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Myat Kyaw

Control

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Table of Contents

Abstract …………………………………………….……………………………………………. 3

Background…………………………………………………….…………..………………….. 3-4

Introduction …………………………………………………………………………… …….. 4

Bluetooth Switching Circuit Design…………………….………………………….. 5

Software Design ……………………………………….……….......................... 5-6

Test Setup ………………………………………………...................................6

Lessons Learned …………….…………………………………….………………………… 6

Conclusion ………………………………………………………….…………………………… 7

Appendix …………………………………………………………………….…………………. 8-14

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Abstract

Control transformers manufactured by Schneider Electric were being tested

manually which is a time consuming process and is also physically taxing for

the test technician. The process involves making visual inspections, taking

voltage measurements, and then comparing the measured values against

the expected values. If the measured values are within a certain range of

the expected values (i.e. 10%), then the test would be considered a “Pass”.

Afterwards, the test technician would have to perform data entry in order to

save the results inside a database file. As one would expect, the testing

process was highly inefficient and also left a lot of room for human error,

which made the test results data unreliable. This white paper discusses a

senior design project at Purdue, which involved the design and construction

of the Automated Control Transformer Tester (ACTT) which is a prototype

system that automates the functional testing of control transformers. The

idea behind this system was to use programmable instrumentation devices

in conjunction with a Bluetooth relay switching circuit, all of which would

communicate with a VB.NET application that would orchestrate these

different devices in order to automatically perform a functional test on a

control transformer. The project was sponsored by Schneider Electric and

took several months to complete. The ACTT was able to significantly reduce

the amount of time required for each test and also removed the possibility

for human error to a great extent.

Background

A control transformer is a device used to step down the higher main circuit

voltage to a lower voltage which is then used to operate the control or

switching components of the main circuit. These devices are commonly used

in starter circuits where the main circuit voltage is too high for the control

circuitry. For example, an electric motor might be designed to operate at

460V which would fry the control circuitry comprising of electrical

components which are rated at a much lower voltage. To supply the voltage

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to the control circuitry without a separate power source, power is tapped off

the main 460V line and passed through the disconnect transformer which

would then lower the voltage to a level that is usable by the control circuitry.

Introduction

The idea for the ACTT was proposed to Schneider Electric and they agreed to

provide sponsorship for the development of a prototype system. The

proposed solution was to use a Bluetooth switching circuit in conjunction

with programmable instrumentation devices, all communicating with a

VB.NET application which would orchestrate the testing. The proposed

system would be able to determine whether the test passed or failed and

display the results to the user. Additionally, if the test failed, the system will

also display to the user the conditions which caused the test to fail. Then the

system will automatically save the test results to a database file upon the

completion of each test.

After Schneider Electric agreed to sponsor the project, the next step was to

create a project charter which had to be approved by the senior design

project instructors. After the project charter was approved, a detailed

project plan was created and continuously updated as the project

progressed. After the project plan was created, an industry expert was

consulted to ensure the feasibility of the design. Once the design was

approved, Schneider Electric was asked to order the required

equipment/parts needed to construct the system. Then the development of

the VB.NET application began while waiting to receive the hardware parts.

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Bluetooth Switching Circuit Design

Please refer to the appendix for

a larger image of Figure B. The

switching circuit which would be

housed inside a wall mount

enclosure is referenced in Figure B.

The switching circuit employs only

9 power relays and allows one

programmable multi-meter to

connect to 15 different transformer

outputs! This is great, considering

that programmable multi-meters

can be quite costly. A Bluetooth

relay board communicating with a

VB.NET application provides the

control connections to the power

relays. The output connections

from the device under test would be plugged into the terminal boards which

are then connected to the power relays as displayed in Figure B.

Software Design

The VB.NET application will use the catalog number input by the user in

order to reference a specific record inside of the database and will use the

information contained in the record to perform the testing in sequential

order by communicating with the programmable instrumentation devices via

serial port connections. The measurements made by the programmable

multi-meter will be populated inside the respective textboxes on the Testing

Form and will be compared against the expected values contained in the

database record to determine if the test passed or failed. For example, If all

of the measured values are within +-10% of the expected values, then the

X1A X2A G X1A X2A G X1A X2A G X1A X2A G X1A X2A G

X1 Dist Block X2 Dist Block X3 Dist Block

4PDT (only 3 poles used)

4PDT (only 3 poles used)

4PDT (only 3 poles used)

4PDT (only 3 poles used)

4PDT (only 3 poles used)

DPDT DPDT DPDT DPDT

+ -

Fig B

Blu

eto

oth

Re

lay M

od

ule

To Multi-meter

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test is considered a “Pass”, otherwise it’s considered a “Fail”. After each test

has been completed, the results will be saved automatically to the database.

Test Setup

Please refer to the appendix

for a larger image of Figure A.

The test set up includes a PC,

printer, programmable AC

source, programmable multi-

meter, test enclosure, device

under test, and the Bluetooth

switching circuit (inside wall

mount enclosure).

Lessons Learned

The most important lesson I learned was that formal communication is

essential to the success of a project. It helps to avoid misunderstandings

which can result from verbal communication and an added benefit is that

you would have saved dialogues for future reference in case you forget

something. Another lesson learned was the importance of planning. Having a

plan gives you a starting point and also allows you to see where you’re

currently at during the course of the project so that you can measure your

progress over time. Last but not least, having a good risk management plan

will make all the difference in ensuring project success: knowing how to

identify risks, forming prevention strategies, and creating a contingency

plan.

Programmable AC Source

Programmable Multi-Meter

Device Under Test

Fig. A

Inp

ut

Sid

e

Output Sidexfrm

Switching Circuit Enclosure

Computer

Xfr

m

DB

Safety Relay

Test Enclosure

Refer to fig. B

Refer to fig. B

Refer to fig. B

Xfrm DB stored in PC HDD

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Conclusion

The Automated Control Transformer Tester prototype system passed the

validation tests and also passed a safety inspection from ERS Automation.

Furthermore, the prototype system met all of the requirements.

Consequently, the system was able to drastically lower the amount of time

required to test an electrical control transformer and also greatly reduce the

chance of human error in the process. The prototype system not only met,

but exceeded the expectations of the project shareholders. In conclusion,

the project was completed successfully.

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Appendix

Test Setup (Figure A)

Programmable AC Source

Programmable Multi-Meter

Device Under Test

Fig. A

Inp

ut

Side

Output Sidexfrm

Switching Circuit Enclosure

Computer

Xfr

m

DB

Safety Relay

Test Enclosure

Refer to fig. B

Refer to fig. B

Refer to fig. B

Xfrm DB stored in PC HDD

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Switching Circuit Design (Figure B)

X1A X2A G X1A X2A G X1A X2A G X1A X2A G X1A X2A G

X1 Dist Block X2 Dist Block X3 Dist Block

4PDT (only 3 poles used)

4PDT (only 3 poles used)

4PDT (only 3 poles used)

4PDT (only 3 poles used)

4PDT (only 3 poles used)

DPDT DPDT DPDT DPDT

+ -

Fig B

Blu

etoo

th R

elay M

od

ule

To Multi-meter

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Image of Test Set Up

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Software Screenshots

Splash Form

Login Form

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Main Menu Form

View Records Form

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Configure Communication Devices Form

Catalog Number Form

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Testing Form (before test begins)

Testing Form (after test completes)