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vb.net barcode reader code and, similarly I2 = in Software
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Code39 Generation In Java Using Barcode drawer for Java Control to generate, create Code 3 of 9 image in Java applications. Making Code 39 Full ASCII In ObjectiveC Using Barcode creation for iPhone Control to generate, create ANSI/AIM Code 39 image in iPhone applications. 2 To draw the phasor diagram, we need only to compute the capacitor current, since we have already computed the other two: ZC = j XC = j 2692 VS = 1783 (1571) A IC = ZC The total current is IS = I1 + I2 + IC = 3125 0 A The phasor diagram corresponding to these three currents is shown in Figure 736 Focus on ComputerAided Tools: A le containing the computergenerated solution to
this problem may be found in the CDROM that accompanies this book
Check Your Understanding
76 Compute the power factor for the load of Example 76 with and without the inductance in the circuit 77 Show that one can also express the instantaneous power for an arbitrary complex load Z = Z as p(t) = I 2 Z cos + I 2 Z cos(2 t + ) ~ VS
+ ~
78 Determine the power factor for the load in the circuit of Figure 737, and state whether it is leading or lagging for the following conditions: a vS (t) = 540 cos( t + 15 ) V i(t) = 2 cos( t + 47 ) A b vS (t) = 155 cos( t 15 ) V i(t) = 2 cos( t 22 ) A 79 Determine whether the load is capacitive or inductive for the circuit of Figure 737 if a b c d pf = 087 (leading) pf = 042 (leading) vS (t) = 42 cos( t) i(t) = 42 sin( t) vS (t) = 104 cos( t 12 ) i(t) = 04 cos( t 12 ) 710 Prove that the power factor is indeed 1 after the addition of the parallel capacitor in Example 78 711 Compute the magnitude of the current drawn from the source after the power factor correction in the circuit of Example 78 TRANSFORMERS
AC circuits are very commonly connected to each other by means of transformers A transformer is a device that couples two AC circuits magnetically rather than through any direct conductive connection and permits a transformation of the voltage and current between one circuit and the other (for example, by matching a highvoltage, lowcurrent AC output to a circuit requiring a lowvoltage, highcurrent source) Transformers play a major role in electric power engineering and Part I
Circuits
are a necessary part of the electric power distribution network The objective of this section is to introduce the ideal transformer and the concepts of impedance re ection and impedance matching The physical operations of practical transformers, and more advanced models, will be discussed in 16 The Ideal Transformer The ideal transformer consists of two coils that are coupled to each other by some magnetic medium There is no electrical connection between the coils The coil on the input side is termed the primary, and that on the output side the secondary The primary coil is wound so that it has n1 turns, while the secondary has n2 turns We de ne the turns ratio N as n2 N= (732) n1 Figure 738 illustrates the convention by which voltages and currents are usually assigned at a transformer The dots in Figure 738 are related to the polarity of the coil voltage: coil terminals marked with a dot have the same polarity Since an ideal inductor acts as a short circuit in the presence of DC currents, transformers do not perform any useful function when the primary voltage is DC However, when a timevarying current ows in the primary winding, a corresponding timevarying voltage is generated in the secondary because of the magnetic coupling between the two coils This behavior is due to Faraday s law, as will be explained in 16 The relationship between primary and secondary current in an ideal transformer is very simply stated as follows: V2 = N V1 I1 I2 = N (733)

