Basically I don\'t have any guidance on these but am looking to know how to solv

Question

Basically I don't have any guidance on these but am looking to know how to solve for these questions, I would appreciate any help, I've read through the chapter but might be to burned to see the obvious PROBLEMS Problems 9-1 to 9-12 refer to the following dc motor: 55 A Praed 15 hp VT- 240 V NF- 2700 turns per pole NSE- 27 turns per pole nnted 1200 r/min RF 100 RA 0.40 n R.di 100 to 4000 Rs 0.04 n Rotational losses are 1800 Wat full load. Magnetization curve is as shown in Figure P9-1. In Problems 9-1 through 9-7, assume that the motor described above can be con- nected in shunt. The equivalent circuit of the shunt motor is shown in Figure P9-2. 9-1. If the resistor RM is adjusted to 175 n what is the rotational speed of the motor at no-load conditions? 9-2. Assuming no armature raction, what is the speed of the motor at full load? What is the speed regulation of the motor? 9-3. If the motor is operating at full load and if its variable resistance R. is increased to 250 n, what is the new speed of the motor? Compare the full-load speed of the mo- 175 n to the full-load speed with R 250 (2. (Assume no amma tor with R. adj ture reaction, as in the previous problem.) 9-4. Assume that the motor is operating at full load and that the variable resistor R. is again 175 n. If the armature reaction is 1200 A turns at full load, what is the speed of the motor? How does it compare to the result for Problem 9-2? 9-5. If R can be adjusted from 100 to 400n, what are the maximum and minimum no- load speeds possible with this motor? 9-6. What is the starting current of this machine if it is started by connecting it directly to the power supply VT? How does this starting current compare to the full-load cur- rent of the motor?

Explanation / Answer

Q.(9-1). If the resister Radj is adjusted to 175 what is the rotational speed of the motor at no load

conditions?

Answer –

According to the problem, In case of shunt machine if the machine is allowed to run on no load by

applying rated voltage across it then first we have back emf Eb = V(rated) = 240 volt as the armature voltage drop is negligible and also at no load as output is zero that’s why the whole no load input is equal to loss means it becomes loss. Therefore, at no load machine runs at rated speed and it is unaffected

by increase in variable resistance Radj .

Note – The whole solution given above is applicable for shunt or compound machine only and also

above practice come under no load test or Swinburne’s test and it done only to determine the constant

losses.

Thank You.

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