Synchronous
machine
1. Construction
Synchronous Machines
Generator
Exciter
View of a two-pole round rotor generator and exciter.
Synchronous Machines
Stator with
laminated iron core
B
A
Slots with
phase
winding
CA+
+
+
N
S
B-
B+
-
+
+
-
Rotor with
dc winding
+
-
-
-
A-
C+
C
Major components of a round rotor two-pole generator
Synchronous Machines
Cross-section of a large turbo generator. (Courtesy Westinghouse)
Synchronous Machines
Metal frame
Laminated iron
core with slots
Insulated copper
bars are placed in
the slots to form
the three-phase
winding
Details of a generator stator.
Synchronous Machines
Rotor block of a large generator. (Courtesy Westinghouse)
Synchronous Machines
Generator rotor with conductors placed in the slots.
Synchronous Machines
Steel
retaining
ring
Shaft
Shaft
Wedges
DCcurrent
current
DC
terminals
terminals
Large generator rotor completely assembled. (Courtesy Westinghouse)
Synchronous Machines
Stator with
laminated iron core
B+
C-
A+
Rotor with
dc winding
N
+
+
+
+
+
A-
S
B-
C+
Two-pole salient pole generator concept.
Slots with
phase
winding
Synchronous Machines
A-
B+
C+
C-
N
-
+
+
+
+
-
A+
S
S
+
+
-
A+
-
+
+
B-
B-
N
C+
A-
CB+
Four-pole salient pole generator concept.
Synchronous Machines
Stator of a large salient pole hydro generator; inset shows the
insulated conductors and spacers.
Synchronous Machines
Large hydro generator rotor with view of the vertical poles.
Synchronous Machines
Slip
rings
Pole
Fan
DC excitation
winding
Rotor of a four-pole salient pole generator.
Synchronous Machines
Exciter rotor
Rotating rectifier
Generator
Exciter stator
Φ
Idc
Field
winding
Phase
windings
Stationary
Rotates
Concept of the brushless exciter system
Operating Concept
Synchronous Machines
Flux Φf
nsy
B+
C+
N
-
A+
B-
-
-
-
+
+
+
A+
S
C+
Operating concept of a synchronous generator
Synchronous Machines
Maximum flux linkage with phase A
C-
No flux linkage with phase A
B+
-
C-
+
B+
-
+
-
N
N
A+
+
-
+
-
A-
A+
+
S
-
B-
-
S
+
+
-
C+
(a) Flux is perpendicular to phase A
B-
+
C+
(b) Flux is parallel to phase A
Rotation produced flux linkage variation.
A-
Synchronous Machines
Φrot
Φlink
ωt
nsy
B+
C+
N
-
A+
-
B-
-
-
+
+
30
+
-
S
A-
+
C+
Rotating flux linkage to phase A.
Synchronous Machines
Main rotating flux
f
n sy =
p
2
ω = 2 π n sy
Φ link (t ) = Φ rot cos(ω t )
Es (t ) = N sta
d Φ link (t )
dt
E s (t ) = − N sta Φ rot ω sin(ω t )
= N sta Φ rot ω cos(ω t + 90°)
E sta =
N sta Φ rot ω
2
The rotating flux generates
the induced voltage
Synchronous Machines
nsy
B+
C+
N
-
Field flux Φf
A+
B-
+
+
-
-
-
30
+
-
S
A+
Armature
flux Φar
C+
Field (Φf) and load generated (Φar) rotating fluxes.
Synchronous Machines
Armature flux
I arm (t ) = 2 I sta cos(ω t )
Φ arm (t ) = Φ ar cos(ω t )
E ar (t ) = N sta
E arm =
dΦ arm (t )
= − N sta Φ ar ω sin (ω t )
dt
N sta Φ ar ω
2
Vt = E sta − E arm
Load current generates a
rotating flux reducing the
main flux and induced
voltage
Synchronous Machines
Armature flux
E ar (t ) = Larm
dI
arm
(t )
dt
= − Larm ω 2 I sta
= − X arm
X arm =
d
dt
sin(ω t )
= Larm
2 I sta sin(ω t )
N sta Φ ar ω
2 I sta
X syn = X arm + X leakage
2 I sta cos(ω t )
Synchronous Machines
Single phase
equivalent circuit
E arm − syn = I sta ( j X syn )
Vt = E sta − E arm − syn = E sta − I sta j X syn
Xsyn
Flux
Esta
Rsta
Ista
Vt
DC
Single-phase equivalent circuit of a synchronous generator.
Synchronous Machines
• The generator is loaded
• The load current produces a rotating flux
• This rotating flux induces a ac three phase voltage in
the stator winding.
• This voltage is
– subtracted from the induced voltage.
– represented by a voltage drop on the synchronous reactance
• The equivalent circuit of a synchronous generator is a
voltage source and a reactance connected in series
Synchronous Machines
Generator Application
–
Power angle:
Angle between the dc
excitation current generated induced voltage and
the terminal voltage
Xad
X1 σ
Isp
R
I
Ub
UV
U
Z
Uˆ = Uˆ b + j X ad Iˆ + j X 1σ Iˆ + R Iˆ
Synchronous Machines
•
Phasor diagram of synchronous
machine
Uˆ = Uˆ b + j X ad Iˆ + j X 1σ Iˆ + R Iˆ
Synchronous Machines
Generator Application
Loading: power is less than angle 90 deg
–
All generators in the system are connected in parallel
All generators rotates with the synchronous speed
The load can be increased by increasing the input mechanical power by
regulating the turbine impute power
The speed does not change, the power angle increases
Maximum power angle is 90 degree, beyond that operation is unstable
•
•
•
•
•
–
–
Reactive power regulation
When the excitation is:
•
•
Increased, the generator reactive power also increases;
Decreased, the generator reactive power also decreases
• Load and excitation dependence
0kap
U
0ind
0,6ind
Un
0,2 kap
0,6 kap
0,6 kap
Ib
0 ind 0,8ind
1
1
0kap
I (Isp)
I
Synchronous Machines
Synchronization
–
Verify that the phase sequences of the two systems are the
same.
–
Adjust the machine speed with the turbine that drives the
generator until the generator voltage frequency is nearly the
same as the frequency of the network voltage.
–
Adjust the terminal voltage of the generator by changing the dc
field (rotor) current until the generator terminal voltage is almost
equal to the network voltage. Acceptable limit is 5%.
–
Adjust the phase angle of the generator terminal voltage by
regulating the input power until it is nearly equal with the
phase angle of the network voltage. Acceptable limits are
about 15°.
Synchronous Machines
• Synchronization
L1
L2
L3
A
NAPÁJENÍ
BUZENÍ
SA
V1
f1
V2
f2
The generator and network power vs power angle
δ := 0deg , 1deg .. 180deg
250
Pg( δ)
kW
200
Stable
operation
Unstable
operation
Maximum
power
150
Pnet( δ)
kW
100
110
Operation
point
50
0
0
30
60
90
δ
deg
120
150
180