Efficient parameters for assessing the state of HV switching devices

Development of power supply markets, construction of new energy facilities and networks and upgrading the existing facilities worldwide stimulate development of switching equipment market, the market of HV circuit breakers in particular. China and Russia in these circumstances become the largest markets and are of great interest for manufacturers and suppliers. A market of instruments for electric equipment state analysis during commissioning and for controlling the state of equipment in operation grows in parallel.

Present-day analyzers are capable to diagnose any types of circuit breakers, including air circuit breakers used at voltages above 220kV, and circuit breakers of foreign manufacture. Simultaneous recording of time, speed and travel characteristics of nodes and mechanisms of the air circuit breakers became very popular. Thanks to systems approach to measured parameters the analyzers allow early detection of faults in the circuit breakers. Deviations of tested parameters from reference values at this stage may not be detected yet. It means that formally the equipment is assumed to be operable, but the developing defect can reveal itself during commutation in the HV networks and cause negative consequences, including emergencies and failures of expensive equipment.


Fig. 1.

Let us consider the operation of SF6 circuit breaker triggering (of foreign manufacture) as an example. This process is mainly characterized by the time of contacts closing. A curve in Fig. 1 shows speed vs travel dependence of all the moving elements of a circuit breaker. When constructing the curve, we single out several sections the operating personnel should pay attention to. Speed jump followed by its drop practically to zero at section 1-2 right after triggering may be due to clearances in the node where a transducer is mounted. At section 2-3 when the main and arch extinction contacts of a circuit breaker are not closed yet, the speed fluctuations occur that are typical for clearances between phases or nippings due to lubrication problems. This defect is most often detected in the backup circuit breakers reserved for the case of emergency. After durable storage the lubricant in the nodes dries up and corrosion may start. Section 3-4 starts from the moment of the arch extinction contacts operation. Peculiarity of this stage lies in the contact move speed and its entering the nozzle with SF6 gas. In approximately 0.5ms from the middle of section 3-4 the amplitude of speed fluctuations increases that means commencement of the main contacts closing. After their operation the speed falls (section 4-5). In the middle of section 4-5 another speed jump is observed that means commencement of buffer operation. Its operation can be analyzed at the end of the graph where sharp speed drop is observed on a very short section of travel. For some circuit breakers it can mean buffer fault. This fault can be detected by comparing the results obtained to a graph of a new (or properly operating) circuit breaker where buffer operation forms a spiral on a large travel section.


Fig. 2.

Operation of the arch extinction contacts is another important parameter that can be assessed by the travel graph analysis.  Fig. 2 shows dependence of contacts status across all the three poles on the travel, where lower position corresponds to the OPEN status and the upper one to CLOSE status. Difference in actuation and 'chatter' of contacts is obvious. Difference between closing time across poles is a very important characteristic that affects operability of all the remaining network equipment, including equipment of power consumers.  Difference of contacts operation across poles between the first closed contact B and the last contact A makes less than 1 ms, which is within tolerances for such types of HV circuit breakers. 'Chatter' of contacts is mainly due to the fact that the arch-extinction contact is displaced from the nozzle center and bounces from the surface at the first touch.

Use of the described method for recording the speed vs time characteristics of HV circuit breakers during equipment commissioning and operation reduces maintenance and repair costs of an operating company by a factor of 1.5. Performing the diagnosis at any time moment and comparing the data obtained to the previous results of measurements the personnel can make a conclusion on the circuit breaker operability or necessity to repair some nodes.

It is worth mentioning that diagnosis for the majority types of circuit breakers does not take more than 5-10 minutes.  Connection of instruments to circuit breakers takes more time, but certain solutions allow its notable reduction.  In addition, availability of a large data base on the results of measurements describing closing/opening processes of new circuit breakers and of worn out equipment simplifies the measurements analysis and decision-making on its further operation. 

Integrated approach to controlled parameters of switching equipment reduces operating costs of companies by a factor of 1.5 and even more! The family of instruments for HV circuit breaker condition assessment that is available at the market is rather big and is capable to meet practically all the needs occurring during operation and at the stage of manufacture and tests of new models.

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