3.2 Experimental Setup
3.2.1 Machine Fault Simulator
The MFS (Make Spectra Quest, USA) simulates very closely the faults that come across on a variety of machines like in IM, shaft, bearings, gearbox and pumps. In order to acquire the data for different faulty machines, various transducers could be installed at particular locations in the MFS. The simulator provides a basic setup for performing experiments and learning signatures of different machine faults. The simulator is designed to be both versatile and easy to operate. In this work, the MFS is used to simulate faults in IMs.
The MFS is constructed with an IM (three phase, 0.373 kW (or 0.5 HP), 50 Hz, 2 pole, pre-wired self-aligning mounting system), a split bracket bearing housing, a sliding shaft, rotors with split collar ends, a flexible coupling, pulleys, a multiple belt tensioning, a variable frequency drive (VFD) with multi-featured front panel programmable controller, a magnetic brake attached with a
gear box, and a photovoltaic sensor; all of which are designed to be easily removed and replaced between various experiments. In the basic setup, an IM (test machines in our work) was connected to the shaft through a flexible coupling. The shaft was mounted on the bearings with the split bracket bearing housing. One pulley was attached at the end of the shaft and the other with the gearbox shaft. They were connected using a multiple belt tensioning mechanism. The gearbox mechanism connected the shaft with a magnetic brake. The magnetic clutch was used to apply mechanical load to the IM externally. A variable frequency AC drive was used to control the speed of the motor. A tachometer was mounted near the coupling to measure the mechanical speed of the shaft, which is required a constant DC power supply source to operate. The base plate of the simulator was attached with the vibration isolators and base stiffener. These all mechanisms were installed in such a way so that they could easily shift, removed and replaced for different experiments. The basic MFS setup is shown in Figure 3.3.
In order to acquire vibration and current signal from test IMs, a tri-axial accelerometer was installed on the top of the test motor near the motor shaft end and three AC current probes were clamped with the power leads of the motor which is easily accessible. The sensors were connected to the DAQ thorough proper instrumentation. A signal monitor with NI LabVIEW data acquisition software was used to analyze the data.
The technical specification of a number of components of the test rig is described in the Table 3.1.
The basic components of the MFS are described in details in this sections. The experimental procedures are discussed in Section 3.3.
Figure 3.3 The basic machine fault simulator (top view)
Table 3.1 Technical specification of the test rig components
No. Component name Technical specification of components Electrical components:
1 IMs Three-phase, 0.372 kW (or 0.5 HP), pre-wired self-aligning mounting system for easy installation and removal, number of rotor bar-34 and number of stator slot-24
2 Speed controller 0.7457 kW (or 1 HP) variable frequency AC drive with multi- featured front panel programmable controller
3 RPM range 0 to 10000 rpm (short duration) variable speed,
4 Voltage 115/230 VAC, single phase, 50 Hz
5 Tachometer Built-in tachometer with LCD display and one pulse per revolution analog output for DAQ purposes. Requires DC power supply unit (range:
30 V/2A)VFD
Shaft Belt-pulley drive Test-motor
Magnetic clutch Gear box Coupling Bearing
Table 3.1 Technical specification of the test rig components (continued) No. Component name Technical specification of components 6 Data acquisition
system
National instrument make NI PXI-8108 Core 2 Duo 2.53 GHz controller with NI PXI-4472, 8 channels, 24 bits, 102.4 kS/s sampling rate for accelerometer module
7 Current measurement Power leads accessible for current measurements Mechanical components:
1 Shaft diameter 19.05 mm diameter; turned, ground & polished (TGP) steel.
2 Bearings Two sealed rolling element in aluminum horizontally split bracket housing for easy replacement, tapped for transducer mount.
Bearing mounts can be mounted in five different positions for variable rotor span
3 Rotor base 360 mm long, completely movable using jack bolts for easy horizontal misalignments and standard shims for vertical misalignments. Pinned for easy realignment.
4 Belt mechanism Two double groove “V” belt with one set screw mounting and one bush/key mounting. Positive displacement lever with turnbuckle plus adjustable gearbox platform.
5 Gear box mechanism Accessible three-way straight cut bevel gearbox with 1.5:1 ratio (number of teeth on pinion-18, number of teeth on gear-27).
6 Torque controller A manually adjustable permanent magnet clutch, of range 0-0.565 N-m.
Table 3.1 Technical specification of the test rig components (continued) No. Component name Technical specification of components
7 Foundation 12.7 mm die cast aluminum base, base stiffener and eight rubber isolators
Measurement sensors:
1 Tri-axial accelerometer Sensitivity: 100.3 mV/g-x axis, 100.7 mV/g -y axis, 101.4 mV/g -z axis,
2 AC-current probe Frequency range: DC to 100 kHz (-3dB with current de-rating) Current range: 100 mV/A: 100 mA to 10 A peak, 10 mV/A: 1 to 100 A peak.
3.2.1.1 Speed Controller or Variable Frequency Drive
A speed controller or Delta Make variable frequency drive (VFD) is a type of motor controller that drives an IM by varying the frequency and voltage supplied to the IM. It is a power electronic based device which converts a basic fixed frequency, fixed voltage sine wave power (line power) to a variable frequency, variable output voltage used to control speed of IMs. It consists of a rectifier bridge converter, a direct current (DC) link, and an inverter. The VFD can simply turn up or turn down the motor speed as per the application’s motor speed requirement change. In this work, a variable frequency AC drive (0.746 kW, Input: 1-phase, 9.2A/3-phase, 5.1A, 200-240V, and 50/60Hz, Output: 3-phase, 4.2A, and 0-240V) was used. In this, the speed can be set with a knob in the range of 0-400 Hz. A VFD, which was used for the experimentation is as shown in Figure 3.4
3.2.1.2 Torque Controller or Magnetic Clutch
A torque controller or Precision Tork™ permanent magnet clutch unit was connected with the gear box mechanism to provide the precise torque adjustment of the IM. This type of controller does not require any external control or power source to operate, therefore their function is independent from power fluctuations. The torque was set with a large knurled adjustment ring. There is infinite adjustability between the minimum and maximum settings. This allows units to be fine-tuned to specific requirement. The torque can be set in the range of 0-0.565 N-m. This unit provides extremely consistent and smooth torque at the low as well as high speeds. Since the torque is transmitted magnetically, there is no friction from which to break away. This means that the static and dynamic torques are almost the same. A torque controller with the gear box mechanism, which was used for the experimentation is shown in Figure 3.5.
Figure 3.4 A variable frequency drive Figure 3.5 A magnetic clutch with a gearbox Magnetic
clutch Gearbox