|Title of Invention||
"A DEVICE FOR DETECTING BEARING INSULATION FAILURE IN LARGE ELECTRIC ROTATING MACHINES"
|Abstract||an electromagnetic transducer such as a split torroidal coil (1) placed around the rotor shaft (2) of the said electric rotating machine and secured to the frame or casing of the said electric rotating machine, an amplifier (3) connected between the output and input terminals of the said torroidal coil (1) having a resistance (4) connected between the said coil and the said amplifier (3) in parallel; the said amplifier (3) connected with the said coil (1) through a shielded cable (5), a filter (6) connected between output and input terminals of the said amplifier (3), a relay (7) connected to the said filter (6) for actuating an alarm for indicating bearing insulation failure in large electric rotating machines.|
|Full Text||This invention relates to a device for detecting bearing insulation failure in large electric rotating machines.
Voltage between the shaft ends is induced during the operation of the rotating electric machines due to disymmetries in the materials and geometry of the magnetic and electrical parts. Therefore the bearings of the big machines such as hydro generator, turbo generator are insulated by the insulated material. However, if the bearing insulation fails the shaft voltage causes shaft current to circulate through the bearing pedestal and other parts of the machines resulting into a serious idamage.
The shaft current is not similar to the currents flowing in
any externally excited circuits. A correct and unambiguous method of
monitoring this current is based on non-invasion method without
recourse to Use of potential differences in the current flowing path.
Further as it is not possible...
to calculate exactly the total impedance of the current path, Hence, a non-contact technique ie the only simple possibility to detect the bearing insulation failure.
A protection system is as such known in the art and is designed to Intercept faults as and when they occure. The protection system comprising a transducer to generate the signal of an impending fault tipically in the form of a voltage or current and is connected to a relay which is provided to switch off the machine. The protection system is designed to intercept faults as and when they occure so as to initiate such actions to ensure that the minimum of further damage occurence and to obviate the eventuality of a machine failure.
The main disadvantage associated with the known protection system is that it is designed to act only in the post-fault periode.
Therefore the main object of the present Invention is to provide a device which can detect the bearing insulation failure by monitoring rotor
shaft current of the machine.
Another object of the present invention is to provide a simple and effective device for condition monitoring of the rotor shaft current to prevent the bearing insulation failure by giving alarm at present shaft current value.
According to this invention, there is provided a device for detecting bearing insulation failure in large electric rotating machines, comprising: (a) an electromagnetic transducer such as a split torroidal coil placed around the rotor shaft of the said electric rotating machine and secured to the frame or casing of the said electric rotating machine; (b) an amplifier connected between the output and input terminals of the said torroidal coil having a resistance connected between the said coil and the said amplifier in parallel; the said amplifier connected with the said coil through a-shielded cable; (c) a filter connected between output and input terminals of the said amplifier; (d) a relay connected to the said filter for actuating an alarm for indicating bearing insulation failure in large electric rotating machines.
In accordance with this invention the said device has a transducer for example a toroidal coil adapted to be placed around the shaft opf a machine. The current flowing in the shaft induces an e.m.f across the terminals of the transducer. The transducer is retro-fitted around the shaft of the machine under surveillance and securely attached to the frame or casing of the machine. An amplifier is connected to the input and output
terminals of the coil having a resistance secured therewith in parallel between the coil and amplifier.
A filter is connected to the output and input
terminals of the amplifier such that to seperate
50/150 Hz components. Further a relay is connected to said amplifier for awitchlng on an alarm in case
of the bearing insulation failure.
A shaft current diagnostic device according to a preferred embodiment is herein described and
illustrated in the accompanying drawings wherein)
Fig.1 shows the plan view ot theddevlce. and
Fig.2 shows the flux lines produced
during the operation of the electric
Referring to the drawings particularly Fig.l the shaft current diagnostic device for detecting bearing insulation failure by monitoring the rotor shaft current of the machine, as a transducer preferably
an electro magnetic transducer such as a split
toroidal coil 1 which is placed around the rotor
shaft of a machine. The coil lis securely attached
to a frame or casing of the machine (not shown)/
and is provided to facilitate the determination of
line integral, H.ds in usual mathematical rotation
which gives the current in the enclosed loop of the
coil 1. An amplifier 3 is connected between the
terminals output and input/of the toroidal coil 1 having a
resistance 4 connected between the coil 1 and the
amplifier 3 in parallel and for measuring the current
producing in the toroidal coil 1. The amplifier 3
is connected with coil 1 through a shielded cable 5.
A filter 6 is connected between the output and
input terminals of the amplifier 3 for seperating
the components of 50/150HZ. A relay 7 is connected to
the filter 6 for actuating an alarm (not shown),
in case the bearing insulation is failed. The
toroidal coil consists of the wire wound arounded former,
the former is circular and axis of the former
correspondence in flow of the current which is to
be major. The current induces flux tubes concentrate
with a current, if the former is a flow magnetism
reluctance, the magnetic flux flowing along the
circular axle of the former lnturn Induce a electro vire source in the coil 1 of the transducer. The e.m.f induce is a major of the current.
Reference is now made to fig.2 the shaft current is generated along the generator shaft 1 and frame by magnetic asymmetric in the generator core 8 . The rotating magnetic field leaves the rotor from the north pole, crosses the air gap into the core & splits into 2 flux paths 9 & 10 at the right andleft sides. The fluxes 9 & 10 are circumferential and each cover 180* around the core 8, an opposite directons to rejoin and enter
the south pole of the rotor 2. The The two counter semi -circular magnetic fields within the machine core symmetrically surround the shaft of the rotor. If the machine core are magnetically perfectly uniform and if the core contains no defect or irregularities, the two magnetic fields would be equal in magnitude and opposite in direction as they rotate with the rotor shaft. No net magnetic (lux would adjust around a closed circular path within the machine core and surrounding the shaft of the rotor. No corresponding voltage wouldtherefore be induced along the rotor shaft.
Whan the toroidal coil 1 enclosea a structure carrying tha circulating currant or the
shaft 2 of a rotating machine,the signal induced
in tha search coil?1 ia proportional to the enclosed
current. In such a coil 1, the changing magnetic
induction causes an e.m.f proportional to the rate
of change of flux threading tha coil. A measure of
the linking flux can be obtained by monitoring the
coil output voltage which ia a direct measure of tha
shaft current. In practice/ it is desirable that
this voltage be large enough to be monitored
easily and accurately, which is achieved here by
uaing electronic amplification.
In addition to ahaft current component**, both current frequency and magnitude are measured
using an FFT (Fast Fourier Transform- ) spectrum analyzer
A filter circuit is introduced which separates
5O/150Hz components. If actuates a microprocessor
relay to give an alarm when the ahaft current exeeds
the present: value and enables the machine to be
tripped, if necessary.
On-line monitoring of shaft current signal spectra, starting from the test bed, and establishment of correlation over a period of time during its
operation makes this device an electromagnetic
diagnostic tool for monitoring the health of large
rotating electrical machines. A reference spectrum
of the shaft current signal is to be obtained from
the machine under surveillance when there is a
reasonable degree of certainty that the equipment is
in a good condition. Subsequent spectra are then
compared with the reference signal/ and if marked
differences e;ist, it implies that something within
the machine has altered. The nature of the change can
Thus the condition monitoring provides advance
warning to the operating staff and thus permits
scheduling outages in the most convenient manner,
resulting in lower downtime and lower capitalised losses.
1. A device for detecting bearing insulation failure in large electric
rotating machines, comprising:
(a) an electromagnetic transducer such as a split torroidal coil (1) placed around the rotor shaft (2) of the said electric rotating machine and secured to the frame or casing of the said electric rotating machine,
(b) an amplifier (3) connected between the output and input terminals of the said _ torroidal coil (1) having a resistance (4) connected between thesaid coil and the said amplifier (3) in parallel; the said amplifier (3) connected with the said coil (1) through a shielded cable (5),
(c) a filter (6) connected between output and input terminals of the said amplifier (3),
(d) a relay. (7) connected to the said filter (6) for actuating an alarm for indicating bearing insulation failure in large electric rotating machines.
2. A device for detecting bearing insulation failures in large electric
rotating machines substantially as herein described and
|Indian Patent Application Number||579/DEL/1995|
|PG Journal Number||44/2004|
|Date of Filing||30-Mar-1995|
|Name of Patentee||BHARAT HEAVY ELECTRICALS LIMITED|
|Applicant Address||BHEEL HOUSE SIRI FORT, NEW DELHI-110 049|
|PCT International Classification Number||G01R 31/02|
|PCT International Application Number||N/A|
|PCT International Filing date|