Voltage Va = 200 v
Armature Resistance Ra = 0.5Ω
Armature Current Ia = 20 A
Induced EMF = Ea = ?
The Induced EMF of a DC machine working as a Motor is
Ea = Va − IaRa
Ea = 200 − 20 × 0.5
Ea = 190 V
Faraday’s 1st laws of electromagnetic induction tell us about the condition under which an e.m.f. is induced in a conductor or coil a when the magnetic flux linking a conductor or coil changes.
Faraday’s 2nd laws of electromagnetic induction give the magnitude of the induced e.m.f in a conductor or coil and may be stated as:
The magnitude of the e.mf induced in a conductor or coil is directly proportional to the rate of change of magnetic flux linkages.
Suppose a coil has N turns and magnetic flux linking the coil increases (i.e. changes) from φ1 Wb to φ2 Wb in t seconds. Now, magnetic flux linkages mean the product of magnetic flux and the number of turns of the coil.
N = e dφ/dt
Lenz Law:- Lenz’s law states: the direction of the induced e.m.f. is such as to oppose the change producing it. Therefore, the magnitude and direction of induced e.m.f. should be written as :
N = −e dφ/dt
Capacitor start and capacitor run motor: Two capacitors are used for starting, but one of them is cut out when speed reaches 70 percent of the synchronous speed. The capacitor start-and-run motor starts with a high value and a low-value capacitor connected in parallel with each other but in series with the starting winding. This provides a very high starting torque. The centrifugal switch disconnects the high-value capacitor at 80 percent speed, but the lower value capacitor remains in the circuit.
Copper loss is proportional to the square of load current. At half load, load current becomes half as voltage remains the same, so the copper loss will become (1/2)2 i.e 1/4 times of full load copper loss.
At full load copper Loss = I2R
At half load copper Loss = (I/2)2 × R = I2/4 × R
400 = I2/4 × R
I2R = 4 × 400
I2R = Full load copper Loss = 1600 W
The average value of the sine wave over one complete cycle is actually zero. Hence, for a sine wave, the average value is defined over half the period. The average value expressed in terms of peak value is given by
Average value = 0.637 × peak value