MSENSE® BM – Safe operation through bushing monitoring
According to the Transformer Reliability Survey conducted by Cigre working group A2.37, 17 % of all transformer failures worldwide can be traced to defective bushings – and they are also one of the main causes of transformer fires and explosions.
A particular problem associated with failures of high-voltage bushings is that, in a significant number of cases, such failures are catastrophic – a failed bushing explodes and starts a fire which spreads over the transformer. Since power transformers are generally filled with large volumes of mineral oil (tens of thousands of liters), an ignition of the oil and the resulting fire can release an enormous amount of energy which is capable of destroying not only the entire power transformer and its components, but also objects located nearby in the substation. Furthermore, such fires pose a danger for the people in or near the substation and also heavily pollute the environment. Large amounts of smoke-carrying, polluting and poisonous compounds are released into the air while the mineral oil and its combustible by-products can also pollute the soil and ground water. And flying fragments of porcelain insulators resulting from a bushing explosion can also damage other parts of the substation.
The requirements on the availability and reliability of power transformers are continually increasing – as is the transformer’s age — which can lead to critical problems during operation particularly since the typical manufacturer-specified service life of high-voltage condenser bushings is typically shorter than the service life of most transformers. This makes the online condition monitoring and evaluation of the bushings extremely important. The new MSENSE® BM manufactured by Maschinenfabrik Reinhausen (MR) makes it possible to detect bushing faults at an early stage and intervene before the transformer is badly damaged.
For electrical field grading, high-voltage bushings above a certain voltage level are almost exclusively equipped with capacitive grading layers, Fig. 1, which are exposed to high electrical, thermal and mechanical stresses during operation. Bushing failures can be caused by transient overvoltages, increased temperatures or temperature fluctuations, as well as by the ingress of moisture, which can quickly lead to a failure of the bushing insulation or even to a major transformer failure.