AC DC 1-5
Page 4: Forms of Energy
Mechanical energy relates to the movement of objects or its position in gravity.
Examples: roller-coaster, swing, moving objects
Sound energy relates to the repetitive compression and rarefaction of molecules in a substance.
Examples: music, tuning fork, sound waves
Chemical energy relates to energy stored in the bonds between atoms in a molecule.
Examples: propane, batteries, fuel
Electrical energy relates to the movement or flow of electrons.
Examples: static electricity, current electricity, magnetic field
Light energy relates to the vibration of an electrical charge or magnetic field that produces electromagnetic waves.
Examples: radio waves, visible light, X-rays
Page 9: Forms of Energy
Heat energy relates to the motion of particles, atoms, or molecules in a substance.
Examples: conduction, convection
Page 10: Forms of Energy
Nuclear energy relates to the potential energy stored in bonds between particles in the nucleus of an atom.
Examples: uranium, nuclear power plants
Page 11: Rotating Electrical Machines
Rotating electrical machines are widely used for converting energy from one form to another.
Page 13: Law that governs Energy Conversion
First Law of Thermodynamics or the "Law of Conservation of Energy": Energy can neither be created nor destroyed, only transformed from one form to another.
Second Law of Thermodynamics or the "Law of Increased Entropy": When energy is transformed, some of the input energy is turned into a highly disordered form of energy, like heat, resulting in energy loss.
Page 14: Machine
A machine is a device that augments or replaces human or animal effort for physical tasks.
A machine consists of fixed and moving parts that convert energy from one form to another.
A DC machine is a rotary electro-mechanical energy conversion device that converts mechanical energy to DC electrical energy or vice versa.
Page 15: DC Machine
DC machines can function as generators or motors.
Generators convert mechanical energy to electrical energy.
Motors convert electrical energy to mechanical energy.
Page 16: Electric Motor
An electric motor produces rotational mechanical energy to drive external physical loads.
It works on the principle that when a current-carrying conductor is placed under a magnetic field, it experiences a torque and has a tendency to move.
Examples of electric motor-driven loads are pumps, compressors, conveyor systems, lifts, etc.
Page 17: Electric Generator
An electric generator generates electrical energy for use in an external circuit.
Electric generators are used when large quantities of electric power are required.
Electric generators are driven by a mechanical machine called the Prime Mover.
Page 18: Electric Generator Prime Mover
A prime mover is an initial source of motive power designed to receive and modify force and motion as supplied by some natural source and apply them to drive machinery.
Examples of prime movers are steam turbines, water turbines, internal combustion engines, wind turbines, electric motors, etc.
Page 23: Construction and Operation of DC Generator
Details about the construction and operation of a DC generator are not provided in the given transcript.
Page 24:
Principle of Generator Action
Requires proper relation between the direction of rotation and the field connection to the armature.
When a conductor is placed in a varying magnetic field, electromagnetic induction occurs.
Page 25:
Parts of DC Generator
According to the one that cuts the magnetic lines of force
Field poles (electromagnets or permanent magnets) produce magnetic flux
Conductors are wound around the armature and rotated between the field poles.
Page 26:
Operation of a DC Generator
Presence of magnetic lines of force
Motion of conductors cutting the flux
Proper relation between the direction of rotation and the field connection to the armature.
Page 27:
Parts of DC Generator
Under the Stator:
Poles rotate under the magnetic lines of force.
Yoke houses the entire machine.
Pole Shoe holds the poles together.
Under the Rotor:
Conductors (windings) on its conductor slots.
Shaft coupled/connected to the prime mover.
Conductors cut the magnetic lines of force.
Page 28:
Parts of DC Generator
Under the Rotor:
Armature
Shaft
Conductors
Page 29:
Parts of DC Generator
Commutator collects the current from the armature windings.
For DC Generator: Split Rings change the current direction every half-rotation.
For AC Generator: Slip Ring maintains a connection between the moving rotor and the stationary stator.
Carbon Brushes harvest the current from the rotating commutator.
Page 30:
Construction of DC Machines
Terminal Yoke
Box Brushes
Field Pole
Pole and Field Core
Field winding
Nameplate
Commutator
Armature
Armature Brushes
Yoke
Armature-Communtator
Laminated Pole Shoe
Page 31:
References
Page 32:
References
Page 33:
Course: EE 2312 ME 2613: AC and DC Machinery / Electrical Machines 1
Instructor: Kevin Lester B. Lobo
Page 34:
Generated Voltage of a DC generator
Page 35:
Faraday's Law
When a conductor moves across a magnetic field, the average generated voltage is directly proportional to the magnetic field strength and the speed of the conductor.
Page 36:
Principle of Generator Action:
Time taken to make 1 complete revolution in a conductor
Total flux cut
Rate of cutting of flux
Total number of conductors
Average generated voltage formula
Page 37:
Measuring device for magnetic flux
Page 38:
Example A:
Armature winding with 648 conductors in 2-parallel paths
Flux per pole and speed of rotation given
Calculation of average generated voltage
Page 39:
Relationship between number of conductors and parallel paths
Example: Determining voltage and current based on given parameters
Page 40:
General voltage equation for DC generator
Speed of rotation, flux per pole, number of poles, and armature conductors
Page 41:
General voltage equation for DC generator
Total generated voltage formula
Flux per pole, number of poles, speed of rotation, and armature conductors
Page 42:
Armature winding and the number of parallel paths
Page 43:
Types of armature windings:
Lap winding
Wave winding
Frog-Leg winding
Page 44:
Lap winding:
Description and characteristics
Page 45:
Wave winding:
Description and characteristics
Page 46:
Number of Parallel Paths and a Machine's "Plex" Value:
The number of revolutions it takes to fill the slots in the armature before terminating in a commutator segment.
Increases the number of parallel paths of lap and wave armature windings by a multiplicity factor that is equal to the number of revolutions made.
Multiplicity Factor, m:
m = 1, for simplex winding
m = 3, for triplex winding
m = 2, for duplex winding
m = 4, for quadruplex winding
Lap Winding:
Number of parallel paths = Multiplicity x Poles
Number of Brushes = Number of Poles
Wave Winding:
Number of parallel paths = Multiplicity x 2
Number of Brushes = 2
Page 47:
Problem 1:
A four-pole generator with a wave-wound armature winding
51 slots, each slot containing 20 conductors
Driven at 1,500 rpm
Flux per pole = 7.0 mWb
Voltage generated in the machine = 357V
Problem 2:
An 8-pole generator
Runs at 1,200 rpm
Armature has 50 slots
Each slot contains 216 conductors
Wave-wound armature winding
Voltage generated in the machine = 432V
Page 48:
Online References:
Various links to images, diagrams, and videos related to energy conversion, DC generators, and turbines.
Page 49:
Online References:
Various links to websites providing information on the construction of DC machines, turbines, and internal combustion engines.
Page 50:
Online References:
Various links to websites providing information on lap and wave winding, parallel paths, and demagnetization.
Page 51:
Course Information:
Course name: EE 2312 ME 2613: AC and DC Machinery / Electrical Machines 1
Instructor: Kevin Lester B. Lobo
Page 52:
Types of DC Generators:
According to Field Excitation
Page 53:
Field Excitation:
When a DC voltage (excitation voltage) is applied to the field windings of a DC generator, current (exciting current) flows through the windings and sets up a steady magnetic field.
DC excitation voltage can be supplied by an external source or produced by the generator itself.
Generator that supplies its own field excitation is called a Self-Excited generator, and a generator that relies on an outside source is called a Separately Excited Generator.
The magnitude of the exciting current (field current) is directly proportional to the amount of flux produced.
Page 54:
Types of DC Generator (according to field excitation):
Independent Excitation:
A DC generator whose field magnet winding is supplied from an external DC source (e.g., battery, DC power supply, etc.)
Ia = IL
Eg = Vt + IaRa
If = Vf Rf
Page 55:
Types of DC Generator (according to field excitation):
Self-Excited DC Generator:
A DC generator whose field magnet winding is supplied from the output of the generator itself.
Categorized based on how the field winding/s is/are connected.
a) Series Wound: field winding (series field) is connected in series to the armature
b) Shunt Wound: field winding (shunt field) is connected in parallel to the armature
c) Compound Wound: has both series and shunt field windings
i. Long Shunt Compound: series field is connected in series to the armature
ii. Short Shunt Compound: series field is connected in series to the load
Page 56:
Two types of field windings used in DC Machines: Series field winding and Shunt field winding.
Series Field winding (Rse) is made with a few turns of large diameter wire, has low resistance, and is connected in series with the armature.
Shunt Field (Rf) winding is made with many turns of small diameter wire, has high resistance, and is connected in parallel with the armature.
Page 57:
Self Excited DC Generator Series connected:
The field is connected in series with the armature.
Eg = Vt + IaRa + IseRse
Ia = IL - Ise
Page 58:
Self Excited DC Generator Shunt Wound Generator:
The field is connected in parallel to the armature.
Vf = Vt
Eg = Vt + IaRa
If = Vf / Rf
Ia = If + IL
Page 59:
Self Excited DC Generator Long-Shunt Compound Generator:
Has both series and shunt field, and the series field is connected to the armature.
Vf = Vt
Eg = Vt + IaRa + IseRse
If = Vf / Rf
Ia = If + IL
Ia = Ise
Page 60:
Self Excited DC Generator Short-Compound Generator:
Has both series and shunt field, and the series field is connected to the load.
Vf ≠ Vt
Isht = Vsht / Rsht
Ia = If + IL
Ise = IL
Vf = Vt + IseRse
Eg = Vt + IaRa + IseRse
Page 61:
Presence of Residual Magnetism:
The field of a DC Generator stores energy as an electromagnetic field.
Residual magnetism or residual flux remains even when the generator is turned off.
Residual flux enables the armature to develop residual voltage, causing a small current to flow through the field windings.
The generated voltage and field current increase until the generator reaches its rated value.
If the field loses its residual flux, it needs to be connected to a separate DC source to produce and retain a small amount of flux (flashing the field).
Page 62:
Saturation Curve of DC Generators:
The field current is directly proportional to the flux created, and the flux created is directly proportional to the generated voltage.
Saturation occurs when the core of the field windings cannot produce more flux, even with an increase in excitation current.
Page 63:
Brush Contact Drop:
Voltage drop over the brush contact resistance when current passes from commutator segments to brushes and the external load.
Its value depends on the amount of current and the value of contact resistance.
Brush contact drop is assumed to have constant values for all loads:
0.5 V for metal-graphite brushes (pair)
2.0 V for carbon brushes (pair)
Page 64:
Problems:
An 8-pole DC shunt generator with 778 wave-connected armature conductors and running at 500 rpm supplies a load of 12.5 Ω resistance at a terminal voltage of 250 V. The armature resistance is 0.24 Ω and the field resistance is 250 Ω. Find the armature current, the induced e.m.f., and the flux per pole.
Answer: 21 A, 255.04 V, 9.83 mWb
A long-shunt compound generator delivers a load current of 50 A at 500 V and has armature, series field, and shunt field resistances of 0.05 Ω, 0.03 Ω, and 250 Ω respectively. Calculate the generated voltage and the armature current. Allow 1 V per brush for contact drop.
Answer: 506.16 V, 52 A
Page 65:
Problems: 3. A 4-pole, long-shunt, lap-wound DC generator runs at 1,200 rpm at a terminal voltage of 500 V. The armature resistance is 0.03 ohm, series field resistance is 0.04 ohm, and shunt field resistance is 200 ohm. The brush drops may be taken as 1.0 V. If the flux per pole is measured at 0.02 Wb, determine the generated e.m.f. and the total number of conductors of this generator.
Answer: 507 V, 1,264 conductors
A separately excited generator has an armature resistance of 0.04 ohm and a total brush drop of 2 V. When running at 1,000 rpm, it supplies a load current of 200 A at 125 V. What will be the load current and terminal voltage when the speed drops to 800 rpm and the field current is unchanged?
Answer: 159.45 A
Page 66:
Online References (not relevant to the main ideas)
Page 67:
Online References (not relevant to the main ideas)
Page 68:
Online References (not relevant to the main ideas)
Page 69:
Course information: ME2613 / EE2312: AC and DC Machinery / Electrical Machines 1
Instructor: Kevin Lester B. Lobo
Page 70:
Voltage Regulation of DC Generators (no further details provided)
Page 71:
Voltage Regulation (%VR)
Definition: percentage change in the terminal voltage of the generator when the generator load is varied
Formula: %𝑉𝑅 = 𝑉𝑡𝑁𝐿−𝑉𝑡𝐹𝐿 𝑉𝑡𝐹𝐿 × 100%
Variables: 𝑽𝒕𝑵𝑳= no-load terminal voltage, 𝑽𝒕𝑭𝑳= full-load terminal voltage
Page 72:
Voltage Regulation of a DC shunt generator
As the load increases, the terminal voltage decreases due to:
Increase in load current and armature current, resulting in voltage drop in the armature and decrease in terminal voltage
Increase in voltage drop in the armature, causing reduction in field voltage, field current, and flux, resulting in decrease in generated voltage and terminal voltage
Production of counter-flux in the armature, reducing total flux and generated voltage, leading to decrease in terminal voltage
Page 73:
Voltage Regulation of DC series generators
At no-load, terminal voltage is either zero or very low
As the load increases, terminal voltage also increases due to:
Increase in load current and series field current, resulting in increase in flux and generated voltage
Saturation of field winding core limits further increase in flux production, causing decrease in terminal voltage
Page 74:
Degree of Compounding Adjustment
Different types of compounding for DC generators
Performance curves of DC generators
Page 75:
Applications of different types of DC generators
Compounded, Shunt Wound, Series Wound, Flat-Compounded, Under-Compounded, Differential-Compound
Various power supply applications, battery charging, arc welding, etc.
Page 76:
Problems
Example problem: A shunt generator has a full-load current of 120A and needs to divert 36A to adjust the terminal voltage. Calculate the value of the diverter resistance.
Example problem: A compound DC generator with specific resistances and currents. Calculate the current flowing to the series field.
Page 78:
Controlling the Terminal Voltage of DC generator
The generated voltage of a DC generator affects the terminal voltage
Two ways to vary the generated voltage: change the speed of the generator or adjust the field currents
Page 79:
Varying the Field Current
Series Field: use of diverter resistance
Shunt Field: use of field rheostat
Page 80:
Problems
Example problem: Calculate the value of the diverter resistance for a compound generator with given resistances and current values.
Example problem: Calculate the voltage of a DC generator at different speeds, assuming constant flux and considering changes in flux