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CENT-112 Fundamentals of Electricity and Electronics1

Generators

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Outline

Generating a voltage sine wave

Rectifying sine wave output

Types of generators

Magnetic amplifiers Developing 3 phase

Oscilloscope

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Interest

Fixed car starter motor knowing

basic motor theory from Navy.

Future of magnetism Levitron.

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InterestGenerators at a Dam

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Generator Construction Generator: Device that changes mechanical

energy into electrical energy.

Rotor: Armature: Revolving coils suspended inthe case resting on bearings.

Brushes: Made of soft carbon to remove theelectricity from the slip rings and deliver it to theregulator.

Slip rings (2): Interface between rotor andregulator.

Commutators: Used to reverse electricalconnections in DC generators

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Generator Construction

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Generator ConstructionField Pole from

Generator at a dam

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Generator Losses Copper Losses (I2R losses)

Losses due to resistance of windings.

Eddy Currents:

Heat produced in the iron core (energy loss)

minimized by thin sections and laminations.

N eddy currents

Hysteresis:

Molecular friction.

Heat loss minimized by using silicon steel and

annealing the armature core.

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Left Hand Rule for Generators

Motion

Flux Field

Current

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Magnetic Induction Three things to induce a voltage

1. A magnetic field.

2. A conductor: = in = out

3. Relative motion between the field and the conductor.

+_

_

_

_ _+

+

+

_

+

T1 T2 T3 T4 T5

+N S

Stator StatorRotor movement

00 900 1800 2700 3600

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Lenzs Law

Definition: The polarity of an inducedelectromagnetic force is such that it produces a

current. The magnetic field of this current always

opposes the change in the existing field.

Simply stated: The field around the conductor is

opposed by the existing field.

Application: Water and steam supply the

mechanical force to turn turbines in large power

plants.

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Formula

E = K

N

Given:

E=induced voltage

K=constant for # of flux lines/volt=10

-8

=magnetic flux lines

N=speed of the machine (RPM)

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Power Supplies

Components and their functionTransformer - Receives the AC input from thedistribution system and either steps up or downthe voltage.

Rectifier - Converts the AC input voltage fromthe transformer to a pulsating DC voltage.

Filter - Smoothes out the DC pulsations or ripplereceived from the rectifier.

Regulator - Receives a smoothed DC voltagefrom the Filter Stage and produces a steady DCvoltage to be used by electronic circuitry.

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Half - Wave Rectifier

VOUTVIN

1 : 1

T1

CR1

R1

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Positive half-cycle the diode is Forward Bias (FB),negative half-cycle the diode is Reverse Bias (RB).

Half - Wave Rectifier Operation

VDC = VPK X .318

Where: VDC = Average DC voltage

VPK = Peak input voltage

.318 = Constant

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Full - Wave Rectifier

VOUTVIN

1 : 1

T1

CR1

R1

CR2

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Positive half-cycle, 1 diode is FB, negative half-cyclethe other diode is FB.

Full - Wave Rectifier Operation

VDC

= VPK

X .637



.637 = Constant

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FullWave Bridge Rectifier

VOUTVIN

1 : 1

T1

CR1

R1

CR2

CR3CR4

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Positive half-cycle, 1 diode is FB, negative half-cycle

the other diode is FB.

Full - Wave Bridge

Rectifier Operation

VDC = VPK X .637



.637 = Constant

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Filters

A filter uses the characteristics of Inductors andCapacitors to smooth the pulsating DC waveform

supplied by the Rectifier.

Types

High Pass - A series RC filter whose output is taken

from the resistor.

Series / Parallel - A filter configuration which uses

combinations of capacitors and inductors to smooth

the voltage and current pulsations from the rectifieroutput.

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Rapid charge time constant for filter capacitors andinductors.

Slow discharge time constant for filter capacitors

and inductors.

Ideal filter characteristics

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Capacitor Filter Configuration

RB

C1

VIN VOUT

Capacitor Input Filter Schematic Diagram

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Capacitor Filter Operation

Charge RC time constant is developed from the internal

resistance of the rectifier diodes and the capacitance of the

filter capacitor. The net result is that the low resistance of the

rectifier diodes develop a rapid charge RC time constant.

Discharge RC time constant is developed from the filter

capacitor and the load resistance. Since the load resistance is

rather large, the discharge RC time constant is somewhat

long.

RB is called the Bleeder Resistorbecause it provides a pathfor the filter capacitor(s) to discharge when power is removed

from the circuit. RB has a very large resistance and usually

draws

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LC Choke Filter Configuration

LC Choke Filter Schematic Diagram

RBC1

VIN VOUT

L1

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LC Choke Filter Operation

Charge RC time constant is developed from the internal

resistance of the rectifier diodes, the Low DC resistance of the

inductor (L1), and the capacitance of the filter capacitor. The

net result is that the low resistance of the rectifier diodes and

inductor (L1) develop a rapid charge RC time constant.

Discharge RC time constant is developed from the filter

capacitor and the load resistance. Since the load resistance is

rather large, the discharge RC time constant is somewhat

long.The Inductor acts to smooth out the current pulsations

produced by the rectifier and / or transformer stage of the

power supply.

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RC PI Filter Configuration

RC PI Filter Schematic Diagram

RBC2

VIN VOUTC1

R1

VOUT(C1)VOUT (C2)

Charge Path

DischargePath

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RC PI Filter Operation

First Capacitor provides most of the filtering action.

Second Capacitor Provides additional voltage

filtering.

Resistor limits current flow to the desired value andestablishes the RC time constants for both filter

capacitors.

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LC PI Filter Configuration

LC PI Filter Schematic Diagram

RBC2

VINC1

L1

VOUT(C1)VOUT (C2)

Charge Path

DischargePath

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LC PI Filter Operation

First Capacitor provides most of the filtering action.

Second Capacitor Provides additional voltage

filtering.

Inductor opposes changes in current flow toreduce current spikes and establishes the RC

time constants for both filter capacitors.

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Voltage Regulator Operation

R1CR1

Vin Vout

VIN

VOUT

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Voltage Regulation

E(no-load)

E(full load) / E(full load) X 100 = % Regulation

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Questions

Q. You plugged your small boat at the Ala Wai

Boat Harbor into 120 VAC shore power and

turned on all loads on your boat that dropped

voltage to 115 VAC, what is the % of voltage

regulation?

W.120-115/115(100) = 5/115(100) =

A. 4.3%

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Shunt Generator Electrical Schematic:

GShuntField

Output

Physical Construction:

Characteristic:

Constant voltage for varying load.

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Series Generator Electrical Schematic:

G

SeriesField

Output


Characteristic:

Not a practical generator for varying load.

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Compound Generator Electrical Schematic:

G

ShuntField

Output


Characteristic: Best overall performance

SeriesField

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Sine Wave Phase Voltage

Schematic symbols

G

Output waveform

0

Phase A Phase B Phase C

Time

ERMS=.707(peak)

EAVG=.637(peak)

Voltage

900 1800 2700 360000

+

_

Phase A lags Phase B by 900

Phase C leads Phase B by 900

Rotor

60RPM1CPS1 Order

00

900

1800

2700

peak

peakto

peak

Phase A B C are out of phase.

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Paralleling Generators

Match voltages

Match frequencies

Shut breaker when SSS = 12

Secure 1 generator. Application: DG to TG at pd.

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Troubleshooting Generators

Excessive brush wear

Excessive bearing wear

Electrical overload

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Magnetic Amplifiers 4 windings

Output, Gate, Load Winding: Voltage to load.

Input, Control Winding: Input voltage.

Bias Winding: Changes operating point. ORAL

Opposing Bias: Shifts toe point right.

Aiding Bias: Shifts toe point left.

Feedback Winding: Changes curve shape. PUND

Positive Feedback: Shifts curve up. Negative Feedback: Shifts curve down.

Magnetic Amplifiers

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Magnetic Amplifiers Characteristic Curves

Ideal Curve

MagneticAmplifiers Curves

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Magnetic Amplifiers Characteristic Curves

Curve with excessive hysteresis losses

Magnetic Amplifiers Curves

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MagneticAmplifiers Curves

Magnetic Amplifiers Bias Curves

Opposing Bias

Aiding Bias

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Magnetic Amplifiers Curves

Magnetic Amplifiers Feedback CurvesPositive Feedback

Negative Feedback

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Basic Schematic SRMA

Magnetic Amplifiers

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Basic Schematic SRMA

Magnetic Amplifiers

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Basic Schematic SSRA Full Wave

Magnetic Amplifiers

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Basic Schematic SRMA Full Wave

Magnetic Amplifiers

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Basic Schematic SRMA with Bias Winding

Magnetic Amplifiers

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Dot-coil method

No convention Signal same.

Dot-coil, dot-coil Signal same.

Dot-coil, coil-dot Signal inverted.

Magnetic Amplifiers

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Saturable Current Potential Transformers Windings

P1-P3: Potential Windings

S1-S3: Secondary, Output, Load Windings: Shunt Field

T1-T3: Current, Input Windings: Primary Windings

L1-L3: Linear Reactors: Used with no load.

SCPTs

W D l Li & Ph V l

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Wye(Star)- Delta Balanced Circuit

Wye- Delta Line & Phase Voltage

W Li & Ph V lt

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Wye(Star) Circuit: E-Line = E-phase/ 3

Wye Line & Phase Voltage

D lt Li & Ph V lt

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Delta Circuit: E-phase = E-Line

Delta Line & Phase Voltage

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CENT-112 Fundamentals of Electricity and Electronics

59

Oscilloscope

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60

Basic Oscilloscope Info

Displays waveforms on a CRT.

Voltage measurement

Volts/div

Probes: 1X and 10X (attenuator probe)

Time period and frequency Calibration: Calibrate before using.

Focus: Used to make wave sharper.

Intensity: Controls brightness of the light beam strikingthe front of the screen.

Additional features: Data acquisition & transfer for PC.

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61

Oscilloscope Front

O ill l k i

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62

Oscilloscope Block Diagram

P bl O ill

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63

Portable Oscilloscope

Oscilloscope Waveforms

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64

Oscilloscope Waveforms

Si l G

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65

Signal Generator

Used to simulate a signal to be viewed on an

oscilloscope for circuit card testing.

S Q i

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66

Summary Questions

Q7) What test device equipment is used to

determine if a magnetic amplifier is

working properly?

A7) Oscilloscope with octopus or Huntron

Tracker

L L d

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Any oil while inspecting the regulator is

from capacitors & should be investigated to

prevent damaging the static exciter

components.

A Simpson multi-meter can provide

troubleshooting indications that a Fluke

cannot suck as polarity spikes.

Carbon deposits should be cleaned using aneraser on all variable resistors for a proper

generator regulator grooming annually.

Lessons Learned

M L L d

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A proper closeout of machinery and

regulators cannot be stressed enough. (i.e.

fires, damage etc.)

Dropped fasteners should be recovered from

rotating machinery using a magnetic

imager. (i.e. prevents rotor damage)

When troubleshooting grounds remember

the possibility of the melamine plasticspacers insulating the regulator framing.

More Lessons Learned

C l i

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Conclusion

Q. What is a use for an oscilloscope?

A. Waveform analysis for troubleshooting circuit

cards.

cent-112-6 ok

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