Shared Radio System

Emerson Trarbach, Marcio Bnunatti, Eduardo Casotto and Jose L. F. Vieira

Electrical Engineering Department Federal University of Espirito Santo

Vit6ria - Espirito Santo - Brazil trdrbach~nitseneenb~ia.com.br, i.vieira(iiele.ufes.br

Abstract-Reclosers are typically used in the power electric plants to protect the system against temporary faults caused by natural effects (e.g., lightning, wind, trees) or permanent faults. Monitoring and controlling reclosers could be an expensive task depending on the type of reclosers that are employed. A simple way to perform these tasks is by using radio communication capabilities.

This paper describes a system to control a net of reclosers over a shared radio based system. A main computer allows monitoring all system status by a GIS (Geographical Information System) based software that facilitates the user operation.

I, INTRODUCTION ~

Generally speaking, the power distribution system is protected by reclosers, which consists of a simple break and an electronic recloser relay that is interconnected. The purpose of the recloser is to reduce the fault time when a temporary problem occurs. Any interruption in the power source can be caused by natural phenomena such as: lightning, wind, trees or cars accidents, overloads, etc.

After the fault, the recloser must reconnect the power source and load again, timed according to its intemal program. If a fault continues, the recloser remains open a n d ' a new timing cycle occurs. This process will repeat until the intemal program counter (typically 3 times) finalizes the process. The recloser remains open until the operation is manually closed.

A recloser without communication capabilities could be a problem at this time, since no alarms are automatically sent to the operators. Only customers can notify their company that a fault problem exists. The problem could be complicated if a recloser is outside of the downtown area. The time to reestablish thepower will be determined by the distance of the fault:

A monitored recloser is the. efficient solution to this problem. Communication facilities increase near the cities, however, outside the area, communication conditions are poor and expensive. A good solution is a radio-based system capable of covering a large area with low costs.

The radio-based system described in this paper takes advantage of a shared radio-based system used in local communication by an electrical company that employs this monitoring system. The radio-based system is a VHF Motorola consisting of a personal radio unit, repeaters and

for Reclosers Control

Paul0 C. A. Aheida Engineering Department

Santa Maria Power and Light Company Colatina, ES - Brazil elfsm(iiell'sm.com.br

vehicular units.

11. SYSTEM OVERVIEW

The main block diagram, that generally describes the system, is shown in the Fig 1.

Base Station

Remote Units

Recloser2 I ;Radio unit Interface .--.-......,

Recloser3 I I Radio unit Marface

Fig. 1 - Monitoring system based on radio control

In order to understand the system, it must be divided into three components:

GlS based software; Base Station; Remote Unit.

The system has one Bass Station (main computer, interface

0-7803-7906-3/03/$17.00 02003 IEEE. 2376

and radio unit) where a GIS based software manages the system. Generally, the Base Station is located in the maintenance center of the electrical company. At the Base Station, the user can perform the following tasks:

Monitoring the recloser status; Open or close a recloser; View the report activities of a specific recloser; Analyze the currents log of specific recloser

Each recloser unit of the system has one interface circuit and a radio unit added, thus resulting in a Remote Unit with a unique address that identifies the recloser in the net. According to the type of the recloser, the Remote Unit should operate in two modes: direct control of the recloser or control using the serial stream of SCADA (Supervisoly Control and Data Acquisition) command (if available). in the first case, the Remote Unit uses its relay outputs and optic-insulated inputs to perform the action. In the second case, the commands, by a

serial stream typically RS485, are sent to a recloser performing the closeiopen action or to read the parameters as phase currents in the main circuit.

The system operates sharing the radio service channel in the Santa Maria Power and Light Company, in Brazil. However, the communication quality is not affected by the system transmissions due to small frame packages and the program strategies employed.

.

111. GIS BASED SOITWARE

The GIS based software in the main computer was developed in order to facilitate the user operation. The main screen shows the electrical network and the reclosers in real coordinates (square points). When the user double clicks on the recloser symbol, a new menu appears over the main screen with the recloser online information. The main screen is shown in Fig 2.

Fig. 2 ~ The main screen with a recloser information window

Each recloser can be included by the user inputting the real

software shows all feeder tiesireclosers and gives the users the ability to navigate upstream or downstream from a selected device and to assign switching tasks.

In addition, the software provides a complete activities report of both recloser and user operations.

coordinates or graphically choosing the point on the map. The Iv. THE BASE STATION

The B~~~ station is responsible for the system, There is only one B~~~ station in the system where the can perform pre-programmed or online tasks. lntemally, the B~~~ station consists of a main computer, an interface and a radio unit.

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The main computer has CIS based software and records all activities from recloser and user operations. The interface between the radio unit and the computer controls the data flux and modem features. The internal block diagram is shown in Fig.3

Microcontroller

PC Filtering and power stage

Fig. 3 - Interface block diagram

The microcontroller provides 'full control of data flux such as: buffering data, currents log' h sk and handling error messages. In' addition, the CRC.cbeck (Cyclical Redundancy Check ) was implemented. The'microcontroller, PIC16F876, from Microchip, was employed to performthese operations.~

The chip modem (TDK 73K222AL) works similar"to a modem in:QPSK (Quadrature Phase Shift Keying) running over 1200 ' hps .with two stream frequencies. The highest channel transfer information from Base Station. to Remote Unit and the, lowest channel receives data. from the.Remote Unit. ' . :. . .

The MODBUS RTU ,protocol was employed 'in' the frame messages with encrypt algorithm to' avoid attacks in' the system.

Basically, all datz. frames received from the computer.are verified for validity using, CRC. A validated frame is sent through the chip modem to the radio using the microphone plug. When. data i s received from the radio (true d a h is considered only when a carrier is detected) the microcontroller verifies the CRC and forwards the frame to the computer.

In the event, the radio channel is busy and the user tries to communicate to the recloser. The recloser will not reply. The interface will automatically send any error mcssagc to tho computer after it has attempted the process.four times.

. . .. . . . .

V. THE REMOTE UNIT

A Remote Unit is installed in each recloser and an address is defined electronically to identify the device in the net. Internally, the interface has one battery, two inputs/outputs to direct control of the recloser and one serial stream designed to SCADA control.

The direct recloser control can he done using the inputloutput of the interface. This method allows the user to use a simple command such as remote close/open. The remote closdopen command has no electrical measurement, however,

digital inputs/outputs can be observed. When a more complex application is required, the SCADA

serial stream should be connected to the recloser. The block diagram of the interface is shown in Fig. 4.

i It- 1 Chip I (Breaker) R S 485

Converter

11 :E: 1200b~o TX a m p g (mamphons) . ~

U (Recloser Relay) 1 Filtering and E j R a d i o unit)

p3wer stage A RXmalog (speaker)

Fig.4 - Diagram block of the interface in the Remote Unit

The microcontroller performs full control on data flux with the CRC 'as a check 'and the microcontroller employed to perform these operations (PIC16F876, from Microchip).

The chip. modem (TDK. 73K222AL) works similar to a modem in QPSK (quadrature phase shift keying) running over 1200 bps with two stream:; frequencies.' All frame messages are forwarded to the microcontroller that perform full control on data flux.

On receiving a message, the interface demodulates and checks the integrity by die CRC. The validated. frame is decoded and performs according to the following rules:

1 . Tlk frame destination is SCADA serial stream. 2 - A command mwt be executed by the interface.

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As in Case-I, the interface waits for a response from the SCADA stream, once completed, the received frame is sent to the Base Station.

In Case 2, using its.VO peripherals, the interface performs the. command that can' be associated to a digital input or a relay output command.

Note, each frame in fhe system has identification (an electronic address) provided by the interface in the Remote Unit. Thus; the Base Station recognizes the frames from different Remote Units,and the data is correctly handled in the main computer.

VI. SYSTEM OPERATION

The available data of Shared Radio System of Reclosers Control can be accessed in ,different ways as shown below:

Direct requisition by the user in the Base Unit; Alarm message from the Remote Unit Communication integrity between Remote Units and Base Station; Consulting the report activities of the reclosers.

In the direct access method, the user, in the Base Station, broadcasts to all Remote Units, a command (the address of Remote Unit are enclosed) to opedclose the recloser or to read the recloser parameters. Only the addressed Remote Unit will answer the command. This process for Remote Unit I is exemplified in the Fig 5

Broadcasting (address 1) 2

Answer from Unit 1

------------ Base Station

Fig.5 -Direct access method

When a fault occurs (recloser trip, power lost, internal battery low), the Remote Unit sends an alarm message to the Base Station. This message will be repeated until the Base Station recognizes the alarm and sends hack an acknowledgement message to the Remote Unit. The process is shown in the Fig 6.

Fault occured

Fig. 6 -Alarm message

~

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Every fifteen minutes, the Base Station begins a scan of all Remote Units. The Remote Unit attempts data solicitation. If this does not occur, an error message is generated and stored in the computer. A new overlayed icon appears matching the recloser on the map, allowing the user to identify the problem on the Remote Unit. This process is known as communication integrity. Fig 7 illustrates the process.

- _ _ _ _ _ _ _ _ _ _ _ 1 Remote Unil3

Fig. 7 -Communication Integrity.

The user can select one or more Remote Units to acquire the currents measurements across the recloser to perform a current log. When activated, this process and the communication integrity occur together. The only difference is that the currents measurements are discarded for non- selected Remote Units.

All activities of the Remote Units such as user commands, alarms and currents log are recorded in the main computer and can be reported at any time to check problems at the electrical plant.

This system was applied in the Santa Maria Power and Light and Company located in Brazil. The results obtained were satisfactory when compared to others similar systems.

A recloser used in the implemented system is shown in Fig.8.

- ’ ‘: V. Conclusion

Fig. 8 -One of the reclosers employed in the system

This paper presented a system designed to control reclosers in a shared radio based system. The system was based on a low cost microcontroller from Microchip and a chip modem provided by TDK. The reclosers applied can be easily changed to non-autonomous breaks and more features can he added in the system such as remote electric measurements. The GIS software interface facilitated user operation with a graphic feedback. The implemented system has presented a good performance in the control and monitoring of Santa Maria Power and Light Company.

References

[ I ] Pcxtran Controlcs Eletrbiiicos LTDA, “Rclcr dc ProtqBo de Sabrecorrcntc Trifisicas ”,vorsaes 2.7.1,4.7.3 c 5.7.4, Nov. 1997.

[2] Herman Moyers , “TakkGln CIS Developer Kcmel (DK)” ., TaTukGIS, www,tatukgis.com, Poland 2003 .

[3] Motorola, Transceptar Bidiiccional GM 300, Manual de Scrvip GM 300, “Part Number”: 68-80902232, c Manual de OperagBo GM 300, “Part Nunbcr”: 68-80903251, Modclo M-3GMC Motorola, Transccptor Bidirccional P 110, Manual de Sewip P 110, “Part Number”: 68.80902230, e Manual de Opera920 P 110, “Pan Number”: 68-80903249, Modelo P43QLC.

[SI Resca, “Opcration Recloser”, Resca 1965. [6] McGraw Edison, ”Bulletin”, McGraw Edison Company 1975. [7] Westinhousc, “Manual de Servip e Opcra~lo do Religadar”.

Wcstinhousc Brazil 1986. [8] Microchip Technology, “yui.microcIiip.com [9] Texas Instruments, “Handbook”. for RS485, 1993 [IO] TDK Scmiconductors, rvww.tdk.com

[4]

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