries are connected through fullwave rectifiers with the same load, you will see that the ripple is now greatly reduced. Please consult the instructor for more help if necessary.