Among the essential components of any electrical power system, the circuit breaker stands out with its reliability being paramount. Therefore, specialized online and offline measurement systems are employed to assess the condition of CBs, whose primary role is to detect any deviations in the breaker’s operation.

The most common method for detecting malfunctions in circuit breakers involves timing measurement, which evaluates the switching time of the breaker operations. During this process, the measured results are compared with specified operating values recommended by the original equipment manufacturer (OEM). However, this approach has limitations in identifying all types of failures, partly due to the relatively low occurrence rates, averaging approximately 6 failures per 100 circuit breakers per year [1]. To complement this method, other tests such as resistance measurement, dynamic resistance measurement and movement measurement during operation are also conducted to provide a more comprehensive understanding of potential failures.

Timing tests, together with coil current and motion measurements, as well as contact resistance measurements, are recommended by international standards among others by IEC 62271-100. If the high voltage circuit breaker (HVCB) mechanical operatons surpasses the manufacturer’s specified operating time limits, it risks being unable to effectively extinguish the arc during the making or breaking process, which leads to a rapid deterioration of the condition of the circuit breakers, and ultimately to an unsuccessful interruption of the fault current and, consequently, breakdown in the power system. Consequently, assessing the condition of the circuit breaker involves meticulously measuring the operating times to validate its integrity and operational efficiency. To achieve this, authors [1] employed graphical representations in terms of voltage drop to visually illustrate the intricate process of the breaking element’s operation (open or close operation).

In the field of circuit breaker testing and condition assessment, the adoption of new approaches and testing methodologies often precede their establishment as industry standards. One such innovative approach is dynamic resistance measurement (DRM). This

method produces comprehensive data sets that include time series acquired during the making or breaking of the circuit breaker. The times series includes the movement of circuit breaker contacts recorded by appropriate motion sensors, along with voltage drop across the contacts and the injected test current which provides sufficient data for computation of the dynamic resistance throughout its operational cycle. Beneficially, DRM can be conducted on fully assembled interrupting chambers. This method often leveraged the initial closed state of the breaker in order to be able to perform the DRM. Furthermore, utilization of the high-power current source yields the necessity for the appropriate connection in the form of weighty testing leads.

It’s important to emphasize that the primary objective of DRM testing is to assess the condition of arcing contacts. When CB operates, during the closing operation, arcing contacts will close first and during the opening operation, arcing contacts will open last, meaning that the arc will be caught at arcing contacts. This imposes deformation and erosion of the arcing contacts due to the

arc formation. These potential arcing contact deformations and structural deviations can not be detected by timing and contact resistance measurement tests solely. This yields the importance and benefits of the DRM test for the arcing contacts condition assessment. The condition of the arcing contacts might be assessed by the visual inspection of the obtained dynamic resistance time series or by extracting the quantitative numerical indicators such as arcing contact overlapping time and arcing contact wipe length (overlapping distance) [2], [3], as well as by comparing the obtained results with those from other poles or with previously obtained reference results.

In terms of performing the DRM test, initially, the car batteries have been used as a DC current source. The deficiency of this approach mainly revolves around safety due to the chemical nature, weight, as well as limitations in terms of the amount of energy. Some authors proposed the use of a micro–ohm meter as a power source for DRM testing on Dead Tank Circuit Breakers – which gave satisfactory results with better safety conditions for operators [4]. Additionally, since the conventional microohmmeters are powered supplied by the power grid, this usually imposes additional noise into the recorded values and time series. This has been improved by the utilization of the battery-powered test modules which yields a significantly better signal-to-noise ratio. This is reflected in terms of cumulative error in the computation of the dynamic resistance based on the acquired voltage drop and injected test current.

To conclude, while a timing test incorporating coil current monitoring and motion measurement is effective in detecting mechanical maladjustments or signs of wear of the main contacts, operating mechanism or other subassemblies, for a more comprehensive assessment of the state of the main and arcing contacts, it is also essential to perform SRM (static resistance measurement) and DRM tests.

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November 13, 2024