Phase-Splitting Split-Phase Induction Motor
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Transcript of Phase-Splitting Split-Phase Induction Motor
Phase-SplittingSplit-Phase Induction Motor
Main Winding contributes “Direct-Axis” flux, d
Auxiliary Winding contributes “Quadrature-flux”, q
Auxiliary Winding is also known as the “Starting Winding”
Equivalent Circuit
Purpose of the “Phase-Splitter”
• Make the current in the Auxiliary Winding out of phase with the current in the Main Winding.
• This results in the quadrature field and the main field being out of phase.
• The locked-rotor torque will be given by
sin
mw aw
lr sp mw aw
i i
T k I I
Example 6-1
• The main and auxiliary windings of a hypothetical 120 V, 60 Hz, split-phase motor have the following locked-rotor parameters:– Rmw=2.00 Ω Xmw=3.50 Ω
– Raw=9.15 Ω Xaw=8.40 Ω
• The motor is connected to a 120 V system. Determine
Example 6-1 continued
• The locked-rotor current in each winding
2.00 3.50 4.0311 60.2511
9.15 8.40 12.4211 42.553mw mw mw
aw aw aw
Z R jX j
Z R jX j
120 029.8 60.3
4.0311 60.2511120 0
9.66 42.612.4211 42.5530
T
mw
mw
T
aw
aw
VI A
ZV
I AZ
Example 6-1 continued
Example 6-1 continued
• The phase displacement angle between the main and auxiliary currents
60.3 42.6 17.7mw awi i
Example 6-1 continued
• The locked-rotor torque in terms of the machine constant
sin
(29.8)(9.66)sin17.7 87.52
lr sp mw aw
lr sp sp
T k I I
T k k
Example 6-1 continued
• External resistance required in series with the auxiliary winding in order to obtain a 30 phase displacement between the currents in the two windings.
Example 6-1 continued
• Phasor diagram for the new conditions
' 60.3 30 30.3awi
Example 6-1 continued
' '
' '
'
'
030.3
'
30.3aw
aw
T T
aw aw
aw aw Z
Z
aw x aw aw
V VI I
Z Z
Z R R jX
Example 6-1 continued
'
'
tan
tan
8.409.15 14.38 9.15 5.23
tan30.3
aw
aw
aw
Z
aw x
aw
x aw
Z
XR R
XR R
R
Example 6-1 continued
• Locked-rotor torque for the condition in d
'
'
'
sin
120 09.15 5.23 8.40
7.2 30.29
(29.8)(7.2)sin30 107.1
107.1
lr sp mw aw
T
aw aw
aw
aw
lr sp sp
lr sp
T k I I
VI I
Z jI
T k k
T k
Example 6-1 continued
• % increase in locked-rotor torque due to the adding of additional resistance
107.1 87.52100% 22.37%
87.52sp sp
sp
k kX
k