Short Notes: Basics of Electrical Machines | Electrical Machines - Electrical Engineering (EE) PDF Download

 Page 1


1 Short Notes: Basics of Electrical Mac hines
1.1 In tro duction
Electrical mac hines are devices that con v ert electrical energy to mec hanical energy (mo-
tors) or mec hanical energy to electrical energy (generators) through a magnetic field as the
coupling medium. These mac hines are fundamen tal to p o w er systems, industrial driv es,
and renew able energy applications. F or GA TE Electrical Engineering, understanding the
principles, construction, and p erformance of transformers, DC mac hines, and A C ma-
c hines (induction and sync hronous) is essen tial. The magnetic field’s high energy storage
capacit y mak es it ideal for e?icien t energy con v ersion.
1.2 Electromec hanical Energy Con v ersion
• Principle : The con v ersion b et w een electrical and mec hanical energy relies on elec-
tromagnetic phenomena. A magnetic field links the electrical and mec hanical sys-
tems, ena bling energy transfer. T w o k ey effects go v ern this pro cess:
– F ar aday’s L aw of Ele ctr omagnetic Induction : When a conductor mo v es in a
magnetic field, an electromotiv e force (EMF) is induced, driving curren t in
generators:
E =-N
d?
dt
where E is induced EMF (V), N is n um b er of turns, ? is magnetic flux (Wb).
– L or entz F or c e : A curren t-carrying conductor in a magnetic field exp eriences a
force, pro ducing torque in motors:
F =I(L×B)
whereF is force (N),I is curren t (A),L is conductor length (m),B is magnetic
flux densit y (T).
• Energy Balance : Energy conserv ation dictates that input energy equals the sum
of losses, stored energy , and useful output. F or motors, electrical energy is con v erted
to mec hanical w ork, while generators con v ert mec hanical energy to electrical output:
Electrical Input = Losses (Copp er + Core)+ Stored Energy (Magnetic Field)+ Mec hanical Output ( Motor)
Mec hanical Input = Electrical Output+ Stored Energy+ Losses ( Generator)
• Applications : Motors driv e pumps, fans, and con v ey ors, while generators are used
in p o w e r plan ts and renew able energy systems.
1.3 T yp es of Electrical Mac hines
• DC Mac hines : Use comm utators to main tain unidirectional curren t, suitable for
precise sp eed con trol in industrial applications.
• A C Mac hines : Op erate on alternating curren t, including induction mac hines
(rugged, lo w main tenance) and sync hronous mac hines (used in p o w er generation).
• T ransformers : Static devices that transfer electrical energy b et w een circuits via
magnetic coupling, essen tial for v oltage transformation in p o w er distribution.
1
Page 2


1 Short Notes: Basics of Electrical Mac hines
1.1 In tro duction
Electrical mac hines are devices that con v ert electrical energy to mec hanical energy (mo-
tors) or mec hanical energy to electrical energy (generators) through a magnetic field as the
coupling medium. These mac hines are fundamen tal to p o w er systems, industrial driv es,
and renew able energy applications. F or GA TE Electrical Engineering, understanding the
principles, construction, and p erformance of transformers, DC mac hines, and A C ma-
c hines (induction and sync hronous) is essen tial. The magnetic field’s high energy storage
capacit y mak es it ideal for e?icien t energy con v ersion.
1.2 Electromec hanical Energy Con v ersion
• Principle : The con v ersion b et w een electrical and mec hanical energy relies on elec-
tromagnetic phenomena. A magnetic field links the electrical and mec hanical sys-
tems, ena bling energy transfer. T w o k ey effects go v ern this pro cess:
– F ar aday’s L aw of Ele ctr omagnetic Induction : When a conductor mo v es in a
magnetic field, an electromotiv e force (EMF) is induced, driving curren t in
generators:
E =-N
d?
dt
where E is induced EMF (V), N is n um b er of turns, ? is magnetic flux (Wb).
– L or entz F or c e : A curren t-carrying conductor in a magnetic field exp eriences a
force, pro ducing torque in motors:
F =I(L×B)
whereF is force (N),I is curren t (A),L is conductor length (m),B is magnetic
flux densit y (T).
• Energy Balance : Energy conserv ation dictates that input energy equals the sum
of losses, stored energy , and useful output. F or motors, electrical energy is con v erted
to mec hanical w ork, while generators con v ert mec hanical energy to electrical output:
Electrical Input = Losses (Copp er + Core)+ Stored Energy (Magnetic Field)+ Mec hanical Output ( Motor)
Mec hanical Input = Electrical Output+ Stored Energy+ Losses ( Generator)
• Applications : Motors driv e pumps, fans, and con v ey ors, while generators are used
in p o w e r plan ts and renew able energy systems.
1.3 T yp es of Electrical Mac hines
• DC Mac hines : Use comm utators to main tain unidirectional curren t, suitable for
precise sp eed con trol in industrial applications.
• A C Mac hines : Op erate on alternating curren t, including induction mac hines
(rugged, lo w main tenance) and sync hronous mac hines (used in p o w er generation).
• T ransformers : Static devices that transfer electrical energy b et w een circuits via
magnetic coupling, essen tial for v oltage transformation in p o w er distribution.
1
1.4 DC Mac hines
• Construction : Consists of a stator (field magnets creating magnetic field), rotor
(armature carrying conductors), comm utator (for curren t rev ersal), and brushes
(for elec trical con tact).
• Op eration : In generators, mec hanical input rotates the armature, inducing EMF.
In motors , curren t in the armature pro duces torque for mec hanical output.
• EMF Equation (Generator) : The induced EMF dep ends on flux, sp eed, and
mac hine co nstruction:
E =
?ZNP
60A
where ? is flux p er p ole (Wb), Z is total armature conductors, N is sp eed (rpm),
P is n um b er of p oles, A is n um b er of parallel paths.
• T orque Equation (Motor) : T orque is pro duced b y in teraction of armature cur-
ren t and m agnetic field:
T =
?ZI
a
P
2pA
where I
a
is armature curren t (A).
• T yp es : Series (high starting torque), sh un t (constan t sp eed), and comp ound (com-
bined c haracteristics) motors, tailored for sp ecific applications lik e traction or cranes.
• Losses : Include copp er losses (I
2
R ), core losses (h ysteresis and eddy curren t), and
mec hanical losses (friction, windage).
1.5 A C Mac hines: Induction Mac hines
• Principle : Op erates on electromagnetic induction, where a rotating stator mag-
netic field induces curren ts in the rotor, pro ducing torque. The rotor sp eed is alw a ys
less than t he sync hronous sp eed.
• Sync hronous Sp eed : Determined b y supply frequency and n um b er of p oles:
N
s
=
120f
P
where f is fre quency (Hz), P is n um b er of p oles.
• Slip : Measures the relativ e sp eed difference b et w een sync hronous and rotor sp eeds:
s =
N
s
-N
r
N
s
where N
r
is rotor sp eed (rpm).
• T orque : Prop ortional to rotor curren t and slip, p eaking at a sp ecific slip v alue:
T =
3
?
s
·
sE
2
2
R
2
R
2
2
+(sX
2
)
2
where ?
s
=
2pNs
60
(sync hronous angular sp eed, rad/s), E
2
is rotor-induced EMF, R
2
is rotor r esistance, X
2
is rotor reactance.
2
Page 3


1 Short Notes: Basics of Electrical Mac hines
1.1 In tro duction
Electrical mac hines are devices that con v ert electrical energy to mec hanical energy (mo-
tors) or mec hanical energy to electrical energy (generators) through a magnetic field as the
coupling medium. These mac hines are fundamen tal to p o w er systems, industrial driv es,
and renew able energy applications. F or GA TE Electrical Engineering, understanding the
principles, construction, and p erformance of transformers, DC mac hines, and A C ma-
c hines (induction and sync hronous) is essen tial. The magnetic field’s high energy storage
capacit y mak es it ideal for e?icien t energy con v ersion.
1.2 Electromec hanical Energy Con v ersion
• Principle : The con v ersion b et w een electrical and mec hanical energy relies on elec-
tromagnetic phenomena. A magnetic field links the electrical and mec hanical sys-
tems, ena bling energy transfer. T w o k ey effects go v ern this pro cess:
– F ar aday’s L aw of Ele ctr omagnetic Induction : When a conductor mo v es in a
magnetic field, an electromotiv e force (EMF) is induced, driving curren t in
generators:
E =-N
d?
dt
where E is induced EMF (V), N is n um b er of turns, ? is magnetic flux (Wb).
– L or entz F or c e : A curren t-carrying conductor in a magnetic field exp eriences a
force, pro ducing torque in motors:
F =I(L×B)
whereF is force (N),I is curren t (A),L is conductor length (m),B is magnetic
flux densit y (T).
• Energy Balance : Energy conserv ation dictates that input energy equals the sum
of losses, stored energy , and useful output. F or motors, electrical energy is con v erted
to mec hanical w ork, while generators con v ert mec hanical energy to electrical output:
Electrical Input = Losses (Copp er + Core)+ Stored Energy (Magnetic Field)+ Mec hanical Output ( Motor)
Mec hanical Input = Electrical Output+ Stored Energy+ Losses ( Generator)
• Applications : Motors driv e pumps, fans, and con v ey ors, while generators are used
in p o w e r plan ts and renew able energy systems.
1.3 T yp es of Electrical Mac hines
• DC Mac hines : Use comm utators to main tain unidirectional curren t, suitable for
precise sp eed con trol in industrial applications.
• A C Mac hines : Op erate on alternating curren t, including induction mac hines
(rugged, lo w main tenance) and sync hronous mac hines (used in p o w er generation).
• T ransformers : Static devices that transfer electrical energy b et w een circuits via
magnetic coupling, essen tial for v oltage transformation in p o w er distribution.
1
1.4 DC Mac hines
• Construction : Consists of a stator (field magnets creating magnetic field), rotor
(armature carrying conductors), comm utator (for curren t rev ersal), and brushes
(for elec trical con tact).
• Op eration : In generators, mec hanical input rotates the armature, inducing EMF.
In motors , curren t in the armature pro duces torque for mec hanical output.
• EMF Equation (Generator) : The induced EMF dep ends on flux, sp eed, and
mac hine co nstruction:
E =
?ZNP
60A
where ? is flux p er p ole (Wb), Z is total armature conductors, N is sp eed (rpm),
P is n um b er of p oles, A is n um b er of parallel paths.
• T orque Equation (Motor) : T orque is pro duced b y in teraction of armature cur-
ren t and m agnetic field:
T =
?ZI
a
P
2pA
where I
a
is armature curren t (A).
• T yp es : Series (high starting torque), sh un t (constan t sp eed), and comp ound (com-
bined c haracteristics) motors, tailored for sp ecific applications lik e traction or cranes.
• Losses : Include copp er losses (I
2
R ), core losses (h ysteresis and eddy curren t), and
mec hanical losses (friction, windage).
1.5 A C Mac hines: Induction Mac hines
• Principle : Op erates on electromagnetic induction, where a rotating stator mag-
netic field induces curren ts in the rotor, pro ducing torque. The rotor sp eed is alw a ys
less than t he sync hronous sp eed.
• Sync hronous Sp eed : Determined b y supply frequency and n um b er of p oles:
N
s
=
120f
P
where f is fre quency (Hz), P is n um b er of p oles.
• Slip : Measures the relativ e sp eed difference b et w een sync hronous and rotor sp eeds:
s =
N
s
-N
r
N
s
where N
r
is rotor sp eed (rpm).
• T orque : Prop ortional to rotor curren t and slip, p eaking at a sp ecific slip v alue:
T =
3
?
s
·
sE
2
2
R
2
R
2
2
+(sX
2
)
2
where ?
s
=
2pNs
60
(sync hronous angular sp eed, rad/s), E
2
is rotor-induced EMF, R
2
is rotor r esistance, X
2
is rotor reactance.
2
• T yp es : Squirrel-cage (robust, lo w main tenance) and w ound-rotor (adjustable re-
sistance for torque con trol).
• Applications : Used in pumps, fans, and industrial driv es due to ruggedness and
simplicit y .
1.6 A C Mac hines: Sync hronous Mac hines
• Principle : The rotor rotates at sync hronous sp eed, lo c k ed with the stator’s rotat-
ing magnet ic field, ac hiev ed b y DC excitation or p ermanen t magnets.
• EMF Equation (Generator) : Induced EMF in alternators dep ends on flux and
frequency:
E = 4.44f?Nk
w
where k
w
is winding factor (t ypically 0.85-0.95).
• T orque : Dep ends on the p o w er angle b et w een rotor and stator fields:
T =
3EV sind
?
s
X
s
where V is terminal v oltage, X
s
is sync hronous reactance, d is p o w er angle.
• T yp es : Sync hronous generators (alternators) for p o w er generation and sync hronous
motors for c onstan t-sp eed applications lik e compressors.
• Characteristics : High e?iciency , but requires DC excitation and complex syn-
c hronization for grid connection.
1.7 T ransformers
• Principle : T ransfers electrical energy b et w een circuits via m utual induction in a
magnetic core, with no mo ving parts. Used for stepping up/do wn v oltage in p o w er
systems.
• EMF Equation : Induced v oltage dep ends on flux and turns:
E = 4.44f?
m
N
where ?
m
is maxim um flux (Wb).
• V oltage T ransformation : Relates primary and secondary v oltages to turns ratio:
V
1
V
2
=
N
1
N
2
where N
1
,N
2
are prim ary and secondary turns.
• E?iciency : A ccoun ts for core and copp er losses:
? =
V
2
I
2
cos?
V
2
I
2
cos?+P
core
+P
copp er
where P
core
is due to h ysteresis and eddy curren ts, P
copp er
=I
2
R .
• Applications : P o w er distribution, v oltage regulation, and isolation.
3
Page 4


1 Short Notes: Basics of Electrical Mac hines
1.1 In tro duction
Electrical mac hines are devices that con v ert electrical energy to mec hanical energy (mo-
tors) or mec hanical energy to electrical energy (generators) through a magnetic field as the
coupling medium. These mac hines are fundamen tal to p o w er systems, industrial driv es,
and renew able energy applications. F or GA TE Electrical Engineering, understanding the
principles, construction, and p erformance of transformers, DC mac hines, and A C ma-
c hines (induction and sync hronous) is essen tial. The magnetic field’s high energy storage
capacit y mak es it ideal for e?icien t energy con v ersion.
1.2 Electromec hanical Energy Con v ersion
• Principle : The con v ersion b et w een electrical and mec hanical energy relies on elec-
tromagnetic phenomena. A magnetic field links the electrical and mec hanical sys-
tems, ena bling energy transfer. T w o k ey effects go v ern this pro cess:
– F ar aday’s L aw of Ele ctr omagnetic Induction : When a conductor mo v es in a
magnetic field, an electromotiv e force (EMF) is induced, driving curren t in
generators:
E =-N
d?
dt
where E is induced EMF (V), N is n um b er of turns, ? is magnetic flux (Wb).
– L or entz F or c e : A curren t-carrying conductor in a magnetic field exp eriences a
force, pro ducing torque in motors:
F =I(L×B)
whereF is force (N),I is curren t (A),L is conductor length (m),B is magnetic
flux densit y (T).
• Energy Balance : Energy conserv ation dictates that input energy equals the sum
of losses, stored energy , and useful output. F or motors, electrical energy is con v erted
to mec hanical w ork, while generators con v ert mec hanical energy to electrical output:
Electrical Input = Losses (Copp er + Core)+ Stored Energy (Magnetic Field)+ Mec hanical Output ( Motor)
Mec hanical Input = Electrical Output+ Stored Energy+ Losses ( Generator)
• Applications : Motors driv e pumps, fans, and con v ey ors, while generators are used
in p o w e r plan ts and renew able energy systems.
1.3 T yp es of Electrical Mac hines
• DC Mac hines : Use comm utators to main tain unidirectional curren t, suitable for
precise sp eed con trol in industrial applications.
• A C Mac hines : Op erate on alternating curren t, including induction mac hines
(rugged, lo w main tenance) and sync hronous mac hines (used in p o w er generation).
• T ransformers : Static devices that transfer electrical energy b et w een circuits via
magnetic coupling, essen tial for v oltage transformation in p o w er distribution.
1
1.4 DC Mac hines
• Construction : Consists of a stator (field magnets creating magnetic field), rotor
(armature carrying conductors), comm utator (for curren t rev ersal), and brushes
(for elec trical con tact).
• Op eration : In generators, mec hanical input rotates the armature, inducing EMF.
In motors , curren t in the armature pro duces torque for mec hanical output.
• EMF Equation (Generator) : The induced EMF dep ends on flux, sp eed, and
mac hine co nstruction:
E =
?ZNP
60A
where ? is flux p er p ole (Wb), Z is total armature conductors, N is sp eed (rpm),
P is n um b er of p oles, A is n um b er of parallel paths.
• T orque Equation (Motor) : T orque is pro duced b y in teraction of armature cur-
ren t and m agnetic field:
T =
?ZI
a
P
2pA
where I
a
is armature curren t (A).
• T yp es : Series (high starting torque), sh un t (constan t sp eed), and comp ound (com-
bined c haracteristics) motors, tailored for sp ecific applications lik e traction or cranes.
• Losses : Include copp er losses (I
2
R ), core losses (h ysteresis and eddy curren t), and
mec hanical losses (friction, windage).
1.5 A C Mac hines: Induction Mac hines
• Principle : Op erates on electromagnetic induction, where a rotating stator mag-
netic field induces curren ts in the rotor, pro ducing torque. The rotor sp eed is alw a ys
less than t he sync hronous sp eed.
• Sync hronous Sp eed : Determined b y supply frequency and n um b er of p oles:
N
s
=
120f
P
where f is fre quency (Hz), P is n um b er of p oles.
• Slip : Measures the relativ e sp eed difference b et w een sync hronous and rotor sp eeds:
s =
N
s
-N
r
N
s
where N
r
is rotor sp eed (rpm).
• T orque : Prop ortional to rotor curren t and slip, p eaking at a sp ecific slip v alue:
T =
3
?
s
·
sE
2
2
R
2
R
2
2
+(sX
2
)
2
where ?
s
=
2pNs
60
(sync hronous angular sp eed, rad/s), E
2
is rotor-induced EMF, R
2
is rotor r esistance, X
2
is rotor reactance.
2
• T yp es : Squirrel-cage (robust, lo w main tenance) and w ound-rotor (adjustable re-
sistance for torque con trol).
• Applications : Used in pumps, fans, and industrial driv es due to ruggedness and
simplicit y .
1.6 A C Mac hines: Sync hronous Mac hines
• Principle : The rotor rotates at sync hronous sp eed, lo c k ed with the stator’s rotat-
ing magnet ic field, ac hiev ed b y DC excitation or p ermanen t magnets.
• EMF Equation (Generator) : Induced EMF in alternators dep ends on flux and
frequency:
E = 4.44f?Nk
w
where k
w
is winding factor (t ypically 0.85-0.95).
• T orque : Dep ends on the p o w er angle b et w een rotor and stator fields:
T =
3EV sind
?
s
X
s
where V is terminal v oltage, X
s
is sync hronous reactance, d is p o w er angle.
• T yp es : Sync hronous generators (alternators) for p o w er generation and sync hronous
motors for c onstan t-sp eed applications lik e compressors.
• Characteristics : High e?iciency , but requires DC excitation and complex syn-
c hronization for grid connection.
1.7 T ransformers
• Principle : T ransfers electrical energy b et w een circuits via m utual induction in a
magnetic core, with no mo ving parts. Used for stepping up/do wn v oltage in p o w er
systems.
• EMF Equation : Induced v oltage dep ends on flux and turns:
E = 4.44f?
m
N
where ?
m
is maxim um flux (Wb).
• V oltage T ransformation : Relates primary and secondary v oltages to turns ratio:
V
1
V
2
=
N
1
N
2
where N
1
,N
2
are prim ary and secondary turns.
• E?iciency : A ccoun ts for core and copp er losses:
? =
V
2
I
2
cos?
V
2
I
2
cos?+P
core
+P
copp er
where P
core
is due to h ysteresis and eddy curren ts, P
copp er
=I
2
R .
• Applications : P o w er distribution, v oltage regulation, and isolation.
3
1.8 Key Notes for GA TE
• Master EMF and torque equations for DC and A C mac hines, fo cusing on n umerical
applications.
• Understand torque-slip c haracteristics of induction motors and p o w er angle in syn-
c hronous mac hines.
• Practice transformer e?iciency , v oltage regulation, and l oss calculations.
• F o cus on energy con v ersion principles, as they underpin mac hine op eration and
p erformanc e analysis.
• Solv e problems on mac hine t yp es, their c haracteristics, and practical applications.
4