Principles of Electric Machines with Power Electronic Applications 2nd. Edition by Mohamed E. El-Hawary | 9780471208129 | 0471208124

Power Electronic, Electrical Machines

Principles of Electric Machines with Power Electronic Applications

70 SOLVED PROBLEMS

Question: 7.9

Consider the motor of Fig. 7.2. Establish the following points (|Ia| and |Ef|) on the V curve corresponding to full-load power output: (a) Stability limit, δ = – 90 deg. (b) Power factor of 0.8 Igging. (c) Unity power factor. (d) Power factor of 0.8 leading. ...

Verified Answer:

We recall the following specifications from Exampl...

Question: 8.A.3

For the motor of Problem 8.A.2, assume that the stator impedance is given by Z1 = 1.86 +j2.56 Ω Find the internal mechanical power, output power, power factor, input power, developed torque, and efficiency, assuming that friction losses are 15 W. ...

Verified Answer:

We need the backward-field impedance

Z_{b}=...

Question: 8.A.2

The forward-field impedance of a one-quarter-hp four-pole 110-V 60-Hz single-phase induction motor for a slip of 0.05 is given by Zf = 12.4 + j16.98 Ω Assume that Xm = 53.5 Ω Find the values of the rotor resistance and reactance. ...

Verified Answer:

We have

Z_{f}=\frac{j0.5X_{m}[0.5(R_{2}^{\p...

Question: 8.A.1

A single-phase induction motor takes an input power of 490 W at a power factor of 0.57 lagging from a 110-V supply when running at a slip of 5%. Assume that the rotor resistance and reactance are 1.78 Ω and 1.28 Ω, respectively, and that the magnetizing reactance is 25 Ω. Find the resistance and ...

Verified Answer:

The equivalent circuit of the motor yields

...

Question: 8.2

For the single-phase induction motor of Example 8.1, it is required that the power and torque output, and the efficiency when running at a slip of 5%, be found. Neglect core and rotational losses. ...

Verified Answer:

In Example 8.1, we obtained

Z_{i}=26.841\an...

Question: 8.1

The following parameters are available for a 60-Hz four-pole single-phase 110-V 1/2-hp induction motor. R1 = 1.5 Ω X1 = 2.4 Ω Xm = 73.4 Ω R’2 = 3 Ω X’2 = 2.4 Ω Calculate Zf, Zb, and the input impedance of the motor at a slip of 0.05. ...

Verified Answer:

Z_{f}=\frac{j\,36.7(30+j1.2)}{30+j37.9}=22....

Question: 7.13

Asynchronous machine is supplied from a constant-voltage source. At no load, the motor armature current is found to be negligible when the excitation is 1.0 p.u. The p.u. motor constants are Xd = 1.0 and xq = 0.6. (a) If the machine loses synchronism when the angle between the quadrature axis and ...

Verified Answer:

(a)

P=\frac{V E_{f}}{X_{d}}\,\mathrm{sin}\,...

Question: 7.12

The machine of Example 7.11 is connected to an infinite bus through a link with reactance of 0.2 p.u. The excitation voltage is 1.3 p.u. and the infinite-bus voltage is maintained at 1 p.u. For a power angle of 25 deg, compute the active and reactive power supplied to the bus. ...

Verified Answer:

We have

\begin{array}{l}{{X_{d}=0.95+0.2=1....

Question: 7.11

The reactances Xd and xq of a salient-pole synchronous generator are 0.95 and 0.7 p.u., respectively. The armature resistance is negligible. The generator delivers rated kVA at unity PF and rated terminal voltage. Calculate the excitation voltage. ...

Verified Answer:

We apply

E_{f}^{\prime}=V_{t}+j I_{a}x_{q}[...

Question: 7.10

An 800-hp three-phase induction motor operated at 0.7 PF lagging from a 2300-V supply. (a) Find the line current. (b) The synchronous motor of Example 7.2 is connected in parallel with the induction motor and is operated as a capacitor (zero power factor). Find the necessary excitation voltage to ...

Verified Answer:

(a) The line current with the induction motor oper...