Utilties and vendors set out to review and evaluate the practical issues and benefits of online monitoring technology for high-voltage (HV) circuit breakers. This three-year project included a comprehensive range of monitoring for the electrical energy, mechanism and SF₆ gas systems. Transducers of various types were installed, and the test breaker was operated more than 1000 times during the test period. This online monitoring project produced many results and enhanced the knowledge base. Monitoring systems provide improvement in the understanding of circuit-breaker operation and additionally, provide input into reliability centered maintenance (RCM) programs.

Project Test Installation

Dorsey HVDC Converter Station, located near Winnipeg, Manitoba, Canada, was chosen as the test location. Dorsey Station has two HVDC Bipoles rated at ± 500 kV and ± 463 kV, capable of transmitting 3600 MW. The ac switchyard consists of 46 230-kV-rated circuit breakers, of which an ABB ELF 240-kV SF₆ breaker was selected for this project. (The type of breaker is independent of the research objective.) The ELF breaker (Fig. 1) is designed with three independent poles, thus enabling different types of monitoring system incorporating a large variety of transducers installed on each phase. The focus of this field initiative was to evaluate monitoring technology, not to evaluate commercially available online monitoring platforms.

Three separate systems were installed in this project, one on each phase of the ELF breaker. ABB CMU and Doble Insite were used on two phases. The third phase of the project used a BC Hydro-engineered system, which was based on Modicon PLC and National Instruments high-speed data-acquisition hardware. (There are several other monitoring packages available to assist in sensor selection, data-collection, data analysis and trend tracking.)

During the three-year monitoring program, the 240-kV breaker operated more than 700 times at rated voltage, plus an additional 300 times during off-load maintenance periods.

Each of the monitoring systems measured the same basic parameters, including contact travel, A and B auxiliary contacts, phase currents, coil currents, heater and pump current, SF₆/CF₄ pressure and temperature. Vibration transducers were installed on each mechanism. Different styles, makes and costs of transducers were used whenever possible. Two separate classes of monitoring systems were installed:

• A protective relay or stand-alone system (Class 1)

• Distributed intelligent systems (Class 2).

The Class 1 system applied to one phase has all of the online intelligence located in the device (Fig. 2). The monitoring algorithms process the data and generate alarms based on preset threshold values. There is limited storage of previous event data and no long-term trending. Remote communications were implemented using a telephone modem. An automated dial-up database system designed in Microsoft Access was able to provide trending information for this system configuration.

Two separate configurations of Class 2 equipment were installed on the other two phases; the equipment located at the breaker was primarily data acquisition (Fig. 3). The data is transmitted to a central data server over a network. The online analysis is performed, and the alarms from the system are generated at the central computer server. Because the data is stored, long-term trending is possible. Remote communication is accomplished through the server.

Monitoring Equipment Installation

The monitoring systems were retrofitted to an existing breaker with each system taking about a week to complete and commission. The phase current signals were not routed via the breaker cabinets, thus a new cable route was required. Table 1 lists the different transducer types that were installed in the existing control panels.

Experience and Insight

Data-acquisition equipment

Data acquisition and a wide variety of transducer components were used to monitor an equally wide variety of circuit-breaker parameters. Phase B system experience showed that, while the integration of standard components into a working system is not a trivial exercise, it is certainly possible to collect data using many standard devices and communication protocols. Transducer failures did occur during the project, but these defects were relatively minor and straightforward to troubleshoot and repair.

Computer and computer peripheral equipment

All of the systems experienced software, operating system, and computer hardware or communication hardware problems. These problems were not as easily resolved, and several attempts or steps were needed to isolate and repair the problems. For example:

• Windows NT server and other software intermittently hung up

• CPUs lost communication and failed to restart until a master reset was performed

• Defective modems and phone switchers

• Defective tape drives

• Failed CPU cooling fans

• Excessively long communication and download times

• Difficulty in upgrading operating systems and/or application software.

System set up or initialization

All of the systems required some degree of set up or initialization by the system providers. The project demonstrated the importance of supporting documentation on the customization of parameters, set points and rule sets. It is possible to have a system “operational” but to have incorrect, invalid or nonexistent data programmed into the system, thereby making the results questionable and erroneous. The implications of this issue are serious. Is a monitoring system that provides no alarms really working? Is the monitored apparatus healthy or does the absence of alarms simply mean that the monitoring system is not functioning?

Each utility needs to assess the skill sets and competencies required to operate, maintain and upgrade monitoring systems. The technicians responsible for high-voltage apparatuses are highly skilled but generally lack the computer troubleshooting or installations skills required to keep these systems operational. As a result, large-scale implementation of online monitoring would require either retraining and/or new personnel with the necessary skills. Instructions must be well documented and sufficiently detailed.

Detailed monitoring and investigation can reveal important information. This knowledge base can be applied to determine the scope and benefits of a monitoring program. One of the benefits of this project is Manitoba Hydro's decision to modify its maintenance practice for ABB ELF breakers and to determine the extent of online monitoring systems for these breakers.

Off-Line Testing Program

The project's monitoring period included off-line testing of timing, vibration and dynamic resistance measurements. Varying operating Conditions allowed for the determination of changes inherent to the breaker. Tests were performed at different ambient temperatures, control dc voltage, SF₆/CF₄ gas pressure and hydraulic energy levels. Variations of up to 10% were observed in the timing performance of the breaker.

The online monitoring systems did provide alarms for some of the conditions. The utility responsible for the circuit-breaker maintenance schedule must decide what action to take on receipt of an alarm. Table 2 indicates the variation because of specified parameter changes. All the recorded parameter changes are within the “normal” operating range for the circuit breaker.

SF₆ Gas-Monitoring Results

The intensive monitoring and investigation produced some interesting results. The SF₆ gas density is calculated by using a temperature compensated method that requires the measurement of gas pressure and gas temperature. Five SF₆/CF₄ gas systems were installed and each system generated erroneous results when the ambient temperature was below -20°C (-4°F). The ELF circuit breaker is equipped with a gasket heater that turns on at -20°C. As shown in Fig. 4, the SF₆ gas temperature recorded for ambient temperature below -20°C is notably disturbed, while the pressure remains linear with temperature. The SF₆ gas density or compensated pressure readings depict corruption below an ambient temperature of -20°C. This systemic error resulted in false alarms from all monitoring systems.

The negative slope of the density line indicates a very small SF₆ leak undetectable by reading the gas-pressure gauge. Further investigation located the leak at the connection to the gauge installed as part of the online monitoring. This example illustrates the strengths and weaknesses of online monitoring. The online system identified a problem; however, the system user had to interpret the data, and the problem itself being the result of the online monitoring installed.

Vibration Analysis

One monitoring system incorporated online vibration measurement using an accelerometer (sensor) with a signal-sampling rate of 40 kHz. The purpose of these measurements was twofold: determine the longevity and consistency of the signals, and derive a method to machine-read the signal.

The results of the measurement were very positive in that the vibration signals were remarkably reproducible. In fact, the signals exhibited a repeatable seasonal variation — evident differences between summer and winter, and about equal characteristics in the spring and autumn. The signals were analyzed using a standard signal processing method and comparison between the processed signals was done using a cross correlation method. The repeatable difference between summer and winter is evident, the peaks being winter and the valleys being summer with spring and autumn in between.

Insights

• Long-term online monitoring systems provide valuable information regarding the performance of a HV breaker. Qualified personnel must still perform data analysis to determine the action plan resulting from the monitoring results. This can be minimized if an expert system is incorporated.

• Monitoring systems are subject to failure. Data acquisition and transducer-related faults are easy to detect and repair. However, computer systems, data servers and software problems can be significantly more time intensive and require computer skill sets to solve. Utilities exploring this technology must be aware of the skill sets required to implement and maintain these online monitoring systems.

• Monitoring systems will require some degree of maintenance. The maintenance program should include a periodic review that the data-acquisition systems are collecting sensible data. This maintenance program should include any software and firmware upgrades, updates or revisions. A maintenance system for tracking software, firmware, and operating system revisions must be in place. Future systems will be expected to be self-diagnostic.

• Monitoring systems require a careful observation period to ensure the system is set up and responding. Two main pitfalls of online monitoring to avoid are the absence of alarms resulting from the improper installation or disabling of the monitoring systems and the generation of a high number of nuisance or false alarms.

• Each piece of monitored apparatus requires study or careful review to customize the monitoring application. Currently, there is not a “one-size-fits-all” monitoring system. The findings from this program were used as inputs to a RCM program for this breaker. As a result, Manitoba Hydro changed the maintenance program for this breaker and clarified the monitoring requirements for this breaker. During the project the breaker did not experience any failures, so there can be no discussion on a monitoring system's ability to detect and determine any trend towards failure. One of the major unanswered questions is:

  “Can a monitoring system detect and predict failure, maintenance requirements or end of life?”

  This prediction must take into account the normal variation of measured and calculated parameters and must not generate trivial or false indications.

The Future

The principal objective of online condition-monitoring systems is to provide information. This information is required to form the basis of maintenance, repair or refurbishment programs for the equipment. Online monitoring and off-line monitoring techniques provide the keys to allow maintenance personnel to make intelligent decisions.

Several areas require continued development and improvement, and this project demonstrated that the reliability of the HV breaker tested is, at least, an order of magnitude higher than the reliability of the monitoring equipment installed. In practice, monitoring systems must be at least as reliable as the equipment they monitor. The reliability of the data-acquisition equipment is nearing this goal, but continued efforts are required to increase the reliability of the computer-based server technology while maintaining reasonable costs. The interface to the end users of the technology can be improved as online monitoring systems can generate large amounts of data. Hence, data handling, storage and conversion into meaningful information require further and continued development. The present approach to equipment monitoring is unlikely to continue, as utilities would be unable to handle a multitude of equipment monitoring systems that could be required for large substations.

Utilities are now moving slowly towards the concept of ITEC (Information Technology Electronics Communications). With ITEC, electronic systems, super-intelligent electronic devices (SIEDs) and plant information (PI) servers will capture data and information. Communication systems will deliver the data and information to the stakeholders in the required time frame with the required quality and security. IT systems will then process the data and information, make decisions and to an ever-increasing degree, execute the decisions.

How will ITEC effect equipment condition monitoring? The most probable answer is that equipment will have to be supplied complete with specified sensors having specified outputs and using a specified communications protocol. Data capture, processing and analysis will then be performed by the utility IT system.

BC Hydro (Vancouver, British Columbia, Canada), one of the project sponsors, has initiated a major project to demonstrate the value of the concept and to date has developed a six-layer conceptual data model for the entire transmission system that will run on a GIS platform. A pilot application is in-progress for a large 500-/230-kV transmission station and the associated transmission system.

Acknowledgment

The author wishes to acknowledge the support and funding for this field project provided by the following project participants: ABB, United States, Switzerland and Canada; ALSTOM, France; BC Hydro, Canada; Doble, United States; ESKOM, South Africa; Manitoba Hydro, Canada; Siemens, Germany; TransAlta Utilities; SPI PowerNet, Australia; PowerLink, Australia; Energy Australia, Australia; Powercor Australia, Australia.

Randy Wachal graduated from the University of Manitoba with the BSEE degree in 1981 and joined Manitoba Hydro. He worked on the Nelson River HVDC System, and in 1995, he was appointed project research manager at Manitoba HVDC Research Centre. Wachal has been project manager for the four-year collaborative research program in Online Monitoring Systems for HV Breakers. He is a registered professional engineer in Manitoba Province and is a member of IEEE.

Table 1. Transducers installed in each phase.

A Phase	B Phase	C Phase
Displacement - optical Primary CT Pump motor - DC shunt Control coil monitoring Injection of 1 kHz signal A/B contacts Heater four locations using auxiliary CT SF6 density - quartz crystal SF6 pressure and temperature Ambient and cabinet temperature (RTD)	Displacement - resistive transducer AC CT: small CT from protection relay DC pump current Coil current using 1 ohm shunt A/B contacts AC heater current SF6 pressure and temperature Weather monitor Mechanism vibration A&B phase Metering IED measuring three-phase currents and voltages	Displacement - optical Three AC phase currents DC pump motor current Trip and close coil - CT A/B contacts Two heater CT in cabinet SF6 pressure and temperature Mechanism vibration Temperature (RTD)

Table 2. Variation in close and open times.

Operation	Temperature 20°C to -20°C	Energy Storage N-2 Close N-1 Open	SF6 Pressure	Energy SF6	All Parameters
Close	2%	5%	1%	5% to 6%	8% to 10%
Open	2% to 3%	2% to 3%	1% to 1.5%	4% to 5%	5% to 6%