Wireless Circuit Breaker Interrogator (WCBI)
Project Design Report
Team number: / May02-11Date submitted: / 12/4/01
Client: / Square D Company
Client contact: / Greg Wiese
Faculty advisors: / Glenn Hillesland
James Triska
Technical advisors: / Mani Mina
Steve Russell
Team members: / Fahad Azeem
Matt Hensler
Neil Peterson
Greg Stamp
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Table of Contents
List of Tables ii
List of Figures ii
Abstract 1
Acknowledgement 1
Definition of Terms 1
Introduction 2
General Background 2
Technical Problem 2
Operating Environment 2
Intended User(s) and Use(s) 3
Assumptions 3
Limitations 3
Design Requirements 3
Design Objectives 3
Functional Requirements 4
Design Constraints 4
Measurable Milestones 4
End-Product Description 5
Approach and Design 5
Technical Approaches 5
Technical Design 5
Testing Description 8
Risks and Risk Management 8
Recommendations for Continued Work 9
Financial Budget 9
Personnel Effort Budget 9
Project Schedule 10
Project Team Information 12
Team Members 12
Faculty advisors 12
Technical Advisors 13
Client 13
Summary 13
References 14
List of Tables
Table 1 - Financial budget 9
Table 2 - Overall personnel effort budget 10
Table 3 – Detailed current personnel effort budget 10
List of Figures
Figure 1 - Existing system 6
Figure 2 - Proposed wireless system 6
Figure 3 – Scheme to increase range 7
Figure 4 - First semester schedule (original and revised) 11
Figure 5 - Second semester schedule 11
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Abstract
Electronic control units on industrial circuit breakers are used to store information about the breaker including its settings and trip history. Certain monitoring equipment can be connected to these electronic controls in order to download the breaker information to a personal computer. This method requires a direct connection between a laptop computer and the control unit. The purpose of this project is to develop a wireless connection, having the ability to efficiently interrogate the breaker control unit.
The general solution for the problem will include establishing a wireless protocol, implementing appropriate hardware, designing and programming the software, and testing and debugging. The tasks will be carried out under close consultation with the technical advisors, the faculty advisors, and Square D.
The expected deliverable is a system that utilizes the interrogator method with at least three breaker control units. This will give the client a more desirable method for interrogating industrial circuit breakers.
Acknowledgement
Square D has provided the trip units, breaker control modules, and software for the existing system. They will be providing wireless circuits and other supplies for the project. In addition, Square D has contributed technical assistance in demonstrating the existing interrogation system. Furthermore, they will help with the development of the wireless interrogation system.
Definition of Terms
ASK-amplitude shift keying
BCM-breaker control/communication module
DSSS-direct sequencing spread spectrum
EMI-electro magnetic interference
FHSS-frequency hopping spread spectrum
FSK-frequency shift keying
GUI-graphical user interface
IC-integrated circuit
ISM-industrial scientific and medical
MODBUS-industry standard software protocol used for transmissions over serial lines
OOK-on-off keying
PC-personal computer
PC card-a type of computer interface
RS 232-recommended standard 232: full duplex serial communication
RS 485-recommended standard 485: 4-wire, half-duplex serial communication
RX#-receiver IC, channel #
TU-trip unit: monitors and controls circuit breaker settings
TX#-transmitter IC, channel #
USB-universal serial bus
WCBI-wireless circuit breaker interrogator
Introduction
General Background
Many industrial circuit breakers have TUs, or trip units, that monitor the breaker settings and tripping history. Communication with the TUs currently requires a direct connection between the BCMs (attached to the TUs) and a laptop. The user has software that displays the information on the laptop screen. The current system makes interrogation of circuit breakers cumbersome and requires disabling power to the breakers when BCMs are wired incorrectly. The purpose of this project is to develop a wireless link that would allow someone using a laptop computer to communicate with the trip units. New hardware and software for the laptop along with new hardware to attach to the BCMs will be developed to create the wireless circuit breaker interrogator, or WCBI. The complete wireless system will reduce time spent on wiring troubleshooting and will speed the process of circuit breaker interrogation.
Technical Problem
The technical approach to solving this problem is to first make sure that a good relationship is maintained with the faculty advisors, the technical advisors, and ultimately the client. In specifically addressing the problem at hand, a wireless communication method must be chosen in order to implement this wireless system. Different factors such as choosing licensed versus unlicensed frequency ranges, transmission range, cost, size of wireless hardware, and transfer rates will come into play in selecting the communication method.
Next, wireless hardware must be implemented in a manner that all the devices will have the ability to interact with one another. In addition, the software design and programming must be developed to make sure that all the components work together.
Finally, when the initial wireless interrogation system is in place, it will go through a cycle of testing and debugging to make sure it will perform to the requirements of Square D. This means that this system must demonstrate the wireless interrogator method with at least three BCMs.
Operating Environment
A typical environment where this system might be utilized is an industrial setting. A factory is a good example. Extreme conditions like heat and humidity should not be a factor. However, because this system is wireless, interference from other wireless communication devices using similar bandwidths could be a factor. In addition, electromagnetic interference from the power system associated with the breaker could affect the performance of the system.
Intended User(s) and Use(s)
The initial user for the wireless interrogator system will be Square D Company. Eventually Square D would sell the wireless system as an added feature to their breakers. In this case the user could then be a factory supervisor or maintenance person. If part of the electrical system is having problems, this interrogation method could be a good way for a supervisor or maintenance person to monitor the problem. In addition, the breaker manufacturer or an electrical contractor may want to monitor the equipment they are installing or have installed. The intended use of the wireless interrogator is to provide a reliable way for someone to rapidly interrogate many breakers within a facility. Under the assumption that this system will be used with a laptop computer, the system will provide an efficient way to move around and take breaker readings within a building.
Assumptions
· The breaker interrogation system will be operated in an industrial environment
· This wireless link will be immune to interference within the environment
· The 24-volt direct current power supply for the BCMs is sufficient to power the wireless communications hardware.
Limitations
· The range of the wireless link is approximately 30 feet.
· Interrogation of only 247 BCMs possible under the MODBUS protocol
· Must work with 24 volts
· Devices must fit in breaker housing which is approximately 3”x3”x5”
· Device attached to laptop should weigh less than 3 pounds
Design Requirements
Design Objectives
· A wireless communications device to attach to each BCM. The device will make use of the RS-485 serial protocol that is used by the BCMs. It will transfer and receive data using FSK. This device will most likely be an integrated circuit that includes all of the components necessary for FSK wireless communication.
· A wireless communications device to attach to the laptop. This device will be similar to the device attached to the BCMs. It will communicate with the laptop through the RS-232 serial port or USB port.
· A Windows-based program for the laptop. The program will be a GUI that makes communicating with the trip units easy. It will display easily viewable and identifiable information.
Functional Requirements
· The wireless communication devices will allow for wireless transmission of data from the BCMs to the laptop.
· The Windows program will communicate with the wireless device through the serial port using the MODBUS protocol. Initially the program will display information from the BCM’s registers only. When finished, the program will be able to display information contained in the tripping units as well. The program will allow the user to communicate with one BCM at a time.
· Important information to display from the tripping units will be the history of tripping events. The history contains what tripping function occurred such as long time trip, short time trip, instantaneous trip, or ground fault trip. Eventually the program will read and/or set information on the breaker such as the present conditions, level, and delay.
Design Constraints
· The wireless link must communicate at approximately 30 feet. Communication at this distance is necessary for an operator to stand near the breakers and retrieve the information in an easy manner.
· The information must be transferred at a reasonable speed. Each breaker should be interrogated in less than 5 seconds. The amount of data being transmitted is very small. The wireless integrated circuits should have acceptable transfer rates for this application.
· The wireless communications are subject to interference. The breakers may be near high voltages that could cause EMI. To handle this problem if it arises, another scheme will be implemented that is less subject to EMI.
· The wireless hardware for the laptop must be non-cumbersome and easily mobile. The weight should be below 3 pounds and the size should be below 3 x 3 x 5 inches. A lightweight solution for the power source of the hardware may be obtaining power through the serial port, from the computer, or from a lightweight battery.
Measurable Milestones
· Wireless communication is possible. Communication with a BCM is possible with the existing software.
· Functional wireless communication distance. The communication should work at least 30 feet during an on site test.
· The time that is required to transfer information. How long does it take to retrieve information from multiple breakers? Is the transfer rate fast enough to not hinder retrieval and cause frustration?
· The size of the hardware attached to the laptop. What is the hardware size and has it met the design constraints to increase mobility?
· Number of breakers that the software can communicate with. Can the software communicate with at least 3 BCMs? Will it work with as many as 247?
· Functional communication with the trip units. Can the software also successfully interrogate the trip units through the BCMs?
End-Product Description
The WCBI consists of a laptop coupled with a wireless communications device and the interrogator software. The necessary components attached to a circuit breaker to add wireless capabilities are the trip unit, the BCM, and the wireless communications interface. The complete system improves the efficiency of obtaining settings such as level, delay, and the history of tripping events from multiple breaker units. It allows for interrogation of up to 247 different breaker units from a distance of up to 30 feet.
Approach and Design
Technical Approaches
This project is composed of researching options and proposing/counter-proposing solutions to Square D. Once the final proposal is validated, purchasing, designing, and implementation of the hardware will follow. Much of the research has been done and possible solutions are in place. However, a decision on what integrated circuits to be used has yet to be made. It has been decided what the circuits need to do, then the best circuits to use in order to meet the design specifications must be selected. Specifically, the circuits should be made by one company, will work in two different frequency ranges within the ISM band, use FSK modulation, and are relatively cheap. Square D has emphasized that they do not want too elaborate of a system and that cost is not a primary concern at this time. Finally, the best way to incorporate the hardware and software will be determined based on compatibility and ease of operation.
Technical Design
There will be two main design areas, software and hardware. The first portion of the project will involve choosing the appropriate wireless communication integrated circuits for the system. Then the functionality of the integrated circuits with the existing software will be determined. Once the hardware is functional, new software will be developed for the interrogation system. All of the above tasks will be carried out with the client in mind. Rigorous testing will be done to ensure the quality of the design. This project will be designed to the highest standard of efficiency and cost effectiveness.
The following diagrams and descriptions show the existing system used to interrogate the circuit breakers and the proposed wireless system.
Figure 1 - Existing system
Figure 2 - Proposed wireless system
The wireless system is created with the addition of ICs that transmit and receive data at the circuit breaker side and the laptop side. The ICs perform FSK modulation of the serial data and transmit in the 900 MHz range. Also, signal conversion is necessary to insure that the proper voltage levels are achieved and that the signals are compatible with RS 232 for the laptop.
The signal conversion may require a comparator on the breaker (left) side. Signal conversion on the right hand side may require a comparator and an RS 485 to RS 232 converter.
Each BCM has a wireless receiver and transmitter IC denoted by RX/TX operating at different frequencies. The communication takes place in the ISM band of 902-928 MHz. For example TX1/RX1 will operate at a frequency of 910 MHz and TX2/RX2 will operate at 920 MHz. The 900 MHz ISM band was chosen because it requires no licensing, many cheap ICs are available, and it meets the basic transmission requirements. The 2.4 GHz ISM band is also a valid solution but the ICs are more expensive and complex.
The ICs will use FSK modulation. FSK was chosen because it is very simple, works well with serial data transmission, many circuits include this technique, and it is less susceptible to interference than ASK and OOK.