# Design of a Novel Electric Diagnostic Technique for Fault Analysis of Centrifugal Pumps
## 1 Introduction  
Breakdown maintenance was common practice in the earlier history of plant maintenance. Maintenance personnel would start the action when the plant was shut down as a result of a problem in any of the components of a machine [1; 2; 3]. As this type of maintenance was performed in reaction to a problem, it was named reactive maintenance. It was costly and time-consuming. Later on, the concept of scheduled maintenance was introduced, in which the parts of the machine were changed after a specific run-time, as recommended by the manufacturers. This maintenance strategy was also not optimal, as some parts were replaced while they were still in good working condition. To rectify these issues, plant engineers introduced the predictive maintenance concept, where the machine parts, performance, and health were monitored continuously, and maintenance was preplanned before the breakdowns [4; 5; 6]. A centrifugal pump is a rotating machine used in the industry for the transfer of liquids through pipes. An unscheduled shutdown of a centrifugal pump in continuous process plants causes a hugefinancial loss in terms of maintenance, cost, and downtime [7]. The maintenance cost distribution for the rotating machines at a petrochemical plant is shown in Figure 1[8; 9]. It has been observed that 70% of the maintenance cost is associated with the pump. Therefore, a significant improvement in maintenance technology is required in order to reduce the maintenance cost associated with pumps. The centrifugal pump, as shown in Figure 2, mainly consists of two parts, which are the induction motor and the pump assembly. The pump assembly has a further two main parts, which are the impeller and the bearings [10; 11]. Impeller faults and pipe blockages are the main reason for the breakdown of a centrifugal pump. In the past, centrifugal pump faults have been investigated through vibration analysis and acoustic emission techniques. The sensors used in the vibration analysis and acoustic emission analysis techniques are expensive. Furthermore, the vibration sensors and acoustic emission sensors need to be installed on the machine for data collection. Some machines in the industry are located in complex positions, and it could be impossible to access the machine for sensor installation. Comparatively, this paper has proposed and developed an electric diagnostic technique that uses stator current sensors that are installed on the electric supply of the machine. Thus, the proposed technique is non-intrusive,  
Figure 1: The distribution of the maintenance costs of a petrochemical plant. Figure 2: The main parts of a centrifugal pump. as it does not require access to the machine for sensor installation. Furthermore, the stator current sensors are cheaper than the vibration sensors. The stator current sensors are usually installed in the plants in order to display the line current, and information from the same sensors could be utilized for fault diagnostic purposes. Thus, the proposed system in this paper is economical when compared with the vibration analysis and acoustic emission techniques [12; 13]. Rotating-machine health can be examined through an analysis of the supply voltage, line current, and instantaneous power. Faults in the machine (i.e., impeller faults or pipe blockages) produce harmonics in the stator current and instantaneous power. An analysis of these harmonic frequencies could give an indication of machine health [14; 15; 16]. It is a non-invasive method, as the measurement of the stator current is performed through the power distribution boxes, without requiring access to the machine position [17]. Thus, this method is useful to examine the health of machines operating in hazardous and extreme environments, and where accessibility to the machine is difficult, for example, in nuclear power plants, chemical plants, paper mills, and on-shore and off-shore facilities [18].