Latvian Maritime academy

MONITORING OF BEARING UNITS OF THE SHIPS
ELECTRICAL AC MACHINES ON THE BASIS OF
MAGNETIC INDUCTION IN AIR GAP
Aleksandrs Gasparjans
Latvian Maritime Academy, 5B Flotes Street, Riga, LV-1016, Latvia,
E-mail: aleksandrs.gasparjans@latja.lv, phone: +371 67161124
Aleksandrs Terebkovs
Latvian Maritime Academy, 5B Flotes Street, Riga, LV-1016, Latvia,
E-mail: aleksandrs.terebkovs@latja.lv, phone: +371 67161124
Anastasia Zhiravetska
Riga Technical University, Kronvalda 1, Riga, LV-1050, Latvia,
E-mail: zhiravecka@eef.rtu.lv, phone: +371 29682242
Abstract
The methods of the investigations of the bearing units of AC machines are analysed in the article. The
work proposes the method of monitoring of the bearing units according to the results of re-distribution of
magnetic induction in air gap of an AC machine. The three-dimension magnetic field in electrical
machine is described mathematically. All the calculations are made on the basis of three components of
magnetic induction. The three-dimension magnetic field in induction machine is analysed for the
symmetrical air gap and different level of shift of rotor axis (the defect of one of the bearings). The
proposed method allows on-the-run monitor of the bearing units of electrical machines without their
stopping, breaking of the technology process and without withdrawal. The data of the monitoring give a
possibility of prognoses of the residual life of the bearing units, transmit a part of sudden failures into the
category of gradual failures and determine the level of the necessary service.
Keywords: electrical machine, monitoring, bearing units, magnetic field, three-dimensional magnetic
induction
Introduction
The AC machines (induction motors and synchronous generators) are widely applied in industry and
maritime transport. They consume from 70 to 80% of all the consumed power. Approximately 20...25 %
of the failures of the industrial installations is the share of induction motors. Most of the failures are
caused with incorrect technical maintenance of the motors or its full absence. Up to 40% of all the
possible failures in turn are in the bearing units of IM. The current monitoring of the bearing units
technical condition of AC machines, especially induction motors, is economically justified and effective,
and timely identifies arising failures and transform them to the category of gradual failures [2, 3, 4, 5].
The most important sources of AC on board the ships are the synchronous generators. Those can be
a component of diesel-generators as well as can operate like shaft-generators. The number of diesel
generators on the vessels is usually 2-4 units. According to their power the synchronous generators can
have either both bearing units or only one back-side. In this case the bearing of the crankshaft of the
diesel is that of front-side of the synchronous generator.
The traditional methods of the units vibro-control are widely known. Alongside with the high
effectiveness of this method it also has a number of drawbacks. It is labour-intensive and requires a
special equipment and high qualified personnel. The defect of the bearing units cause harmonics and redistribution
of magnetic induction in air gap of the induction motor resulting in the deformation of the
spectral distribution of the consumed current. In the real machines except the basic harmonic there are a
lot of higher harmonics of magnetic field in the air gap [1, 3, 7]. The higher harmonics are traditionally
divided into temporal and space.
The temporal harmonics are defined with the voltage spectral distribution and non-linear changing
of the rotation torque on the machine shaft and frequency of its rotation. The space harmonics of the field
in the air gap are caused by the non-linear parameters of the machine and its constructive features. If the
power of motor is comparable with that of generator like in autonomous networks (e.g. ship power
installations) then non-sine field in the air gap will result in non-sine form of voltage across the terminals
of the machine so that the currents of the high harmonics are closed across the load. [2, 3, 7]. The basic
space harmonics are also tooth harmonics, MMF harmonics, those caused by the non-linear parameters of
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