VIBRATION ANALYSIS

According to a recent CIGRÉ survey on high-voltage circuit breakers, 44% of major failures and 39% of minor failures are of mechanical origin. These figures reflect the actual situation prevailing at Hydro-Québec TransÉnergie. In fact, new market regulations result in additional operations on specific applications of circuit breakers (power plants, capacitor banks and shunt inductors).

The improvement of mechanical reliability can be achieved by two separate means. For the products in the certification process, mechanical endurance requirements can be upgraded. As for the existing equipment, the strategy relies on having tools with better detection capabilities to find problems before major defects can occur.

The initial strategy consisted of analyzing the market to know what was available. In this case, the products offered did not fulfill Hydro-Québec TransÉnergie's needs. In fact, the sampling frequency, resolution and vibration analysis software were inadequate for diagnosing the mechanical condition of the various types of SF6 circuit breakers. For these reasons, IREQ, Hydro-Québec's research center, was given the mandate to develop a measuring device prototype. The method and algorithms were validated through real cases simulated in a laboratory as well as field testing. The latter was often followed by internal inspection in order to validate the diagnosis. Once the efficiency of the device was proven, Hydro-Québec TransÉnergie's industrial partner, Zensol Automation Inc. (Québec), developed an industrial version of the vibration analyzer. Once again, the validation took place through field testing.

Vibration analysis allows the detection of mechanical anomalies on the mechanism or interrupting chamber of high-voltage SF6 circuit breakers. The measuring system includes accelerometers, conditioning modules and a data-recording system, including the corresponding Zensol software. In addition to vibration signals, the system can record any analog signal relevant to the analysis of the circuit breaker's condition, such as contact displacement and position. Two parameters are used to assess the breaker's condition: amplitude deviation measured in decibels and time deviation measured in milliseconds. Universal threshold values were determined based on research works of other authors in that field and were validated through lab and field testing.

ABNORMAL END OF TRAVEL IMPACT

In the following case, accelerometers were positioned at the top end of each interrupting chamber and inside the operating mechanism (Fig. 7) of a gang-operated, staggered-pole, 120-kV SF6 circuit breaker cumulating more than 4000 operations.

The comparison between data recorded two years earlier led Hydro-Québec TransÉnergie to identify the presence of an abnormal end of travel impact on phase C. The internal inspection demonstrated traces of an impact on the crank located at the bottom end of the support insulator (Figs. 7 and 8). Even if the accelerometers were located far from the defect, detection was possible. The circuit breaker was then readjusted to avoid further degradation of the mechanical linkage.

MAINTENANCE TOOL DEVELOPMENT STRATEGY

The need for tools to give the actual condition of the interrupting chamber components emerged with the arrival of SF6 breakers whose internal inspections are complex because of gas handling and recovery. The search for potential solutions must go through an analysis of the products already offered on the market. When the available products do not fit the utility's needs, the development of new diagnosis tools becomes necessary.

After the development phase, Hydro-Québec TransÉnergie will determine the need to be associated with an industrial partner. The partner is in charge of the evolution of the instrumentation by taking into account the needs of and feedback from different users, thus enhancing the reliability and the precision of the diagnosis. This also facilitates the smooth integration of adding the new methods to the traditional maintenance plan.

Traditional maintenance tests remain helpful when the aging of circuit breakers is progressive. However, in cases where anomalies appear suddenly on a family of breakers, new diagnosis methods such as the dynamic resistance and the vibration analysis can definitely help to precisely assess the condition of the apparatus and to better determine the priority level of a given intervention. In all, it is by clearly defining its needs and by developing tools that fulfill them that Hydro-Québec TransÉnergie can remain at the edge of technology while assuring the longevity of its electrical equipment.

Olivier Turcotte received his BEEE degree from Sherbrooke University in 2003. Since 2004, he has been working for Hydro-Québec's transmission division, Hydro-Québec TransÉnergie, in the Electrical Apparatus group, where he is involved in the certification and maintenance of circuit breakers and surge arresters, and is in charge of R&D projects on new diagnosis methods for SF6 circuit breakers. He is a Canadian member of IEC Technical Committee 37 (surge arresters) and a registered professional engineer in Québec. Turcotte.Olivier@hydro.qc.ca

Robert Gauthier received his BEEE degree from École Polytechnique in 1980. He started his career at Hydro-Québec in 1981 and has worked in the Commercial department of Hydro-Québec's transmission division, Hydro-Québec TransÉnergie, since 1999. Gauthier.Robert@hydro.qc.ca