Continuous and alternating current machinery problems; by Ryan William Thomas 1882-

Author:Ryan, William Thomas, 1882- [from old catalog]
Language: eng
Format: epub
Tags: Electric machinery, Electrical engineering
Publisher: New York, J. Wiley & sons, inc.; [etc., etc.]
Published: 1915-03-25T05:00:00+00:00

Fig. 6.—Illustrating Method of Solving Problem 17.

18. A 15-horse-power, 220-volt, single-phase motor, power factor 90 per cent, efficiency 90 per cent is connected to a generator by a transmission line having a resistance of 0.5 ohm. Required the generator voltage.

19. A 20-horse-power, 220-volt, two-phase motor, power factor 90 per cent, efficiency 90 per cent, is connected to a two-phase generator by a transmission line, the resistance of each wire being 0.6 ohm and the inductive reactance 0.3 ohm. Required the generator voltage.

20. Required the generator voltage if the motor in problem 19 were three-phase, and if three of the wires specified in problem 19 were used.

21. Six hundred 25-watt, 110-volt Mazda lamps are

connected to a generator through a transmission line having a resistance of 0.05 ohm and 0.03 ohm inductive resistance. Required the generator voltage.

Note. The power factor of incandescent lamps may be taken as unity.

22. What frequency will give resonance in a circuit having 1 ohm resistance, 10 micro-farads capacity, and 0.350 henry inductance.

23. An induction motor taking a lagging current of 50 amperes, power factor 80 per cent, is connected in parallel with an over-excited synchronous motor which is taking a leading current of 60 amperes, power factor 90 per cent. Required current taken by the two motors and the resultant power factor.

CHAPTER VII THE ALTERNATING-CURRENT GENERATOR

1. Determine the frequency in cycles per second of a current given by a ten-pole alternator running at 720 r.p.m. (6) A generator is to be direct-connected to a Corliss engine running at 120 r.p.m. If the frequency is to be 60 cycles per second^ how many poles must the alternator have?

2. (a) A single-phase generator has a safe current-carrying capacity of 100 amperes and is rated at 250 volts. What would the rating be in kilovolt amperes? (6) A two-phase alternator has a safe current-carrying capacity of 100 amperes per phase, and is rated at 250 volts. Required the rating in kilovolt amperes, (c) A three-phase alternator has a safe current-carrying capacity of 100 amperes per line and is rated at 250 volts. Required the rating in kilovolt amperes.

3. A 200-kilovolt ampere alternator delivers 100 kilowatts at 80 per cent power factor to a number of induction motors. How many 40-watt Mazda lamps at unity factor will the generator carry in addition. The total lines losses are to be 10 per cent.

4. A certain alternator is observed to require 10 amperes exciting current when delivering normal full-load current of 80 amperes at the rated full load e.m.f. of 125 volts and unity power factor. The armature impedance is found to be 0.35 ohm and the resistance 0.15 ohm. Required the total induced e.m.f. of the machine when the exciting current is 10 amperes.

5. A three-phase generator has equal loads of 50 kilo-

THE ALTERNATING-CURRENT GENERATOR 27

watts, 100 per cent power factor delta-connected across each phase. Voltage across each phase is 125. (a) What is the current in each line wire? (6) If the alternator were Y-connected what would the current be in each winding? (c) What would it be if the alternator were delta-connected?

6.

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