# Fault Investigation of Circulation Pumps to Detect Impeller Clogging
## 1 Introduction  
In the industry and the service sectors, pumps are applied to transport liquids. Pumps are driven by different types of electric motors. In the past, induction motors (IM) were used as the motor in most cases. Due to their higher efficiency, permanent magnet synchronous motors (PMSM) are now increasingly applied. A field of application where pumps are used the transportation of water in heating systems. In Europe alone, the operation of over 100 million circulation pumps accounts for 2-3% of total electrical energy consumption [1]. In order to meet the efficiency requirements of the European Union, they are constructed as PMSM driven wet-rotor pumps [2, 3]. Control, frequency converter, motor and impeller are combined in one integrated product [4] (see Figure 1). Microcontrollers are used to control these pumps. In addition to current tasks, such as controlling the pump [5] and motor [4] or determining parameters such as flow or head [6], the electronics provide a platform for implementing fault detection algorithms. A few hard faults, such as overvoltage, overheating and rotor blockage can already be detected by new types of circulation pumps [7, 8]. It is shown in the literature that in addition to a potential failure, faults can also reduce the efficiency of a motor or pump [9]. Due to the large number of pumps in operation, a large amount of energy could be saved by the application of fault-detection algorithms. In circulation pumps, faults can be bearing wear, deformation of the can, dry-running or contamination of the rotor space, impeller damage, clogging of the impeller or cavitation. Before an application of fault detection algorithms is discussed in detail, it is necessary to analyze which faults and on the basis of which method can be detected. In order to save additional costs for sensors, the analysis should be limited to the data that is available anyway. For circulation pumps only the motor current is available [4]. The most widespread approach for motor fault detection on the basis of motor current evaluation is the motor current signature analysis (MCSA). The MCSA is based on the Fourier analysis of the motor current in stationary operation [10]. The MCSA, which was developed for fault detection of IM, is used today for different motor types, as well as the PMSM. Ref. [11] gives an overview of potential faults of PMSM including magnet damage and demagnetization, eccentricity, unbalanced magnetic pull, bearing damage and stator winding faults. Another current based approach is the space vector angle fluctuation method. This method is mainly used for fault detection of IM [12]. While several approaches for the detection of typical motor faults can be found in the literature, there are significantly fewer approaches for the detection of faults in pumps that are based on the motor current evaluation. In [13] it is shown that damaged impeller and pipe blockages can be detected by analyzing the pattern of the d-q-current. In [14], damaged impellers are analyzed with the help of MCSA. It is shown that the fault slightly influences the amplitude of a sideband in MCSA. In [15] a clogged impeller is examined and a decrease in the effective value of the motor current is detected. Ref. [16] shows a successful detection of cavitation phenomena using an adapted MCSA. The papers [13; 14; 15; 16] are all based on driving the pump via IM. In [17], an approach to detect dry running, bearing failure and impeller clogging based on MCSA is shown, where the pump is operated by PMSM. Since circulation pumps are driven by PMSM and the d-current is controlled to zero, approaches based on the d-q-current pattern are not applicable. After analysis of the state of the art, the application of MCSA looks promising. However, as is well known, the implementation of spectral analysis requires a large storage capacity and computing power from the electronics. Not all applications can provide this.