1. Subject : Electronic Machines
Presented by: Shivali. M. Panchal.
( )
Roll no. :- 14ELCE310
Discipline: EC 3rd Sem.
Guided by: Ravi Patel

2. Topics :- 3 Point & 4 Point starter. Speed control method.
Swinburne's & break test of Dc Shunt motor.

3. Starters for DC motors Needed to limit the starting current .
1. Two point starter
2. Three point starter
3. Four point starter

4. Working Principle of 3 Point starter
A 3 point starter in simple words is a device that helps in the starting and running of a shunt wound DC motor or compound wound DC motor.
Now the question is why these types of DC motors require the assistance of the starter in the first case. The only explanation to that is given by the presence of back emf Eb, which plays a critical role in governing the operation of the motor.
The back emf, develops as the motor armature starts to rotate in presence of the magnetic field, by generating action and counters the supply voltage. This also essentially means, that the back emf at the starting is zero, and develops gradually as the motor gathers speed.
The general motor emf equation E = Eb + Ia.Ra, at starting is modified to E = Ia.Ra as at starting Eb = 0.

5. Construction of 3 Point Starter
Construction wise a starter is a variable resistance, integrated into number of sections as shown in the figure beside. The contact points of these sections are called studs and are shown separately as OFF, 1, 2,3,4,5, RUN. Other than that there are 3 main points, referred to as
1. 'L' Line terminal. (Connected to positive of supply.) 2. 'A' Armature terminal. (Connected to the armature winding.) 3. 'F' Field terminal. (Connected to the field winding.) And from there it gets the name 3 point starter.

6. called overload release (OLR) as shown in the figure.
The point 'L' is connected to an electromagnet
called overload release (OLR) as shown in the
figure.
The other end of 'OLR' is connected to the
lower end of conducting lever of starter
handle where a spring is also attached with it
and the starter handle contains also a soft iron
piece housed on it.
This handle is free to move to the other side
RUN against the force of the spring. This
spring brings back the handle to its original
OFF position under the influence of its own
force. Another parallel path is derived from
the stud '1', given to the another electromagnet
called No Volt Coil (NVC) which is further
connected to terminal 'F'.
The starting resistance at starting is entirely
in series with the armature. The OLR and NVC
acts as the two protecting devices of the starter.

7. Working Principle of Four Point Starter
The 4 point starter like in the case of a 3 point starter also
acts as a protective device that helps in safeguarding the
armature of the shunt or compound excited dc motor
against the high starting current produced in the absence of
back emf at starting.
The 4 point starter has a lot of constructional and
functional similarity to a three point starter, but this special
device has an additional point and a coil in its construction,
which naturally brings about some difference in its
functionality, though the basic operational characteristics
remains the same.

8. Construction and Operation of Four Point Starter
A 4 point starter as the name suggests has 4 main operational points, namely
'L' Line terminal. (Connected to positive of supply.)
2. 'A' Armature terminal.
(Connected to the armature
winding.)
'F' Field terminal. (Connected to the field winding.)
A 4th point N. (Connected to the No Voltage Coil)

9. Dc motor Dc motor Converts Electrical energy into Mechanical energy.
Construction is same for Generator and motor.
Working principle : Whenever a current carrying conductor is placed in the magnetic field , a force is set up on the conductor.

10. Swinburne’s Test:-
Swinburne’s test is carried out at no-load condition hence the testing of series motor cannot be done using this method.
The motor is run at no-load at rated speed. Also, the field current is adjusted to a rated value for correct determination of no-load loss. The circuit diagram is shown in figure.
At no load the machine would run at a higher speed & have a higher armature voltage.
To reduce or control the rated voltage a series resistor is added in the armature circuit such that the motor armature runs at rated speed. Power input, Pi = VIL (where IL is load current) Total power loss, PL = Copper loss + Iron loss + stray losses Power output, Po = Pi – PL
Motor efficiency,

11. Advantages of Swinburne’s Test
It is a convenient & economical method of testing dc machines since the power required to test large machine is small.
The efficiency can be predetermined at any load because constant losses are known.

12. Disadvanges of Swinburne’s Test
No account is taken of the change in the iron loss caused due to change from no-load to full load condition.
As the test is carried out at no load, it does not indicate the communication status at full load.
This test applicable to machines in which flux is almost constant.
Series machines cannot be tested by this method as they cannot be run on light load & even the speed varies greatly.

13. Break Test This is a direct method of testing the DC motor.
It is done by applying a direct load on the motor using a belt & pulley arrangement as shown in figure.
The load acting on the motor can be varied by varying the belt tension.
The power developed by the DC motor is deliberately made to go waste by the banking effect of the belt.
Using the setup as shown in figure the power output can be found.
Total force acting = 9.81(S1-S2)N
Where S1 & S2 are spring balance reading.

14. Considering the motor rotates at N rpm & has ‘R’ radius, its torque developed can be given as,
And hence the corresponding output power can be started as,
The efficiency of the systems,

15. Speed Control in Shunt DC Motors
Armature Voltage Control:
Ra and If are kept constant and the armature terminal voltage is varied to change the motor speed.
For constant load torque, such as applied by an elevator or hoist crane load, the speed will change linearly with Vt. In an actual application, when the speed is changed by varying the terminal voltage, the armature current is kept constant. This method can also be applied to series motor.

16. Field Control:
Ra and Vt are kept constant, field rheostat is varied to change the field current.
For no-load condition, Te=0. So, no-load speed varies inversely with the field current.
Speed control from zero to base speed is usually obtained by armature voltage control. Speed control beyond the base speed is obtained by decreasing the field current. If armature current is not to exceed its rated value (heating limit), speed control beyond the base speed is restricted to constant power, known as constant power application.

17. Armature Resistance Control:
Vt and If are kept constant at their rated value, armature resistance is varied.
The value of Radj can be adjusted to obtain various speed such that the armature current Ia (hence torque, Te=KafdIa) remains constant.
Armature resistance control is simple to implement. However, this method is less efficient because of loss in Radj. This resistance should also been designed to carry armature current. It is therefore more expensive than the rheostat used in the field control method.

18. Applications Shunt Motor:
Blowers and fans
Centrifugal and reciprocating pumps
Lathe machines
Machine tools
Milling machines
Drilling machines

19. Thank you…