FIELD OF INVENTION
The present invention generally relates to a mechanism for turbogenerator core
vibration monitoring. More particularly, the invention relates to a device for
monitoring of core vibration of turbogenerators adaptable to a vibration
monitoring system.
BACKGROUND OF INVENTION
A core of the turbogenerator constitutes the bed-rock of a generator. Many core-
related problems for example, fracturing or cracks in the stampings, slackness of
the wedges and/or, the bars in the slots, extraneous noise generation all such
problems are the genesis of excessive core-vibration. Such problems are
generally caused due to magnetic force generation at twice the operation
frequency i.e. 100/120 Hz in case of 2-pole generators and lead to deformation
of the core into the form of an ellipse. This magnetic force is proportional to the
square of flux density in the air gap.
In order to obtain a smooth operation, the generators are periodically scheduled
for maintenance and inspection. Generally, the core is accessible through the
manhole cover in most of the known generators.
The device(s) for vibration monitoring on core/core packets-directly or indirectly,
are known.

A disadvantage/limitation of the known device is that it employs optical-fibre
sensors with reflectors which is indirect measurement and may lead to inaccurate
measurement of the core vibration, while the subject device uses commonly
available piezoelectric sensors which can be directly installed on core packets.
Another disadvantage of the prior art device is that the installation of probes is
quite cumbersome. Although the optical probes can be installed more
conveniently during bar laying process of the manufacturing cycle, however,
installation of the probes in-situ at site is extremely difficult. Since the sensors
are disposed in a known device between a ripple spring and the wedge, the
known device is more suitable for vibrations monitoring of generator top bar slot
only.
A still another disadvantage of the prior art device is that it monitors the wedge
tightness through direct measurement of strain on the ripple spring. The wedge
tightness being subjective and may result in inaccurate strain levels.
Further disadvantage of the prior art device, is that the optical fibre-itself being a
fragile material, is difficult to handle.
SUMMARY OF THE INVENTION
According to the invention, the device utilizes the manholes of the
turbogenerator for core vibration monitoring. Thus, the device can be bolted to
the manhole casing provided on any/all desired manholes. Accordingly, the
device enables easy interfacing of any known vibration monitoring system to the
plurality of piezoelectric accelerometers along with their associated cables
disposed on core packets inside the casing, for continuous on-line core vibration

monitoring. The data thus generated can be utilized for localized fault finding
and maintenance thereon during shut down of the machine.
The inventive device comprises a steel plate, circular or oval shape, installed on a
matching manhole cover of the generator. The steel plate has central circular
opening where a flange is welded. The flange has a plurality of threaded blind
holes. On this flange, at least one multi-miniature connector lead-in-plate is
bolted. The multi miniature UNF connectors of 10-32 type are utilized for inside
and outside connections of the piezoelectric accelerometers through the lead-in-
plate. This forms a complete assembly of the device. The existing manhole cover
is then replaced with the inventive device which is bolted on to a desired
manhole. Further, the device is provided with a leak-proofing means for the
cooling medium i.e. hydrogen/air.
According to the invention, the known piezoelectric accelerometers can be
installed on desired core points (packets) axially as well as radially towards the
casing end by opening the manhole cover(s). The probes are then connected
with leads to the inner pins and the outer pins are correspondingly connected
through the external leads to the monitoring system.
The device is simple, user-friendly, easy to handle and can be installed in-situ
and used for on-line, continuous core vibration monitoring.
OBJECTS OF THE INVENTION
An object of the present invention is to propose an improved device for direct
monitoring of core packets of turbogenerators radially and axially adapting a
vibration monitoring system.

Another object of the invention is to propose an improved device for direct
monitoring of core packets of turbogenerators radially and axially adapting a
vibration monitoring system, in which the vibration monitoring system is
interfaced to the plurality of accelerometers disposed on the core packets.
A still another object of the invention is to propose an improved device for direct
monitoring of core packets of turbogenerators radially and axially adapting a
vibration monitoring system, which is enabled to provide direct connectivity of a
plurality of miniature 10-32 UNF connectors.
Yet another object of the invention is to propose an improved device for direct
monitoring of core packets of turbogenerators radially and axially adapting a
vibration monitoring system, which allows in-situ and easy mounting of the
plurality of accelerometers disposed on the core packets of the turbogenerator.
A further object of the invention is to propose an improved device for direct
monitoring of core packets of turbogenerators radially and axially adapting a
vibration monitoring system, which prevents leakage of cooling medium of the
turbo generator.
A still further object of the invention is to propose an improved device for direct
monitoring of core packets of turbogenerators radially and axially adapting a
vibration monitoring system, which remains fixed/bolted to the generator casing.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure - 1 shows a circular steel plate with a welded flange of the device
according to the invention.

Figure - 2 shows a circular lead-in-plate with multi-miniature connectors pins
according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION.
As shown in figure 1, the device comprises a circular steel plate-(l) which is
made-up of hard tempered mild steel. The shape and dimensions for example,
diameter, thickness etc. correspond to those of the existing manhole cover. On
its central opening, a steel flange (2) is welded which has a plurality of blind
threaded holes towards outer side of the casing for bolting a lead-in-plate (3) as
shown in figure 2. The lead-in-plate (3), has provision for inside and outside
connections of a plurality of multi-miniature connector pins (4).
The circular steel plate (1) has at least one O-ring (5) at its periphery to prevent
hydrogen/air leakage through the generator. A plurality of threaded holes (6) for
bolting to the casing as provided.
The lead-in-plate (3) is fabricated and machined as per figure 2. The number of
miniature connector pins (4) can be selected according to monitoring points. The
present device has 9-pins having 10-32 UNF threads cut. These are machined
from a rectangular block of silver rich copper alloy material. A hole is drilled
through out the length for inserting the central conductor. The miniature
connector pins (4) are fixed by using sintered glass material. Further, the central
conductor is fixed inside the pin (4) using a resin-hardner mix. The lead-in-plate
(3) further has a provision for at least one O-ring.....

to prevent the leakage of hydrogen/air. The lead-in-plate (3) is made to undergo
following tests before use :-
a) Insulation Resistance (IR) Test.
b) Leakage Test.
The IR value between the pins (4) and their central conductors, at Ik VDC, and
between the pins (4) and the steel body of the Lead-in-Plate (3) at 2Kv DC,
should be more than 100MO. For the leakage test, the Lead-in-Plate (1) shall be
able to withstand a nitrogen/helium pressure of 16 bar for a minimum period of
half an hour without any leakage.
After opening of the manhole covers, the accelerometers are directly
mounted/glued on designated core packets. This can be done at the
manufacturing phase or at site in stand still condition of the machine. The inside
cables are taken out through the flange (2) and connected to inside pins (4) of
the lead-in-plate (3). Thereupon, the lead-in-plate (3) is bolted to the circular
steel plate (1), which, in turn, is bolted to the casing. The internal accelerometer
leads are connected to inner ends of pins (4) and corresponding outer ends are
connected to vibration monitoring by the external leads/cables.

WE CLAIM
1. An improved device for directly connecting a plurality of piezoelectric
accelerometers to an external vibration monitoring system to monitor
core vibration in turbogenerator, the accelerometers being mountable
on the core-packets of the turbogenerator, the device comprising :
- a metallic circular plate (1), matching dimensionally with the existing
manhole covers, and having a flange (2) welded, providing routing of
probe cables from the core to the monitoring system through the
generator casing, and being releasably fixed on the casing via a set of
hexagonal bolts; and
- a metallic lead-in-plate (3) having a plurality of miniature connector
pins (4) to allow connections from inside/outside of the generator, and
being releasably fixed on the flange (2) via a set of alien bolts.
2. The device as claimed in claim 1, wherein the metallic plate (1) is
produced from hard tempered mild steel, and wherein the plate (1) is
configured to have a central opening.
3. The device as claimed in claim 1, wherein the metallic plate (1) is
formed of a material corresponding to that of the metallic lead-in-plate
(3).
4. The device as claimed in 1, wherein the plate (1) and the lead-in-plate
(3) are circular in shape.
5. The device as claimed in any of the preceding claims, wherein the
plurality of miniature connectors on the metallic lead-in-plate (3)
comprises 9-pins, and wherein the plurality of accelerometers
corresponds to a number equivalent or more than the number of
accelerometers a single manhole location.
6. The device as claimed in claim 1, comprising at least one groove
configured on the metallic plate (1) and the lead-in-plate (3) for
sealing by using at least one 'O' ring to prevent leakage of the cooling
medium.
7. An improved device for directly connecting a plurality of
accelerometers to an external vibration monitoring system as
substantially described and illustrated herein with reference to the
accompanying drawings.

The invention relates to an improved device for directly connecting a plurality of
piezoelectric accelerometers to an external vibration monitoring system to
monitor core vibration in turbogenerator, the accelerometers being mountable on
the core-packets of the turbogenerator, the device comprising a metallic circular
plate (1), matching dimensionally with the existing manhole covers, and having a
flange (2) welded, providing routing of probe cables from the core to the
monitoring system through the generator casing, and being releasably fixed on
the casing via a set of hexagonal bolts; and a metallic lead-in-plate (3) having a
plurality of miniature connector pins (4) to allow connections from inside/outside
of the generator, and being releasably fixed on the flange (2) via a set of Allen
bolts.