Stator Conductors Flashcards
(29 cards)
what are stator conductors made of
stator conductors are a set of 3phase coils with identical turns wound around stator core so that each phase winding has 2 parts coming out going in
windings of same phase are
directly opposite each other, and each part has a different defined current direction from the other
3 phase current what is happening for phase A at a point 1 (example graph)
at point 1:
phase A current is its positive max point
use right hand rule while observing defined current direction on conductors A1 and A2
reinforced field in between middle of this these 2 in direction of arrows
3 phase current what is happening for phase B at a point 1 (example graph)
-ve values, reinforced field is oriented at 60 deg above phase A’s reinforced field in between B2 and B1
current isnt at max or min -> mag is lower than phase A
3 phase current what is happening for phase C at a point 1 (example graph)
-ve vales
-ve values
reinforced field is oriented at 60 deg above phase A’s reinforced field in between c1 and c2, same magnitude as B
combining the reinforced phase
the strongest reinforced field line is the one in phase A at point 1
2 groups of flux lines B2, A1, C2 and C1,A2,B1
allows us to have 2 poles one S bottom of arrow and N at top of arrow
other points - point 2 A and C decreasing, B increasing
Phase B field is not present due to 0 phase B current so 2 groups of lfux lines are A1 AND C2 AND C1 AND A2
other points - B maximum
the strongest reinforced field line is the one in parallel with phase A at point 1
2 groups of flux lines B2, A1, C1 and C2,A2,B1
for a 4 pole 3 phase motor
12 stator conductors winding slots 30 degres apart
how does 2 pole differ to 4 pole in rotation
in 2 pole, poles make full rotation around stator when ac current changes polarity
in 4 pole, the only do half rotation
what is synchornous speed (fs)
speed at which the field rotaes depending on number of pole pairs (on form sheet)
rotation in caged rotor no load (inital stage)
- initally rotor is stationary, stator is energised and creates rotating magnetic field aroung the rotor , rotor isnt moving so it sweeps pas rotor conductors, changing magnetic flux induced emf, so Ir flows thru
2nd stage
rotor current +magnetic field -> force (torque) rotates in same direction as stator field
3rd stage
rotor speeds up, relative motion between rotor and rotating field decreases,
4th stage
if rotor reaches excat synchronours speed, no changing magnetic field, so Er = 0 and Ir = 0, no torque
5th stage
if it slows before synchronous speed, Er is induced again, Ir flows again, torque is produced again
slip (fs)
difference between synchronous speed and actual rotor speed percentage
slip speed (fs)
actual difference rad/s
s =1
when rotor is stationary
s=0
rotor speed is equal to the synchronous speed
what happens as rotor rotates
rotor conductors experience changes in flux, induced emf and rotor current are changing sinusoidally and their freq fr depends on slip speed because flux cutting only happens when Ω < Ωo
what is induced emf in rotor circuit
Er(ph) due to individual stator phase currents
magnitude og induced emf is depedant on slip speed
𝐸𝑟(𝑝ℎ) = 𝑠𝐸2
where e2 = emf when rotor is stationary (s=1 and fr=f)
What causes current in the rotor of an induction machine?
Relative motion between the stator’s rotating magnetic field and the rotor induces EMF in the rotor, causing current to flow.
