The existence of a stator fault could be detected using the line currents of the machine. Under ideal conditions, the current Park vector components , are calculated in terms of mains phase variables , , as [ 19 — 21 ]: The space vector magnitude is given as follows: The corresponding representation of 3 is a circular locus centered at the origin of the coordinates, as shown in Figure 4. Asynchronous Cage Motors are divided into two categories, depending on the construction of the cage, cast and fabricated.
The material used for cast cage is aluminum, whereas for fabricated is copper. For high-power motors, fabricated cage rotors are used. Broken bar faults are caused by a variety of reasons: These stresses originate from human, manufacturing, and functioning errors causing asymmetry to the geometry of the machine and consequently inducing asymmetrical spatial strain.
The currents in a healthy rotor are presented in Figure 6.
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Upon the occurrence of this type of fault, the characteristic frequency of the supply current that occurs is [ 9 — 14 , 22 — 25 ]: As the fault severity increases, the amplitudes also increase considerably. Bearing faults are very common in both low- and high-voltage electric motors and special attention is required. For high-power motors, both rolling ball and sleeve bearing are used. The major causes for bearing failures are the thermal, mechanical, and electrical stresses, contamination and corrosion, improper installation, and improper lubrication.
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It is generally believed that bearing failures develop from general roughness and gradually lead to defect of the bearing components [ 9 — 13 , 16 , 26 , 27 ]. Bearings faults condition monitoring is important for asynchronous and permanent magnet machines that are used in the electric ship, while any bearing defection will cause speed and torque pulsations, thus reducing the efficiency of the machine.
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The diagnosis of the bearing failure can also be done through the examination of the current spectrum, the characteristic frequencies are given as follows [ 9 — 13 , 27 ]: Machine eccentricity is the condition where unequal air gap exists between the rotor and the stator. If the degree of the eccentricity becomes large, the resulting unbalanced radial forces may cause rub between the stator and the rotor leading to the destruction of the machine. There are two kinds of eccentricity: In the case of the static air gap eccentricity, the position of the minimum radial air gap length is fixed in space.
On the other hand, in the case of the dynamic eccentricity the center of the rotor does not coincide with the center of rotation, thus the position of the minimum air gap rotates with the rotor.
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The main causes of static eccentricity are the ovality of the stator core or the incorrect positioning of the stator or the rotor at the commissioning stage. However, dynamic eccentricity may be caused by a bent rotor shaft, misalignment or wear of the bearings, mechanical resonance at a critical speed, and so forth.
However, machine manufacturers keep the total level of eccentricity even lower in order to reduce vibration and noise [ 9 ]. Investigating the current spectrum, eccentricity-fault-related harmonics are given as follows [ 9 — 13 ]: Usually, in practical cases there is a combination of static and dynamic eccentricity, and the frequency harmonics that indicate the fault are given as follows: Moreover, in [ 28 ] the diagnosis of dynamic eccentricity fault in PM motors is achieved investigating the current harmonics given by where is an integer.
Monitoring the magnet status of PM motors is very important since local or uniform demagnetization caused by operating stresses lead to irreversible degradation of motor efficiency. Defects leading to demagnetization or disintegration of permanent magnets are caused by thermal, mechanical, or environmental stresses [ 5 , 29 ]. Investigating the current spectrum, permanent magnet-fault-related harmonics are given as follows [ 29 ]: In this paper, a review of electrical and mechanical faults of asynchronous and permanents magnet machines is presented.
Moreover, for each type of fault, the characteristic frequencies of the current spectrum that indicate the presence and severity of the failure are given. In the literature, it has also been proposed that other signals can be used for the fault diagnosis, like the torque, the power, the supply voltages, and the motor speed. Using a combination of these signals and the appropriate signal processing techniques, the engineer can extract accurate information about the condition of the machine.
The field of condition monitoring, fault diagnosis, and fault prognosis is of great research interest; the last years and novel frequency ranges are investigated as fault indicators while state-of-the-art signal processing techniques are applied for the online condition monitoring of the machines under varying operating conditions. Advances in Power Electronics.
Abstract Electric propulsion systems are today widely applied in modern ships, including transport ships and warships. Introduction The idea to use electric power for the propulsion of ships is not new, as from the beginning of the twentieth century electric ship propulsion systems had shown advantages compared to the traditional ones using internal combustion engines. In this paper, the most common electrical and mechanical faults of these machines are presented.
Modern Electric Ship Propulsion System The vast majority of ships are propelled directly from fossil fuel powered engines using mechanical transmission and gearboxes, as shown in Figure 1. Propulsion system with mechanical transmission [ 5 ]. Propulsion system in an electric ship [ 5 ]. The current Park vector representation under ideal conditions. Sketch of the rotor of an induction machine: For planned papers, a title and short abstract about words can be sent to the Editorial Office for announcement on this website.
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Advancements in Electric Machines
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