Systems and Concepts of Electric Equipment Maintenance Service
In modern economy management conditions, when agricultural producers suffer a shortage of material resources, condition-based maintenance of electrified machinery evaluated with the use of diagnostics maintenance methods and prediction of its total service and remaining operational lifetime has to be considered as the most effective concept. First of all, it applies to electric motors that are commonly used as basic power drive units in agriculture. Their failures much more often, compared to other equipment components, lead to long-term maintenance time-outs in technological cycles associated with substantial economic damage. Annually, up to 25% of all installed electric motors, depending on type of equipment stock appear a subject of failure, while motor windings cause up to 80% of all failures. Agricultural production can be characterized by rather wide range of maintenance factors that in various combinations affect operation of electric motors and contribute to their wear (Lachuga, Yu,F., Strebkov D.S., Nekrasov A.I., etc. 2001, Nekrasov, A.A. 2010, Strebkov, D.S. 1995, Syrykh, N.N., Rabdin, M.Ye. 2007). In rural areas, only about 20% of all electric motors are operated in friendly environment conditions while approx. 35% and 20% are exposed, respectively, to moist and damp conditions, extremely wet environment with corrosive gases and agents. About 15% of electric motors operate in dusty premises and 10% of them `are installed outdoors. Besides, electric motors operation reliability and safety may depend on installation works quality, alarm mode protection, varying loads and many other factors. In squirrel-cage type electric motors, windings and bearing assemblies are the major resource-forming components whose failures make a principal contribution to electric drivers’ inoperability. That is why monitoring of operational status of these components is one of the first-priority tasks of maintenance service units.
Trends in critical components’ operational status shall be analyzed on the basis of data acquired by regular sampling of most important parameters of electric motors including winding insulation resistance and clearance of bearings and their beds. In this work, generic requirements are considered related to winding insulation resistance and bearing assemblies of electric motors, trends of change in winding insulation resistance and clearance of bearings and their beds in real conditions of agricultural production. New prediction methods have been developed for current values of winding insulation resistance and radial clearance in bearing assemblies.
Electric equipment preventive maintenance and repair system at agricultural enterprises (EEPMR System) is based on standardized industry-averaged scope of maintenance and repair operations carried out regularly on electric equipment, their periodicity and duration, stock list of materials and spare parts and their consumption rate for each operation (Agropromizdat, 1987, Yashura, A.I. 2008). One of the important integral components of this system is the maintenance and repair concept that, in accordance with GOST 24212-80, presents a system regulating conditions and procedures of preventive maintenance activities and equipment operational status control, in the course of its operation. The major investigated and commonly applied in agriculture strategies are the following:
Afterfailure maintenance strategy of electric equipment does not include any preventive activities. Thus, failed electric equipment or its components are subject to replacement only upon a failure.
Intermittent-duty service strategy includes due equipment maintenance activities performed at specified intervals independing on its current operational status and factual running time after recovery following the previous failure.
Runtime-dependent maintenance strategy includes remedial actions performed either at planned maintenance service intervals or upon a failure provided that it has occurred within the interval between the planned maintenances works. With this strategy, preventive measures are also taken with a certain periodicity but the runtime countdown has to be launched every time after each service activity (either alarm-conditioned or scheduled one).
All of those maintenance service strategies under consideration have their specific application features while the effectiveness of their use can be evaluated by comparison of specific average maintenance service cost for each particular implemented strategy.
The condition-based maintenance strategy is the least investigated one. It includes recovery maintenance activities depending on factual operational status of electric equipment that are regularly evaluated in the course of diagnostic operations with the use of dedicated soft- and hardware. To implement this strategy, certain technical, methodological and organizational problems have to be solved.
Diagnostics makes it possible to predict forthcoming failures of electric devices’ components and to take timely preventive measures on recovery of rated parameter values of their basic component or assembly (Syrykh, N.N., Rabdin, M.Ye. 2007, Taran, V.P., Andriets, V.K., Sinelnik, A.V. 1983, Khomutov, S.O. 2010. To insufficiently studied issues that require special research and scientific substantiation of their application in agriculture belong those of electric equipment operation and service based on monitoring its operational status and diagnostics data analysis. These issues were investigated, and mathematical models have been developed, based on works of prominent scientists Smirnov, N. N., Itskovich, A. A. 1987, Gertsbakh, I. B. 1959, Barzilovich, Ye.Yu, Glukhov, V.V., Yemelianov, V.Ye. 1999, Ventsel, Ye.S., Ovcharov, L.A. 1991, Mehdi Khosrow-Pour. 2017, Gertsbakh, I.B. 1959, Smirnov, N.N. 2001, Smirnov, N.N., Pandian Vasant, Gerhard-Wilhelm Weber, Vo Ngoc. Dieu. 2016).
Existing methods and hardware for diagnostics of electric equipment have been analyzed that can be applied to substantiate and implement the condition-based maintenance strategy for electric equipment in agriculture aimed to save material and labor cost of electric plants maintenance service.