Experment 6Characterstc of a permanent magnet dc motorAim of the experiment Study the characteristics of a permanent magnet dc motor.Since the DC motor studied in this experiment is going to be used in other experiment understanding the motor characteristics is important for the controlling.

Motor Applied Voltage12346891010.12

Current(Amperes)0.110.040.040.040.050.060.060.070.07

Speed(rev/sec)0911142431384142

As you see from the graph speed proportional to the applied voltage .

For 6VCurrentSpeed

No Load0.05A24V

Loaded0.4 A12V

We saw that current increased and the speed decreased.They are inversely proportional.f we apply negative (-) 12 volts (Reversed);

Motor Applied Voltage-1-2-3-4-6-8-9-10-10.6

Current(Amperes)-0.08-0.07-0.07-0.08-0.09-0.09-0.10-0.10-0.10

Speed(rev/sec)4912162633384444

*In this figure, changing voltage properties effect the starting speed of the motor it is because of the back e.m.f effect. When Applied current is sufficient to rotate the rotor then there will be no back e.m.f so current will decrease. And then it is increasing linearly.*Direction of rotation is reversed.Its direction became counterclockwise from clockwise.*As you see from the datas the same speed range will be seen after a while.* No load current is not same as you see from the the experimental data. Because a parallel load is added to the circuit which means armature current will decrease as a result of decreasing armature speed. Speed of rotor is directly proportionally to the current on the armature.Problem 1 : Types of D.C. GeneratorsAccording to the way in which their fields are excited, generators are classified into:1.Separately excited D.C. Generatorare those whose fieldmagnets are energized from an independent source of D.C. Current. Separately excitedgenerators are often used in feedback control systems when control of thearmature voltage over a wide range is required.

2. Self excited D.C. Generators ; are those whose fieldmagnets are energized by the currents produced by the generatorsthemselves.There are 3 types of self-excited D.C. Generators named according tothe manner in which their field coils are connected to the armature.These are : Shunt wound D.C. GeneratorSeries wound D.C. GeneratorCompound wound D.C. Generator 3.Shunt wound D.C. Generatorhave field windings and armature windings connectedin parallel (shunt). The output varies inversely with load current. It contains many turnsof fine wires. When a generator is in operation, whether or not it is delivering loadcurrent, the shunt field is always excited.

4. Series wound D.C. Generatorhave field windings and armature windings connectedin series. Outputs vary directly with load currents. Series-wound generators have fewpractical applications. It has few turns of heavy wires. When a generator is in operation,the series field is excited only when a load current is being supplied. In series generator,therefore, the terminal voltage is very low at light loads because of the excitation or loadcurrent is low.

Problem 2:Series WoundThe series DC motor is an industry workhorse for both high and low power, fixed and variable speed electric drives.Applications range from cheap toys to automotive applications.They are inexpensive to manufacture and are used in variable speed household appliances such as sewing machines and power tools. Its high starting torque makes it particularly suitable for a wide range of traction applications.Shunt WoundFixed speed applications such as automotive windscreen wipers and fans.Separately ExcitedTrain and automotive traction applications.Universal MotorsUniversal motors are often used in power tools and household appliances such as vacuum cleaners and food mixers.Problem 3:DC machines continue to be widely used in many applications including mining. No comprehensive condition monitoring tools for large industrial DC machines are available on the market. . Here focuse on the analysis of experimental data obtained in steady state at different loading and speed. After initial evaluation of the machine steady state performance, spectral characteristics of the experimentally obtained armature current, armature voltage, flux density under the main pole and flux density in the commutation zone are developed. Frequency components revealed in the spectra are discussed with relation to their cause, role in brush and commutator wear and their importance for the condition monitoring tool development.