1) Synchronous motors and alternators operate based on the same principles - they have a rotor that is synchronized to rotate at the same speed as the rotating magnetic field in the stator. 2) Alternators produce voltage through the interaction of a magnetic field and a conducting coil moving through this field. They require a conducting path, magnetic field, and relative motion between the two to generate an electromotive force (EMF). 3) Synchronous machines can operate in parallel by ensuring their frequencies, voltages, phase sequences, and synchronization are identical to share load demand. Proper synchronization is critical for parallel operation.

1. 3 Phase Synchronous Machines
Learning 10 & 11
L/O 10 & 11 jh 3/05 1

2. A cage type induction motor will travel at a speed slightly slower than
synchronous speed due to slip.
If there were no slip the motor would travel at synchronous speed…..a
cage motor can not deliver torque at synchronous speed.
A SYNCHRONOUS MOTOR has special DC windings which latch onto
the rotating magnetic field.
The RMF drags the rotor around at synchronous speed.
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3. In simple terms….
A motor can generate and a generator can be made to motor.
A synchronous motor and an alternator are one and the same machine.
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4. DC field
AC output on rotor
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5. L/O 10 & 11 jh 3/05 5

6. An alternator can motor and under bad circumstances drive the diesel
engine like a compressor !
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7. Synchronous motor rotor
Rotor & amortisseur windings (bars)
www.tecowestinghouse.com L/O 10 & 11 jh 3/05 7

8. Stator
Salient poles on rotor
Pony motor Excitation gear AC/stator windings
www.panasia.com
Synchronous Motors
L/O 10 & 11 jh 3/05 8

9. Synchronous motor rotor with DC excitation unit. AC is induced into rotor of exciter and rectified to
smooth DC for the DC fields which are embedded in the laminations. 4 pole ??
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10. Construction details.
• Large diameter rotors for slow moving
machines. Often salient pole type.
• Small rotors for faster machines eg; 6,4,2
pole machines
• Stators are essentially the same for all
speeds
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11. Frequency and speed.
n x p
f = ------------ Hz.
120
n = RPM
f = frequency in hertz
P = number of poles
120 = 60 x 2 Pairs of poles eg 1 x N & 1 x S
Minutes to seconds
P 251 L/O 10.2 L/O 10 & 11 jh 3/05 11

12. For an ALTERNATOR.
What do we need to produce an EMF ????
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13. For an ALTERNATOR.
What do we need to produce an EMF ????
1. Conducting path
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14. For an ALTERNATOR.
What do we need to produce an EMF ????
1. Conducting path
2. Magnetic field
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15. For an ALTERNATOR.
What do we need to produce an EMF ????
1. Conducting path
2. Magnetic field
3. Relative motion between the 2
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16. This is for explanation only
Consider this
Not in the exam.
equation
Vg = 4.44 x Ø x f x N x kd x kp
4.44 = 4 x 1.11 (form factor)
Ø = flux per pole
f = frequency (speed of cutting)
N = number of turns in coil
Kd & Kp = winding type and style
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17. Different shapes of sine waves
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18. Shows how each conductor/coil contributes
to the sine wave within the alternator.
For interest only. L/O 10 & 11 jh 3/05 15

19. Voltage regulation.
L/O 11.2 p 254 L/O 10 & 11 jh 3/05 16

20. No load volts Full load No load
Voltage regulator
catches load.
100% load @ .8pf Vert = 20V/div Horiz = 1s/div
750kVA Alternator L/O 10 & 11 jh 3/05 17

21. Alternator
Alt
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22. Alternator
Load
Alt
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23. Alternator
XL
Internal
Impedance
R Load
Alt
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24. As an alternator goes on load, the
internal losses cause the output
voltage to drop.
The powerfactor of the load
affects the output voltage.
Jenneson p 254 L/O 10 & 11 jh 3/05 19

25. Drop to internal
losses.
Jenneson p 254 L/O 10 & 11 jh 3/05 20

26. Voltage regulation
Read carefully the example 11.3 p 254
Important….you
need to know
this !!
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27. Frequency .. No load to 100% FLC
Horiz = 1sec/div
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28. Nameplate data
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L/O 10.4 etc
NRG turbine set

29. Main Altnr. bearing Exciter
NRG Turbine set
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30. L/O 10 & 11 jh 3/05 25
NRG gas turbine

31. L/O 10 & 11 jh 3/05 26

32. Sliprings
To take DC
to the rotor
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33. The effects of change in excitation of an alternator.
Read carefully 11.3.4 this is difficult stuff.
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34. L/O 11.1 p 255 L/O 10 & 11 jh 3/05 29

35. A stand alone alternator is one which delivers
power to its own isolated load away from the
power grid.
L/O 11.1 p 255 L/O 10 & 11 jh 3/05 29

36. A stand alone alternator is one which delivers
power to its own isolated load away from the
power grid.
Paralled machines are either supplying load to a
grid system or they could be supplying a common
load along with one or more alternators.
L/O 11.1 p 255 L/O 10 & 11 jh 3/05 29

37. A stand alone alternator is one which delivers
power to its own isolated load away from the
power grid.
Paralled machines are either supplying load to a
grid system or they could be supplying a common
load along with one or more alternators.
A machine could be
•“tied to the grid”
•Separate from the grid
•Paralled to one or more machines
L/O 11.1 p 255 L/O 10 & 11 jh 3/05 29

38. Parallel operation
1. Waveforms the same
2. Same phase sequence
3. Same voltages
These are usually ”user
4. Voltages in phase changeable”
5. Same frequency
Jenneson p 255
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39. The frequencies must be the same.
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40. Phase sequence need to be the same
The voltages and sequence need to be identical between
the mains and the incoming machine.
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41. Alternator at Gladstone
Base Hospital (one of 3
sets throughout the L/O 10 & 11 jh 3/05 33
hospital.)

42. 3 phase Dunlite machine
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43. Small 1 phase portable 5kVA unit
750W portable unit
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44. Synchronous motors
In simple terms….
A DC field in the rotor “locks into” the rotating
magnetic field of the stator and the rotor gets
dragged around at synchronous speed.
Ref. to Ralph’s pp
Jenneson p 259 L/O 11 L/O 10 & 11 jh 3/05 36

45. Dragline machines L/O 10 & 11 jh 3/05 37
The square grey machines are sync. motors

46. Transportable sub-station to
power dragline. L/O 10 & 11 jh 3/05 38

47. L/O 10 & 11 jh 3/05 39