Rotational speed measurement using electrostatic sensors with single or double electrodes

Rotational speed is a key parameter for condition monitoring and control of rotating devices in the energy, power, transport and manufacturing industries. Especially in wind farms it is essential to monitor the operating performance of wind turbines in real-time to monitor its operating condition and detect potential fault at an early stage. This paper presents a novel rotational speed measurement technique using electrostatic sensors with single or double electrodes in conjunction with autocorrelation and cross-correlation algorithms. Preliminary investigations show the electrostatic charge accumulated on the surface of the rotating equipment due to friction between air and other media contains useful information about the operating condition of the rotating equipment. Electrostatic charge induced on the sensing electrodes adjoining to the rotating equipment can be detected with a suitable electronic signal processing circuit. The system consists of a sensing unit, signal conditioning unit, signal processing unit and system control unit. The rotational speed measurement system has been evaluated on a laboratory scale test rig under a range of conditions. The experimental data demonstrate that the electrostatic sensing technology has the advantages of high accuracy, robustness and resolution. Applicability and performance of the measurement system with single or double electrodes are discussed. The new technique has advantages of low cost, simple structure, easy installation and suitability for hostile environments over conventional methods.