Malfunctions of electric motors and their elimination. The main types of malfunctions in electric motors and their causes. Four Strategies for Success
Every year, gasoline engines are increasingly being replaced by electric motors installed in a new type of car called electric vehicles. However, just like internal combustion engines, electric powertrains can break down, causing problems in vehicle operation. The bulk of electric motor malfunctions occur due to severe wear of mechanism parts and aging of materials, which is supported by improper operation of such a car. There can be many reasons for the appearance of characteristic problems, and we will now tell you about some (the most common) ones.
Causes of motor failure
All possible malfunctions of the electric vehicle engine can be divided into mechanical and electrical. The causes of mechanical problems include distortions of the electric motor housing and its individual parts, loosening of fasteners and damage to the surface of the constituent elements or their shape. In addition, overheating of bearings, oil leakage and abnormal operating noise are common problems. The most typical malfunctions of the electrical part are attributed to short circuits inside the windings of the electric motor, as well as between them, short circuits of the windings to the housing and breaks in the windings or in the external circuit, that is, in the supply wires and starting equipment.
As a result of the occurrence of certain problems, The vehicle may experience the following problems: inability to start the motor, dangerous heating of the windings, abnormal speed of the electric motor, unnatural noise (hum or knock), unequal current strength in individual phases.
Typical motor problems
Let's look at the breakdowns of electric motors in more detail, identifying their possible causes.
AC motor
Problem: when connected to the power supply, the electric motor does not develop the rated speed and makes unnatural sounds, and when the shaft is scrolled by hand, uneven operation is observed. The reason for this behavior is most likely a break in two phases when the stator windings are connected in a triangle, or a break when connected in a star.
If the motor rotor does not rotate, emits a strong hum and heats up above the permissible level, it can be said with confidence that the stator phase failure is to blame. When the engine hums (especially when trying to start), and the rotor rotates at least slowly, but often the cause of the problem is a break in the phase of the rotor.
It happens that with a rated load on the shaft, the electric motor works stably, but its rotational speed is somewhat less than the rated one, and the current in one of the stator phases is increased. As a rule, this is a consequence of a break in the phase when the windings are connected in a triangle.
If at idle speed of the electric motor there are local overheating of the stator active steel, this means that due to damage to the intersheet insulation or burnout of the teeth due to damage to the winding, the sheets of the stator core are closed to each other.
When the stator winding overheats in separate places, when the motor cannot develop the rated torque and hums strongly, the cause of this phenomenon should be sought in the turn circuit of one phase of the stator winding or interphase circuit in the windings.
If the entire electric motor overheats evenly, then the ventilation system fan is faulty, and overheating of plain bearings with ring lubrication is due to one-sided attraction of the rotors (due to excessive wear of the liner) or poor fit of the shaft to the liner. When a rolling bearing overheats, making abnormal noise, it is likely that the reason for this lies in the contamination of the lubricant, excessive wear of the rolling elements and raceways, or inaccurate alignment of the shafts of the unit.
Knocking in the plain bearing and in the rolling bearing is due to serious wear of the liner or destruction of the tracks and rolling elements, and increased vibration is a consequence of the imbalance of the rotor due to interaction with pulleys and couplings, or the result of inaccurate alignment of the shafts of the unit and misalignment of the connecting halves.
A DC motor can also have its own characteristic malfunctions:
Under a serious load, the armature of the machine may not rotate, and if you try to turn it around with an external force, the engine will run “out of order”. Causes: poor contact or complete open circuit of the excitation circuit, interturn or short circuits inside the independent excitation winding. Under the conditions of the nominal values of the mains voltage and excitation current, the armature speed may be less or more than the established norm. In this case, the culprits for this situation are the brushes shifted from the neutral position in the direction of rotation of the shaft or against it.
It may also be that the brushes of one sign spark a little more than the brushes of another sign. It is possible that the distances between the rows of brushes are not the same around the circumference of the collector, or there is an interturn short circuit in the windings of one of the main or additional "pluses". If the blackening of the collector plates, which are located at a certain distance from each other, is also added to the sparking of the brushes, then the culprit of this situation is most likely a poor contact or short circuit in the armature winding. Also, do not forget about the possibility of a break in the armature coil attached to the blackened plates.
In cases where only every second or third collector plate darkens, the cause of the malfunction may be a weakened pressing of the collector or a protruding micanite of insulating tracks. Brushes can spark even with normal heating of the motor and a fully functional brush apparatus, which is explained by unacceptable wear of the collector.
The reasons for the increased sparking of the brushes, overheating of the collector and the darkening of most of it are usually insulation tracks (they say that the collector “beats”). When the motor armature rotates in different directions, the brushes also spark with different intensity. There is only one reason - the displacement of the brushes from the central.
If there is an increased sparking of the brushes on the collector, then it is worth checking the tightness of their fit, as well as diagnosing for defects in the working surface of the brushes. In addition, the reason may lie in the unequal pressure of the brushes or in their jamming in the brush holder. Naturally, if any of the listed problems is detected, it must be correctly eliminated, but quite often only highly qualified specialists can do this.
Troubleshooting the motor
High-quality overhaul of electric motors can only be carried out at specialized enterprises. During the current repair work, the power unit is disassembled and the subsequent partial replacement of worn parts is carried out. Let's look at the order in which all actions are performed using the example of an asynchronous electric motor.
At the initial stage, using a screw puller, a pulley or half-coupling is removed from the motor pulley. After that, you need to unscrew the bolts securing the fan casing and remove it. Further, using the same screw puller, you need to unscrew the locking screw and remove the fan itself. If necessary, the same tool can be used to remove the bearings from the motor shaft, and then, by unscrewing the mounting bolts, dismantle their covers as well.
After that, unscrew the bolts securing the bearing shields and remove these shields with light blows of a hammer through a wooden gasket. In order not to damage the steel and windings, a cardboard spacer is placed in the air gap, on which the rotor is lowered. The assembly of the electric motor is carried out in the reverse order.
After performing repair work (the specifics of the performance depend on the nature of the breakdown), the electric motor should be tested. To do this, simply turn the rotor by holding the pulley, and if the assembly is done correctly, the unit should rotate easily. If everything is fine, the engine is installed in place, connected to the network and checked for operability in idle mode, after which the motor is connected to the machine shaft and tested again. Let's look at the options for troubleshooting an electric motor using some typical breakdowns as an example.
So, let's imagine that the motor does not start due to a lack of voltage in the network, a shutdown of the machine or blown fuses. The presence of voltage can be checked using a special device - an AC voltmeter with a scale of 500 V, or using a low-voltage indicator. You can fix the problem by replacing blown fuses. Note!If at least one fuse blows, the engine will emit a characteristic hum.
An open phase of the stator winding can be detected with a megger, but before that, all ends of the motor windings must be released. If a break is detected inside the winding phase, then the motor will have to be sent for professional repair. The permissible rate of voltage drop at the motor terminals when it is started is considered to be an indicator of 30% of the nominal value, which is due to losses in the network, insufficient power of the transformer or its overload.
If you notice a decrease in voltage at the terminals of the electric motor, it is necessary to replace the supply transformer or increase the cross section of the supply line wires. The absence of a power supply contact in one of the stator windings (phase loss) causes an increase in current in the element windings and a decrease in the number of revolutions. If you leave the motor running on two windings, it will simply burn out.
In addition to the listed electrical problems, electric motors can also suffer from mechanical problems. So, the cause of excessive heating of the bearings is often the incorrect assembly of these parts, poor alignment of the motor, contamination of the bearings, or excessive wear of the balls and rollers.
In any case, before proceeding to direct action, a complete diagnosis of the electric motor and the parts interacting with it should be carried out. The inspection procedure begins with a battery check., and if it is in good condition, then the next step is to check the power supply to the controller circuitry (the ECU that controls the speed of rotation of the electric motor). It is quite possible that on the way from the battery to the board you will find a wire break. Breakdown of an electronic board is an infrequent phenomenon, but if there is even the slightest doubt about its serviceability, then it is better to immediately visually assess the condition of the part. If there was a strong heating of the board elements, you will immediately find blackened and swollen areas with possible smudges.
In the event that the car owner has at least minimal knowledge in the field of electronics, he can independently check the fuses, semiconductor parts (like diodes and transistors), all contacts, capacitances and soldering quality.
When, in the on state, there is an operating voltage at the output of the computer, then, as a rule, the cause of the malfunction should be sought in the electric motor itself. The complexity of repairing the unit depends on the specific malfunction and type of mechanism. So, when examining rotary-fed AC electric motors, first of all, it is necessary to check the contact brushes, because they are most often the cause of breakdowns of engines of this type. After that, the windings should be checked for an open or short circuit. In the event of a break, the tester will not show any resistance value, and in the event of a short circuit, the resistance indicator will correspond to zero or one Ohm.
Having found a malfunction, it, of course, must be eliminated. This can be done either by repairing and replacing failed parts (for example, brushes), or by replacing the entire motor with a working analogue.
Asynchronous electric motors are the most common in production and are often found in everyday life. With their help, various machines are set in motion: turning, milling, grinding, lifting mechanisms, such as an elevator or a crane, as well as various kinds of fans and hoods. Such popularity is due to the low cost, simplicity and reliability of this type of drive. But it happens that even a simple technique breaks down. In this article, we will consider typical malfunctions of asynchronous squirrel-cage motors.
Types of malfunctions of asynchronous motors
Faults can be divided into three groups:
The engine is heated;
The shaft does not rotate or does not rotate normally;
Noise, vibrate.
In this case, the engine housing can be heated completely or some separate place on it. And the motor shaft may not move at all, may not develop normal speed, its bearings may overheat, make sounds that are abnormal for its operation, and vibrate.
But first, brush up on its design, and the illustration below will help you with this.
The causes of malfunctions can also be divided into two groups:
Electrical;
Mechanical.
Most faults - by comparing the phase currents and rated current, and other measuring instruments. Consider typical faults.
Electric motor does not start
When voltage is applied, the motor does not start to rotate and does not make any sounds and the shaft does not "try" to move. First of all, check whether power is coming to the engine. This can be done either by opening the engine boron and measuring at the connection points of the supply cable, or by measuring the voltage at the supply switch, contactor, starter or circuit breaker.
However, if there is voltage at the motor terminals, then the entire line is normal.
By measuring the voltage at the beginning of the line - on the machine you only know that the voltage is applied, but it may not reach the end consumer as a result of cable breaks, poor connections along its entire length or due to faulty, as well as low-current circuits.
If you are convinced that the voltage is coming to the engine, its further diagnostics consists in the continuity of the windings for a break. You need to check the integrity of the winding, so at the same time you will check the breakdown on the case. You can ring the windings and, but such a check is not considered accurate.
To check the windings without ringing them and without opening the boron of the engine, you can use current clamps. To do this, measure the current in each of the phases.
If the motor windings are connected by a star and two windings are broken at the same time, there will be no current in any of the phases. With a break in one of the windings, you will find that the current is in two phases, and it is increased. When connected according to the triangle scheme, even if two windings burn out, current will flow in two of the three phase wires.
In the event of a break in one of the windings, the motor may not start under load, or it may start, but rotate slowly and vibrate. Shown below is an engine vibration measuring instrument.
If the windings are in good condition, and the current during the measurement is increased and at the same time the machine knocks out or the fuse blows, the shaft or the actuator driven by it is probably jammed. If possible, after turning off the power, they try to turn the shaft by hand, while disconnecting it from the driven mechanism.
When you determine that it is the motor shaft that does not rotate, check the bearings. In electric motors, either plain bearings or rolling bearings are installed. Worn bushings (plain bearings) are checked for lubrication, if the bushings do not have external flaws, it is possible to simply lubricate them, having previously cleaned them of dust, chips and other contaminants. But this rarely happens, and this method of repair is more relevant for low-power household appliance engines. In powerful engines, bearings are often simply replaced.
Problems with reduced speed, heat, shaft immobility and increased bearing wear can be associated with uneven loading on the shaft, its misalignment, deformation and bending. If the first two cases are correctable by proper installation of the shaft or actuator, as well as by reducing the load, then the deformation and sagging of the middle part of the shaft requires its replacement or complex repair. This is particularly common in large motors with long shafts.
When one of the bearings is worn, the shaft often "bites". At the same time, as a result of the expansion of the metal due to heating during friction, the shaft may first begin to rotate, but either not gain full speed, and in a particularly neglected case, it will stop altogether.
Rolling bearings also require regular lubrication and wear out during operation, especially quickly if the lubrication is low or contaminated.
The engine is warm
The first cause of engine heating is problems with the cooling system. With such a malfunction, the motor housing heats up completely. Most engines use air cooling. For this, the cases are made with fins, and on one side a cooling fan is installed on the shaft, the air flow of which is directed by means of a casing along the ribs.
If the fan is damaged, or if it, for example, flies off the shaft, an overheating problem arises. Powerful engines use a liquid cooling system. In addition, there are engines without fans - cooled by natural convection.
If the fan is normal, you need to continue the diagnosis.
When the engine is heated, check the heating of the bearings. To do this, they feel the surface of the case from the side of the back cover with a hand (where there are no protruding rotating shafts - safety is paramount).
If the bearing caps are hotter than other parts of the housing surface, check the presence and condition of the lubricant in them, and if using liners, replace them.
In the event that changing the grease in the ball bearing did not correct the situation, they should also be replaced.
Local heating of the housing - a situation in which some of its sections are clearly hotter than all the others, is observed during inter-turn short circuits. In such cases, diagnostics are carried out using current clamps - the currents in the phases are compared. If in one of the phases the current clearly exceeds the currents in the other phases, then the malfunction of the motor windings is confirmed. In this case, the repair consists in partial or complete rewinding of the stator.
Increased heating of an asynchronous electric motor can also occur when the stator plates are shorted.
Engine vibrates, makes noise, and makes abnormal noises
Motor noise can also be related to bearing wear. You probably noticed, like kitchen appliances - this is the reason. Shaft vibrations occur during its axial shift and deformation, which we talked about earlier.
Vibrations, noise or overheating of the active steel are also possible if the rotor touches the stator during rotation. This happens either when the rotor is bent, or when the stator plates are damaged. In the latter case, it is disassembled and the plates are repressed. The place of contact of the plates can be found by irregularities or it will be polished by the rotor.
Conclusion
We examined a number of malfunctions of the electric motor, how to eliminate them and the causes of their occurrence. Operation of an overheated motor is fraught with premature failure of the winding insulation. After a long period of inactivity, it is impossible to start the engine without measuring the resistance between the windings and the housing using a megohmmeter.
Insulation resistance of the order of 1 MΩ per 1 kV of supply voltage is considered normal. That is, a motor with a winding insulation resistance of at least 0.5 MΩ can be considered suitable for operation in a network with a voltage of 380 V. Otherwise, you risk damaging it. If the insulation resistance is less, the motor is dried, often removing the casing or back cover from it. During operation, the resistance of the winding gradually increases - due to the evaporation of moisture during heating.
Subject to the operating mode, rules of operation and maintenance, as well as normal power supply, an asynchronous motor lasts a long time, often recycling its resource at times. In this case, the main repair consists in lubricating and replacing bearings.
The asynchronous motor does not turn on (the fuses blow or the protection trips). The reason for this in motors with slip rings may be shorted positions of the starting rheostat or slip rings. In the first case, it is necessary to bring the starting rheostat to the normal (starting) position, in the second case, raise the device that short-circuits the contact rings.
It is also not possible to turn on the electric motor due to a short circuit in the stator circuit. You can detect a short-circuited phase by touch by increased heating of the winding (feeling should be done by first disconnecting the electric motor from the network); by the appearance of charred insulation, as well as by measurement. If the stator phases are connected in a star, then the values of the currents consumed from the network by the individual phases are measured. A phase having shorted turns will draw more current than undamaged phases. When connecting individual phases in a triangle, the currents in two wires connected to a defective phase will have greater values than in the third, which is connected only to undamaged phases. When measuring, use a lower voltage.
When turned on, the asynchronous electric motor does not budge. The reason for this may be a break in one or two phases of the power circuit. To determine the location of the break, first inspect all elements of the circuit that feeds the electric motor (check the integrity of the fuses). If during an external examination it is not possible to detect a phase break, then the necessary measurements are performed with a megohmmeter. For what the stator is previously disconnected from the mains. If the stator windings are connected in a star, then one end of the megger is connected to the zero point of the star, after which the other ends of the winding are touched alternately with the second end of the megger. Connecting a megohmmeter to the end of a good phase will give a zero reading, connecting to a phase that has an open circuit will show a high resistance in the circuit, i.e., the presence of an open in it. If the zero point of the star is not available, then the two ends of the megohmmeter touch all stator terminals in pairs. Touching the megger to the ends of healthy phases will show a zero value, touching the ends of two phases, one of which is defective, will show great resistance, i.e., a break in one of these phases.
In the case of connecting the stator windings into a triangle, it is necessary to disconnect the winding at one point, and then check the integrity of each phase separately.
A phase that has a break is sometimes detected by touch (remains cold). If a break occurs in one of the stator phases while the motor is running, it will continue to run, but will start to hum more than under normal conditions. Look for the damaged phase as described above.
During the operation of an asynchronous motor, the stator windings are strongly heated. Such a phenomenon, accompanied by a strong hum of the electric motor, is observed when there is a short circuit in any of the stator windings, as well as when the stator winding is double-circuited to the housing.
A running asynchronous motor began to hum. At the same time, its speed and power are reduced. The reason for the violation of the operating mode of the electric motor is a break in one phase.
When you turn on the DC motor, it does not budge. The reason for this can be blown fuses, an open in the power circuits, an open in the resistance in the starting rheostat. First, they carefully inspect, then check with a megger or test lamp with a voltage of not more than 36 V the integrity of these elements. If it is not possible to determine the location of the break in the indicated way, they proceed to checking the integrity of the armature winding. An open in the armature winding is most often observed at the junctions of the collector with the winding sections. By measuring the voltage drop between the collector plates, the fault location is found.
Another reason for this phenomenon may be an overload of the motor. You can check this by starting the motor idly, having previously disconnected it from the drive mechanism.
When the DC motor is turned on, the fuses blow or the maximum protection trips. The shorted position of the starting rheostat may be one of the reasons for this phenomenon. In this case, the rheostat is transferred to the normal starting position. This phenomenon can also be observed when the rheostat handle is withdrawn too quickly, therefore, when the electric motor is turned on again, the rheostat is withdrawn more slowly.
During operation of the electric motor, increased heating of the bearing is observed. The reason for the increased heating of the bearing may be insufficient clearance between the shaft journal and the bearing shell, insufficient or excess oil in the bearing (check the oil level), oil contamination or the use of inappropriate oils. In the latter cases, the oil is replaced by pre-washing the bearing with gasoline.
When starting or during operation of the electric motor, sparks and smoke appear from the gap between the rotor and the stator. A possible cause of this phenomenon may be the grazing of the rotor on the stator. This occurs when the bearings are significantly actuated.
When the DC motor is running, sparking occurs under the brushes. The reasons for this phenomenon can be the wrong selection of brushes, their weak pressing on the collector, the insufficiently smooth surface of the collector and the incorrect arrangement of the brushes. In the latter case, it is necessary to move the brushes, placing them on the neutral line.
During the operation of the electric motor, increased vibration is observed, which may appear, for example, due to insufficient strength of the fixing of the electric motor on the foundation plate. If the vibration is accompanied by overheating of the bearing, this indicates the presence of axial pressure on the bearing.
In industry, electric motors are ubiquitous and are becoming more and more complex, which can often make it difficult to keep them running at peak efficiency. It is important to remember that the causes of failures in electric motors and drives are not limited to one area of specialization: they can be both mechanical and electrical in nature. And only the right knowledge separates costly downtime and life extension.
The most common malfunctions of electric motors are winding insulation damage and bearing wear. occurring for many different reasons. This article focuses on early detection of the 13 most common causes of insulation failure and bearing failure.
Power quality
Variable Frequency Drives
Mechanical causes
Power quality
1. Transient voltage
Transient voltages can come from a variety of sources both inside and outside the facility. Turning on and off nearby loads, banks of power factor correction capacitors, or even weather events can all create transient voltages in distribution networks. These processes with arbitrary amplitude and frequency can destroy or damage the insulation of electric motor windings.
Finding the source of transients can be challenging because they occur intermittently and their effects can manifest themselves in different ways. For example, transients can show up in control cables and may not necessarily harm the equipment directly, but they can disrupt its operation.
Impact: damage to the motor winding insulation leads to early failures and unplanned downtime.
Criticality: high.
2. Voltage asymmetry
Three-phase distribution networks often feed single-phase loads. Resistance or load unbalance can cause voltage unbalance on all three phases. Possible faults may be in the wiring of the motor, at the motor terminals, as well as in the windings themselves. This asymmetry can cause overloads in each phase circuit of a three-phase network. In a word, the voltage on all three phases must always be the same.
Impact: unbalance causes overcurrents in one or more phases, which cause overheating and damage to the insulation.
three-phase power quality analyzer Fluke 435-II .
Criticality: average.
3. Harmonic distortion
In simple terms, harmonics are any unwanted additional high frequency voltage or current fluctuations that enter the motor windings. This additional energy is not used to rotate the motor shaft, but circulates in the windings and ultimately leads to a loss of internal energy. These losses are dissipated as heat, which degrades the insulating properties of the windings over time. Some harmonic distortion of the current waveform is normal for systems supplying electronic loads. Harmonic distortion can be measured with a power quality analyzer by monitoring the currents and temperatures at the transformers and making sure they are not overloaded. For each harmonic, an acceptable level of distortion is approved, which is regulated by the IEEE 519-1992 standard.
Impact: a decrease in the efficiency of the electric motor leads to additional costs and an increase in the operating temperature.
Measurement and diagnostic tool: three-phase power quality analyzer Fluke 435-II .
Criticality: average.
Variable Frequency Drives
4. Reflections on drive output PWM signals
Variable frequency drives use pulse width modulation (PWM) to control the output voltage and frequency of the motor supply. Reflections occur due to a mismatch between source and load impedances. Impedance mismatches can result from improper installation, improper component selection, or equipment degradation over time. The reflection peak in the drive circuit can be as high as the DC bus voltage.
Impact: damage to the motor winding insulation leads to unplanned downtime.
Device for measurement and diagnostics: Fluke 190-204 ScopeMeter® 4-channel handheld oscilloscope with high sampling rate.
Criticality: high.
5. Standard deviation of current
Impact: arbitrary opening of the circuit due to the passage of current through the protective earth.
Device for measurement and diagnostics: Fluke 190-204 ScopeMeter oscilloscope with wideband (10 kHz) current clamp (Fluke i400S or equivalent).
Criticality: low.
6. Working overload
Motor overload occurs when it is running under increased load. The main symptoms of a motor overload are excessive current draw, insufficient torque and overheating. Excessive heat generation of the electric motor is the main cause of its failure. When a motor is overloaded, individual components - including bearings, windings, and other parts - may operate normally, but the motor will overheat. Therefore, troubleshooting should begin with checking exactly the overload of the electric motor. Since 30% of all motor failures are due to motor overload, it is important to understand how to measure and determine motor overload.
Impact: premature wear of the electrical and mechanical components of the electric motor, leading to irreversible failure.
Measurement and diagnostic tool: Fluke 289 digital multimeter.
Criticality: high.
7. Misalignment
Misalignment occurs when the drive shaft is not properly aligned with the load or the gear that connects them is misaligned. Many experts believe that a flexible connection eliminates and compensates for displacement, however, a flexible connection protects only the transmission itself from displacement. Even with a flexible connection, a misaligned shaft will transmit damaging cyclic forces along its length to the motor, causing increased wear on the motor and increasing the actual mechanical load. In addition, misalignment can cause vibration of the shafts of both the load and the drive. There are several types of misalignment:
- Angular misalignment: shaft axes intersect but not parallel;
- Parallel displacement: the axes of the shafts are parallel, but not coaxial;
- Compound offset: A combination of angular and parallel offsets. (Note: misalignment is almost always complex, but practitioners treat them as the sum of offset components, since it is easier to resolve misalignment separately - angular and parallel components).
Influence:
Device for measurement and diagnostics: Fluke 830 Laser Shaft Alignment Tool .
Criticality: high.
8. Shaft imbalance
Unbalance is the state of a rotating part when the center of mass is not located on the axis of rotation. In other words, when the center of gravity is somewhere on the rotor. Although it is impossible to completely eliminate motor imbalance, it is possible to determine if it is out of acceptable range and take measures to correct the situation.
Imbalance can be caused by various reasons:
- accumulation of dirt;
- lack of balancing weights;
- manufacturing deviations;
- unequal mass of motor windings and other factors associated with wear.
A vibration tester or analyzer will help determine if a rotating mechanism is balanced or not.
Influence: premature wear of mechanical drive components causing premature failures.
Device for measurement and diagnostics: Fluke 810 Vibration Meter.
Criticality: high.
9. Shaft looseness
Looseness occurs due to excessive clearance between parts. Looseness can occur in several places:
- Rotational looseness occurs due to excessive clearance between rotating and stationary parts of the machine, such as in a bearing.
- Non-rotational looseness occurs between two normally stationary parts, such as between a support and a base, or a bearing housing and a machine.
As with all other sources of vibration, it is important to be able to identify the looseness and fix the problem without causing a loss. Looseness in a rotating machine can be determined using a tester or vibration analyzer.
Influence: accelerated wear of rotating components causing mechanical failure.
Device for measurement and diagnostics: Fluke 810 Vibration Meter.
Criticality: high.
10. Bearing wear
A failed bearing has increased friction, heats up more, and has reduced efficiency due to mechanical, lubrication, or wear problems. Bearing failure can be the result of various factors:
When bearing failures begin to show up, it also causes a cascade effect that accelerates engine failure. 13% of engine failures are caused by bearing failures, and over 60% of mechanical failures in a plant are caused by worn bearings, so it's important to know how to fix these potential problems.
Influence: accelerated wear of rotating components leads to bearing failure.
Device for measurement and diagnostics: Fluke 810 Vibration Meter.
Criticality: high.
Factors associated with incorrect installation
11. Loose base
A loose fit is caused by an uneven motor or driven component mounting base, or an uneven mounting surface on which the mounting base sits. This condition can create the annoying situation where tightening the mounting bolts actually introduces new loads and misalignment. Loose support often occurs between two diagonally spaced fixing bolts, as is the case with an uneven chair or table that swings diagonally. There are two types of base looseness:
- Parallel base looseness - occurs when one mounting foot is higher than the other three;
- Angled Base Loose - Occurs when one of the mounting posts is not parallel or perpendicular to the mounting surface.
In both cases, loose footing of the base can be caused by unevenness in the mechanism mounting foot or in the mounting foot on which the foot sits. In any case, the loose fit must be found and repaired before the shaft is centered. A quality laser centering tool can determine if the base of a given rotating machine is loose.
Influence: misalignment of mechanical drive components.
Device for measurement and diagnostics: Fluke 830 Laser Shaft Alignment Tool .
Criticality: average.
12. Piping tension
Piping tension refers to the condition in which new loads, tensions, and forces acting on the rest of the equipment and infrastructure are transferred back to the motor and drive, resulting in misalignment. The most common example of this is in simple motor/pump circuits where something is affecting the piping, such as:
- displacement in the foundation;
- a recently installed valve or other component;
- an object that strikes, bends or simply presses on the pipe;
- broken or missing pipe fixtures or wall fittings.
These forces can have an angular or shearing effect, which in turn leads to displacement of the motor/pump shaft. For this reason, it is important to check the alignment of the machine, not only during installation - accurate alignment is a temporary condition and may change over time.
Influence: misalignment of the shaft and subsequent stresses on rotating components leading to premature failures.
Device for measurement and diagnostics: Fluke 830 Laser Shaft Alignment Tool .
Criticality: low.
13. Shaft voltage
When the voltage on the motor shaft exceeds the insulating characteristics of the bearing grease, breakdown occurs on the outer bearing, causing pitting and grooving of the bearing raceway. The first signs of a problem are noise and overheating as the bearings lose their original shape, as well as the appearance of metal chips in the lubricant and increased bearing friction. This can lead to the destruction of the bearing after a few months of operation of the electric motor. Bearing failure is a costly problem both in terms of motor recovery and machine downtime, so preventing this by measuring shaft voltage and bearing current is an important part of diagnosis. Shaft voltage is only present when the motor is energized and spinning. The carbon brush mounted on the probe allows you to measure the voltage on the shaft when the motor rotates.
Influence: arc flashes on the bearing surface cause pitting and grooving, which in turn leads to excessive vibration and subsequent bearing failure.
Device for measurement and diagnostics: isolated 4-channel portable oscilloscope Fluke-190-204 ScopeMeter, AEGIS probe with carbon brushes for measuring shaft voltage.
Criticality: high.
Four Strategies for Success
Motor control systems are used in important processes in factories. Equipment failure can lead to large financial losses associated with both the potential replacement of the electric motor and its parts, and the downtime of systems that depend on this electric motor. By empowering service engineers and technicians with the knowledge they need, prioritizing work, and performing preventive maintenance to monitor equipment and fix hard-to-find problems, workload-induced breakdowns can often be avoided and downtime costs can be reduced.
There are four key strategies to eliminate or prevent premature failure of the motor and rotating parts:
- Record operating conditions, equipment specifications, and performance tolerance ranges.
- Regular collection and recording of critical measurements during installation, before and after maintenance.
- Create an archive of reference measurements for trending and state change detection.
- Plot individual measurements to identify major trends. Any change in the trend line by more than +/- 10-20% (or any other specified amount, depending on system performance or criticality) should be investigated to determine the cause of problems.
Have you found that your diesel generator is malfunctioning or has stopped starting altogether? First of all, it is necessary to inspect the equipment for visible problems. In this article, we will look at the main types of malfunctions of diesel generator sets (diesel generator sets), their causes, and also tell you how to fix them.
Diesel Generator Inspection Before Starting
The first thing to do when troubleshooting is to check the generator for external damage (which, by the way, is recommended before each start): if you see cracks, dents or other flaws on the body, then most likely the cause of the failure is mechanical damage. Also make sure that there are no foreign objects inside the device.
6 most common types of diesel generator malfunctions
- generator does not start
- does not generate voltage
- stutters while working
- uses more oil than it should
- a loud noise is heard while the engine is running
- strange color of exhaust gases (black, white-blue)
Let's consider each type in detail.
Generator won't start
There may be several reasons for this:
- Broken fuel pump: This is indicated by low or uneven fuel supply.
- The cold start device is broken. This is most likely due to waxing of the fuel, which usually occurs at cold temperatures. To prevent this from happening to your equipment, use seasonal fuel and do not use the device in cold weather.
- The fuel is of low quality or contaminated. To avoid this, use only tested, clean, undiluted fuel: saving on it can lead to serious repair costs.
- The starter has failed, and as a result, its insufficient frequency of rotation. There are two reasons: a) the use of low quality oil, b) a weak battery.
The generator does not produce voltage
Attention! Before checking any electrical part, completely disconnect the equipment from power to avoid electric shock.
The diesel generator works, but does not produce voltage: perhaps the contacts have moved away or are missing or there is a problem in the brushes. Check their connection according to the instructions.
Another cause may be a problem in the voltage regulator or winding wear: inspect their condition.
DGU stalls during operation
In this case, there are 7 main reasons, some of which you can identify and eliminate yourself:
- there is not enough fuel in the tank
- air got into the fuel
- additional resistance in the fuel supply system or the system for draining excess fuel into the tank, as well as in the intake or exhaust systems
- dirty air filter
- injector failure
- incorrect idle speed setting
Generator uses more oil than it should
Check the oil system for leakage: oil may leak into other systems, such as the fuel system. To prevent depressurization, use only high quality oils.
Loud noise heard while engine is running
Most often, knocking indicates wear or breakage of the following parts:
- nozzles
- valve springs
- piston rings
- cylinder-piston group
- crankshaft bearing
- camshaft
If the listed parts are in order, check the adjustment of the valve clearance, the distribution mechanism and the setting of the injection moment. Is it normal too? Then it's the presence of air in the fuel system or low-quality fuel.
