FIELD OF INVENTION:
This invention pertains to the Shaft Current Monitoring System (SCM) for large
Hydro generators and large motors. More particularly, the invention relates to a
method of implementing the monitoring device that will continuously compute
fundamental and third harmonic component of shaft leakage current and issue
an alarm and trip signals whenever the leakage current exceeds the alarm and
trip set values in addition to displaying them. This implemented device also has
the capability to view the trend of shaft current over a period and it can
communicate over MODBUS master device to send the values of shaft current
time to time to SCADA.
BACKGROUND OF THE INVENTION AND PRIOR ART:
Shaft Current Monitoring System (SCM) is an important and very essential
condition monitoring device for large rotating machinery such as hydro
generators, large motors, and pumps which provides an early indication or
warning against the stray currents or ground leakage currents that are generated
due to machine dissymmetry.
The operating principle of shaft current monitoring device starts with the
measurement of fundamental and third harmonic component of shaft current
using moving window based discrete Fourier transform obtained from output of
toroidal Current transformer. The trend of this measured shaft current will be
utilized to issue alarm and trip signals to the respective protection device
avoiding the possible failure and forced shutdown.
Provision has been implemented to communicate to other devices over MODBUS
serial (RS-485) and MODBUS TCP/IP [203]. It can also communicate to station
SCADA in the form of 4-20 mA signal to transfer the shaft current values to
SCADA [203]. It is enabled with the feature of viewing the trend plots of shaft
current over a period of time graphically along with continuous viewing of shaft
current parameters and protection status signals in the form of interactive
graphical user interface.

Few related examples can be found in the earlier patents mentioned below:
CA2380280A1 - SHAFT VOLTAGE AND CURRENT MONITORING SYSTEM:
A rotating machinery monitor provides a warning that is indicative of a
developing problem with the rotating machinery. The rotating machinery monitor
has at least one current sensor for detecting shaft grounding current in the
rotating machinery, at least one voltage sensor for detecting shaft voltage in the
rotating machinery, a change detector for determining rate of change in the shaft
grounding current and a change detector for determining rate of change in the
shaft voltage, and an evaluation system for producing a warning as a function of
the change in the shaft grounding current, the rate of change in the shaft voltage,
the shaft grounding current and the shaft voltage.
CN103846735A – SYSTEM FOR MONITORING SHAFT CURRENT:
The invention relates to a system for monitoring a shaft current. When a machine
tool is in the drilling technique of work pieces, a device for clamping the work
pieces is arranged on a rotary shaft; after the work pieces are fixed, holes are
processed by rotating the rotary shaft; when the rotary shaft is rotated, the
rotating speed thereof is very quick, so shaft current is generated; most of
components on the machine tool are made of metal, they are easily conductive
and very dangerous, so the shaft current need be neutralized; because the shaft
current of the rotary shaft is not determined in operation, the shaft current
cannot be accurately measured and totally neutralized, the system has great
potential risks. The system for monitoring shaft current comprises a CPU and a
power supply, wherein a current sensor is arranged in the monitoring system.
The operator can randomly neutralize the shaft current according to information
on the displayer at any time, and thus the machine tool processing is safer.
US7337613B2 – METHOD FOR MONITORING AND CONTROLLING STEAM
TURBINE SYSTEM PH USING SHAFT CURRENT
The invention involves a system for controlling the electric charge within the
exhaust hood and condenser of a steam turbine by using shaft current as an

indirect measurement of exhaust charge, and then adjusting the pH accordingly.
The present invention uses the turbine-generator shaft instead of a probe, and
therefore measures the potential of the current in the shaft to the ground. This
measurement is then fed into a control unit which adjusts the chemical feed to
the feed water supply of the steam turbine system.
OBJECTS AND SUMMARY OF THE INVENTION:
One or more drawbacks of conventional systems and process for a method for
improving yield strength of a workpiece and an apparatus are overcome, and
additional advantages are provided through the apparatus and a method as
claimed in the present disclosure. Additional features and advantages are
realized through the technicalities of the present disclosure. Other embodiments
and aspects of the disclosure are described in detail herein and are part of the
claimed disclosure.
The foregoing summary is illustrative only and is not intended to be in any way
limiting. In addition to the illustrative aspects, embodiments, and features
described above, further aspects embodiments, and features will become
apparent by reference to the drawings and the following detailed description.
The main object of the invention is the interfacing of shaft current monitoring
system including hardware and software with the toroidal current transformer
which will sense the shaft leakage current and to monitor the shaft leakage
current and protect the shaft from excessive leakage currents generated in rotor
shaft.
The other objective of the invention is the hardware architecture of the
monitoring system that contains base board [106] which serves the purpose of
analog signal acquisition, signal conditioning, filtering, sending analog signal out
[103], relay driver circuit, [104] LED indication circuit [104], and serial and
TCP/IP communication interface {105, 107].

The hardware also contains processor module [102] that will receive the filtered
shaft current and process it. SBC also have digital output ports that will trigger
the relay driving circuit [202] depending on the condition of the shaft current
magnitude, serial communication ports (RS-232, RS-485) that will be utilized for
the front-end display communication and MODBUS serial communication
respectively [203]. It also contains TCP/IP communication port utilized for the
MODBUS TCP/IP communication.
The hardware also contains power supply module [110,111] for 24V DC input to
base board. The hardware also contains interactive front-end display module
[206] for continuous monitoring of the computed values from the software
module. The hardware also contains enclosure that will accommodate the base
board, processor board, front end LED panel, back plate field signal interface,
power supply, and front-end display module.
The other objective of the invention is the software design developed in dynamic
C environment for computation of fundamental and third harmonic components
of measured shaft current, frequency computation, continuous data exchange
to the front end display device over serial port (RS-232), continuous data
exchange over MODBUS Serial (RS-485) and MODBUS TCP/IP, algorithm of over
current protection for alarm and trip indication of shaft leakage current
measured, provision to set the reference values of alarm and trip from front end,
provision to set processor RTC time, provision to calibrate remotely the measured
shaft leakage current, provision to plot the trend of shaft current in the given
interval of time specified from front end display device. Software also contains
front end display developed in visual studio-based programming environment
suitable to the front-end display device.
The main objective of the invention is hardware architecture that contains base
board that connects to processor board [106] and its arrangement in the device,
power supply module and its arrangement in the device, front end display device
and its arrangement in the device, field connector arrangement, and enclosure
arrangement containing all the components mentioned here in this claim.

The other objective of the invention is design of the software module in dynamic
C for signal conditioning, protection function implementation, bi-directional data
transfer to front end display device, and MODBUS communication over serial
(RS-485) and TCP/IP, and development of interactive front end graphical user
interface developed in visual studio C# environment for continuous data
exchange, changing protection settings and to set the other calibration settings
between processor module and display device.
Various objects, features, aspects, and advantages of the inventive subject
matter will become more apparent from the following detailed description of
preferred embodiments, along with the accompanying drawing figures in which
like numerals represent like components.
It is to be understood that the aspects and embodiments of the disclosure
described above may be used in any combination with each other. Several of
the aspects and 10 embodiments may be combined to form a further
embodiment of the disclosure.
The foregoing summary is illustrative only and is not intended to be in any way
limiting. In addition to the illustrative aspects, embodiments, and features
described above, further aspects, embodiments, and features will become
apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
It is to be noted, however, that the appended drawings illustrate only typical
embodiments of the present subject matter and are therefore not to be
considered for limiting of its scope, for the invention may admit to other equally
effective embodiments. The detailed description is described with reference to
the accompanying figures. In the figures, the left-most digit(s) of a reference
number identifies the figure in which the reference number first appears. The
same numbers are used throughout the figures to reference like features and
components. Some embodiments of system or methods in accordance with

embodiments of the present subject matter are now described, by way of
example, and with reference to the accompanying figures, in which
Fig 1 shows the general card arrangement of the various cards in the enclosure
cabinet and their arrangement.
Fig 2 shows general arrangement of Graphical terminal and field connectors in
the enclosure along with front end graphical user interface.
The figures depict embodiments of the present subject matter for the purposes
of illustration only. A person skilled in the art will easily recognize from the
following description that alternative embodiments of the structures and
methods illustrated herein may be employed without departing from the
principles of the disclosure described herein.
DETAILED DESCRIPTION OF THE INVENTION:
It should be noted that the description and figures merely illustrate the
principles of the present subject matter. It should be appreciated by those skilled
in the art that conception and specific embodiment disclosed may be readily
utilized as a basis for modifying or designing other structures for carrying out
the same purposes of the present subject matter. It should also be appreciated
by those skilled in the art that by devising various arrangements that, although
not explicitly described or shown herein, embody the principles of the present
subject matter and are included within its spirit and scope. Furthermore, all
examples recited herein are principally intended expressly to be for pedagogical
purposes to aid the reader in understanding the principles of the present subject
matter and the concepts contributed by the inventor(s) to furthering the art and
are to be construed as being without limitation to such specifically recited
examples and conditions. The novel features which are believed to be
characteristic of the present subject matter, both as to its organization and
method of operation, together with further objects and advantages will be better
understood from the following description when considered in connection with
the accompanying figures.

As used in the description herein and throughout the claims that follow, the
meaning of “a”, “an” and “the” includes plural reference unless &e context clearly
dictates otherwise. Also, as used in the description herein, the meaning of “in”'
includes “in” and “on” unless the context clearly dictates otherwise.
The terms "comprises", “comprising”, or any other variations thereof used in the
disclosure, are intended to cover a non-exclusive inclusion, such that a device,
system, assembly that comprises a list of components does not include only
those components but may include other components not expressly listed or
inherent to such system, or assembly, or device. In other words, one or more
elements in a system or device proceeded by “comprises... a” does not, without
more constraints, preclude the existence of other elements or additional
elements in the system, apparatus or device.
These and other advantages of the present subject matter would be described in
greater detail with reference to the following figures. It should be noted that the
description merely illustrates the principles of the present subject matter. It will
thus be appreciated that those skilled in the art will be able to devise various
arrangements that, although not explicitly described herein, embody the
principles of the present subject matter and are included within its scope.
Shaft current monitoring system designed using an enclosure which is being
powered by single phase 230V 50 Hz AC power supply. The base board module
is designed for the analog signal acquisition, conditioning and filtering of the
acquired analog signal, to send analog output in the form of 4-20 mA to SCADA,
driving the digital outputs through relay driver circuit for alarm and trip
contacts, driver circuit for LED indication, to communicate over RS-232 from
processor to front end display unit, and to transfer data over MODBUS serial
(RS-485) and MODBUS TCP/IP. All these functionalities are controlled and
coordinated by processor module sitting on top of the base board. Shaft current
measured using toroidal CT is the input from the field which will be conditioned
and filtered and finally sent to processor module for computation and protection
operation.

The placement of base board along with processor board and power supply inside
the enclosure is shown in Fig1. The arrangement of graphical terminal, field
interface connectors and communication ports arrangement are shown in Fig 2.
Base board and processor module are powered by 24V DC which is derived by
230V AC 50 Hz Power supply. Field supply is provided by rear side of the rack.
The detailed functionalities of base board are explained in detail as follows.
1. The analog inputs from the field such as shaft current/ shaft voltage are
being band limited and amplitude scaled before being given to processor
module for digitization.
2. Interface circuit that will route the digital output signals from processor
module to the relay driving circuit and setting alarm and trip contacts.
3. Power conditioning circuit which will convert 24V DC to +/- 15V DC for
internal analog circuit.
4. Analog output circuit that will give 4-20 mA output to the SCADA.
5. LED driving circuit to drive digital outputs from processor to front panel
LED display.
6. Arrangement of Interface connectors for analog, digital and serial
communication from processor to base board.
7. Arrangement of filed communication ports for TCP/IP and Serial (RS485)
communication and RS232 serial communication from base board to
display unit.
Application code is developed in C language in Dynamic C environment. The
hardware interrupt-based timer implemented in the software module provides
greater timing accuracy. The total application is divided into multiple functions
which will be called repetitively at fixed interval utilizing the timer functionality.
Algorithms have been developed for Analog Data acquisition, Measurement of
fundamental and harmonics, computation of base frequency, Sequence of
Events (SOE) recording, Alarms and fault recording with time stamp and Data

transfer over MODBUS serial and TCP/IP protocols. The various functional
modules and their responsibilities are:
Measurement and protection module:
This module will perform the following functionalities.
1. Capturing the digitized signal from the output of the ADCs present on the
processor and compute the RMS value fundamental and third harmonic
component.
2. Computation of Base frequency of the field captured analog signal.
3. Perform over current operation based on the alarm and trip levels set by
the operator from front end graphical user interface.
4. Generate alarm event and fault recording with time stamp.
Metering:
This module will perform the following functionalities.
1. Continuous data transfer to front end graphical user interface over serial
port RS232.
2. Receive protection, calibration, and date time settings of processor clock
from front end display unit to the processor.
3. Send events and fault recordings with time stamp from processor to front
end display.
4. Send data over MODBUS serial (RS485) and MODBUS TCP/IP.
When Shaft current monitoring device is powered ON, the application software
loads the protection settings file and calibration settings file which are used by
the protection and calibration functions in the software module.
An interactive Front-End Graphical User Interface provides the following features
1. Download protection settings to processor to perform protection operation
against measured shaft current/shaft voltage.

2. Download calibration settings to the processor to calibrate measurement
device against base board analog data acquisition circuit.
3. Download date and time settings to set the processor date and time for the
first time and whenever required by the user required to set the same.
4. Metering page to continuously monitor and update the shaft
current/shaft voltage parameters such as fundamental and third
harmonic component, base frequency, peak value of shaft current/shaft
voltage, maximum value and minimum value of shaft current/shaft
voltage.
5. Soft acknowledge button on the metering page allow the operator to
acknowledge the alarm and trip indications.
6. Trend plotting of shaft current/shaft Voltage
Each of the appended claims defines a separate invention, which for
infringement purposes is “reorganized as including equivalents to the various
elements or limitations specified in the claims. Depending on the context, all
references below to the “invention” may in some cases refer to certain specific
embodiments only. In other cases, it will be recognized that references to the
“invention” will refer 1o subject matter recited in one or more, but not necessarily
all, of the claims.
Groupings of alterative elements or embodiments of the invention disclosed
herein are not to be construed as limitations. Each group member can be referred
to and claimed individually or in any combination with other members of the
group or other elements found herein. One or more members of a group can be
included in, or deleted form, a group for reasons of convenience and/or
patentability. When any such inclusion or deletion occurs, the specification is
herein deemed to contain the group as modified thus fulfilling the written
description of all groups used in the appended claims.
With respect to the use of substantially plural and/or singular terms herein,
those having skill in the art can translate form the plural to the singular and/or

from the singular to the plural as is appropriate to the context and/or
application. The various singular/plural permutations may be expressly set forth
herein for sake of clarity.
It still be understood by takes within the art that in general, terms used herein,
and especially in the appended claims (e.g, bodies of the appended claims) are
generally intended as “open” terms (eg, the term “including” should be
interpreted as “including but not limited to,” the term “having” should be
interpreted as “having at least”, the term “includes” should be interpreted as
“includes but is not limited to” etc.)- It will be further understood by those within
the art that if a specific number of an introduced claim recitation is intended,
such an intent will be explicitly recited in the claim, and in the absence of such
recitation no such intent is present. For example, as an aid to understanding,
the following appended claim may contain usage of the introductory phrases “at
least one” and “one or more” to introduce claims recitations. However, the use of
such phrases should not be construed to imply that the introduction of a claim
recitation by the indefinite articles “a” or “an” limits any particular claim
containing such introduced claim recitation to inventions containing only one
such recitation, even when the same claims includes the introductory phrases
“one or more” or “at least one” and indefinite articles such a “a” or “an” (e.g, “a”
and/or “an” should typically be interpreted to mean “at least one” or “one or
more”); the same holds true for the use of definite article used to introduce claim
recitations. In addition, even if a specific number of an introduced claim
recitation is explicitly recited, those skilled in the art will recognize that such
recitation should typically be interpreted to mean at least the recited number
(e.g the bare recitation of “two recitation,” without other modifiers, typically mean
at least two recitations, or two or more recitations). Furthermore, in those
instances where a convention analogous to “at least one of the A, B and C, etc.”
is used, in general such a construction is intended in the sense one having skill
in the art would understand the convention (eg. “a system having at least one A,
B and C etc. would include but not be limited to systems that have A alone, B
alone, C alone, A and B together, A and C together, B and C together, and/or A,

B and C together etc.). In those instances , where a convention analogous to “at
least one of A, B, or C, etc.” is used, in general such a construction is intended
in the sense one having skill in the art would understand the convention (e.g.,
“a system having at least one of A, B or C” would include but not be limited to
systems that have A alone, B alone, C alone, A and B together, A and C together,
B and C together and/or A, B and C together etc.). It will be further understood
by those within the art that virtually any disjunctive word and/or phrase
presenting two or more alternative terms, whether in the description, claims, or
drawings, should be understood to contemplate the possibilities of including one
of the terms, either of the terms or both terms. For example, the phrase “A or B”
will be understood to include the possibilities of “A” or “B” or “A and B”.
The above description do not provide specific details of manufacture or design of
the various components. Those of skill in the art are familiar with such details,
and unless departures from those techniques are set out, techniques, known
related art or later developed deigns and materials should be employed. Those
in the art are capable of choosing suitable manufacturing and design details.
The technology used herein is for the expose of describing particular
embodiments only and is not intended to be limiting of the present disclosure. It
will be appreciated that several of the above-disclosed and other features and
functions, or alternative thereof, may be combined into other systems or
application. Various presently unforeseen or unanticipated alternatives,
modification, variation, or improvements therein.

WE CLAIM:
1. A shaft current monitoring system for electrical machines in which base
board (106) along with processor board is provided that comprises:
- analog input and output interface circuit;
- digital output interface circuit;
- at least a communication port;
- the power conditioning circuit to provide different DC voltages required
for the analog to digital conversion circuit;
- analog filtering circuit to filter out noise and other higher order
harmonic signals from the shaft leakage current and shaft voltage;
wherein the processor board and base board are interfaced to obtain the
output signal from a processor module and coupled to a relay circuit to
determine an event of fault and generate an alarm.
2. The system as claimed in claim 1, comprising of a protection module to
obtain the output signal and compute the parameters to determine an
event of fault.
3. The system as claimed in claim 1, comprising of a metering module for
continuous transfer of data to a front-end graphical user interface, and to
send Sequence of Events (SOE) recording, Alarms and fault recording with
time stamp over MODBUS serial and TCP/IP protocols.
4. The system as claimed in claim 1 and 3, wherein it provides metering and
display of shaft current and voltage.

5. A shaft current monitoring system for electrical machines in which base
board (106) along with processor board, as substantially described and
illustrated herein with reference to the accompanying drawings.