S.P.E.M ASSINGMENT
NAME: Shantanu Uttam Naykodi
BRANCH: F.Y ELECTRICAL
ROLL NO : 10303320171129310023

What is synchronous reluctance motor why it is so called
1.
The Synchronous Relutance Motor is an Electrical rotating machine that converts the electrical
Power into Mechanical Power.
Reultance Motor Operate On the Principle that forces are established that tend to cause iron
poles carrying a magnetic Flux to align with each other.
It is Called as Synchronous Reluctane motor Due to its Constant Speed Revolution, even though
the load Change the speed of the motor remains the Same
2.
3.

Explain construction and working of a typical synchronous reluctance motor
Construction of S.R.M
1. The Reluctance motor Basically has two parts the Stator & Rotor, the stator has laminated
construction, made up of Stampings.
2. The Stampings are slotted on its periphery to carry the winding called Stator Winding. The Stator
Carries only one winding. This is Excited by single-phase A.C Supply. The Laminated Construction
Keeps Iron Losses to a minimum. The Stampings are made up of material from Silicon Steel
which Minimises the Hystersis Loss. The Stator Winding is Wound For Certain definite number of
poles.
3. The Rotor has a particular Shape. Due to its Shape, the air gap between the stator & rotor is not
uniform. No D.C Supply is given to the rotor. The Rotor is free to rotate. The Reluctance i.e the
resistance of the magnetic circuit depends on the air gap. More the air gap, more is the
relictance and vice-versa. Due to varibale air gap between stator & rotor , when the rotor rotates
reluctance between stator & rotor changes.
FIG 1.1 Construction of Synchronous Reluctance Motor
WORKING OF S.R.M
4.
5.
The Stator consists of a Single Winding Called main winding. But Single winding cannot produce
rotating magnetic field. So for production of rotating magnetic field, there must be at least two
windings separated by the certain phase angle.
Hence Stator consists of an additional winding called auxillary winding which consists of a
capacitor in series with it.
6.
7.
8.
9.
Due to the flux produce by two windings, the flux react together to produce a rotating magnetic
field. The technique is called as Split Phase technique. The speed of this field is the synchronous
speed which is decided by the number of poles for which stator winding is wound.
The Rotor Carries the short-circuited copper or aluminium bars and it acts as a squirrel-cage
rotor of an induction motor. If an iron piece is placed in a magnetic field, it aligns itself in a
minimum reluctance position and gets locked magnetically.Similarly, in the reluctance motor,
rotor tries to align itself with the axis of rotating magnetic field in a minimum reluctance
position. But due to rotor inertia, it is not possible when the rotor is at standstill.
So rotor starts rotating near synchronous speed as a squirrel cage induction motor. When the
rotor Speed is about synchronous, stator magnetic field pulls rotor into synchronism I.e
minimum reluctance position and keeps it magnetically locked. Thus finally a reluctance motor
runs as a synchronous motor.
The Resistance of the motor must be very small and the combined inertia of rotor and the load
should be small to run the motor as a Synchronous motor.
 List out the major advantages and limitations of synchronous reluctance motor.
Advantages:
1. Simple and robust rotor construction:
the rotor has a simple structure consisting of sheet electrical steel, without magnets
and short-circuited winding.
2. Low heat:
since there are no currents in the rotor, it does not heat up during operation, increasing
the service life of the electric motor .
3. No magnets:
the final price of the electric motor is reduced since rare earth metals are not used in
production. In the absence of magnetic forces, the maintenance of the electric motor is
simplified.
4. Low moment of inertia of the rotor::
since there is no winding and magnets on the rotor, the moment of the inertia of the
rotor is lower, which allows the electric motor to accelerate faster and save energy.
5. Speed control:
in view of the fact that synchronous reluctance motor for its operation requires
a frequency converter, it is possible to control the speed of rotation of reluctance
motor in a wide range of speeds.
Limitations:
6. Frequency control:
to work requires a variable frequency drive.
7. Low power factor:
due to the fact that the magnetic flux is generated only by the reactive current. Solved
by the use of a variable frequency drive with power correction.

Explain the Torque – Speed characteristics and its significance in the operation of
synchronous reluctance motor.
1.
The torque speed characteristic of synchronous reluctance motor is shown in fig. The
motor starts at anywhere from 300 to 400 percent of its full load torque (depending on
the rotor position of the unsymmetrical rotor with respect to the field winding) as a two
phase motor. As a result of the magnetic rotating field created by a starting and running
winding displaced 90° in both space and time.
2.
At about ¾th of the synchronous speed a centrifugal switch opens the starting winding
and the motor continues to develop a single phase torque produced by its running
winding only. As it approaches synchronous speed, the reluctance torque is sufficient to
pull the rotor into synchronism with the pulsating single phase field. The motor
operates at constant speed up to a little over 20% of its full load torque. If it is loaded
beyond the value of pull out torque, it will continue to operate as a single phase
induction motor up to 500% of its rated speed.
FIG 1.2 Torque Speed Characteristics
 Draw and discuss the phasor diagram for synchronous reluctance motor
and hence obtain the e m f equation.
PHASER DIAGRAM OF SYNCHRONOUS RELUCTANCE MOTOR
The synchronous reluctance machine is considered as a balanced three phase circuit, it is
sufficient to draw the phasor diagram for only one phase. The basic voltage equation
neglecting the effect of resistance is
V = E – j IsdXsd – j Isq…………(1.1)
Where
V is the Supply Voltage
Is is the stator current
E is the excitation emf
Ȣ is the load angle
ɸ is the phase angle
Xsd and Xsq are the synchronous reactance of direct and quadrature axis
Isd and Isq are the direct and quadrature axis current
I = Isd + Isq…………….(1.2)
Isd is in phase quadrtur with E and Isq is in phase with E.
V = E – j IsdXsd – j IsqXsq
Equation (9) is the torque equation of synchronous reluctance motor.
Plotting the equation (9) as shown in fig indicates that the stability limit is reached
at Ȣ =± ᴨ /4
And by increasing g load angle torque also increases.
In synchronous reluctance motor, the excitation emf(E) is zero.

What is Vernier motor? Why it is so called
1.
A Vernier motor is an unexcited (or reluctance Type) inductor synchronous
motor.
2.
It is also named because it operates on the principle of a vernier. The peculiar
feature of this kind of motor is that a small displacement of the rotor produces a
large displacement of the axes of maximum and minimum permeance.
3.
When a rotating magnetic field is introduced in the air gap of the machine, rotor
will rotate slowly and at a definite fraction of the speed of the rotating field.
4.
This rotating field can be produced either by feeding poly phase current to the
stator winding or by exciting the stator coil groups in sequence.
5.
AS the rotor speed steps down from the speed of the rotating field, the motor
torque steps up. A vernier motor works as an electric gearing.
6.
This kind of motor is attractive in applications which require low speed and high
torque and where mechanical gearing is undesirable.