FIELD OF THE INVENTION:

This invention relates to the development of a working model of wear testing set-up for grounding wire brushes used for turbomachinery related applications.
BACKGROUND OF THE INVENTION:
Rotating machinery components used in equipment such as turbines, compressors, etc. are inevitable in various sectors like power generation, chemical processing, fertilizer production, etc. These components are used for purposes such as transferring torque, compressing air or rotating magnetic poles for generating power. Such components are often placed in bearing housings due to their extremely high rotating angular velocities. Within each bearing housing, there is a thin layer of oil between the rotating component and the bearing pads in order to lubricate the bearing. Such lubrication is essential in order to maintain the rotational speeds as well as to prevent it from ceasing.
In many cases it was observed that the thrust pads of the bearings fail during normal operation without any process abnormalities. Upon examination of the thrust pads of the bearings, features such as welding spots, sparking damage, electric current erosion, frosting damage, fluting, spallation, babbit deterioration, pitting morphology on babbit, obtained during etc. Extensive analysis of the evidence many such failures concluded the main cause for this failure was due to electrical arcing between the rotating

component and the bearing parts such as babbit material, etc. Also similar failures were observed in bearing sleeves and seals.
Shaft currents are caused mainly due to the non-symmetry of the magnetic circuits in the equipment and is strongly dependant on the bearing clearance. They might also find their existence due to magnetic particle testing of components, etc. These shaft currents may be of electromagnetic nature which may be nullified by demagnetization or electrostatic nature which have to be grounded by a highly conducting grounding brush. Hence, the grounding brushes came into existence in order to prevent electrostatic damage by grounding these stray shaft currents, thereby, increasing the working life of both the shaft and the bearings.
Grounding brushes are made up of various materials with excellent electrical conductivity such as Cu-alloys, Graphite, Carbon Nano Tubes, etc. These brushes being extremely conductive are capable of grounding the stray currents. Actual usage life of the existing brushes or the brushes being developed using modified compositions has to be ascertained. This is possible either by employing a prototype model of rotor in the laboratory simulating the actual conditions at site or testing the newly designed brushes on actual components or by the current invention which enables 6 pairs of brushes to be tested at once using either AC or DC currents for each pair at 3 different circumferential speeds. Also, data collection for online monitoring is also possible using data acquisition module.

OBJECTS OF THE INVENTION:
The object of the present invention is to develop a working model for a novel equipment to do complete wear testing of the grounding wire brushes by combination of electrical and Mechanical wear mechanism principle.
Another object of the invention is to determine the condition of rotor being used for rotating machine through wear testing.
Further object of the invention is to employ a prototype model of a rotor simulating the actual conditions at site and testing newly designed brushes.
SUMMARY OF THE INVENTION:
A wear testing machine as working model is developed, which is capable of testing 6 pairs of brushes in simulated AC or DC working environment of the shafts used for turbomachinery applications at multiple speeds along with data logging capabilities for extracting data every second.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1: Schematic arrangement of Motor, Plummer and discs of Wear Test Machine.
Figure 2: Dimensions of Discs and distance between discs Arrangement.
Figure 3: Actual Working Wear Test Machine.
Figure 4: Circuit diagram for electric power supply panel for Alternating Current (A.C)

and Direct Current (D.C).
Figure 5: Actual Working electric panel with Display of A.C and D.C values.
Figure 6: Brush assembly actual in contact with Wear Test Machine and Electrical
Connections for infusing Current and Voltage measurement.
Figure 7: AC and DC Values infuser and data logger for measuring currents values.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION:
The wear testing machine mentioned in the above sections was developed for studying electric-mechanical wear testing as per the design detailed as follows. This machine consists of a shaft fixed on a mild steel plate/ stand with the help of 3 bearings and mild steel support. One end of the shaft is supported by a Plummer block bearing (2) unit and its protrusion outside consists of tier coupling to a 10 HP motor) which drive this shaft by transferring torque. This 3 phase motor (1) is also placed on the mild steel plate/ stand which in turn rests on a hard rubber sheet which is 10 mm thick in order to avoid vibrations and reduce audible noise. The other end of the shaft is also supported by a Plummer block bearing (2) unit while the centre of the shaft consists of a bush bearing unit (6). The bearings included in this study are all lubricated by grease applied through an opening provided in each of the bearing unit. The shaft also consists of 6 discs which form the basis for carrying out the electrical wear testing. All the above mentioned components are indicated in Figure 1. This whole equipment is assembled on a concrete block.

Each disc (7) is made up of highly insulating Hylam material. The purpose of using Hylam material is to insulate each disc independently to avoid current flow through all the discs of same value mounted on wear test machine. The periphery of each disc consists of a shrunk fit metallic disc made up of Rotor grade (1Cr1Mo0.25V steel).This material can beso chosen with reference to the actual material that the brush will be used on. This ensures that the electrical wear is tested precisely between the brush and the material it will be in actually be in contact with during service. There are 3 different diameters, i.e., 350 mm, 465 mm and 582 mm of the composite discs and two different discs of each diameter clamped onto the shaft at positions as shown in Figure 2. These different diameters are made essentially to test 3 different circumferential speeds simultaneously. Figure 3 gives a glimpse of the actual system. The angular velocity while testing these brushes is set to 3000 rpm with the help of a gear system connected to the motor (1).
The specialty of this invention is that the electrical wear testing can be done using either AC or DC current simultaneously for each disc. This is made possible with the help of another part of this equipment, i.e., an external electric panel which supplies AC or DC current simultaneously for each disc as per the requirement while testing. An Ammeter and Voltmeter are present to check the currents and voltages being supplied simultaneously. Electric panel circuit diagram is indicated in Figure 4 and actual electrical panel developed is shown in Figure 5 while testing. 0, 40, 80, 120V; AC/DC;

1mA-10mA @ 1mA for DC; 1A-10A @ 1A for AC.
The wear test brush holders (3 numbers) of each disc are located at 90o, 180o, 270o to the line connecting the disc centre to the base plate along the support structure. Each wear test brush holder is again insulated further to avoid grounding of current supplied to the brush. The brush so developed with a special design to apply constant force onto the brush which in turn applies onto the bristles thereby, generating a mechanical contact with the metallic circumference of the composite disc. A separate current inducing mechanism is utilized for introducing currents on the contact brushes. This holder consists of a Hylam flange which consists of slots for fixing the brush and also to insulate the brush assemble so that no electrical grounding takes place. The Hylam flange is attached to three threaded studs which go through the mild steel support frame. In between the Hylam flange and frame, there are springs provided for each stud which are compressed while fixing the other end of the stud coming out of the frame using a nut. This way the force applied onto the holder is uniform and continuous. Thus, when a brush is fixed to the holder, the above arrangement ensures that the brush is held perfectly such that the bristles experience continuous force thereby, ensuring mechanical and electrical contact and they are also bent as in the actual case. Actual brush holder assembly is indicated in Figure 6.
AC/DC monitor for data logging; VAR (Voltage Ampere Reactance) system was utilised for data logging capable of recording 50 measurements at a time per second.

Process: Placing 3 brushes at diametrically opposite ends and 1 diametrically opposite to the base and made to touch with the help of spring loaded brush; the wheels are made to rotate at 3000rpm using 10HP motor(1); simultaneously current and voltage are supplied through one of the brush and is collected on the other side of the brush; another brush is used as a reference to measure voltage difference on respective brushes which is simulated in the form of wear. The difference in voltage gives inference about the conductivity and metal contact of the brushes. This process is continued till runaway condition of brushes is reached, i.e., till brushes are worn out. By observing this runaway condition, bristle life is established. 6 discs with varying diameters are used for this machine to create varying surface speeds on the brushes and its effect is studied by using AC and DC currents in separate discs and voltages simultaneously to reduce the time span of experiments. This method is used to simulate a number of working conditions at one go. With the wear of the bristles, voltage values on corresponding brushes changes which helps us in establishing physical wear of the brushes. The voltage and current readings were collected using VAR system having a facility of taking 50000 readings. The collected data can be tabulated in graphical form to show clearly wear of the bristles. Mechanical wear of the bristles and contact with the disc is maintained using springs having spring property – for proper contact all the time till runaway condition is obtained. The size of the disc is so chosen to maintain circumferential speed ranges from 300-500 feet/s (surface speed) as is experienced in industrial condition at 3000rpm. A special mechanism is introduced to check the

temperature rise on the bristles in contact with the disc and its distribution through the bristle holder using temperature measurement system (non-contact method). This process is continued till the brushes reach runway condition (24h day). The test mechanism is so designed to carry out wear testing in dry or oil condition. Constant supply of current and voltages to the brushes at all times/ continuously (not pulsed).

WE CLAIM:
1. A model test set-up for wear testing of grounding brushes (8) comprising:
a) A motor (1)
b) Bearing (2)
c) Plummer block bearing unit (3)
d) Rotor material steel ring (4)
e) Base plate support (5)
f) Bush bearing unit (6)
g) Disc with Hylam flange (7)
wherein, steel rim (4) disposed over insulating hylam material for isolating current and
voltage to each individual disc;
a control panel configured to introduce variable current and voltage both AC and DC in
multiple of 0.5 A;
a monitoring device to monitor current and voltage on each disc and from each brush;
an instrument panel configured to measure variable current and voltages both AC and
DC in multiples of 0.5 A, and voltages also reading individual outputs for each pair of
brushes (8) being tested;
a VAR based data logging means for input voltage, input current, output voltage, output
current to register 50 recordings at a time;

The test set up as claimed in claim 1, wherein the brush (8) along with brush holder located at 90°, 180° and 270° to the line connecting the disc centre to the base plate, characterized to apply constant force on to the brush, which in turn applies to bristles thereby, generating a mechanical contact with metallic circumference of the composite disc.
The brush holder as claimed in claim 2, comprises of hylam flange having slots for fixing the brush and also to insulate the brush assembly to avoid electrical grounding wherein, the hylam flange is attached to three threaded studs; between the hylam flange and frame, springs provided to each stud, which are compressed while fixing the other end of the stud coming out of the frame using nut ensuring the force applied to the holder being uniform and continuous.
A method to carryout wear testing of grounding brushes (8) placing three brushes diametrically opposite ends and one diametrically opposite to the base and made to touch with the help of spring loaded brush; the wheels made to rotate at 3000 rpm, simultaneously current and voltage supplied through one of the brushes and collected on the other side of the brush; another brush used as a reference measuring voltage difference on respective brushes and simulated in the form of a wear; the difference in voltage gives inference about the conductivity and metal contact of the brush, wherein the method continued till runaway condition of the brushes to ascertain bristle life.

The method as claimed in claim 4, wherein 6 discs of varying diameters used to create varying surface speed on the brushes and the effects studied using AC/DC current in separate discs and voltages simultaneously reducing time of test and simulating number of working conditions.
The method as claimed in claim 4, wherein voltage and current reading collected in large numbers using VAR system and collected data are tabulated in graphical form to show early wear of the bristles.
The method as claimed in claim 4, wherein temperature rise on the bristles in contact with the disc and its distribution through the holder using non-contact method are recorded till the runaway condition of the bristles.


The method as claimed in claim 4, wherein the test mechanism is configured to carryout wear testing in dry or oil condition.