4.3 Pump Applications
4.3.2 FMEA on the System Components
Each of the components identified in the previous section, see Table 4.3, is in this section described with respect to the functionality of the components, the faults in the compo-nents, and the disturbing events affecting the components. Here a fault denotes an event causing malfunction of a given component, and therefore should be detected. Whereas a disturbing event is an event affecting the component, but should not be detected. The faults and disturbing events, and their effects on each component are analysed using the FMEA. The full result of this analysis is presented in Appendix A, whereas only the faults and disturbing events are presented in this section. Beside the faults, disturbing
Electrical and mechanical part of the motor.
Hydraulic and mechanical part of the pump
The shaft
One of the impellers and guide vanes
Inlet part
Outlet part
Figure 4.8: A real pump example of the component chosen for the FMEA. The pump is a CR5-10 Grundfos pump drived by a 1.5 [KW] induction motor.
events, and their effects on the components, the propagation matrices are presented in Appendix A.
c1: Electrical part of the induction motor
This component contains the electrical parts of the induction motor driving the centrifu-gal pump. This includes the grid connections, the stator windings, and the rotor bars.
This component converts electrical energy from the grid to mechanical energy on the shaft of the pump. The faults identified in the component are,
fem1 Loss of one or more phases of the supply voltage.
fem3 Short circuit between windings in the motor.
Electrical part of the motor
Outlet of the pump Sup. voltage
Load torque
Inlet flow
press. diff.
Vib.
Inlet flow
Temp.
Motor torque Mech.
dynamics Shaft
Motor speed
Imp. speed
Hyd. part of the pump Mech. part
of the motor
Mech. part of the pump
Vib.
Current
Temp.
Temp.
leakage flow
Vib.
Inlet of the pump
Impeller eye pres.
Pressure drop at the inlet Inlet pressure
Outlet flow Vib.
Impeller head
Pressure difference
1 2
3
4
7
5
6
8
9
Figure 4.9: The functional connection between the components used in the FMEA of the pump system.
Table 4.3: Description if the components in the centrifugal pump.
Comp. Name
c1 Electrical part of the induction motor c2 Mechanical dynamics
c3 Mechanical part of the induction motor c4 Shaft
c5 Hydraulic part of the centrifugal pump c6 Mechanical part of the centrifugal pump c7 Inlet part of the pump
c8 Outlet part of the pump c9 Pressure difference
fem4 Short circuit to ground.
fem5 Broken rotor bar.
fem6 Eccentric air gab due to bend or misaligned motor shaft.
The main effects of all these faults are higher harminics oscillations in the motor current and torque respectively.
Beside the faults described above the following set of disturbing events can affect the component.
dem1 Unbalanced supply voltage.
dem2 Increased supply voltage.
dem3 Decreased supply voltage.
dem4 Increased supply frequency with constant V/f relationship.
dem5 Decreased supply frequency with constant V/f relationship.
c2: Mechanical dynamics
This component contains the mass of all rotating parts in the pump. It is introduced in the functional model to cover the convertion from torque to speed. As it is not a physical component, but a functional signal transformation, no faults are identified in the component.
c3: Mechanical part of the induction motor
This component contains the ball bearings and the shaft of the motor. The functionality of the component is to transfer torque produced by the electrical part of the motor to the shaft connecting the centrifugal pump and the motor. The faults identified on the component are:
fmm1 Ware of the bearings in the motor.
fmm2 Rub impact between the stator and the rotor due to a bend or misaligned motor shaft.
The main effect of these faults is vibrations in the mechanical structure of the motor, beside that small torque oscillation can occur.
c4: Shaft mechanics
This component contains the shaft and the shaft connection attaching the motor and pump shaft. The functionality of the component is to transfer the torque on the motor shaft to torque on the pump shaft. The faults identified on the component are,
fsh1 Broken shaft.
fsh2 Misalignment between the motor and pump.
fsh3Bend shaft.
The main effect of these faults are mechanical vibrations and, in the case of the last two faults, torque oscillations.
c5: Hydraulics of the centrifugal pump
This component contains the impeller, the diffuser, the volute, and the guide vanes of the centrifugal pump. The component converts mechanical energy from the shaft to hydraulic energy induced into the liquid pumped by the pump. The faults identified in the component are the following,
fi1 Dry running.
fi2 Impurities fixed on the impeller, causing inbalance.
fi3 Wear of the impeller.
fi4 Blocked or partial blocked flow field inside the impeller.
fi5 Blocked impeller rotation.
fi6 Wear of the sealing ring.
fi7 Missing sealing ring.
fi8 Loss of the impeller.
The main effects of these faults are changes in the value of pressure and the load torque generated by the impeller at a given flow. Moreover some of the faults can induce pres-sure oscillations. These prespres-sure oscillations can be either harmonics of the rotational frequency, or noise like signals covering a larger frequency span.
Beside the faults described above the following set of disturbing events can affect the component.
di1 Decreased flow through the pump.
di2 Increased flow through the pump.
c6: Mechanical part of the pump
This component contains those mechanical parts of the pump not directly involved in the energy transformation from mechanical to hydraulic energy (the parts involved in the energy transformation are contained in componentc5, hydraulics of the centrifugal pump). This means that parts such as the shaft of the pump, bearings inside the pump, and the casing are included in this component. The functionality of the component is to secure the hydraulic parts in the right possition, and to lead the liquid to and from the hydraulic part of the pump. The faults identified in the component are the following:
fmp1 Dry running.
fmp2 Inlet flow equal to zero.
fmp3 Ware of the bearings in the pump.
fmp4 Ware of seals.
fmp5 Rub impact between the impeller and the cassing.
The first two of these faults are connected to the cooling of the pump, and therefore the main effect of these faults is an increased temperature of the pump. The main effects of the last four faults are mechanical vibrations and leakages from the pump casing.
Beside the faults described above the following set of disturbing events can affect the component.
dmp1 Decreased flow through the pump.
dmp2 Increased flow through the pump.
c7: Inlet of the pump
This component includes the inlet parts of the pump, which can contain a suction pipe and/or a filter. The functionality of the component is to lead the liquid to the impeller.
The faults identified in the part are the following, fip2 Low pressure at the inlet of the pump.
fip3 Opstruction of the inlet of the pump.
The main effect of these faults is that the inlet pressure to the impeller becomes too low.
Beside the faults described above the following set of disturbing events can affect the component.
dip1 Decreased flow through the pump.
dip2 Increased flow through the pump.
dip3 High frequency pressure oscillations.
c8: Outlet of the pump
This component includes the outlet part of the pump, which can contain an outlet pipe or a riser pipe. The length of this pipe is defined by the two points where the pressure difference generated by the pump is measured. The component is leading the liquid from the pump to a given distination. The faults identified in this component are:
fop2 Leakage on the outlet pipe.
fop3 Opstruction of the outlet pipe.
The main effects of these faults are leakages from the system and decreased pressure produced by the pump.
Beside the faults described above the following set of disturbing events can affect the component.
dip1 Decreased flow through the pump.
dip2 Increased flow through the pump.
c9: Generated differential pressure
This component is not a physical component, but a collection of the pressure effects affecting the pressure difference across the pump. The component is necessary in the functional model as the effects on the pressure difference is a function of head losses in the inlet and the outlet components and the hydraulics of the centrifugal pump.
Sensor components
This work is not concerned with sensor faults, even though it is an important field.
Instead sensors are seen as components, which are able to measure special effects on the system. Hence, they collect the end-effects used in the sensor analysis.
The list of possible sensors is long, some of the most important, with respect to the centrifugal pump applications, are the following,
• Current sensors.
• Voltage sensors.
• Vibration sensors on the stator and/or the pump mechanics.
• Pressure difference sensor (between outlet and inlet).
• Absolute pressure sensor at the inlet and/or the outlet of the pump.
• Flow sensor at the inlet and/or the outlet of the pump.
• Temperature sensors inside the stator, bearings and/or seals.
• Speed sensors, on the motor and/or the pump shaft.
Of these especially the pressure difference sensor is often used for control purposes.
Likewise, if the speed of the motor is controlable normally expressions of the currents and the voltages of the motor are also available. If the system is equipped with a surveil-lance system, a subset of all the sensor information can be available. Unfortunately, this is only the case in very few centrifugal pump applications.