. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. it returns as much energy as is sent Out. Hence, the totalwork done during each period is zero, indicating that although a currentbe flowing, this current is not capable of doing external work. Ques. Is the condition as just described met with inpractice? Ans. No. i Ques. Why not? Ans. The condition just described involves that the circuithave no resistance
. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. it returns as much energy as is sent Out. Hence, the totalwork done during each period is zero, indicating that although a currentbe flowing, this current is not capable of doing external work. Ques. Is the condition as just described met with inpractice? Ans. No. i Ques. Why not? Ans. The condition just described involves that the circuithave no resistance, all the load being reactance, but it is im-possible to have a circuit without some resistance, though the 1,112 HAWKINS ELECTRICITY resistance may be made very small in comparison to the react-ance so that a close approach to wattless current is possible. Ques. Give some examples where the phase differenceis very nearly 90:. Ans. If an alternator supply current to a circuit having a verysmall resistance and very large inductance, the current wouldlag nearly 90° behind the pressure. The primary current of atransformer working with its secondary on open circuit is apractical example of a current which represents very little § 3 a J? Fig. —Performance carves of Gen Ques. When the phase difference between the currentand pressure is 90:, why is the current called wattless? Ans. Because the product of such a current multiplied by thepressure does not represent any watts expended. A man lifting a weight, and then allowing it to descend the samedistance to its initial position, as shown in figs. 1,355 to 1,357, presentsa mechanical analogy of wattless current. THE POWER FACTOR 1,113 Let the movement of the weight represent the current and the weightthe pressure. Then calling the weight 10 pounds (volts), and thedistance two feet (amperes). The work done by the man (alternator)on the weight in lifting it is 10 pounds X 2 feet = 20 foot pounds (1) (10 volts X 2 amper
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