ABB Technologies Ltd. ���

INNOVATIVE SOLUTIONS FOR HANDLING ELECTRICAL TRANSMISSION NETWORKS

Ronen Aharon

ABB Technologies Ltd. (Israel)

SUMMARY

The increasing complexity of power transmissionnetworks and the demanding requirements concerningthe availability and the quality of power supply have asignificant impact on the performance required from theautomation and protection systems in power substations.Furthermore worldwide economic changes and stiffcompetition demand better utilization of electricalassets.

The fast developing microelectronics technology isbeing implemented in protection and control systems.Numerical devices and communication links in modernSubstation Automation Systems (SAS) give the usernew, enhanced possibilities to improve operation andmaintenance of substations.

The know-how gained through years of experiencetogether with the huge amount of data that is availabletoday in SAS, must be handled properly to provide theright information at the right time.

This paper presents the substation automation concept,its benefits and new IT solutions for data analysis.

1. INTRODUCTION

Modern state-of-the-art SAS is based on numericaltechnology that covers protection, control,tele-metering, power quality analysis and conditionmonitoring of substation assets.

The integrated solutions offered by the substationautomation concept make network handling moreefficient and user friendly, and improve overallperformance of the electrical system. This applies to thecontrol and protection functions, both within theprimary equipment and between process andhigher-level information systems.

New IT tools are offered today as an integral part of theSAS, providing the substation/utility personnel withuseful information within a short time following thefault and without the need of human intervention.

2. TECHNOLOGICAL CHANGES

The essential changes caused by the numericaltechnology have been presented and discussed forseveral years.

Numerical technology implemented in SubstationAutomation Systems can be characterised by: • High degree of self-supervision• The integration of more and more functions within

a common hardware structure• Decentralized systems with distributed intelligence

covering control and protection applications• The use of a hardware platform with a software

library of functions instead of strictly dedicatedproducts

• Increased communication capabilities with opticallinks

• Synergy between protection and control andavailability to realize new functionality

• Reduced life cycle costs for the entire life of theinstallation

3. SYSTEM ARCHITECTURE

SAS for power transmission and distribution consist ofseveral intelligent electronic devices interconnectedthrough digital communication links. From thearchitectural point of view, the following mainhierarchical levels can be identified in SAS (asillustrated in figure 1):

Station LevelThis level comprises the station wide control andsupervision scheme. The station server includes highperformance hardware and software.

Hardware: High end PC server; communication cardhandling the high stream of data; GPS for absolute timesynchronization; Ethernet card for backbonecommunication to local LAN or WAN; printer serverfor connecting the event and hard copy printers; and analarm unit for watchdog alarm.

Software: Multi tasking operating system, highperformance real time database including auxiliaryservices, tools for data engineering, systemconfiguration and picture editing, disturbance recordingevaluation and Advanced Report Tool (ART).

The software conforms to international standards suchas ODBC/SQL, API, TCP/IP, DDE/DDE Net,IEC-870-5-101, etc., and enables integration of standardapplications into the Substation Automation System.

ABB Technologies Ltd. ���

Figure 1: Block Diagram of modern Substation Automation System

Bay level

This level includes all secondary equipment associatedwith the control and protection of bays and feeders.Bay protection and control units are installed inswitchgears or in separate control panels to perform thecontrol, automation and data acquisition.The bay level system is built in a decentralizedarchitecture to increase the availability and reliability ofthe whole SAS system.

• Protection functionality allocated per bay• Control (collection of the switching objects

positions, command of the switching objects fromthe bay and from remote station level)

• Bay interlocking• Automation features such as bay and inter-bay logic

functions, frequency and voltage load shedding,synchrocheck, recloser, circuit breaker failureprotection, etc.

• Event recorder with 1mSec time-tag• Disturbance recorder for wave form capture• Metering and measurements• Power quality analysis• Condition monitoring such as breaker wear for

prediction maintenance, trip coil supervision etc.

Bay unit can be used as a protection unit, a control unitor a combined protection/control unit. The appropriatefunctions including metering and power quality can beselected by the user. The platform is prepared tocommunicate with different types of units.

Communication system

The communication network in the substation enablesdata flow within the bay level (horizontalcommunication) and between bay level and station level(vertical communication). An additional communicationlink is established between the station level and remote

workstation or maintenance center, which enables theshare of data between key persons in the organization.

The communication infrastructure is based on opticalfibers to reduce the amount of cabling and provide theuser with reliable information that is immune toelectrical interference. Furthermore, the bus must beable to transfer the synchronization impulses, in order tosynchronize the time-tagged events memorized at baylevel. This synchronization mechanism is essential toassure 1 mSec resolution between events.

The inter-bay bus communication in the bay levelprovides the functionality of bay to bay communicationincluding implementation of interlocking conditions.

4. DATA ANALYSIS

SAS generates a large amount of data, the analysis ofwhich is crucial for optimal utilization of networkassets. To maximize the benefit from the generated datait is essential to have the proper IT tools to handle thedata and convert it into useful information for operators,electrical engineers and managers within the utility orindustrial organization.The following data can be generated by the StationAutomation System:

• Events and alarms from the protection system• Events and alarms from the control system• Disturbance recording data• Condition monitoring data• Power quality data• Metering and measurement data

Figures 2 and 3 include the software tools, which handlethe disturbance recording data and harmonic distortionof voltages (power quality data).

ABB Technologies Ltd. ���

Figure 2: Disturbance Recording Data

Figure 3: Power Quality Data

Transient dataTransient data generated at the time the fault occursincludes very important information that may lead toidentifying the cause.The following data must be evaluated:

• Station & feeder name • Protection name • Protection type • Protection starting time with 1mSec time tag • Protection trip time with 1 mSec time tag • Short circuit or load current in KAmp • Total trip time

A detailed report including this data and sorted by itsappearance in time provides a clear and distinct pictureof the transmission system’s behavior during the fault- figure 4. Additional complimentary information forthis report is the disturbance-recording file, whichrepresents the changes in analogue values during thefault over time.

Figure 4: Protection Operation Report

Additional information can be obtained by executingtransformations of the data.For example, protection start statistics is an excellenttool for observing instability phenomena in thetransmission system as described in figure 5.

Figure 5: Protection Start Statistics

Monitoring dataThe monitoring data is steady state informationavailable from primary equipment like powertransformers, circuit breakers, etc. This informationaddresses mainly the wear and ageing caused by normalor temporary abnormal working conditions.

Example of maintenance information for circuitbreakersIn this report the number of trips and the aggregatecurrent during each trip of every circuit breaker in thesubstation is recorded. The fault or load current (highestof the three phases) is measured and recorded. Thecorresponding value is transferred to the SAS where it isadded to the last total current for particular circuitbreaker. Fast and slow auto-reclosure attempts are alsorecorded.The service personnel can view the trips and theaggregate rupture current and determine the best timefor the next maintenance.

ABB Technologies Ltd. ���

Figure 6: Circuit breaker switching statistics

Example of power transformer loadingThere might be an opportunity to overload thetransformer in order to gain financial benefits resultingfrom additional sales of transmission capacity. Such anoverload, however, will result in the shortening of thelife of the transformer. The result is the damaging oftransformer insulation if the operating temperatureexceeds the design limits.The overloading of transformers has several financialimplications. Thus, to perform cost/benefit analysis ofoverloading a transformer, information is needed abouttransformer loading, ambient conditions and financialfactors.

Figure 7: Trends in transformer loading

5. Conclusions

Implementation of Substation Automation Systemtogether with innovative IT tools creates real addedvalue to the customer in control, protection meteringand condition monitoring.Having explicit knowledge about the behavior of thetransmission system during fault and in pre-fault

conditions improves network availability and reducesthe occurrence and length of power outages.

Condition monitoring assists in better asset managementand optimizes maintenance policy.

As in any IT system, it is vital that management at allorganisational levels, will be committed to assimilatingthe system into the organization in order to gain thebenefits of modern substation automation system.

REFERENCES

(1) De Mesmaeker I. and Augé O., “Experience,Benefits and Trends in Integrated Protectionand Control”, GCC CIGRE SEVENTHSYMPOSIUM, Sultanat of Oman, 30-31October 1996

(2) De Mesmaeker I., Brockett P. and Landau H.,“Advantages of modern protection and controlsystem architecture and the operationalconsequences for utilities”, CIGRE 34-109,Session Paris, August/September 1998

(3) Tellarini M., Novosel D., Peterson W. andBacchini G.“Fault generation and analysis in modernsubstation automation systems” CIGREOctober 1999.

(4) Kreuzer A.“Station automation and integration in user’scommunication system”, ETG-Tagung"Modernes Anlagekonzept in der HS-Technik", Mai 2000 in Zurich