equation of ac machine
In simple, number of turns of armature, intensity of magnet and speed of machine are major factor affecting induced emf in dc generator. If speed is increased, voltage will be increased simultaneously. Also Voltage is greater if number of turns are increased. Electro-magnet in the poles of a DC Generator also play an important role in the induced EMF. If intensity of magnet is exceeds, voltage also increased as well.
In dc motor, the armature conductors are revolving in the magnetic field and emf is induced in the armature conductors. The direction of the induced emf is in opposite direction to the applied voltage as per Flemings left hand rule. So, the induced emf in motor is called as back emf or counter emf. Vydehi
A rotating d.c. motor generates a back-emf which opposes the supply voltage and reduces the current drawn by the motor. When the motor is stationary, it cannot generate this back emf and, so, the only opposition to current is the resistance of its windings which is relatively low. So, on startup, the current is large; as the machine starts to run, the resulting back emf, acts to reduce the current.
What motor is NOT suitable for use as a DC machine?
All types of generators induce EMF in sinusoidal wave form. (A.C.) In a D.C. generator the function of a commutator is to convert A.C. EMF into D.C. The commutator rectifies the output that is the alternating current so as to produce unidirectional alternating current (pulsating DC). This reverses the negative polarity current to a positive one so as the output is a pulsating DC.
The equation for the average over time T is integral 0 to T of I.dt
when the pole flux is zero there is no induced emf in the armature conductor of dc machine as a result of this there is no back emf for controlling action so speed become dangerously high or we can say it will be infinite.
During the operation of a DC motor, EMF is created across its terminals using an external source. Whereas, in a DC generator EMF is created across its terminal based on principle of dynamically induced EMF. So talking in terms of EMF, in DC motor EMF is consumed by the motor coil and utilized to rotate the axle. On the other hand, in DC generator EMF developed across coil is transfered to a load or a battery and consumed by them.
only in dc motor...
In simple, number of turns of armature, intensity of magnet and speed of machine are major factor affecting induced emf in dc generator. If speed is increased, voltage will be increased simultaneously. Also Voltage is greater if number of turns are increased. Electro-magnet in the poles of a DC Generator also play an important role in the induced EMF. If intensity of magnet is exceeds, voltage also increased as well.
Electro Magnetic Field
In dc motor, the armature conductors are revolving in the magnetic field and emf is induced in the armature conductors. The direction of the induced emf is in opposite direction to the applied voltage as per Flemings left hand rule. So, the induced emf in motor is called as back emf or counter emf. Vydehi
The fluctuation of the AC which sets up an magnetic field and causes a reverse emf is lost with DC because there is no variation in the field.
increased Back emf
It depends entirely on the design of the motor.
bad connection
They are Same for dc motor