DC MACHINES -...
Transcript of DC MACHINES -...
DC MACHINES
AE1BSP1
Doc. Ing. Pavel Pivoňka, Csc.
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
TYPICAL DC MACHINE
DC ROTATING MACHINE CAN WORK EITHER AS A MOTOR OR A GENERATOR
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
DC MACHINE MAIN PARTS
CONDUCTORS from supply ARMATURE winding
COMMUTATOR
HOLDER with BRUSHES
ROTOR CORE from iron sheets
PERMANENT MAGNETS (or excitation winding)
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
CROSS-SECTION VIEW DC MACHINE
gn
N1
N2
stator
rotor(armature)
n
φ
If
Ia
pole
air gapδ
field winding
armaturewinding
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
Ua
Ui
Ra,La
Ia
Rf,LfIf
Uf
SCHEMATIC DRAWINGS
FIELD WINDING ARMATURE WINDING
BEHAVIOR DEPENDS ON WINDINGS INTERCONNECTION
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
THREE BASIC TYPES OF DC MACHINES
Ua
I
UiRf,Lf
If
Ia
Rfr
UaUiRf,LfIf
Ia
Uf
Ua
If=Ia
UiRf,Lf
IfIa
SEPARATELY EXCITED SERIES SHUNT
(also permanent magnet)
COMPOUND MACHINE = combination of shunt and series
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
PRINCIPLES OF OPERATION
ω
-
+
+
-ui1
ui2
φ t
u
ui1
ui2
duration of 1 turn
ua
ia
+
-
N SN NS
τp
magnetic field of main poles
dtdAB
dtdue i =Φ
==
lBvue i
•×== )(
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
GENERATOR ACTION
lBve
•×= )(
)(222 Θ=== BlrBlrBlve ωω
∫ ∫ Θ⋅=Θ⋅=π π
ωππ 0 0
.21.1 dlrBdeeav
∫ Φ==⋅⋅=π
ωπ
ωπ
ωπ 0
222 BAdaBeav
ω..Φ== cUE iav
ua
ia
B1
B2
ω
-
+
+
-ui1
ui2
+
- φ
t
u ua
Ua
duration of 1 turn
IF Ra = 0 Ua=Ui=Eav
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
ωωπ
⋅Φ⋅=⋅Φ⋅⋅
= cne 2
aai icinT ⋅Φ⋅=⋅Φ⋅⋅
=π
2
dtdi
LiRu fffff ⋅+⋅=
edtdiLiRu a
aaaa +⋅−⋅−=
dtdJTTT miω
⋅+∆+=
BASIC EQUATIONS OF DC GENERATORS
UaUiRf,LfIf
Ia
Uf
aaout iup ⋅=
)( fieldin pTp +⋅= ω
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
SEPARATELY EXCITED GENERATOR
UaUiRf,Lf
If
Ia
load
Uf
Ui
If
Ui (If )Ua0=Uin
Ur
Ifn
edtdiLiRu a
aaaa +⋅−⋅−=
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
VOLT-AMPERE (LOAD) CHARACTERISTICS
U
Ia
In
Ua0Ui
Ui-RaIaUa
Uan
Difference due to ARMATURE REACTION
UaUiRf,LfIf
Ia
Uf
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
ARMATURE REACTION
N SN NS
τp
magnetic field of main poles
magnetic field of armature and interpoles
resulting magnetic fieldDEFORMATION due to armature
reaction
MAIN POLES INTERPOLES
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
COMMUTATION PROCESS
If
If
gn
φ f
φ a Ia
n
n
φ a
φ fφ
gn
SHIFTED NEUTRAL AXIS
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
AUXILIARY COMMUTATION POLES
φf
φf
φaφip
φipn
main poles
auxiliary poles(interpoles)
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
SHUNT GENERATOR
Ua
I
UiRf,Lf
If
Ia
load
Rfr fa uu =
fa iii −=
dtdi
LiRiRu ffffrfff ⋅+⋅+⋅=
edtdiLiRu a
aaaa +⋅−⋅−=
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
EXCITATION OF SHUNT GENERATOR
Ui
If
Ui (If )
∆U = Rfc . If
A1A2A3
Ur
frffc RRR +=
! POLARITY of the field winding !
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
COMPARISON OF GENERATORS
U
Ia
In
Isc
sep. excited
shuntseries
SHUNT: nsc II << welding machines
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
ENERGY BALANCE (POWER DIVISION)
Shunt field
Pel ω T
Series fieldBrush
ArmatureFriction
Stray-load
ELECTROMAGNETICPOWER
Ea.Ia
armature circuit 3 to 6%Pin
rotational losses 3 to 15%Pin
shunt field 1 to 5%Pin
MOTOR GENERATOR
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
MOTOR ACTION
)( BlIF
×⋅=
F = B . i . l . sinΘ
T = 2.F.r = 2.B.ic.l.r
∫ ∫ ⋅Φ⋅=⋅⋅=Θ⋅⋅⋅⋅⋅⋅=π π
πππ 0 0
2.221 idaBidBrliTav
aiav icTT ..Φ==
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
ωωπ
⋅Φ⋅=⋅Φ⋅⋅
= cne 2
aai icinT ⋅Φ⋅=⋅Φ⋅⋅
=π
2
dtdi
LiRu fffff ⋅+⋅=
edtdiLiRu a
aaaa +⋅+⋅= dtdJTTT m
miω
⋅++∆=
BASIC EQUATIONS OF DC MOTORS
BEHAVIOR DEPENDS ON WINDINGS INTERCONNECTION
• SEPARATELY EXCITED (also permanent magnet) – SEM
• SERIES – SRM
• SHUNT – SHM
Subject number 21
DC Motor Basic Description
SEPARATELY EXCITED, SEM (also permanent magnet, PMM) wide range of speed and power SHUNT, SHM SERIES, SRM high starting M, parallel operation, damped transients traction universal motors COMPOUND (combination of shunt and series)
ωωπ
Φ=Φ== capNue i
ai icT Φ=
dtdi
LiRu fffff +=
edtdiLiRu a
aaaa ++=
dtdJTTT miω
++∆=
Subject number 22
DC SEM Characteristics
STEADY STATE OPERATION Schematic picture Equations Characteristics
ΦΩ== cUE i
fff IRU =
EIRU aaa +=
TTIcT mai +∆=Φ=
Rf,Lf
If
Ia
Uf
Ui
Ra,La
Ua
Φ−
=Φ
==Ωc
IRUcE aaaω
a
aa R
EUI −=
)( aIf=ω
)(Tf=ω
0≠Φ!
Subject number 23
DC SEM speed+mechanical curves
T(Ia)
ω
0
ω0
Tn
ωn
If < Ifn; Ua = Uan; Ra
If = Ifn; Ua = Uan; Ra
If = Ifn; Ua < Uan; Ra
If = Ifn; Ua = Uan Rax = Ra + Rx
TLOAD
Φ−
=c
IRU aaaω
Φ≅
cTIaa
aaa kIc
IRcU
−=Φ
−Φ
= 0ωωΦ
=cRk a
armature reaction influence
natural characteristics
working points
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
INFLUENCE OF Ra ON n=f(T) CURVE
n
T
n0
Ratotal
Φ⋅⋅−
=Φ⋅
==Ωc
IRUc
E aaaω
addedaatotal RRR +=
base speed
Subject number 25
DC SEM Starting
by direct connection to Ua = Un Ia = (10 to 30) In decrease current by variable Ua or Ra
to produce sufficient torque fully excited or slightly overexcited If ≥ Ifn
Φ−
=c
IRU aaaω
max1
a
aa I
UR =
Ia (M)
ω
0
ω0
Iamax
Ra
Ra2 > Ra3 … > Ra
Ra1 > Ra2
1
2
3
Iaminmin
max
3
2
2
1 .....a
a
a
ax
a
a
a
a
II
RR
RR
RR
====
quasistationnery working points
Subject number 26
DC SEM Braking
DYNAMIC (rheostatic)
-I a
(-T)
ω
0
ω1
-Iamax
Ra
Ra2 > Ra3 … > Ra
Ra1 > Ra2
3
-Iamin
2
1Ui
Rf,Lf
Ra,La
R
Subject number 27
DC SEM Braking
REVERSE CURRENT (plugging) by active load torque by passive load torque
T
ω
0
ω1
B
Ra
R1>Ra
ω2
A
T
ω
0
ω1
Ra
R1>Ra
Subject number 28
DC SEM Braking
REGENERATIVE by decreasing armature voltage by changing load activity The power supply must be able to accept generated energy !!!
T
ω
0
ω1
ω2Ua
TLOAD
ω=0 T
ω
0
ω1
ω2
TLOAD-TLOAD
MOTORGENERATOR
Subject number 29
DC SEM Reversal
change polarity of Ua (see starting and braking) change polarity of If
Machine could be mechanically and electrically damaged If polarity change cannot be used on running machine !!!
Φ−
=Φ
=c
IRUcE aaaω
0=Φif!
0≠Φ!
Φ−=−
cEω
∞→ω
++∆=Φ=
dtdJTTIcT mai
ω ∞→aIΦ
−=
cIRU aaaω
I fIfn
ωmax
Ua=const.
ω
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
DC SEM Speed Change
T
ω ω
ω
Ua
If
Uan
Ifn
ωmax
Ua=const.=Uan
If = const.=Ifn
Uan ; Ifn
Ua
If
Φ⋅⋅−
=Φ⋅
==Ωc
IRUc
E aaaω constant power
constant torque
base speed
Subject number 31
DC SHM Characteristics
STEADY STATE OPERATION Schematic view Equations Characteristics
Ua
I
UiRf,Lf
If
Ia
RfrωΦ== cUE i
ffrff IRRU )( +=
EIRU aaa +=
TTIcT mai +∆=Φ=fa III −=
Φ−
=Φ
=c
IRUcE aaaω
a
aa R
EUI −=
)( aIf=ω
)(Tf=ω
Subject number 32
DC SHM Behavior
Basic behavior similar to separately excited Speed and mechanical characteristics are practically identical Starting, braking and speed control by variable Ua or Ra Reversal by changing polarity of armature or field windings
No difference in design: all SEM can work as SHM
Advantage: no separated power supply for excitation
Φ−
=c
IRU aaaωa
aa R
EUI −= aIcT Φ≅
Subject number 33
DC SRM Characteristics
STEADY STATE OPERATION Schematic picture Equations Characteristics
Ua
If=Ia
UiRf,Lf
IfIa
Ra,La
ωξω ai IcUE =Φ==
aff IRU =
ωξ aafafaaa IIRRUEIRU ++=++= )(
TTIIcT maai +∆==Φ= 2ξ
)( aIf=ω)(Tf=ω!
fa II =
0≠aIa
aatotala
IIRU
ξω −
=
ξi
aTI =
)( aIfT =
Subject number 34
DC SRM speed+torque+mechanical curves
ω
T
4
TSTART0
dtdJTTT mi
ω++∆=
advantage by start with load: ω
I a
1
2
3
4
0
T
1 3
ξ is not constant !!! (Φ=f(Ia) is not linear)
ξξξω atotal
a
a
a
aatotala RI
UI
IRU−=
−=
ξi
aTI =
1 = natural characteristics 2 = lower Ua 3 = lower If (by shunting field winding) 4 = higher Ra
ξξω atotal
i
a RT
U−=
base speed
Subject number 35
DC SRM Starting
by variable Ua
by variable Ra: ω
Ia
Ra
0
Ramax
IamaxIamin
maxmax
a
aa I
UR =
ξξω atotal
a
a RI
U−=
UaUi
Rf,LfRa Rn R1
Ramax
Subject number 36
DC SRM Braking
DYNAMIC (rheostatic)
-I a
ω
0
ω1
Ra
R1 < Rmax
Rmax
Ui
Rf,Lf
Ra,La
R
Ua
I a
Ua
0
ω1
R
ω2 < ω1
ωn
1
2
n-1
Subject number 37
DC SRM Braking
REVERSE CURRENT (plugging) by active load torque by passive load torque REGENERATIVE – possible only with chopper connected
T
ω
0
ω1
B
Ra
R1>Ra
ω2
A
TLOAD
T1T2 T
ω
0
ω1
Ra
R1>Ra
AB
C
Subject number 38
DC SRM Reversing
Not to change polarity of terminal voltage: Change armature voltage or Change field votage
T
ω
0
Ui
Rf,Lf
Ra,La
+
-
Ui
Rf,Lf
Ra,La
+
-
Ui
Rf,Lf
Ra,La
+
-
Subject number 39
DC SRM Speed Change
Variable Ra – not frequently used (high loss)
Variable Ua – most frequent
Shunting field winding (decrease If) limitations: power, commutation
Grouping by multimotor drives : serial/parallel
ξξξω atotal
a
aatotal
a
a RIc
URI
U−
Φ=−=
ω
T0
Uamax
U
Mot4Mot3Mot2Mot1
U Mot4Mot3
Mot2Mot1
ξξω atotal
i
a RT
U−=
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
COMPARISON OF MOTORS
ω
TTn
sep. excited and shunt
compound
series
ωn
0
©NOTES - Doc. Ing. Pavel Pivoňka, CSc.
STARTING AND ROTATION REVERSAL
Φ⋅⋅−
=c
IRU aaaωa
aa R
EUI −=
SEPARATELY EXCITED AND SHUNT start: by Un is Is = 10 to 30 In ----> variable Ua or Ra reversal: change polarity of Ua or If (only on not running machine - flux must not be zero !!!)
SERIES start: variable Ua - machine must not be unloaded !!! reversal: change polarity of Ua or If
aIcT ⋅Φ⋅≅