Dc Current
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DC motors
FIELDS, VOLTAGES, AND CURRENTS Geometry of an elementary DC motor
Flux through a coil of a rotating DC machine
flux linkages of the coil through the coil would change, if the rotor were to rotate at a constant angular velocity, ω
a voltage will be induced in this coil, vcoil,
Points 1 – 5 represent the coil positions.
If a number of coils are placed on the rotor, each connected to a commutator segment, the total induced voltage to the coils, E will be:
where k is proportional to the number of coils.
A coil of a DC motor and a commutator with brushes
If the electrical machine is connected to a load or a source the induced voltage and terminal voltage will be related by:
Example A DC motor, when connected to a 100V source and to no load runs at 1200rpm. Its stator resistance is 2Ω. What should be the torque and current if it is fed from a 220V supply and its speed is 1500rpm? Assume that the field is constant. The first piece of information gives us the constant k. Since at no load the torque is zero and T = ki, then the current is zero as well. This means that for this operation: V = E = kω
FIELDS, VOLTAGES, AND CURRENTS Geometry of an elementary DC motor
Flux through a coil of a rotating DC machine
flux linkages of the coil through the coil would change, if the rotor were to rotate at a constant angular velocity, ω
a voltage will be induced in this coil, vcoil,
Points 1 – 5 represent the coil positions.
If a number of coils are placed on the rotor, each connected to a commutator segment, the total induced voltage to the coils, E will be:
where k is proportional to the number of coils.
A coil of a DC motor and a commutator with brushes
If the electrical machine is connected to a load or a source the induced voltage and terminal voltage will be related by:
Example A DC motor, when connected to a 100V source and to no load runs at 1200rpm. Its stator resistance is 2Ω. What should be the torque and current if it is fed from a 220V supply and its speed is 1500rpm? Assume that the field is constant. The first piece of information gives us the constant k. Since at no load the torque is zero and T = ki, then the current is zero as well. This means that for this operation: V = E = kω
