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AC Theory ch 32
An Introduction to Three-Phase Systems
| Question | Answer |
|---|---|
| 1. What is meant when we say two voltage waves are in-phase with each other? | reach 0 180 and 360 at the same time |
| 2. The word "phase" is often represented by the Greek letter phi, whose symbol is ____ | see page 421 |
| 3. Define polyphase as it applies to electrical distribution systems | power distributed on multiple wires |
| 4. Most electrical power generated today is ___ | three- phase |
| 5. A single-phase power souce can be generated by rotating a ___ through a single stationary coil. | magnetic field |
| 6. A three-phase power souce can be produced by rotating a magnetic field through ___ set(s) of coils arranged ___ apart. | 3, 120 degrees |
| 7. The voltage produced by a generator is zero for some period of time for the ___-phase power system. The voltage falls to zero ___ time() for each cycle. | single, 2 |
| 8. THE HORSEPOWER RATING OF THREE-PHASE MOTORS AND THE KVA RATING OF THREE-phase transformers are about ____ percent of single-phase motors and transformers of about the same physical size. | 150 |
| 9. A balanced three-phase system requires conductors of about ___ the size of the conductors for a single-phase two-wire system for the same kVA rating. | 58% |
| 10. There are two basic wiring schemes for 3-phase systems. These are the ___ and ___ connections. | wye, delta |
| 11. For a(N) ____ connected device, the line voltage is higher than the phase voltage by a factor of _____ | wye, 1.73 |
| 12. For a ___ connected device, the line voltage is equal to the phase voltage. | Delta |
| 13. For a ___ connected device, the line current is equal to ___ times the phase current. | Delta, 1.73 |
| 14.For a __ connected device, the line current is equal to the phase current. | wye |
| 15. A system that has a common connection for all three windings is ___ connected. | wye |
| 16. read the question on page 422 | |
| 17. Another name sometimes used to refer to the wye connection is the ___ connection. | star |
| 18. read page 422 | |
| 19.The wye connection in #18 has a winding voltage of 120 volts and a current of 15 amps . If a resistive load is connected phase to neutral on one winding, how much power is delivered by that winding. | 1800 120 * 5 |
| 20. If three single phase loads are connected line to neutral to the generator at 15 amps, what is the total power supplied. | 5400 1800 * 3 |
| 21. Use the three-phase power equation to calculate the power delivered by each of the genertor armatures in question 18. | Wye: 5398 Delta + 5398 see page 423 for math |
| 22. Compare the power delivered by the Wye armature, the Delta armature, and the three single phase loads of question 20. How does the power differ between the connections | the same |
| 23. The wye connection requires ___ conductors to connect the generator to a 3-phase wye load | 4 |
| 24. The delta connection requires ___ conductors to connect the generator to a 3-phase load. | 3 |
| 25 and 26 look in book page 424 |
Created by:
JoshHampton