ব্যাখ্যা: They improve the waveform of generated EMF Le. generated EMF can be made to approximate to sine wave more easily and the distorting harmonics can be reduced or totally eliminated.

ব্যাখ্যা: Counter emf or back emf makes the DC motor a self- regulating machine. Le. It makes the DC motor to draw armature current which is just enough to develop the required torque. Thus it helps in energy conversion and it is always less than applied voltage.

ব্যাখ্যা: Field winding in a DC motor is not a rotating part. It is present away from the motating part of the machine. So, temperature rise in the machine will not produce any effect on the machine rotation. Thuse field winding can sustain the maximum temperature rise.

ব্যাখ্যা: As increased load means that it requires more torque to turn at that speed. The motor is not producing that torque. So motor will slow or decrease a little bit.

ব্যাখ্যা: Power is measured in watt. Joules. Strength of current measured in Amperes. Ampere-hour is the unit of quantity of electricity of electric charge.

ব্যাখ্যা: The field winding is connected across the armature. The resistance offered by the field is constant so the current is constant. Therefore the speed of the DC shunt motor depends on the back EMF.

ব্যাখ্যা: Negative sequence over current relays are used to detect the unbalanced load on a generator which may cause excessive rotor heating. The relay is also used to detect unbalanced load currents in motors.

ব্যাখ্যা: The starting winding also known as the auxiliary winding is used to create the torque needed to start a single phase motor. The starting winding is placed in the stator and also parallel of rotor of the motor.

ব্যাখ্যা: Slip ring induction motor is a type of motor where its external circuit is connected using some rings. This rings attached with high resistance acts as an external circuit for the rotor. This external circuit helps in developing a high starting torque with low current

ব্যাখ্যা: If back emf vanishes suddenly, motor circuit will try to retain emf by drawing more current from supply. If supplying unit didn't trip down by this time, excess current in armature may heat up the armature.

ব্যাখ্যা: N₁= 120f/P = 120x50/4 = 1500 грm

ব্যাখ্যা: Differential compound motor gives low starting torque, examined by torque current characteristic.

ব্যাখ্যা: The art of welding refers to a fabrication process that causes coalescence between materials such as metals, thermoplastics and others. In welding, heat is used to melt the workpieces and a filler materials is used to form a weld pool or molten material.

ব্যাখ্যা: E = V- laRa ⇒ 110 = 120-la x0.5 la = 20 A

ব্যাখ্যা: The direction of the induced emf is always such as to result in opposition to the change producing it. This law is known as Lenz's law

ব্যাখ্যা: When the DC motor is connected across the supply without load then it will draw a small amount of current form supply. As low current will flow through the field winding as well as armature widing so main flux produced will be lesser. As, main flux is lower. speed will tend to increase. As speed increases back em also increases and thus current drawn from the supply will become more and more lower and thus main flux will also become more and more lower and thus speed will tend to increase more and more.