01․ A series generator is connected in series to a feeder having 0.5Ω resistance to boost the voltage. The induced voltage is given by Eg = 0.6Ia, Ra = 0.2Ω and Rs = 0.3Ω. Find the voltage boosted by the generator, when delivering 400 Amp?
02․ When an electric train is moving down a hill, the DC motor will operate as
Normally in electric traction DC series motors are employed. At above condition the back emf is greater than supply voltage hence it will operate as series generator.
03․ The DC generator runs at a speed of 1000 rpm and flux per pole is 0.2 Wb, number of poles are 2 the winding is wave wound and having 480 conductors. The critical speed is 1200 rpm. Then the generated emf ( Eg )
If the critical speed of machine is less than the speed of the machine, then only emf will generate. In above case critical speed is greater than speed of machine. Hence no emf will generates i.e., 0 V.
04․ A 4 pole dynamo with wave wound armature has 51 slots contains 20 conductors in each slot. If induced emf 357 Volts and speed is 8500 rpm, flux per pole will be
05․ What is the full form of MNP?
The plane through the axis, along which no emf is induced in the armature conductor is known as MNP ( Magnetic neutral plane ).
06․ A shunt generator has a critical field resistance of 300 Ω at a speed of 800 rpm if the speed is raised to 1000 rpm the critical field resistance is
Given critical resistance = 300 Ω at 800 rpm. For generator, Eg ∝ N. So the critical field resistance also increases slightly with speed.
07․ The polarity of a DC generator can be reversed by
In a DC generator, if we reverse the field current then the polarities of voltage generated is reversed as the current flows in opposite direction.
08․ The principle of dynamically induced emf is utilized in
In generator emf is generated due to relative motion between a magnetic field and rotation of conductors. So the emf generated is dynamically induced emf.
09․ Emf induced in a coil rotating in a uniform magnetic field will be maximum when the
According to Faraday’s law of electromagnetism, emf induced in a coil rotating in a uniform magnetic field is directly proportional to the rate of change of flux linkage. So emf induced will be maximum when rate of change of flux linkage is maximum.
10․ Magnetic field in a DC generator is produced by
Magnetic field in DC generators is produced by passing current through the field windings present on the core of the stator. So the magnetic field is produced by electromagnets.