31-01-2012, 12:52 PM
SYNCHRONOUS MOTORS
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Synchronous Motors …Steady-state Operation
for field current less than value related to IA,min armature current is lagging, consuming reactive power, while when field current is greater than value related to IA,min armature current is leading, and supplying Q to power system
Therefore, by adjusting the field current, reactive power supplied to (or consumed by) power system can be controlled
Syn Motor…Steady-state Operation 2nd Example
The 208, 45 kVA, 0.8 PF leading, Δ connected, 60 Hz syn. motor of last example is supplying a 15 hp load with an initial PF of 0.85 PF lagging. If at these conditions is 4.0 A
(a) sketch initial phasor diagram of this motor, & find IA & EA
(b) motor’s flux increased by 25%, sketch new phasor diagram of motor. what are EA, IA & PF ?
© assume flux in motor varies linearly with If, make a plot of IA versus If for a 15 hp load
STRATING SYNCHRONOUS MOTORS
Sofar, in study of syn. motor, it is assumed that motor is initially turning at syn. Speed
However, how did motor get to synchronous speed?
realizing that for a 60 Hz motor at moment power applied to stator, rotor is stationary, and BR is stationary
Stator magnetic field BS is starting to sweep around at syn. speed
At t=0 BR and BS are exactly lined up.
Tind= k BR x BS would be zero
STRATING SYNCHRONOUS MOTORS
2- use an external prime mover to accelerate motor up to syn. Speed, follo the paralleling procedure and bring machine on the line as a generator, turning off the prime mover will make syn. Machine a motor
3- use damper windings or amortisseur windings. Its function described next
