When the speed of DC motor is increased back EMF decreases and current drawn increases?
Explanation: In case of DC motor, the speed is proportional to the back emf (Ea ∝ N). So, with the increase in speed, the back emf also increases. Therefore, armature current is also decreased, in case of series motor, armature current is equal to the line or load current. 4.
When the speed of a DC motor increases its armature current?
The speed of a dc motor is changed by changing the current in the field or by changing the current in the armature. When the field current is decreased, the field flux is reduced, and the counter emf decreases. This permits more armature current. Therefore, the motor speeds up.
What is the relation between back EMF and speed?
Back EMF is directly related to speed, so when the speed decreases, so does the induced back EMF. From the equation above, we can see that if there is less back EMF, the voltage (and, therefore, current) across the motor will increase.
What is the back emf in DC motor?
back EMF in Electrical Engineering
Back EMF is the system in the coil of an electric motor that opposes the current flowing through the coil, when the armature rotates. When the speed varies, the winding characteristics may fluctuate, resulting in variation of back EMF.
What happens if the back emf of a DC motor suddenly vanishes?
Detailed Solution. If back emf of a dc motor vanishes suddenly, motor circuit will try to retain back emf by drawing more current from supply. As the back emf vanishes zero, the whole supply voltage appears across armature and heavy current flows.
How can we increase the speed of a DC motor?
Thus, the speed of a DC motor can be controlled in three ways:
- By varying the supply voltage.
- By varying the flux, and by varying the current through the field winding.
- By varying the armature voltage, and by varying the armature resistance.
Why is the speed of DC shunt motor dependent on back emf?
Right Answer is:
The field winding is connected across the armature. The resistance offered by the field is constant so the current is constant. As current is constant flux also becomes constant b the cause flux is directly proportional to current. Therefore the speed of the DC shunt motor depends on the back EMF.
When speed of a DC generator decreases the armature current?
Hint: The speed of DC motor can be changed by changing the current in the field or current in armature. When the current in the field is decreased then the flux through armature also decreases. This leads to the decrease in the back emf which leads to flow of the armature current through it.
The speed of DC motor is directly proportional to back emf and inversely proportional to flux per pole. Since the flux is constant. Thereby the speed is only depends on the back emf and the speed isis proportional to the back emf. Hence speed is also increased by 5% with in increase 5% of back emf.
How do you calculate the emf of a DC motor?
EMF equation of a DC generator
- Average emf generated per conductor is given by dΦ/dt (Volts) … eq. …
- Flux cut by one conductor in one revolution = dΦ = PΦ …. (Weber),
- Number of revolutions per second (speed in RPS) = N/60.
- Therefore, time for one revolution = dt = 60/N (Seconds)
- From eq.
How do you sense back EMF?
Methods for detecting back EMF
The simplest is to compare the back EMF to half the DC bus voltage using a comparator. Figure 4a shows a schematic of such a system. In this case, the comparator is connected to coil B; a complete system would have a comparator connected to every coil.
How is back EMF measured on an AC motor?
Back EMF = Applied Voltage minus (Input Current times Measured Resistance) How speed of the DC shunt motor can be increased?
6. How speed of the DC shunt motor can be increased? Explanation: For a constant load, load current will remain constant. Decreasing armature current will help in increasing speed for DC shunt motor.