1. Unit IV- Electrical Machines and Measuring Instrumentation
Working Principle, Construction and application of DC machine & AC machines (Single Phase Transformer, Single Phase Induction Motor: Split Phase, Capacitor start and capacitor start and run motors).
Basic Principles & Classification of Instruments – Moving coil and Moving Iron instruments.

2. Overview of Direct Current (DC) Machines
Direct-current (DC) machines are divided into dc generators and dc motors.
Most DC machines are similar to AC machines: i.e. they have AC voltages and current within them.
DC machines have DC outputs just because they have a mechanism converting AC voltages to DC voltages at their terminals.
This mechanism is called a commutator; therefore, DC machines are also called commutating machines.
DC generators are not as common as they used to be, because direct current, when required, is mainly produced by electronic rectifiers.
While dc motors are widely used, such automobile, aircraft, and portable electronics, in speed control applications…

3. DC Machine – Pictorial Representation

4. Construction of DC Machine.

5. Picture View of DC machine
Cutaway view of a dc motor
Stator with poles visible.

6. Yoke or Frame Poles: Field winding Made by silicon steel lamination.
Silicon steel- reduce hysteresis loss
Lamination- reduce eddy current loss.
Pole shoe : Ensure uniform flux distribution and air gap between the poles and rotating armature.
Field winding
Winding is series connection to the other poles.
Poles get magnetized to N and S poles alternatively.

7. Commutator: AC emf in to pulsating DC emf.
Armature:
Laminated silicon steel core supported on a solid shaft.
Cylindrical drum consisting of thin circular stamping of silicon steel.
Thickness of stamping – 0.35mm to 0.5mm.
Winding:
Lap winding : no of parallel path equal to no of poles; total current divides equal among them; no of brushes equal to no of poles. ( Large current machine)
Wave winding: no of parallel path is 2;
Commutator: AC emf in to pulsating DC emf.
Brushes: made of carbon or graphite; gentle touch with commutator.

8. Working Principle – DC Generator

9. Use Commutator

10. Working Principle – DC Motor

12. Types of DC Generator Separately excited generator
Self excited generator
Series generator
Shunt Generator
Compound Generator
Application
Charging batteries
Compensation in transmission line for line drop
Arc welding.

13. Classification of DC motors
DC motors are mainly classified into three types as listed below:
Shunt motor
Series motor
Compound motor
Differential compound
Cumulative compound

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

15. Applications: Series Motor: Cranes Hoists , Elevators Trolleys
Conveyors
Electric locomotives

16. Applications: Cumulative compound Motor: Rolling mills Punches Shears
Heavy planers
Elevators

17. Transformer - Introduction
A transformer is a static machines.
The word ‘transformer’ comes form the word ‘transform’.
Transformer is not an energy conversion device, but is a device that changes AC electrical power at one voltage level into AC electrical power at another voltage level through the action of magnetic field, without a change in frequency.
It can be either to step-up or step down.
Generation Station
Distributions
Transmission System
33/13.5kV
13.5/6.6kV
6.6kV/415V
Consumer 17

18. Transformer- Types
Core - type construction
Shell - type construction

19. Transformer Lamination

20. Laminated Core: Winding: Transformer tank: Transformer oil:
Made up of, L, E,I,U shaped stampings depends on the types.
Silicon steel (reduced hysterics loss); Lamination (reduced eddy current loss)
Winding:
Primary and secondary winding made of copper are placed on the vertical limbs of the core.
Transformer tank:
Core and windings is placed in an aluminum tank.
The tank acts as an enclosure and cooling surface.
Transformer oil:
Used mineral oil; cooling medium; insulator between tank and transformer assembly.
Conservator:
Its placed over a tank through the pipe connection; partially filled oil.
Breather:
Oil expanded the level – conservator raised and the air is released;
It’s a small vessel containing drying agent silica gel.
Buchholz Relay:
Moisture entering the transformer – affect the insulating property of oil in transformer; This relay sense this condition.

21. Ideal Transformer
An ideal transformer is a transformer which has no loses, i.e. it’s winding has no ohmic resistance, no magnetic leakage, and therefore no I2 R and core loses.
However, it is impossible to realize such a transformer in practice.
Yet, the approximate characteristic of ideal transformer will be used in characterized the practical transformer. V1 V2
N1 : N2 E1 E2 I1 I2
V1 – Primary Voltage
V2 – Secondary Voltage
E1 – Primary induced Voltage
E2 – secondary induced Voltage
N1:N2 – Transformer ratio

22. Transformer Equation
Where, ‘a’ is the Voltage Transformation Ratio; which will determine whether the transformer is going to be step-up or step-down
Step Down Transformer
For a >1
E1 > E2
Step Up Transformer
For a <1
E1 < E2

23. Applications

27. Step Up Transformer at Power Plant

28. Induction Motors

29. Introduction
Three-phase induction motors are the most common and frequently encountered machines in industry
simple design, rugged, low-price, easy maintenance
wide range of power ratings: fractional horsepower to 10 MW
run essentially as constant speed from no-load to full load
Its speed depends on the frequency of the power source
not easy to have variable speed control
requires a variable-frequency power-electronic drive for optimal speed control

30. Construction - Stator

31. Stationary part of the motor.
Outer solid circular metal part – Yoke or frame.
Laminated cylinder drum – Stator drum.
Required no of stator conductor are embedded in slots.
Electrically connected in series; arranged to form balanced three phase winding.

32. Construction – Squirrel Cage Rotor

33. Each rotor slot accommodates a rod or bar made of a good conducting material.
Rotor rod in short circuited in both ends
Rotor circuit forms short circuited for a closed path in a current flow through it.

34. Construction – Slip Ring Wound Rotor

35. Large no of conductor embedded in a rotor slots.
The conductor are electrically connected to form a balanced three phase winding.
Another point connected the three slip ring for make a closed circuit.

36. Construction
Squirrel cage rotor
Wound rotor
Notice the slip rings

37. Construction Slip rings
Cutaway in a typical wound-rotor IM. Notice the brushes and the slip rings
Brushes

38. AC Machines Single Phase Induction Motor: Split Phase Capacitor start
Capacitor start and run motors

39. Split Phase Induction Motor
Single-phase induction motor cannot develop a rotating magnetic field
Needs an “auxiliary” method
That method is another (auxiliary) winding

40. Single-Phase Squirrel-Cage Induction Motor
There are two “Main Poles”
Squirrel-Cage Rotor
Single-Phase Mains Supply

41. Excite the Main Winding
Stator flux is produced across the air gap – as shown, it is increasing in the downward direction.
The squirrel-cage rotor responds with a mmf in the opposite (upward) direction.
Magnetic axis of the rotor is in line with the magnetic axis of the stator – no rotation!

42. Current “out of” the page
“Main” pole flux (Φ) increasing in the downward direction
Rotor mmf develops in the upward direction
Current “into” the page

43. Cause the rotor to turn clockwise
Rotor conductors cut through the main pole flux.
Current is induced in the rotor bars as shown, producing a magnetic flux perpendicular to the main pole flux. This is known as “Quadrature” flux.

44. The quadrature flux is sustained as the rotor conductors shift their positions – other conductors replace them.

45. Phase Relationship Between the Direct and Quadrature Flux
The “speed” voltage is in phase with the flux that created it, and the flux due to current is in phase with the current that caused it. The instantaneous amplitudes of the direct and quadrature flux are shown above.

46. Animation

47. Split Phase Induction Motor
Single-phase induction motor cannot develop a rotating magnetic field
Needs an “auxiliary” method
That method is another (auxiliary) winding

48. Split phase (or) resistance start induction motor

49. Construction: Operation:
Main winding (M) and Auxiliary winding (A) (placed in stator).
M – Running Purpose, Highly inductive; A – Starting purpose, Highly resistive.
A – Centrifugal switch placed it; for the use of rest in motor.
Operation:
Current given to M & A; create phase angle ; the angle near to 90; starting torque proportion to sin 
Motor attain 75% of speed switch is open and “A” is disconnected.
the starting torque is 150 to 200% of full load torque.

50. CAPACITOR START INDUCTION MOTOR

51. Construction: Operation:
Same type of the construction; replace the resistance with capacitor in Auxiliary winding.
Operation:
Phase angle () is equal to 90;
Starting torque is high compare to previous type.
Better starting power factor.

52. CAPACITOR START AND RUN INDUCTION MOTOR

53. Construction: Operation: Same construction in previous type
Main winding added one capacitance permanently.
Operation:
Similar in previous one.
The advantage are follows
Low noise in running condition.
Higher power factor.
High Efficiency.
Improved Over load capacity.

54. Applications Fans Pumps Refrigerator Air conditioners Blowers
Washingmachines