Construction

1
Construction Terminology
2
Synchronous Generator Chapter 5

• Construction
• Basic Principle
• Circuit Model
• Performance
• MW Control
• MVAR Control
• Operating Limits

a Vt - n
Ra
-Ear
Ll
Ia
Ea -
3
Construction Terminology
4
Construction Terminology
Rotor (Field) carries dc current produce main
magnetic field Turbine provides mechanical power
to turn rotor at constant speed Stator has 3
coils displaced 120 deg in space Flux from
rotor(field) links Stator coils generates 3 phase
ac voltage Terminal voltage drives current and
power into power system
Armature(Stator)
3 phase ac
Turbine Mechanical Power
Field(Rotor)
If dc
5
Modeling of synchronous generators
Construction Terminology
Field q Axis
Phase a Axis
Field q Axis
Phase a Axis
?
Field d Axis
Field d Axis
a
SALIENT
ROUND
a is the position of an observer who measures
radial flux through air gap T is the position of
the rotor with respect to a fixed, vertical, axis
6
Modeling of synchronous generators
Construction Terminology -- Developed View
d
a
q
a
q
q
d
0
p/2
-p/2
p
7
Modeling of synchronous generators
Circuit Model
Flux due to field Rotating field due to
stator Induced Voltage Circuit
8
Modeling of synchronous generators
Construction Terminology -- Flux density due
to field for rotor position ?0
d
a
q
q
d
q
d
d
Field mmf
A rotor field winding Distributed across the
Surface creates a stepped mmf Waveform intended
to approximate A sinusoid
0
p
p/2
a
9
Modeling of synchronous generators
Construction Terminology -- Flux density due
to field for rotor position ?0
d
a
q
Field mmf
q
q
A rotor field winding Distributed across the
Surface creates a stepped mmf Waveform intended
to approximate A sinusoid
d
0
p
p/2
a
10
Modeling of synchronous generators
Steady State Model from Fields-Terminal voltage
under balance conditions

• Voltage induced in phase ( a) by Field Flux(Ea)
• Excitation, Induced Voltage, Generated Voltage,
  Open Circuit Voltage

Bf(a,?) Bfmax cos(a-?)
11
Modeling of synchronous generators
Steady State Model from Fields-Terminal voltage
under balance conditions
Poles
? electrical frequency rad /s ?mmechanical
speed rad /s ? (P/2) ?m P of Poles
N S
N S
N S
1 revolution 2 ac cycles
1 revolution 1 ac cycle
12
Modeling of synchronous generators
Construction Terminology -- Flux density due
to stator phase a
d
Phase a MMF and Flux Density(B) is a function of
observer position a. Flux density is essentially
radial through air gap The current in phase a is
a sinusoid with frequency ? so are mmf and flux
density MMFa(a,?) MMFamax cos(a)cos(?t) Observe
r at a sees a flux density that varies
sinusoidally in time Ba(a,?) Bamax cos(a)
cos(?t) Combined with the flux density from
phase b and c, the net stator flux density will
turn out to be a rotating field!
a
q
Stator phase a winding is also
actually Distributed across the Surface creates
a stepped mmf Waveform intended to approximate A
sinusoid
13
Modeling of synchronous generators
Net Stator Field Rotating Magnetic
Field- balanced positive sequence operation
d
a
d
a
Schematic of Net Stator Field Phases a,b,and c At
t0
q
q
Ba(a) (3/2)K Iamax cos(a)
Schematic Representation Of Phase a flux
density Ba(a) K Iamax cos(a) cos(?t)
14
Modeling of synchronous generators
d
d
d
a
a
a
q
q
q
t0
t2p/3?
t4p/3?
15
Modeling of synchronous generators
d
d
d
a
a
a
q
q
q
Bs(a,t) K Iamax cos(a) cos(?t) K
Iamax cos(a-2p/3) cos(?t -2p/3)
K Iamax cos(a2p/3) cos(?t 2p/3) Bs(a,t)
(3/2)K Iamax cos(a- ?t ) ROTATING FIELD
16
Modeling of synchronous generators
d
d
d
a
a
a
q
q
q
t0
t2p/3?
t4p/3?
17
Modeling of synchronous generators
d
a
Steady State Model from Fields Terminal voltage
under balance conditions
q

• The terminal voltage comprises of
• Voltage induced in phase ( a) by Field Flux
• Voltage induced by net stator flux
• Resistive voltage drop
• Inductive voltage drop in parts of the winding
  outside air gap (Overhang)
• Inductive voltage drop in individual phase from
  leakage flux

18
Modeling of synchronous generators
Steady State Model from Fields-Terminal voltage
under balance conditions
a Vt - n
Ra
-Ear
Ll
Ia
Round Rotor
Ea -

• The terminal voltage comprises of
• Voltage induced in phase ( a) by Field Flux(Ea)
• Excitation, Induced Voltage, Generated Voltage,
  Open Circuit Voltage
• Voltage induced by net stator flux(Ear)
• -Armature Reaction
• Resistive voltage drop (Ra armature resistance)
• Inductive voltage drop in parts of the winding
  outside air gap (Overhang),Inductive voltage drop
  in individual phase from leakage flux (Ll leakage
  inductance)

19
Modeling of synchronous generators
Steady State Model from Fields-Terminal voltage
under balance conditions

• Voltage induced in phase ( a) by Net Stator
  Flux(Ear)
• Armature reaction

Bs(a,t) (3/2)K Iamax cos(a- ?t )
?
d
a
q
q
a
a
a
20
Modeling of synchronous generators
Steady State Model from Fields-Terminal voltage
under balance conditions
Voltage induced in phase ( a) by Field Flux(Ea)
?
Ea?N? /?o
d
? rms value of flux , depends on field current
Ia
a
q
Ear?N(3K) Ia/-90 -j?LaIa
q
a
a
a
Vt Ea- j?LaIa- j?Ll Ia RaIa Vt Ea- -jXsIa-
RaIa
21
Modeling of synchronous generators
Steady State Model from Fields-Terminal voltage
under balance conditions
Model
If (dc)
Ra
jXS
Ia
Ea /d?N? /d -
Vt -
?
Fe
? rms value of flux , depends on field current
If
d
Fm
Ea induced, generated or open circuit voltage
phase Vt terminal voltage Ia line
current Vt Ea-jXsIa- RaIa
q
q
a
a
a
22
Modeling of synchronous generators
Steady State Model from Fields-Terminal voltage
under balance conditions
Model
If (dc)
Ra
jXS
Ia
Ea /d -
Vt -
S
Tm Te
Vt Ea /d -jXsIa- RaIa
Tm mechanical tprque from turbine Pm Tm ?
mechanical power from turbine Te Electrical
counter torque Pe Te ? Converted electric
power S Generated(Delivered) Electrical Complex
Power 3Vt Ia Pe Re(S) 3 Ia2 Ra
a
23
Modeling of synchronous generators
Steady State Model from Fields-Terminal voltage
under balance conditions
Model
If (dc)
Ea
Ra
jXS
Ia
Ea /d -
Vt -
S
jXsIa
Tm Te
Vt
RaIa
Ia
Vt Ea /d -jXsIa- RaIa
Ea
Pm Tm ? mechanical power from turbine Te
Electrical counter torque Pe Te ? Re(S) 3
Ia2 Ra Converted Power Pmech loss Mechanical
losses Pm PePmech loss S 3Vt Ia
a
If
Open circuit curve Shows field current needed
For desired generated Voltage Ea