Jero Ahola

Diagnosis tool for motor condition monitoring

In the modern industrial environment there is increasing demand for automatic condition monitoring. With reliable condition monitoring, faults such as mechanical motor failures could be identified in their early stages and further damage to the system could be prevented. Successful monitoring is a complex and application-specific problem, but a generic tool would be useful in preliminary analysis of new signals and in verification of known theories. A generic condition diagnosis tool is introduced in this paper. The tool is based on discriminative energy functions which reveal discriminative frequency-domain regions where failures can be identified. The tool was applied to induction motor bearing fault detection and succeeded in finding characteristic frequencies which allow accurate detection of bearing faults.

Frequency-Converter-Based Hybrid Estimation Method for the Centrifugal Pump Operational State

Research on utilization of a frequency converter and sensorless methods in the drive system diagnostics has been mostly limited to the motor and to the frequency converter itself. However, it has been shown that a frequency converter also allows the sensorless estimation of the operational state of a centrifugal pump providing new opportunities for the diagnostics and control of pumping systems. In this paper, a novel hybrid estimation method for the centrifugal pump operational state is proposed. It is based on the identification of the process by using those flow rate and head estimates produced by QP-curve-based method, which are known to be relatively accurate. After the identification phase, the process model can be used together with the estimates of the frequency converter for the sensorless operational state estimation of the pump. The method is evaluated by laboratory measurements, and its applicability to industrial pumping and fan systems is also discussed.

Power-line communication-based network architecture for LVDC distribution system

In smart grids, a communication network with bidirectional data transmission between network components is required for functionalities, such as grid monitoring, control and protection. These functionalities set different requirements for communication. This paper focuses on the use of power-line communication (PLC) as a data transmission method for monitoring, control and protection functions in a proposed novel smart grid concept - low-voltage direct current (LVDC) distribution system. Hence, a PLC-based communication architecture for the LVDC system is proposed, its feasibility analyzed theoretically and verified by measurements. Channel capacity and practical data transmission tests are performed in a laboratory environment. Finally, the suitability of the proposed network architecture for the LVDC system and its compliance with the set requirements are analyzed.

A new approach to data transmission between an electric motor and an inverter

In electrical drives data transmission between a motor and an inverter is required due to sensors, installed at the motor, that are used in the motor diagnostics or controlling. Generally, the data transmission is carried out using additionally installed cabling, such as, twisted pairs. In this article a new method is proposed that provides an Ethernet based communication link between the electric motor and the inverter. The method uses a motor feeder cable as a media and power line communications (PLC) as a communication method. Laboratory measurements with the method are carried out and the results of the measurements are analyzed

PLC Concept for LVDC Distribution Systems

The basis for smart grids is the implementation of active functionalities that interconnect the power system stakeholders, such as electricity end users (customers), producers, retailers, and system operators in a novel manner. Not only electric energy but also data flows are required between all the actors involved. A communication network between components and actuators is needed for functionalities such as grid operation, monitoring, and protection. This article studies powerline communication for a low-voltage direct current distribution system. An LVDC system is considered as part of future smart grids. The channel characteristic measurements carried out for an LVDC laboratory setup and the subsequent theoretical and practical analysis show that the studied LVDC distribution system provides a suitable medium for the high frequency band PLC between 5 and 20 MHz when an inductive PLC signal coupling method is used. Moreover, the article proposes an IP-based PLC network concept for the LVDC system; the concept is based on commercial industrial compliant HF band PLC modems.

Applicability of ZigBee technology to electric motor rotor measurements

The purpose of this work is to determine the applicability of the ZigBee technology to electric motor rotor measurements. Requirements for data transmission, electrical structure and powering of a sensor are discussed. A prototype wireless ZigBee-based torque sensor is built and tested. The results of the tests are analyzed

Design considerations for current transformer based energy harvesting for electronics attached to electric motor

Energy harvesting or scavenging from environment is being researched intensively. The main motivation of the research is to develop a maintenance free energy source for ubiquitous electronics, such as wireless sensors or sensor networks. The on-line condition monitoring of electric motors requires also sensors that are installed at the motor. In this case, the energy required by sensors could be harvested from a magnetic field. In this article, current transformer based energy harvesting is considered. A switch-mode power supply utilizing current transformer is designed. It is tested in laboratory with the mains supply and variable speed drive. According to the tests carried out, the current transformer based power sources are a feasible alternative to supply the electronics attached to an electric motor.

Loss Definition of Electric Drives by a Calorimetric System With Data Processing

An accurate measurement of power or heat losses of high-efficiency electrical devices is difficult with input and output powers. In the calorimetric method, these losses are measured directly. In this paper, a functional heat loss measurement concept with adequate data processing methods is suggested for heat losses up to 2 kW. Such a heat loss range can be applied to present-day power electronic converters with the rated power of up to 110 kW and motors up to 37 kW. The measurement system does not require a complex mechanical structure or a large footprint area on the measurement site. The concept is scalable to different sizes. New features to the balance type calorimeter data processing are introduced. These include a mass flow correction, a technique to detect the thermal equilibrium, and a method to correct measured heat losses to improve the measurement repeatability and reduce the measurement uncertainty. The measurement uncertainty of the proposed calorimetric concept is 0.4%. Laboratory measurements are carried out both for a commercial frequency converter and an electric motor. These are measured at the same time with two calorimeters. The losses of these devices are measured both by the input-output and calorimetric methods.

Bearing damage detection based on statistical discrimination of stator current

In this study, a method is presented for discriminating stator current signals from two classes, motors in normal condition and ones with a bearing failure. The study has two main objectives, to verify the former results on the bearing fault detection based on the stator current, and to show the applicability of the proposed method for the diagnosis based on frequency content. The method is based on statistical analysis of Gabor filter responses. In the empirical part of this study where the method is applied to the real measurements, the results indicate that it is not possible to detect a bearing fault if the internal radial clearance of the bearing is not adequate.

Influence of motor operating parameters on discharge bearing current activity

While the cause-and-effect chains of inverter-induced bearing currents have been well understood today, not much is known about the damage mechanism inside the bearings. Research has suggested that the bearing degradation is approximately proportional to the frequency of occurrence of the bearing currents. For bearing currents that occur statistically distributed-such as discharge bearing currents-this parameter has not been thoroughly researched yet. In this paper, we present an analysis of the influence of different motor operating parameters on the frequency of occurrence (“discharge activity”) of discharge bearing currents, using a non-intrusive detection method. When analyzed individually, the motor speed, motor shaft temperature, inverter switching frequency, and inverter dc-link voltage influence the discharge activity. However, the overall running time of the motor, the state-steady-state versus instantaneous-and the “operating history” on the time-scale of several days have the strongest effect on the frequency of the discharge bearing current occurrence.