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Circuit Breaker Failure Analysis

Sai Zhung Ho

ECE-498 Senior Capstone Project

Advisor: Professor James N. Hedrick

Electrical, Computer, and Biomedical Engineering Department

Union College

Schenectady, NY 12308

November 20, 2018

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REPORT SUMMARY

The purpose of this senior capstone project is to develop an affordable, cost-effective and

reliable method for analyzing circuit breaker failures by designing an automated, computer-

controlled system to test several circuit breakers in parallel through a microcontroller.

The proposed system should be computer-controlled, manipulate large amounts of current from

20A to 40A to test the trip performance of individual circuit breaker and develop low-cost

modules, each individual module is used for testing a single circuit breaker to experiment with a

desired number of circuit breakers per test. The paper discusses an alternative approach for

testing circuit breaker performance through a computer-controlled power supply. A

semiconductor device called TRIAC will be used to reduce the cost of implementing a current

control system for concurrent, automated testing of multiple circuit breakers. The system should

allow the user to visualize the performance of circuit breaker through a computer and use the

data compiled for analytical purposes. Once the circuit breaker trips, an open circuit is created to

prevent further heat current to pass through and avoid an electrical fire. The project aims to

analyze the performance of TRIACs and DIACs in series paired with a step-down transformer as

the load to control a large current across the circuit breaker and shunt attached in the secondary

of the transformer. A microcontroller and Analog-to-Digital Converter will be used to measure

and convert data; as well as, act as a potentiometer to manipulate the current at the gate of the

TRIAC. The project will experiment with single-pole thermal circuit breakers and a step-down

transformer will be used to drop the voltage from 120V/1PH to 12V/1PH. Low-voltage operation

is recommended to reduce likelihood of electric shocks and manipulate large loop current located

in the circuit breaker and shunt. The circuit breakers will be differentiated in terms of current

rating, age, and the manufacturing brand for reliability assessment.

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TABLE OF CONTENTS REPORT SUMMARY................................................................................................................................ 2

TABLE OF CONTENTS ........................................................................................................................... 3

1. INTRODUCTION .................................................................................................................................. 4

1.1 MOTIVATION ....................................................................................................................... 5

1.2 CIRCUIT BREAKER TESTING........................................................................................... 6

1.3 PREVIOUS WORK................................................................................................................. 9

1.4 COMPUTER CONTROLED CURRENT SOURCE......................................................... 10

2. DESIGN REQUIREMENTS .............................................................................................................. 11

2.1 GENERAL SPECIFICATIONS .......................................................................................... 11

2.1.1 POWER SUPPLY.................................................................................................. 11

2.1.2 SHUNT ................................................................................................................... 11

2.1.3 CIRCUIT BREAKER .......................................................................................... 12

2.1.4 ANALOG-TO-DIGITAL CONVERTER ........................................................... 12

2.1.5 SOFTWARE REQUIREMENTS ........................................................................ 12

3. TRIAC SYSTEM DESIGN ................................................................................................................. 13

3.1 TRIAC CURRENT TEST CONTROL .............................................................................. 13

3.2 MODIFIED TRIAC CURRENT CONTROL SYSTEM .................................................. 14

4. IMPLEMENTATION ......................................................................................................................... 16

4.1 PROPOSED IMPLEMENTATION .................................................................................... 16

4.1.1 COMPUTER CONTROLLER ............................................................................ 18

` 4.1.2 POWER SUPPLY ................................................................................................. 18

4.1.3 CIRCUIT BREAKER .......................................................................................... 18

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4.1.4 SHUNT ................................................................................................................... 19

4.1.5 ANALOG-TO-DIGITAL CONVERTER ........................................................... 19

4.1.6 TRIAC AND DIAC ............................................................................................... 19

4.2 ALTERNATIVE ENGINEEERING DESIGN METHODS ............................................. 21

5. PRELIMINARY PROPOSED DESIGN ........................................................................................... 22

5.1 FIRING ANGLES AND CONDUCTION ANGLES ........................................................ 24

6. CONCLUSION AND FURTHER WORK ........................................................................................ 25

7. REFERENCES ..................................................................................................................................... 25

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1. INTRODUCTION

1.1 MOTIVATION

The fire departments in the United States respond to “an average of one home fire every 86

seconds” [1]. All house fires are investigated by a fire marshal to determine the probable cause

of the fire and a large percentage of house fires are discovered to be caused by an electrical fault.

Every year approximately 51,000 homes are determined to be electrical fires that account over

500 deaths, 1400 injuries, and $1.3 billion due to property loss [2]. For public health and safety,

there exist equipment such as Ground-Fault-Circuit-Interrupter (GFCIs) and Circuit Breakers

used to counteract and minimize the odds of an electrical fire due to overload. These electrical

devices are found prominently in residential buildings to protect electrical systems from

‘overloading’ due to supplying more heat current which the circuit cannot handle. When

overheated, the electrical conductor will burn out and create an electrical fire which spreads

around the building. The large number of electrical fire reports and fire investigations across the

nation show inconclusive results about the relationship between fires and circuit breaker

malfunction. In order to determine if a circuit breaker is considered to be faulty, a low-budget

automated system will be developed to test large quantities of circuit breakers at the same time.

Overall, this capstone project aims to produce a cost-effective, reliable circuit breaker failure

analysis system in order to understand and determine the trip performance operation of single-

pole, thermal circuit breakers and reduce electrical fires due to faulty circuit breakers. The design

challenge for this project will depend on successful implementation for computer-controlled

large currents. This capstone report explores the concept of an automated system to trigger

circuit breakers trip performance at a cost-effective method for controlling large currents through

the circuit breakers.

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1.2 CIRCUIT BREAKER TESTING

In order to to determine the reliability of a circuit breaker, a set of procedures and requirements

must be defined to analyze operating circuit breaker in one of the following categories: correct,

marginal, and flawed. The circuit breaker will be hooked in series with the shunt and the

computer-controlled power supply. First, the circuit breaker will be operated at 135% of its

current rated and is expected to trip within an hour as defined at the UL489 criterion. A

successful circuit breaker ‘trip’ is recognized in the computer controller when the digital data

received from the measurements at the shunt start displaying zeroes in the system [3]. If the

system fails to trip in the first hour, then the current will be held at a constant rate for one hour as

shown in Figure 4. Once again, failure for the circuit breaker to trip in the second hour will lead

to a linear increase in current until the circuit breaker trips within the third hour similar to the

example depicted in Figure 5. However, the severity or magnitude of a flawed operation can

differ depending on the individual circuit breaker. In case the circuit breaker fails to trip in the

third hour, the test will be ceased and the circuit breaker will be marked as faulty.

Correct operation of a circuit breaker requires the breaker to trip within an hour at 135% of the

current rating based on manufacturer specifications as shown in Figure 3. Marginal operation is

considered when the circuit breaker does not trip in the first hour at 135% and later the current is

held at a constant rate of 135% for another hour to trip as shown in Figure 4. Flawed operation is

recognized as a circuit breaker that fails to trip by the end of the second hour at 135% of current

rated, then the current will be increased linearly until trip occurs within the third hour of

operation as shown in Figure 5. Often, the severity of circuit breaker failure can differ

drastically based on a range of workable percent current rated operation of 135% to 150%. The

calibration failure shown in Figure 5 tripped at 31A or 155% of the rated current is considered

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as a ‘minor’ failure behavior since the tripping occurs at 5% above the workable percent current

rated operation previously stated [3]. The reliability of the circuit breaker used in the experiment

will be evaluated in terms of age, current rating, and manufacturer.

Figure 1. Jammed FPE-Lok® 2-pole circuit breaker. Mechanism for creating an ‘open’ is

inhibited at point-of-contact in C [3].

Figure 2. Tripped FPE-Lok® 2-pole circuit breaker. The point-of-contact mechanism in C is

open [3].

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Figure 3. Correct operation of 20A, FPE Stab-Lok® circuit breaker [3].

Figure 4. Marginal operation of 20A, FPE Stab-Lok circuit breaker (Aronstein, p. 4).

Figure 5. Flawed operation due to calibration failure of 20A FPE Stab-Lok® breaker fails to trip

at 135% rated current requirements at an hour [3].

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1.3 PREVIOUS WORK

This project is an extension of the work done by Johnny Villatoro and Quintin Lenoci who drew

inspiration on the research of Dr. Aronstein. Over time, the research will improve

implementation current control methods and data collection with a zero crossing analysis where

the voltage is equal to zero in a sinusoidal signal. The circuit analysis failure system developed

previously by Quinin Lenoci and Johnny Villatoro provided unreliable results produced with the

VARIAC implementation for controlling large RMS current produced at the secondary of the

transformer.

In the past, Dr. Aronstein has developed an expensive solution to test circuit breakers for his

research by using an Audio Amplifier (Class-B circuit with a push-pull and op amp) and DC

Coupling method. The implementation was based on frequency in terms of voltage.

The proposed system for this project will use a fixed, custom toroidal transformer to manipulate

low voltage at large currents across the circuit breaker and shunt. Since power dissipation at the

circuit breaker goes down, the shunt resistance will also go down. The power supplied in the

shunt and power supply should be equal.

On the other hand, the circuit breaker failure analysis method by Quintin Lenoci and Johnny

Villatoro required a VARIAC to change voltage through a variable autotransformer with a DC

motor to change the current flow through the circuit breaker and shunt. This version is more

affordable than the original implementation utilized by Dr. Aronstein. However, this technique

for current control is indirect and imperfect due to the difficulties in controlling current through

mechanical components such as DC motors.

The design of the proposed circuit breaker failure analysis system will revolve around the

implementation of a solid-state electronic device known as a TRIAC. In other words, the system

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will no longer rely on a brushless DC motor and VARIAC to control current across the circuit

breaker. The previous setup by Quintin Lenoci and Johnny Villtatoro turned out to be

challenging to manipulate with the microcontroller since mechanical systems such as DC motors

are hard to use for current control. For this project, the design choices will allow the user to

directly control the current flow in the circuit breaker through a computer controlled current

source system.

1.4 COMPUTER CONTROLLED CURRENT SOURCE SYSTEM

The circuit breaker failure analysis system must provide direct control of high current in the

circuit breaker and shunt. The system must work in reliable manner by computer-controlled

phase to adjust the firing angle of the TRIAC output waveform. The system shall have

concurrent, automated testing of various circuit breakers per trial. The failure analysis system

will be later implemented as a soldered circuit and re-designed as a Printed Circuit Board for the

final product of the capstone project. The TRIAC is a great option for current control showing

‘abrupt cuts’ due to the trigger points for low-power applications commonly used for power

switching. For this project, the semiconductor device will be used for manipulating the RMS

current in the circuit breaker by adjusting the phase of the firing signal to the input signal.

Figure 6. General block diagram of the circuit breaker analysis system.

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2. DESIGN REQUIREMENTS

2.1 GENERAL SPECIFICATIONS

The system will record independent measurements based on testing parameters to start and run.

The current controller must implement a zero-crossing detection for analog-to-digital conversion

of input sine waves with a microcontroller. In terms of the accuracy of the controller, the current

must be able to be set within a 0.5 mA and capable to be measured at 0.5A. The time measured

will increase by increments of 1 minute and up to the 3 hours of maximum operation of a circuit

breaker performance. The failure analysis system will be capable of concurrent automation for

multiple circuit breakers with a microcontroller to control the ‘loop’ current. In addition, the

project aims to develop low cost modules under $200.00 and each individual module will test a

single circuit breaker to provide testing for the desired number of circuit breakers per test.

Furthermore, the computer-controlled power supply will contain a customized 10:1 step-down

toroidal transformer to lower the 120VAC low current primary to voltage high secondary for TX-

1. The second transformer TX-2 will be an iron core transformer to step-down the voltage

produced at the circuit-breaker for the Arduino as demonstrated in Figure 10. The computer

controlled power supply will provide current control of the circuit by designing a TRIAC/DIAC

RMS voltage control circuit for use in the primary of the step down transformer. Modular design

will be useful to add/replace components and reduce changes in the setup.

2.1.1 POWER SUPPLY

The power supply must be capable of producing a variable current IRMS from 0 to 40A.

2.1.2 SHUNT

The shunt will be the load of the circuit to handle very large amounts of current. Calculating the

voltage at the load depends on Ohm’s Law, V = IR and the power dissipated through the shunt

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can be computed through the expression for Power, P = VI. The power supplied at both the

primary and secondary of the transformer should be equivalent. The shunt will be heavily

monitored due to the significant concerns associated with high levels of power dissipation.

2.1.3 CIRCUIT BREAKER

The circuit breaker will vary depending on several factors: age, manufacturer, and current rating.

A range of circuit breakers will need to be tested in order to produce consistent results in regards

to the reliability of circuit breakers.

2.1.4 ANALOG-TO-DIGITAL CONVERTER

The Analog-to-Digital Converter (ADC) will be used to collect data points for the voltage and

current across the load. The ADC shall use a sampling rate twice of the maximum frequency as

suggested in the Nyquist Theorem: 𝑓" > 2𝐵. In addition, a thermal sensor and computer will be

used to control the automated system. The experiment will take place in closed-environment at

room temperature.

2.1.5 SOFTWARE REQUIREMENTS

The in-built software system of the project will contain a clean interface for visualizing the

change of current (y-axis) over time (x-axis). The measurement for current will be in milliamps

(mA) and should be capable of showing the maximum amount of current the circuit breaker can

handle before the tripping occurs. The automation will be accomplished through a programming

language called MATLAB. The programming language and computing environment from

MathWorks is licensed by Union College for educational purpose only. Therefore, code

development can be completed outside of the laboratory.

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3. TRIAC SYSTEM DESIGN

3.1 TRIAC CURRENT TEST CONTROL

The switching depends on the current seen at the gate of the TRIAC. The thyristor used for the

experiment with part number MAC212A8 from Littlefuse and is used for full-wave AC control

applications such as light dimmers. The capacitor takes time to charge and discharge the current.

This rate for charging is dependent to the RC or 𝜏 constant of a first-order RC circuit. Therefore,

changing the resistance value through a variable resistor such as a potentiometer will allow the

user to adjust the VRMS.

𝑣 𝑡 = 𝑣*𝑒,-//0

𝜏 = 𝑅𝐶

𝑣 𝑡 = 𝑣*𝑒,-/3

The circuit shown in Figure 7 is a simple implementation of current control capabilities of the

TRIAC by varying the resistance at the gate through a potentiometer. The TRIAC is able to

change the phase of firing signal to input signal in order to vary the current flow through the

circuit breaker.

Figure 7. Circuit diagram of TRIAC light dimmer.

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3.2 MODIFIED TRIAC CURRENT CONTROL SYSTEM

Figure 8. Modified Current Computer Controlled system for circuit breaker failure analysis.

The failure analysis system will be powered through a 120VAC, single-phase power supply from

the electrical outlet and stepped down through a custom-made transformer TX-1 of 10:1 turns

ratio. The goal is to use the small amount of current produce in the primary winding to

manipulate a large amount of ‘loop’ current from the secondary winding of the toroidal

transformer as shown in Figure 8. The circuit breaker will be placed in series with a shunt with

roughly 12VAC and 27 W of power across the circuit. An analog-to-digital converter and Arduino

Due will be hooked at the shunt to measure the change of RMS current over time. The shunt

allows the user to find the current across the circuit breaker which would be too large to measure

with an ammeter. Adjustments for current control will be made through a zero-crossing analysis

from the output of the TRIAC RMS current waveform. The microcontroller will accomplish the

bulk of the load by storing data points which convert from negative to positive at some bound

time t based on the TRIAC output waveform. The computer will enable the user the ability to

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control the rate for current supplied at the circuit breaker, visualize the performance of the circuit

breaker, and send commands to the power supply. The procedure of examining circuit breaker

performance ranges from one to four hours and the system processes will be automated through a

recursive loop powered by MATLAB. The project will proceed on assembling the system and

testing circuit breakers over the break. Furthermore, the student will produce a functioning

perfboard or soldered circuit and design a throughole printed-circuit board (PCB). The final

design of the circuit breaker failure analysis system will be completed with a surface mounted

PCB design using Autodesk EAGLE.

Throughout this fall term, the student has been working on testing the function of the TRIAC for

current adjustment and design the overall system with the TRIAC and DIAC configuration for

current control to test circuit breakers. The project is led by Sai Zhung Ho under the guidance of

Professor James N. Hedrick from the Electrical, Computer, and Biomedical Engineering (ECBE)

Department. The student is thoroughly thankful for the ECBE Department and the Student

Research Grant (SRG) committee for the financial support of making this project possible.

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4. IMPLEMENTATION

4.1 PROPOSED IMPLEMENTATION

The system will be powered by 120VAC commercial power to provide the test current. The power

supply, circuit breaker and shunt are connected as a loop current and the analog current signal is

sent back as digital data voltage signal VSIG to the computer controller to adjust the power supply

parameters as shown in Figure 9. The voltage signal VSIG is equal to the RMS voltage VRMS and

since RMS current is proportional to RMS voltage by dividing the resistance of the shunt

RSHUNT.

Figure 9. Block diagram of the primary elements in the failure analysis circuit breaker system.

Figure 10. Block diagram of the modified power supply system with circuit breaker and shunt.

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The overall design of the experimental setup is shown in Figure 11. The experimental setup

shares traits similar to the predecessor. However, the method utilized in this project will allow

direct current control at the primary-side of the transformer. Thus, accurate manipulation of the

large current ‘loop’ produced to drive the circuit breaker and shunt will be theoretically possible.

The ADC attached at the shunt to measure the RMS current output produced from the TRIAC.

At large quantity of ‘heat current’ the circuit breaker will reach a threshold point and fail to

tolerate the power dissipated. As a result, the circuit breaker should trip and prevent further

heating to burn the electrical system and cause an electrical fire.

Figure 11. Block Diagram of the Circuit Breaker Failure Analysis System.

The circuit breaker failure analysis system will be redesigned for direct current control via

TRIACs and a step-down transformer to 1) control large currents through circuit breaker and

load or shunt series connection through small current from the TRIAC output and 2) vary voltage

to the primary of the transformer. In turn, circuit breaker performance measurements will be

more reliable and a direct method for current control via TRIAC/DIAC configuration with an

Analog-to-Digital converter will improve the software interface commands.

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The power supply provides 120VAC at 60Hz to the TRIAC and step-down through a transformer

with 10:1 turns ratio which supplies current to the circuit breaker and shunt. The 120VAC

voltage supply will follow a second step-down transformer to a TRIAC current control unit

which is manipulated by a computer. The incoming current or voltage is read to obtain real-time

data about the behavior of the circuit and re-assess parameters in the power supply.

4.1.1 COMPUTER CONTROLLER

The computer controller receives a digital signal from the Analog-to-Digital Converter based on

the measured current at the load or shunt. In addition, the computer controller will output a signal

to set the current at the power supply through MATLAB.

4.1.2 POWER SUPPLY

The power supply is an electrical power distribution system that provides computer-set current to

the circuit breaker and shunt. In addition, a control mechanism exists within the power supply to

adjust the high voltage, low current through a solid-state device known as a TRIAC or “TRIode

from Alternating Current”. The system includes a pair of step-down transformers TX-1 and TX-2

to lower the high voltage, low current presents the primary to deliver a low voltage, high current

in the secondary of the transformer. The first transformer TX-1 delivers the step-down voltage to

the circuit breaker and shunt. The second transformer TX-2 delivers current to the TRIAC

current control. The function for the TRIAC current control system is to sample the high current

produced from TX-2 to sense the behavior of the system. The circuit diagram in Figure 10

provides the detailed circuit elements of the power supply.

4.1.3 CIRCUIT BREAKER

The circuit breaker is an electrical device installed in residential buildings for electrical fire

prevention and safety. The circuit breaker is a thermal sensing device that handles high, thermal

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current through the electrical system. Once the circuit breaker cannot tolerate the heat current

dissipated through the electrical circuit, the system automatically senses excess current or

overload and produces an open circuit to interrupt current flow after a fault is detected. The types

of circuit breakers for this experiment will be commercially available.

4.1.4 SHUNT

The shunt is installed in series with the circuit breaker to provide a load for measuring the

current produced in the electrical system. The shunt receives analog voltage coming from the

current produced at the circuit breaker. The analog voltage measurements are sent to the Analog-

to-Digital Converter. The load contains a low-resistance of 0.033 ohms to maintain the large loop

current through the circuit.

4.1.5 ANALOG-TO-DIGITAL CONVERTER

The Analog-to-Digital converter is a system that converts inputs analog signal and outputs a

digital current signal. This digital output is read through the computer as a plot of RMS current

(in milliamps, mA) over time (in milliseconds, ms).

4.1.6 TRIAC AND DIAC

The TRIAC and DIAC configuration in the power supply will improve the reliability of the

failure analysis system by direct current control. The output waveform in the TRIAC is trimmed

for some time t due to charging and discharging properties in the solid-state semiconductor

device. The TRIAC acts as a bi-directional switch to turn on and off. The gate of the TRIAC is

connected in parallel to a resistor and capacitor. Once the capacitor is charged up, a voltage will

be fired to the gate of the solid-state device and produce the RMS current used to control in the

circuit breaker. Due to Ohm’s Law, the RMS current (IRMS) is analogous to the RMS voltage

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(VRMS) multiplied by the resistance of the load (RSHUNT). Below, is the mathematical expression

for the Root Mean Square (RMS) Voltage.

𝐼/56 =𝑉/56𝑅689:;

𝑉/56 =1𝑇 𝑣> 𝑡 𝑑𝑡

;

@

The equation is an expression for the square root of an integral for the area under the curve for

some signal v as a function of time t from a time interval of 0 to T period. As a result, the

waveform of the TRIAC output can be represented as an RMS value over time by performing a

transient simulation of the TRIAC/DIAC circuit in Figure 12. The ripple produced in the RMS

value (blue function) is a product of continuous calculations in the program; nonetheless,

constant RMS values from experimental measurements is expected.

Figure 12. TRIAC transient waveform with RMS value (blue signal).

The RMS value is a voltage measurement obtained through the RMS function of the difference

between the voltage nodes of V1 and V4. The slight ripple can be approximated at VRMS ≈ 100V

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with a high VRMS = 102.22V and a low VRMS = 83.79V. The RMS voltage divided by the fixed

shunt resistance will allow the user to find the RMS current in the circuit breaker.

In addition, the TRIAC output (green) from the transient simulation can be represented in terms

of phase 𝜃 in degrees. The phase from 0° to 90° is known as ‘half a period’ or T/2. In Figure 13,

the firing angle of the TRIAC is at roughly 2.5 ms and around 60°. The firing angle is an

adjustable parameter that will be important for changing the current flow in the circuit breaker by

manipulating the on/off time of the TRIAC output waveform.

Figure 13. Firing angle measurement of TRIAC transient.

4.2 ALTERNATIVE ENGINEERING DESIGN METHODS

Some methods for alternative engineering design: 1) Use an integrated circuit (IC) to act as an

RMS voltage converter or 2) mathematically calculated RMS voltage through MATLAB. The

former method to compute RMS utilizes less processor time and the cost of purchasing an

integrated circuit RMS-to-DC converter is between $4.15 to $61.53 according to DigiKey. For

the project, the student will consider a low-cost RMS-to-DC converter.

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5. PRELIMINARY PROPOSED DESIGN

The circuit breaker will be computer controlled, designed to be modular, and allow concurrent

circuit breaker testing. Based on previous experimental work, we believe the TRIAC and DIAC

implementation will be the optimal method to provide reliable and efficient circuit breaker

failure systems without breaking the bank. Alternative possibilities would rely on expensive

solid-state devices or field-effect transistors (FETs) and the efficiency produced in fancier power

electronics devices is mostly found in motor design or HVAC systems. The circuit breaker will

depend on the IRMS for tripping. As time passes, more current will be supplied to the breaker and

the load to measure the performance of a circuit breaker. In other words, we want to understand

the amount of wear-and-tear a circuit breaker can hold before it pops!

Figure 14. Circuit diagram of the TRIAC/DIAC test circuit using an RC phase-shift network.

The TRIAC/DIAC test circuit shown in Figure 14 was simulated through Multisim and the

simulated transient response is shown in Figure 15. The input current appears as a sine wave

(red) in the Multisim simulation. The output sine wave from the TRIAC will look like a AC

trimmed waveform (green). The trimming of the AC waveform takes time to turn on and turn

off. The on/off switching depends on the RC time constant, the capacitor takes time to charge.

For the experiment, the resistance was changed using a potentiometer to act as a variable resistor.

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Figure 15. TRIAC Transient simulation with input (red) and output (green) voltage waveforms.

The definition of power is P = VI. Similarly, RMS power can be represented as PRMS = V IRMS

For instance,

𝑃CDECFD-HEIJKIE = 𝑃"LFM-

120𝑉×30𝐴 = 3600𝑊

𝑃 = 2 30 = 60𝑊

The power dissipated at the primary of the transformer sees 120VAC at 0.5A with PIN = 60W and

the secondary of the transformer sees 2VAC at 30A with POUT = 60W. To verify calculations,

𝑃T: = 120𝑉 0.5𝐴 = 60𝑊

𝑃W9; = 2 30𝐴 = 60𝑊

Therefore, the TRIAC will allow the user to control large amount of current (e.g. 30A) in the

circuit breaker and shunt. At the primary of the transformer can be controlled at high voltage,

low current.

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5.1 FIRING ANGLES AND CONDUCTION ANGLES

The firing angle from 0 to π is the 0 to T/2 period is the positive waveform of the TRIAC output.

Similarly, the TRIAC will output the negative waveform from π to 2π or for some period

between T/2 to T. The switching occurs at some time t after the capacitor is charged to trigger

and turn on the TRIAC. The same effect takes place for some time t to discharge the capacitor in

order to turn off the TRIAC. The trimming of the charge/discharge time can be adjusted by

varying the resistance seen at the gate with a pot. Initial tests with the TRIACs, affirmed our

hypothesis since the oscilloscope was able to detect the TRIAC output shown in Figure 16.

Future progress will attempt to control the current with a microcontroller to adjust the time t for

sampling the zero crossings in the TRIAC output for current control in the power supply.

Therefore, the TRIAC provides simple control of the large loop current at the circuit power and

shunt.

Figure 16. Output voltage waveform from TRIAC from an oscilloscope.

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6. CONCLUSION AND FURTHER WORK

All in all, this fall trimester has been the culmination of the capstone project topic and design.

The student and advisor decided to move forward in a project related to power electronics due to

the student’s interest in learning about a mixture of power systems and electronics. Most of the

discussion laid out in this report attempt to capture the fundamental concepts and define

important design specifications necessary for successful implementation of the circuit breaker

failure analysis system with a computer-controlled power supply.

Further work will be undertaken over the winter break to assemble the testing system for the

circuit breakers with the modified power supply containing the TRIAC for current control. In

addition, an addendum Student Research Grant (SRG) proposal will be submitted for the January

31st deadline to reimburse parts ordered over the winter break and winter term that will be used

for the computer controlled current source system such as an Integrated Circuit (IC) RMS

voltage converter. The student is hopeful to have a working prototype by the start of Winter term

and will be working diligently over the break with Professor Hedrick to expedite the capstone

project and meet the requirements for ECE499.

7. REFERENCES

[1] NFPA.org. Fire Facts. https://www.nfpa.org/Public-Education/Campaigns/Fire-Prevention-

Week/Fire-Facts.

[2] ESFI. Home Electrical Fires. https://www.esfi.org/resource/home-electrical-fires-184.

[3] J. Aronstein. “ESTIMATING FIRE LOSSES ASSOCIATED WITH FPE STAB-LOK®

CIRCUIT BREAKER MALFUNCTION: ATTACHMENT B”. IEEE Transactions on Industry

Applications, Vol. 48, No. 1, Jan/Feb 2012, pp. 3-5.