৪৯তম বিসিএস ⎯ তথ্য ও যোগাযোগ প্রযুক্তি (EEE) [ ৮৯২] · তারিখ অনির্ধারিত · ৩০ প্রশ্ন
Leakage flux does not link the intended winding/armature and does not contribute to energy conversion
Leakage flux induces leakage reactance which leads voltage drop
Smaller air gap improves flux linkage that means less leakage
E=−NdΦ/dt
E=NΔΦ/Δt=200×(0.02/0.01)=400V
Lenz’s law states that the induced EMF opposes the cause producing it
E = (P * Φ * Z * N) / (60 * A)
E: is the generated EMF in volts.
P: is the number of poles in the generator.
Φ: is the flux per pole in Webers.
Z: is the total number of armature conductors.
N: is the speed of the armature in revolutions per minute (RPM).
A: is the number of parallel paths in the armature winding
E=Blv=1×0.5×10=5V
the induced emf is directly proportional to the speed i.e E∝N
E=Mdi/dt=0.5×4=2V
AC supply produces AC magnetic field
Core losses = hysteresis + eddy current losses.
Pe ∝ f2B2t2
B is the maximum flux density
f is the frequency of the magnetic field
t is the thickness of the material
Laminations increase resistance to eddy current paths.
Induced circulating currents in metallic core due to flux change
E = PΦZN/60A , where P denotes the number of poles.
The commutator rectifies the generated AC into DC
In a shunt generator, the field winding is connected parallel to the armature.
Residual magnetism provides the initial flux needed to start EMF generation
Armature reaction distorts the main field which affects commutation.
The open-circuit characteristic (OCC) or No load characterstics is also called the magnetization curve
Shunt generators maintain nearly constant voltage with varying loads.
EMF is directly proportional to speed (?∝?). so same amount changes will occur
interpoles reduce sparking and improve commutation by neutralizing armature reaction
Voltage regulation is the change from no-load to full-load voltage it is expressed in percentage.
Lap winding has more parallel paths, suitable for high-current applications
Load characteristic plots terminal voltage vs load current.
Maximum efficiency occurs when variable copper losses equal constant iron losses
In separately excited generators, field winding is supplied from an external DC source
E=V+IaRa =200+(100×0.1)=210V