The document provides details about the syllabus of an Electrical Machines course. It covers 5 units: 1) Construction and operation of DC machines including generators and motors. 2) Performance characteristics of DC machines like torque equations and efficiency. 3) Starting, speed control and testing methods for DC machines. 4) Construction, operation and testing of single phase transformers. 5) Three phase transformer connections and testing. The summary covers the main topics covered in each unit at a high level.

1. ELECTRICAL MACHINES-I
Mrs. G. Sree Lakshmi
Assistant Professor
Department of EEE
( Unit No-1: D.C Machines)
(R19C202.1, PO-1,2 )

2. UNIT–I:
Construction and Operation of DC machines
Construction and principle of operation of DC machine – emf equation for generator –
classification of DC machines based on excitation – OCC of DC shunt generator –
applications of DC Generators
UNIT–II:
Performance of DC Machines
Torque and back- emf equations of dc motors – Armature reaction and commutation –
characteristics of separately-excited, shunt, series and compound motors – losses and
efficiency-applications of dc motors.
UNIT-III:
Starting, Speed Control and Testing of DC Machines
Necessity of a starter – starting by 3 point and 4 point starters – speed control by armature
voltage and field control.
Testing of DC machines – brake test, Swinburne’s method – principle of regenerative or
Hopkinson’s method – retardation test – separation of losses.

3. UNIT–IV:
Single-phase Transformers
Types and constructional details – principle of operation – emf equation – operation on
no load and on load –phasor diagrams of transformers - equivalent circuit – regulation –
losses and efficiency – effect of variation of frequency and supply voltage on losses –
all day efficiency.
UNIT-V
Testing of Transformers and 3-Phase Transformers
Tests on single phase transformers – open circuit and short circuit tests – Sumpner’s test
– separation of losses- parallel operation with equal voltage ratios – auto transformer –
comparison with two winding transformers.
Polyphase connections - Y/Y, Y/∆, ∆/Y, ∆/∆ and open ∆ – Scott connection.

4. Electric Current:
The electric current is the rate of flow of electric charge through a conducting or semi-conducting
medium with respect to time.
Voltage:
The potential difference between two points is known as Voltage.
Power:
Power is the measurement of energy transfer over time
Energy:
Electrical Energy is defined as the overall work done in an electrical circuit
W = VQ =V*I t

5. Ohm’s Law:
It states that the electric current passing through a conductor is directly proportional to
potential difference across it, provided that the temperature remains constant. The
constant of proportionality is the resistance of the conductor.
I 𝛂 V I=KV
I=V/R (K=1/R)
V=I*R
Power P= V*I = I*R*I = I2R = V2/R Watts
Energy W= V*I*t = I2Rt = V2*t/R Joules

6. Energy conservation principle:
The law of conservation of energy states that energy can neither be created nor be destroyed.
Although, it may be transformed from one form to another.
Faraday’s First Law:
Whenever a conductor is placed in a varying magnetic field, an electromotive force is induced. If the
conductor circuit is closed, a current is induced which is called induced current.
Faraday’s Second Law:
The induced emf in a coil is equal to the rate of change of flux linkages.
Lenz’s law:
It states that an induced electric current flows in a direction such that the current opposes the
change that induced it.

7. Constructional Details of D.C Machine

8. Yoke:
•The outer frame of a dc machine is called as yoke. It is made up of cast iron or steel.
•It supports the pole cores and provides mechanical protection to the inner parts of the
machines.
•It provides a low reluctance path for the magnetic flux.
Pole Core and Pole Shoes:
•Poles are joined to the yoke with the help of bolts or welding. They carry field winding and
pole shoes are fastened to them.
•It supports the field or exciting coils.
•They spread out the magnetic flux over the armature periphery more uniformly.
Field winding or Field coil:
Field coils are the coils of a conductor wounded across the pole core. When current is
passed through these coils the poles reacts as an electromagnet and magnetic flux is
produced in it.

9. Armature core:
Armature core is the rotor of a dc machine. It is cylindrical in shape with slots to carry
armature winding. The armature is built up of thin laminated circular steel disks for reducing
eddy current losses. It may be provided with air ducts for the axial air flow for cooling
purposes. Armature is keyed to the shaft.
Armature winding:
The armature windings are in a wound form. These windings are insulated from each other
and normally copper winding are generally used in it. The Armature winding is distributed on
the armature slots in which emf is induced . Two types of the winding are used - Wave and
lap.
Lap Winding: In lap winding, the conductors are connected in such a way that the number of
parallel paths is equal to the number of poles.
Wave Winding: In wave winding, the conductors are so connected that they are divided into
two parallel paths irrespective of the number of poles of the machine.

10. Commutator
It provides a collection of currents from the armature winding. It converts the alternating
current which is induced in the armature conductors into direct current (DC). It is
a cylindrical shaped and have wedge shaped segments. These segments are insulated from
each other. The number of segments are equal to the number of armature coils.
Each segment is connected to the armature conductor. commutator is keyed to the shaft.
Brushes:
Brushes are usually made from carbon or graphite. They rest on commutator segments and
slide on the segments when the commutator rotates keeping the physical contact to collect or
supply the current.
Shaft:
The shaft is made of mild steel with a maximum breaking strength. The shaft is used to
transfer mechanical power from or to the machine. The rotating parts like armature core,
commutator, cooling fans, etc. are keyed to the shaft

11. Principle of Operation of D.C Generator
• The main function of DC Generator is to convert mechanical energy into electrical
energy.
• DC Generator works on the principle of Faraday’s law of electromagnetic
induction. This law states that when a conductor moves in a magnetic field it cuts
magnetic lines of force, which induces an electromagnetic force (EMF) in the
conductor.
• The magnitude of this induced EMF depends upon the rate of change of flux linkage
with the conductor. This EMF will cause a current to flow if the conductor circuit is
closed.
• Hence the most basic two essential parts of a generator are:
1.The magnetic field
2.Conductors which move inside that magnetic field.

12. Induced EMF in armature coil:

13. Ѳ=90 Ѳ=270
Working of Commutator:

14. Fleming’s Right Hand Rule
The direction of induced e.m.f. or induced current is found by using Fleming’s Right hand Rule

15. E.M.F Equation of D.C Generator

18. Classification of DC Generators

19. Separately Excited D.C Generator

20. D.C Shunt Generator

21. D.C Series Generator

22. D.C Long-shunt Compound Generator

23. D.C Short-shunt Compound Generator

24. Cumulative Compound Generator Differential Compound Generator

25. Open Circuit Characteristics of D.C. Generator

26. Applications of DC Generators
Separately Excited DC Generators
•Used in laboratories for testing as they have a wide range of voltage output.
•Used asa supply source of DC motors.
Shunt wound Generators
•Used for lighting purposes.
•Used to charge the battery.
•Providing excitation to the alternators.
Series Wound Generators
•Used in DC locomotives for regenerative braking for providing field excitation current.
•Used as a booster in distribution networks.

27. Cumulative compound wound generators
•These are generally used for lighting, power supply purpose and for heavy power
services because of their constant voltage property.
•Also used for driving a motor.
Differential compound wound generators
•These are used for arc welding where huge voltage drop and constant current is required.

28. Principle of Operation of D.C Motor
An Electric DC motor is a machine
which converts electric energy into
mechanical energy.
The working of DC motor is based
on the principle that when a current-
carrying conductor is placed in a
magnetic field, it experiences a
mechanical force

31. Classification of DC Motors

32. Separately Excited D.C Motor

33. D.C Shunt Motor

34. D.C Series Motor

35. Long Shunt D.C Compound Motor

36. Short Shunt D.C Compound Motor

37. Cumulative Compound Motor
Differential Compound Motor

38. 1. A shunt generator delivers 450 A at 230 V and the resistance of the shunt field and
armature are 50 Ω and 0.03 Ω respectively. Calculate the generated e.m.f?
2. A four pole generator having wave-wound armature winding has 51 slots, each slot
containing 20 conductors. What will be the voltage generated in the machine when
driven at 1500 rpm assuming the flux per pole to be 7.0 mWb ?
3. The armature of 2-pole, 200V, and wave wound DC machine has 400 conductors and
runs at 300 rpm. Calculate the machine flux per pole.
4. A 400V, 8-pole, 600 rpm DC machine has 100 slots. Each slot contains 40 conductors.
The flux per pole is 0.01 Weber .what type of winding is used?
Problems:

39. 5. A 4 pole generator with wave wound armature has 51 slots each having 24 conductors.
The flux per pole is 10 mWb. At what speed must the armature rotate to give an
induced emf of 0.24 kV. What will be the voltage developed, if the winding is lap
connected and the armature rotates at the same speed?

40. 6. A 4 pole, dc generator has a wave wound armature with 792 conductors. The flux per poleis 0.0121Wb. Determine
the speed at which it should run to generate 240 V at no load.

41. 7. A dc generator when driven at 1000 r.p.m. with a flux per pole of 0.02 Wb, produces an
e.m.f. of 200V. If the speed is increased to 1100 r.p.m. and the flux per pole is reduced to
0.019 Wb per pole what will be the new value of e.m.f.

42. 8. A short shunt compound generator delivers a load current of 30 A at 220V and has Ra =
0.05ohm, Rse= 0.3 ohm and Rsh= 200 ohms. Calculate the induced e.m.f. and Ia.
Allow 1V per brush as contact drop.

43. 9. A long shunt compound generator delivers a load current of 30 A at 220V and has
Ra =0.05ohm, Rse= 0.3 ohm and Rsh= 200 ohms. Calculate the induced e.m.f. and Ia.
Allow 1V per brush as contact drop.

44. 10. A 4 pole, lap wound, long shunt generator has flux per pole of 0.07 Wb. The armature
winding consists of 220 turns and the resistance per turn is 0.004Ω. Calculate the
terminal voltage if the resistance of shunt and series field are 100 Ω and 0.02 Ω
respectively; when the generator is running at 900 r.p.m. with armature current of 50A.
Also calculate the power output of the generator

45. 11. A separately excited motor runs at 1045rpm, with a constant field current, while
taking an armature current of 50A at 120V. The armature resistance is 0.1 Ω if the load
on the motor changes such that it now takes 95A at 120V, determine the motor speed at
this load.