Fault Diagnosis in a Centrifugal Pump Using Active Magnetic Bearings

Abstract

The number of rotors running in active magnetic bearings (AMBs) has increased over the last few years. These systems offer a great variety of advantages compared to conventional systems. The aim of this article is to use the AMBs together with a developed built-in software for identification, fault detection, and diagnosis in a centrifugal pump. A single-stage pump representing the turbomachines is investigated. During full operation of the pump, the AMBs are used as actuators to generate defined motions respectively forces as well as very precise sensor elements for the contactless measurement of the responding displacements and forces. In the linear case, meaning small motions around an operating point, it is possible to derive compliance frequency response functions from the acquired data. Based on these functions, a model-based fault detection and diagnosis is developed which facilitates the detection of faults compared to state-of-the-art diagnostic tools which are only based on the measurement of the systems outputs, i.e., displacements. In this article, the different steps of the modelbased diagnosis, which are modeling, generation of significant features, respectively symptoms, fault detection, and the diagnosis procedure itself are presented and in particular, it is shown how an exemplary fault is detected and identified.order to satisfy these requirements an integrated failure detection and diagnosis becomes increasingly important for these machines.The demand on using magnetic bearings in turbomachines has strongly increased over the last five years. This is stated in several recent publications such as Gopalakrishan (1999), Hergt (1999), and in the proceeding of the last magnetic bearing conference (ISMB, 2000). Most importantly here are the active magnetic bearings (AMBs), a typical mechatronic system. Rotors in AMBs already offer a variety of advantages compared to conventional systems. Some of them are the tuning possibilities for stiffness and damping, the absence of wear, the reduction of friction, the high running speeds, and possible unbalance compensation. In various applications the feasibility and profitability of using AMBs in turbomachines have been demonstrated, e.g., Allaire et al. (1989) and McGinnis et al. (1990). However, there is much more potential in such systems than using them as a simple bearing. AMBs also have to be used as sensor and actuator elements. They work in this new generation of turbomachines as an integrated identification and diagnosis tool. In this way it will be possible to design new machines with higher performance, higher reliability, and longer lifetimes.Equation (1) shows the linear description of the dynamic behavior of a rotor with stiffness, damping, and inertia characteristics, expressed by the matrices M, D and K. We assume that the rotor matrices are time-invariant but depend on the running speed and the actual operating condition. Mẍ(t) + Dẋ(t) + Kx(t) = f(t)[1]The forces f(t) are considered as the system inputs and the displacements x(t) as the system...

Development of a Novel Approach for Quantitative Estimation of Rotor Unbalance and Misalignment in a Rotor System Levitated by Active Magnetic Bearings

“…Kasarda (2000) gave an overview on applications of active magnetic bearing systems in high-speed large turbomachinery. Aenis et al (2002) and Nordmann and Aenis (2004) utilized active magnetic bearing technology for the fault detection and diagnosis in turbomachinery, such as centrifugal pumps. Srinivas et al (2018) discussed the working principle of AMBs, their hardware components and applications in flexible rotating systems.…”

On-Site Identification of Dynamic Annular Seal Forces in Turbo Machinery Using Active Magnetic Bearings: An Experimental Investigation

“…Examples of method i are more common and thoroughly documented in the literature with testing performed at university laboratories [14 -16]. Examples of method ii where AMBs are used to identify and characterize fluid film forces are reported in [12, [17][18][19][20][21][22]. The design of a full scale magnetic bearing test-facility to levitate and excite the rotor with an annular test-seal mounted in the center of the rotor is presented in [17].…”

“…Stiffness and damping coefficients are determined using a frequency domain identification method, utilizing an FE rotor model which is adjusted to match the characteristics of the test rotor in free-free conditions. The use of AMB for identification of fluid film forces of a journal bearing have been investigated among others in [18][19][20][21]. Here the forces are measured by use of hall sensors and the dynamics of the journal bearing is represented by mass, stiffness and damping matrices which are a function of the rotational speed and pocket pressure ratio.…”

Impact of frequency switching on the efficiency of a fully suspended active magnetic bearing system

“…The use of magnetic bearings in turbo-machinery, pumps, compressors, motors and generators has strongly increased over the last few years, since users expect that their machines are running safe and reliable and that they have high efficiency and availability (Gopalakrishan, 1999;Nordmann et al, 2004).…”