Electric Machines 5th. Edition by D.P. Kothari; I.J. Nagrath | 9789352606405 | 935260640X | Holooly

Electric Machines [EXP-57611]

225 SOLVED PROBLEMS

Question: 10.5

A (1/2) kW, 4-pole, 50 Hz, 220 V, two-value capacitor motor has the following circuit model parameters: R1m = 4.2 Ω , X1m = 11.3 Ω R1a = 5.16 Ω , X1a = 12.1 Ω X = 250 Ω , a = 1.05 Ω R2 = 7.48 Ω , X2 = 7.2 Ω Friction, windage and core losses = 45 W (a) Calculate the starting torque and current if

Verified Answer:

(a) s = 1

\bar{Z}_{f}=\bar{Z}_{b}=j 2...

Question: 7.57

A 10 kW, 250 V, dc shunt motor with an armature resistance of 0.8 Ω and a field resistance of 275 Ω takes 3.91 A, when running light at rated voltage and rated speed. (a) What conclusions can you draw from the above data regarding machine losses? (b) Calculate the machine efficiency as a

Verified Answer:

(a) Shunt field loss,

P_{s h}...

Question: 8.23

A 10 MV A, 13.8 kV, 50 Hz synchronous generator yields the following test data: OC test If = 842 A at rated voltage SC test If = 226 A at rated armature current (a) Calculate its pu adjusted synchronous reactance OC test revealed that the armature resistance per phase is 0.75 Ω . (b) The

Verified Answer:

(a)

X_{s}...

Question: 7.18

A 100 kW, 200 V, 1000-rpm dc shunt generator has Ra = 0.03 Ω . The generator is driven at rated speed and excitation is such that it gives a rated voltage of 200 V at no-load. The data for the magnetization characteristic of the generator are as follows: If^* (A) 0 1 2.2 3.3 4.5 7.1 EMF(V) 10 32.5

Verified Answer:

The magnetization characteristic is drawn in Fig. ...

Question: 7.16

A 100 kW, 200 V, long-shunt commutative compound generator has equivalent armature resistance of 0.03 Ω and a series field resistance of 0.004 Ω . There are 1200 shunt turns per pole and 5 series turn per pole. The data of its magnetization characteristic at 1000 rpm is given below: If (A) 0 1 2.2

Verified Answer:

The schematic diagram of long-shunt compound gener...

Question: 8.37

A 100-MV A, 22-kV, 50-Hz synchronous generator is operating open circuited and is excited to give rated terminal voltage. A 3-phase (symmetrical) short circuit develops at its terminals. Neglecting dc and double frequency components of current. (a) find the initial current, and (b) find the

Verified Answer:

(a) Initial current,

...

Question: 8.39

A 1000 kVA, 6.6 kV, 50 Hz, Y-connected synchronous generator has a no-load voltage of 11.4 kV at a certain field current. The generator gives rated terminal voltage at full load 0.75 lagging power factor at the same field current. Calculate: (a) The synchronous reactance (armature resistance

Verified Answer:

I_{a}(f l)=\frac{1000}{\sqrt{3} \times 6.6...

Question: 8.8

A 1000 kW, 3-phase, star-connected, 3.3 kV, 24-pole, 50 Hz synchronous motor has a synchronous reactance of 3.24 Ω per phase; the resistance being negligible. (a) The motor is fed from infinite bus-bars at 3.3 kV. Its field excitation is adjusted to result in unity pf operation at rated load.

Verified Answer:

(a) The operation of motor at infinite bus-bars is...

Question: 8.31

A 12 pole, 50 Hz synchronous motor has saturated Xd = 0.8 pu and Xq = 0.5 pu. It is supplying full load at rated voltage of 0.8 pf leading. Draw the phasor diagram and calculate the excitation emf in pu. Calculate its pu synchronizing power per degree elect. and pu synchronizing torque per degree

Verified Answer:

The phasor diagram is drawn in Fig. 8.92.

...

Question: 9.7

A 15 kW, 415 V, 4-pole, 50 Hz delta-connected motor gave the following results on test (voltages and currents are in line values): No-load test 415 V 10.5 A 1,510 W Blocked-rotor test 105 V 28 A 2,040 W Using the approximate circuit model, determine: (a) the line current and power factor for

Verified Answer:

O P_{0}=10.5 A

\cos...

Loading...