• Energy Research

Ship power systems are characterised by a comparatively high level of various power quality disturbances, such as voltage deviations, frequency deviations, voltage waveform distortions and sometimes voltage unbalance, which exert a detrimental effect on energy receivers. Among other things, power quality disturbances may cause an extraordinary increase in power losses occurring in on-board induction motors as well as ineffective utilisation of their mechanical output power. In this study, the results of empirical research which demonstrates how power quality disturbances in real ship microgrids affect induction motors are shown. The results of power quality monitoring in ship power systems from the point of view of the energy-efficient operation of induction motors are presented for various vessels and operating conditions. Recommendations concerning the revision of power quality standards and rules are elaborated to provide more energy-efficient ship operation.

The presented paper deals with the problems of electrical power quality estimation, especially in multi-disturbances conditions. The synergy effect of different kinds of supply voltage disturbances have been pointed out and it have been described in relation to additional temperature rise of induction motor windings. The practical consequences for power quality analysis have been singled out. Proposed solution has been laid and commented on.

This paper deals with the effect of lowered voltage quality in ship power systems on windings temperature of low-power induction cage machines. The results of investigations carried out with experimental and analytical methods are presented. The thermal impact of power quality disturbances permitted by ship classification societies is discussed. A proposal of new power quality regulations for ship classification societies is made.

One of the features of ship power systems is the presence of different power quality disturbances, such as frequency and voltage root-mean-square (rms) value deviations, unbalance, and voltage waveform distortions. The disturbances (including their synergy) cause an increase in the windings temperature of marine induction machines that are exposed to overheating, even if the voltage parameters fulfill the requirements of ship classification societies. Effective protection of marine induction machines against overheating requires an appropriate method of power quality assessment. This paper proposes a new power quality factor, the value of which is proportional to the windings temperature of induction machines supplied with voltage of lowered quality. The power quality factor has been experimentally verified. The results of the thermal tests based on the dedicated laboratory stand to validate the new power quality factor are presented. The time characteristics of the power quality factor based on voltage monitoring on ships are shown.

This paper deals with problem of signals spectrum estimation in systems with varying frequency and harmonic content. The shortcomings of methods described in current IEC standards have been pointed out. Further, the application of chirp-z transform for the aim has been discussed. Especially, its application concurrently with wavelet transform has been shown and the results of measurement of testing signals have been presented. As a result, the reliable spectrum estimation with acceptable computational complexity has been obtained.

The chief aim of the proposed paper is to compare the behavior of supply voltage registered onboard three vessels equipped with high power converters during normal operation. The vessels considered are a chemical tanker with shaft generator working via power converter, a research-training ship with bow thruster, and a research vessel with dynamic positioning (DP) and electrical propulsion. In the case of the two latter ships, power electronic loads are present, which include a bow thruster adjustable speed drive equipped with the six pulse uncontrolled rectifier and the adjustable speed drive with an active front end (AFE) for propulsion system. For each ship, instantaneous frequency is determined and subsequently fluctuations of fundamental components and chosen harmonics are calculated using zoom-DFT. The characteristics of these irregular fluctuations are compared and commented on. Next, phase portraits and Poincare map of the registered voltages are calculated and compared. Moreover, the impact of ship rolling and pitching on the oscillatory behavior is assessed for the DP ship. The final conclusions identify reasons for oscillatory behavior in electric power systems of marine vessels containing high power converters on the source side and load side. The feasibility of using voltage trajectories as well as Poincare maps for oscillatory behavior detection is assessed.

This paper presents problems related to transient detection and monitoring in electric power systems. It consists of two parts. Firstly, a problem of frequency characteristic of real impulses is considered. Parameters of the selected transient and notching disturbances are determined after extracting disturbances by pass-band filters with various cut-off frequencies. Further, results of wavelet transform application for estimation of selected disturbances are presented. Secondly, basic features of the prototype of original multi-parameter instrumentation for power quality assessment are shown and its transient monitoring capabilities are described on the basis of laboratory research of the testing signals. This new measurement instrument utilizes the digital signal processor (DSP) technique.

Abstract The paper presents original methods and algorithms of measurement of power quality parameters which were implemented in a new measurement device called an estimator-analyzer of power quality. The main idea was to overcome the shortcomings of current power quality analyzers, namely sensitivity to fast fluctuations of input signal parameters. This was attained with regard to the algorithm’s overall computational complexity. Complementary application of discrete wavelet transform (DWT) with Fourier transforms and chirp z-transform (CZT) was proposed for the aim. Next, a new concept of estimator mode was devised. It consists in multistage signal processing and applied methods depending on input signal character – its frequency and existing waveform distortions – as well as the chosen set of reference parameters. It further improves device performance in terms of time of computation. Description of the estimator-analyzer hardware and results of experimental research will be presented in the second part of the paper.