SITUATION:

An older dc shunt motor is intended to be used to drive a load whose output power requirement varies between 5 and 15 hp but will only tolerate a small speed variation. The name plate rating of the machine is given as 15 hp, 230 volts, 57.1 A., 1,400 rpm. It is known that the field circuit resistance is 115 ? and its armature resistance is 0.13 ?. No data or test results are available on its no-load characteristics.

Problem 3.1

REQUIREMENTS:

The machine needs to be analyzed as to its suitability for the speed requirements (i.e., speed regulation) and its efficiency over the various load requirements. It has already been decided that the accuracy of the analysis does not require taking into account any effect that armature reaction might produce. The data needed for making a judgment on using this machine are:

1. No-load and 5 hp line currents.

2. No-load and 5 hp speeds.

3. Efficiency at both 5 and 15 hp.

SOLUTION

For the conditions stated (disregard armature reaction since data is unavailable on no-load characteristics) one can make a simplified equivalent circuit (or, for those more comfortable with using a dependent source type model, it is also shown). And, for keeping one's thought process ordered, it is recommended that a power flow...